CECW-EG

Engineer Manual1110-2-2300

Department of the ArmyU.S. Army Corps of Engineers

Washington, DC 20314-1000

EM 1110-2-2300

31 July 1994

Engineering and Design

EARTH AND ROCK-FILL DAMS - GENERAL DESIGN AND

CONSTRUCTION CONSIDERATIONS

Distribution Restriction StatementApproved for public release; distribution is

unlimited.

US Army Corpsof Engineers

ENGINEERING AND DESIGN

EM 1110-2-230031 July 1994

Earth and Rock-Fill Dams-General Design andConstruction Considerations

ENGINEER MANUAL

DEPARTMENT OF THE ARMY EM 1110-2-2300U.S. Army Corps of Engineers

CECW-EG Washington, DC 20314-1000

ManualNo. 1110-2-2300 31 July 1994

Engineering and DesignEARTH AND ROCK-FILL DAMS—GENERAL DESIGN

AND CONSTRUCTION CONSIDERATIONS

1. Purpose. This manual presents fundamental principles underlying the design and construction ofearth and rock-fill dams. The general principles presented herein are also applicable to the design andconstruction of earth levees. The construction of earth dams by hydraulic means was curtailed in the1940’s due to economic considerations and liquefaction concerns during earthquake loading and arenot discussed herein.

2. Applicability. This manual applies to HQUSACE elements, major subordinate commands, districts,laboratories, and field operating activities having responsibility for the design and construction of earthand rock-fill dams.

FOR THE COMMANDER:

WILLIAM D. BROWNColonel, Corps of EngineersChief of Staff

___________________________________________________This manual supersedes EM 1110-2-2300, dated 10 May 1982.

DEPARTMENT OF THE ARMY EM 1110-2-2300U.S. Army Corps of Engineers

CECW-EG Washington, DC 20314-1000

ManualNo. 1110-2-2300 31 July 1994

Engineering and DesignEARTH AND ROCK-FILL DAMS—GENERAL DESIGN

AND CONSTRUCTION CONSIDERATIONS

Table of Contents

Subject Paragraph Page Subject Paragraph Page

Chapter 1IntroductionPurpose . . . . . . . . . . . . . . . . . . . . . . 1-1 1-1Applicability . . . . . . . . . . . . . . . . . . . 1-2 1-1References . . . . . . . . . . . . . . . . . . . . 1-3 1-1Overview of Manual . . . . . . . . . . . . . 1-4 1-1

Chapter 2General ConsiderationsGeneral. . . . . . . . . . . . . . . . . . . . . . . 2-1 2-1Civil Works Project Process. . . . . . . . 2-2 2-1Types of Embankment Dams. . . . . . . . 2-3 2-2Basic Requirements. . . . . . . . . . . . . . 2-4 2-5Selection of Embankment Type. . . . . . 2-5 2-5Environmental Conditions. . . . . . . . . . 2-6 2-6

Chapter 3Field Investigations andLaboratory TestingGeological and Subsurface Explorations

and Field Tests. . . . . . . . . . . . . . . . 3-1 3-1Laboratory Testing. . . . . . . . . . . . . . . 3-2 3-3

Chapter 4General Design ConsiderationsFreeboard. . . . . . . . . . . . . . . . . . . . . 4-1 4-1Top Width . . . . . . . . . . . . . . . . . . . . 4-2 4-1Alignment . . . . . . . . . . . . . . . . . . . . . 4-3 4-1Embankment. . . . . . . . . . . . . . . . . . . 4-4 4-1Abutments . . . . . . . . . . . . . . . . . . . . 4-5 4-1Earthquake Effects. . . . . . . . . . . . . . . 4-6 4-2Coordination Between Design and

Construction . . . . . . . . . . . . . . . . . . 4-7 4-2Value Engineering Proposals. . . . . . . . 4-8 4-2

Partnering Between the Ownerand Contractor . . . . . . . . . . . . . . . . 4-9 4-3

Chapter 5Foundation and AbutmentPreparationPreparation. . . . . . . . . . . . . . . . . . . . 5-1 5-1Strengthening the Foundation. . . . . . . 5-2 5-2Dewatering the Working Area. . . . . . . 5-3 5-3

Chapter 6Seepage ControlGeneral. . . . . . . . . . . . . . . . . . . . . . . 6-1 6-1Embankment. . . . . . . . . . . . . . . . . . . 6-2 6-1Earth Foundations. . . . . . . . . . . . . . . 6-3 6-1Rock Foundations. . . . . . . . . . . . . . . 6-4 6-4Abutments . . . . . . . . . . . . . . . . . . . . 6-5 6-5Adjacent to Outlet Conduits. . . . . . . . 6-6 6-5Beneath Spillways and Stilling

Basins . . . . . . . . . . . . . . . . . . . . . . 6-7 6-6Seepage Control Against Earthquake

Effects . . . . . . . . . . . . . . . . . . . . . . 6-8 6-6

Chapter 7Embankment DesignEmbankment Materials. . . . . . . . . . . . 7-1 7-1Zoning . . . . . . . . . . . . . . . . . . . . . . . 7-2 7-1Cracking . . . . . . . . . . . . . . . . . . . . . . 7-3 7-5Filter Design . . . . . . . . . . . . . . . . . . . 7-4 7-8Consolidation and Excess Porewater

Pressures. . . . . . . . . . . . . . . . . . . . 7-5 7-8Embankment Slopes and Berms. . . . . . 7-6 7-8Embankment Reinforcement. . . . . . . . 7-7 7-9

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Subject Paragraph Page Subject Paragraph Page

Compaction Requirements. . . . . . . . . . 7-8 7-9Slope Protection . . . . . . . . . . . . . . . . 7-9 7-13

Chapter 8Appurtenant StructuresOutlet Works. . . . . . . . . . . . . . . . . . . 8-1 8-1Spillway . . . . . . . . . . . . . . . . . . . . . . 8-2 8-1Miscellaneous Considerations. . . . . . . 8-3 8-1

Chapter 9General ConstructionConsiderationsGeneral. . . . . . . . . . . . . . . . . . . . . . . 9-1 9-1Obtaining Quality Construction. . . . . . 9-2 9-1Stage Construction. . . . . . . . . . . . . . . 9-3 9-1Stream Diversion. . . . . . . . . . . . . . . . 9-4 9-2Closure Section. . . . . . . . . . . . . . . . . 9-5 9-3Construction/Design Interface. . . . . . . 9-6 9-3Visual Observations. . . . . . . . . . . . . . 9-7 9-3Compaction Control. . . . . . . . . . . . . . 9-8 9-4Initial Reservoir Filling. . . . . . . . . . . . 9-9 9-4Construction Records and

Reports . . . . . . . . . . . . . . . . . . . .9-10 9-5

Chapter 10InstrumentationGeneral. . . . . . . . . . . . . . . . . . . . . .10-1 10-1Instrumentation Plan

and Records. . . . . . . . . . . . . . . . .10-2 10-1Types of Instrumentation. . . . . . . . . 10-3 10-1Discussion of Devices. . . . . . . . . . .10-4 10-1Measurements of Seepage

Quantities. . . . . . . . . . . . . . . . . . .10-5 10-2Automatic Data Acquisition . . . . . . . 10-6 10-2

Appendix AReferences . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1

Appendix BFilter Design . . . . . . . . . . . . . . . . . . . . . . . . . B-1

Appendix CSlope Protection . . . . . . . . . . . . . . . . . . . . . . C-1

Appendix DAutomatic Data AcquisitionSystems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D-1

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Chapter 1Introduction

1-1. Purpose

This manual presents fundamental principles underlyingthe design and construction of earth and rock-fill dams.The general principles presented herein are also applicableto the design and construction of earth levees. The con-struction of earth dams by hydraulic means was curtailedin the 1940’s due to economic considerations and lique-faction concerns during earthquake loading and are notdiscussed herein.

1-2. Applicability

This manual applies to HQUSACE elements, major subor-dinate commands, districts, laboratories, and field

operating activities having responsibility for the designand construction of earth and rock-fill dams.

1-3. References

Required and related references are listed in Appendix A.

1-4. Overview of Manual

The objective of this manual is to present guidance for thedesign and construction of earth and rock-fill dams. Themanual is general in nature and is not intended to sup-plant the judgment of the designer on a particular project.

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Chapter 2General Considerations

2-1. General

a. Introduction. The design of earth and rock-filldams involves many considerations that must be examinedbefore initiating detailed stability analyses. Followinggeological and subsurface explorations, the earth and/orrock-fill materials available for construction should becarefully studied. The study should include the determ-ination of the quantities of various types of material thatwill be available and the sequence in which they becomeavailable, and a thorough understanding of their physicalproperties is necessary. Failure to make this study mayresult in erroneous assumptions which must be revised ata later date. For example, a rock-fill dam was originallydesigned to utilize sandstone in rock-fill shells. However,subsequent investigations showed that the sandstonewould break down during excavation and compaction, andit was necessary to redesign the embankment as an earthdam.

b. Embankment. Many different trial sections forthe zoning of an embankment should be prepared to studyutilization of fill materials; the influence of variations intypes, quantities, or sequences of availability of variousfill materials; and the relative merits of various sectionsand the influence of foundation condition. Althoughprocedures for stability analyses (see EM 1110-2-1902and Edris 1992) afford a convenient means for comparingvarious trial sections and the influence of foundationconditions, final selection of the type of embankment andfinal design of the embankment are based, to a largeextent, upon experience and judgment.

c. Features of design.Major features of design arerequired foundation treatment, abutment stability, seepageconditions, stability of slopes adjacent to control structureapproach channels and stilling basins, stability of reservoirslopes, and ability of the reservoir to retain the waterstored. These features should be studied with reference tofield conditions and to various alternatives before initiat-ing detailed stability or seepage analyses.

d. Other considerations. Other design considera-tions include the influence of climate, which governs thelength of the construction season and affects decisions onthe type of fill material to be used, the relationship of thewidth of the valley and its influence on river diversionand type of dam, the planned utilization of the project (forexample, whether the embankment will have a permanent

pool or be used for short-term storage), the influence ofvalley configuration and topographic features on waveaction and required slope protection, the seismic activityof the area, and the effect of construction on theenvironment.

2-2. Civil Works Project Process

a. General. The civil works project process for adam is continuous, although the level of intensity andtechnical detail varies with the progression through thedifferent phases of the project development and imple-mentation. The phases of the process are reconnaissance,feasibility, preconstruction engineering and design (PED),construction, and finally the operation, maintenance,repair, replacement, and rehabilitation (OMRR&R).

b. Reconnaissance phase. A reconnaissance studyis conducted to determine whether or not the problem hasa solution acceptable to local interests for which there is aFederal interest and if so whether planning should proceedto the feasibility phase. During the reconnaissance phase,engineering assessments of alternatives are made to deter-mine if they will function safely, reliably, efficiently, andeconomically. Each alternative should be evaluated todetermine if it is practical to construct, operate, and main-tain. Several sites should be evaluated, and preliminarydesigns should be prepared for each site. These prelimi-nary designs should include the foundation for the damand appurtenant structures, the dam, and the reservoir rim.The reconnaissance phase ends with either execution of aFeasibility Cost Sharing Agreement or the major subordi-nate command (MSC) Commander’s public notice for arepo r t r ecommend ing no Fede ra l ac t i on(ER 1110-2-1150).

c. Feasibility phase. A feasibility study is con-ducted to investigate and recommend a solution to theproblem based on technical evaluation of alternatives andincludes a baseline cost estimate and a design and con-struction schedule which are the basis for congressionalauthorization. Results of the engineering studies aredocumented in an engineering appendix to the feasibilityreport. A general design memorandum (GDM) is norm-ally not required. However, design memorandums arerequired to properly develop and document the engineer-ing and design studies performed during preconstructionengineering and design phase. The engineering data andanalyses cover hydrology and hydraulics, surveying andmapping, real estate, geotechnical, project design, con-struction, and marketability of hydroelectric power. Anoperation and maintenance plan for the project, includingestimates of the Federal and non-Federal costs, will be

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developed. All of the project OMRR&R and dam safetyrequirements should be identified and discussed with thesponsor and state during the feasibility phase. A turnoverplan for non-Federal dams that establishes a definite turn-over point of the dam to the sponsor should be docu-mented in the initial project management plan and in thefeasibility report. The turnover of the dam should occurimmediately following the first periodic inspection. Ade-quate engineering data must be obtained and analyzed andsufficient design performed to define the appropriate levelof risk associated with the contingencies assigned to eachcost item in the estimate (ER 1110-2-1150).

d. Preconstruction engineering and design phase.During the preconstruction engineering and design (PED)phase, it may be determined that a GDM is necessarybecause the project has changed substantially since admin-istration review of the feasibility report (with engineeringappendix) or authorization, the project was authorizedwithout a feasibility report, there is a need to readdressproject formulation, or there is a need to reassess projectplans due to changes in administration policy (ER 1110-2-1150 will be followed). For a complex project such as adam, results of the engineering studies for individualfeatures of the project such as the spillway, outlet works,embankment, and instrumentation will be submitted inseparate design memorandums (DMs) with sufficientdetail to allow preparation of plans and specifications(P&S) to proceed during the review and approval process.Contents and format of a DM are given in ER 1110-2-1150, Appendixes B and D, respectively. A significantlevel of geological investigation and exploration and stud-ies on the availability of construction materials are accom-plished to support the DM. While final design parametersare not selected at this stage of design, it is necessary thatthe testing for engineering properties of materials andhydraulic model testing that may be necessary for theproject be in progress. In preparation for the beginning ofeach major construction contract, engineering will preparea report outlining the engineering considerations andproviding instructions for field personnel to aid them inthe supervision and inspection of the contract. The reportwill summarize data presented in the engineering appen-dix to the feasibility report but will also include informaldiscussions on why specific designs, material sources, andconstruction plant locations were selected so that fieldpersonnel will be provided the insight and backgroundnecessary to review contractor proposals and resolveconstruction problems without compromising the designintent (ER 415-2-100). Format of the report on engineer-ing considerations and instructions for field personnel isgiven in Appendix D of ER 1110-2-1150.

e. Construction phase.This phase includes prepa-ration of P&S for subsequent construction contracts,review of selected construction contracts, site visits, sup-port for claims and modifications, development of opera-tion and maintenance (O&M) manuals, and preparationand maintenance of as-built drawings. Site visits must bemade to verify that conditions match the assumptions usedin designing the project features. Site visits may also benecessary to brief the construction division personnel onany technical issues which affect the construction. TheO&M manual and water control manual will be completedand fully coordinated with the local sponsor during thisphase of the project. As-built drawings are prepared andmaintained by engineering during the construction phase(ER 1110-2-1150).

f. Operation and maintenance phase. The projectis operated, inspected, maintained, repaired, and rehabili-tated by either the non-Federal sponsor or the FederalGovernment, depending upon the project purposes and theterms of the project cooperation agreement (PCA). ForPCA projects and new dams turned over to others, theCorps needs to explain up front the O&M responsibilities,formal inspection requirements, and responsibilities toimplement dam safety practices. Periodic inspections willbe conducted to assess and evaluate the performance andsafety of the project during its lifetime. Modifications tothe features of a project which occur during the operatinglife of a project will be reflected in the as-built drawings(ER 1110-2-1150).

2-3. Types of Embankment Dams

a. Introduction. The two principal types ofembankment dams are earth and rock-fill dams, dependingon the predominant fill material used. Some generalizedsections of earth dams showing typical zoning for differ-ent types and quantities of fill materials and various meth-ods for controlling seepage are presented in Figure 2-1.When practically only one impervious material is avail-able and the height of the dam is relatively low, ahomogeneous dam with internal drain may be used asshown in Figure 2-1a. The inclined drain serves to pre-vent the downstream slope from becoming saturated andsusceptible to piping and/or slope failure and to interceptand prevent piping through any horizontal cracks travers-ing the width of the embankment. Earth dams withimpervious cores, as shown in Figures 2-1b and 2-1c, areconstructed when local borrow materials do not provideadequate quantities of impervious material. A verticalcore located near the center of the dam is preferred overan inclined upstream core because the former provides

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Figure 2-1. Types of earth dam sections

higher contact pressure between the core and foundationto prevent leakage, greater stability under earthquakeloading, and better access for remedial seepage control.An inclined upstream core allows the downstream portionof the embankment to be placed first and the core laterand reduces the possibility of hydraulic fracturing.

However, for high dams in steep-walled canyons theoverriding consideration is the abutment topography. Theobjective is to fit the core to the topography in such away to avoid divergence, abrupt topographic discontinu-ities, and serious geologic defects. For dams on perviousfoundations, as shown in Figure 2-1d to 2-1f, seepage

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control is necessary to prevent excessive uplift pressuresand piping through the foundation. The methods forcontrol of underseepage in dam foundations are horizontaldrains, cutoffs (compacted backfill trenches, slurry walls,and concrete walls), upstream impervious blankets, down-stream seepage berms, toe drains, and relief wells. Rock-fill dams may be economical due to large quantities ofrock available from required excavation and/or nearbyborrow sources, wet climate and/or short constructionseason prevail, ability to place rock fill in freezing cli-mates, and ability to conduct foundation grouting withsimultaneous placement of rock fill for sloping core anddecked dams (Walker 1984). Two generalized sections ofrock-fill dams are shown in Figure 2-2. A rock-fill damwith steep slopes requires better foundation conditionsthan an earth dam, and a concrete dam (or roller-compacted concrete dam) requires better foundation con-ditions than a rock-fill dam. The design and constructionof seepage control measures for dams are given inEM 1110-2-1901.

b. Earth dams. An earth dam is composed of suit-able soils obtained from borrow areas or required exca-vation and compacted in layers by mechanical means.Following preparation of a foundation, earth from borrowareas and from required excavations is transported to thesite, dumped, and spread in layers of required depth. Thesoil layers are then compacted by tamping rollers, sheeps-foot rollers, heavy pneumatic-tired rollers, vibratoryrollers, tractors, or earth-hauling equipment. One advan-tage of an earth dam is that it can be adapted to a weakfoundation, provided proper consideration is given tothorough foundation exploration, testing, and design.

c. Rock-fill dams. A rock-fill dam is one com-posed largely of fragmented rock with an imperviouscore. The core is separated from the rock shells by aseries of transition zones built of properly graded mater-ial. A membrane of concrete, asphalt, or steel plate onthe upstream face should be considered in lieu of animpervious earth core only when sufficient impervious

Figure 2-2. Two types of rock-fill dams

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material is not available (such was the case at R. W.Bailey Dam; see Beene and Pritchett 1985). However,such membranes are susceptible to breaching as a resultof settlement. The rock-fill zones are compacted in layers12 to 24 in. thick by heavy rubber-tired or steel-wheelvibratory rollers. It is often desirable to determine thebest methods of construction and compaction on the basisof test quarry and test fill results. Dumping rock fill andsluicing with water, or dumping in water, is generallyacceptable only in constructing cofferdams that are not tobe incorporated in the dam embankment. Free-draining,well-compacted rock fill can be placed with steep slopesif the dam is on a rock foundation. If it is necessary toplace rock-fill on an earth or weathered rock foundation,the slopes must, of course, be much flatter, and transitionzones are required between the foundation and the rockfill. Materials for rock-fill dams range from sound free-draining rock to the more friable materials such as sand-stones and silt-shales that break down under handling andcompacting to form an impervious to semipervious mass.The latter materials, because they are not completely free-draining and lack the shear strength of sound rock fill, areoften termed “random rock” and can be used successfullyfor dam construction, but, because of stability and seepageconsiderations, the embankment design using such mater-ials is similar to that for earth dams.

2-4. Basic Requirements

a. Criteria. The following criteria must be met toensure satisfactory earth and rock-fill structures:

(1) The embankment, foundation, and abutmentsmust be stable under all conditions of construction andreservoir operation including seismic.

(2) Seepage through the embankment, foundation,and abutments must be collected and controlled to preventexcessive uplift pressures, piping, sloughing, removal ofmaterial by solution, or erosion of material by loss intocracks, joints, and cavities. In addition, the purpose ofthe project may impose a limitation on the allowablequantity of seepage. The design should consider seepagecontrol measures such as foundation cutoffs, adequate andnonbrittle impervious zones, transition zones, drainageblankets, upstream impervious blankets, and relief wells.

(3) Freeboard must be sufficient to prevent over-topping by waves and include an allowance for the nor-mal settlement of the foundation and embankment as wellas for seismic effects where applicable.

(4) Spillway and outlet capacity must be sufficientto prevent overtopping of the embankment.

b. Special attention. Special attention should begiven to possible development of pore pressures infoundations, particularly in stratified compressible mate-rials, including varved clays. High pore pressures may beinduced in the foundation, beyond the toes of the embank-ment where the weight of the dam produces little or novertical loading. Thus, the strengths of foundation soilsoutside of the embankment may drop below their originalin situ shear strengths. When this type of foundationcondition exists, instrumentation should be installed dur-ing construction (see Chapter 10).

2-5. Selection of Embankment Type

a. General. Site conditions that may lead to selec-tion of an earth or a rock-fill dam rather than a concretedam (or roller-compacted concrete dam) include a widestream valley, lack of firm rock abutments, considerabledepths of soil overlying bedrock, poor quality bedrockfrom a structural point of view, availability of sufficientquantities of suitable soils or rock fill, and existence of agood site for a spillway of sufficient capacity.

b. Topography. Topography, to a large measure,dictates the first choice of type of dam. A narrowV-shaped valley with sound rock in abutments wouldfavor an arch dam. A relatively narrow valley with high,rocky walls would suggest a rock fill or concrete dam (orroller-compacted concrete). Conversely, a wide valleywith deep overburden would suggest an earth dam. Irreg-ular valleys might suggest a composite structure, partlyearth and partly concrete. Composite sections might alsobe used to provide a concrete spillway while the rest ofthe dam is constructed as an embankment section (Golze1977, Singh and Sharma 1976, Goldin and Rasskazov1992). The possibility of cracking resulting from archingin narrow valleys and shear cracks in the vicinity of steepabutments must be investigated and may play a role in theselection of the type of dam (Mitchell 1983). At MudMountain Dam, arching of the soil core material within anarrow, steep-sided canyon reduced stresses making thesoil susceptible to hydraulic fracturing, cracking, andpiping (Davidson, Levallois, and Graybeal 1992). Haulroads into narrow valleys may be prohibited for safetyand/or environmental reasons. At Abiquiu and WarmSprings Dams, borrow material was transported by a beltconveyor system (Walker 1984). Topography may alsoinfluence the selection of appurtenant structures. Natural

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saddles may provide a spillway location. If the reservoirrim is high and unbroken, a chute or tunnel spillway maybe necessary (Bureau of Reclamation 1984).

c. Geology and foundation conditions. The geologyand foundation conditions at the damsite may dictate thetype of dam suitable for that site. Competent rockfoundations with relatively high shear strength and resis-tance to erosion and percolation offer few restrictions asto the type of dam that can be built at the site. Gravelfoundations, if well compacted, are suitable for earth orrock-fill dams. Special precautions must be taken toprovide adequate seepage control and/or effective watercutoffs or seals. Also, the liquefaction potential of gravelfoundations should be investigated (Sykora et al. 1992).Silt or fine sand foundations can be used for low concrete(or roller-compacted concrete) and earth dams but are notsuitable for rock-fill dams. The main problems includesettlement, prevention of piping, excessive percolationlosses, and protection of the foundation at the downstreamembankment toe from erosion. Nondispersive clay foun-dations may be used for earth dams but require flatembankment slopes because of relatively low foundationshear strength. Because of the requirement for flatterslopes and the tendency for large settlements, clay foun-dations are generally not suitable for concrete (or roller-compacted concrete) or rock-fill dams (Golze 1977,Bureau of Reclamation 1984).

d. Materials available. The most economical typeof dam will often be one for which materials can befound within a reasonable haul distance from the site,including material which must be excavated for the damfoundation, spillway, outlet works, powerhouses, andother appurtenant structures. Materials which may beavailable near or on the damsite include soils for embank-ments, rock for embankments and riprap, and concreteaggregate (sand, gravel, and crushed stone). Materialsfrom required excavations may be stockpiled for later use.However, greater savings will result if construction sched-uling allows direct use of required excavations. If suit-able soils for an earth-fill dam can be found in nearbyborrow pits, an earth dam may prove to be more econom-ical. The availability of suitable rock may favor a rock-fill dam. The availability of suitable sand and gravel forconcrete at a reasonable cost locally or onsite is favorableto use for a concrete (or roller-compacted concrete) dam(Golze 1977, Bureau of Reclamation 1984).

e. Spillway. The size, type, and restrictions onlocation of the spillway are often controlling factors in thechoice of the type of dam. When a large spillway is to

be constructed, it may be desirable to combine thespillway and dam into one structure, indicating a concreteoverflow dam. In some cases where required excavationfrom the spillway channel can be utilized in the damembankment, an earth or rock-fill dam may be advanta-geous (Golze 1977, Bureau of Reclamation 1984).

f. Environmental. Recently environmental consid-erations have become very important in the design ofdams and can have a major influence on the type of damselected. The principal influence of environmental con-cerns on selection of a specific type of dam is the need toconsider protection of the environment, which can affectthe type of dam, its dimensions, and location of the spill-way and appurtenant facilities (Golze 1977).

g. Economic. The final selection of the type ofdam should be made only after careful analysis and com-parison of possible alternatives, and after thorough eco-nomic analyses that include costs of spillway, power andcontrol structures, and foundation treatment.

2-6. Environmental Conditions

This policy applies to all elements of design and construc-tion. Actions to be taken in some of the more importantareas are:

a. Overflow from slurry trench construction shouldnot be permitted to enter streams in substantial quantities.Settling ponds or offsite disposal should be provided.

b. Borrow areas must be located, operated, anddrained to minimize erosion and sediment transport intostreams.

c. Alterations to the landscape caused by clearingoperations, borrow area operations, structure excavations,and spoil areas must be controlled and treated by finalgrading, dressing, turfing, and other remedial treatmentsas to minimize and eliminate adverse postconstructionenvironmental effects, as well as to eliminate unsightlyareas and promote aesthetic considerations. General stateand local requirements on erosion control, dust control,burning, etc. should be followed. Such postconstructionalterations planned for these purposes must be compatiblewith the requirements of safety and performance of thedam.

d. Study with a view to their elimination must begiven to other potentially undesirable by-products of con-struction operations related to the particular environment

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of a given damsite. Public Law 91-190, NationalEnvironmental Policy Act of 1969, as amended,establishes a national policy promoting efforts which will

prevent or eliminate damage to the environment andbiosphere.

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Chapter 3Field Investigations and LaboratoryTesting

3-1. Geological and Subsurface Explorations andField Tests

a. General requirements.

(1) Geological and subsurface investigations at thesites of structures and at possible borrow areas must beadequate to determine suitability of the foundation andabutments, required foundation treatment, excavationslopes, and availability and characteristics of embankmentmaterials. This information frequently governs selectionof a specific site and type of dam. Required foundationtreatment may be a major factor in determining projectfeasibility. These investigations should cover classifica-tion, physical properties, location and extent of soil androck strata, and variations in piezometric levels in ground-water at different depths.

(2) A knowledge of the regional and local geologyis essential in developing a plan of subsurface investiga-tion, interpreting conditions between and beyond boringlocations, and revealing possible sources of trouble.

(3) The magnitude of the foundation explorationprogram is governed principally by the complexity of thefoundation problem and the size of the project. Explora-tions of borrow and excavation areas should be under-taken early in the investigational program so thatquantities and properties of soils and rock available forembankment construction can be determined beforedetailed studies of embankment sections are made.

(4) Foundation rock characteristics such as depthof bedding, solution cavities, fissures, orientation of joints,clay seams, gouge zones, and faults which may affect thestability of rock foundations and slopes, particularly inassociation with seepage, must be investigated to deter-mine the type and scope of treatment required. Further-more, foundations and slopes of clay shales (compactionshales) often undergo loss in strength under reduction ofloading or by disintegration upon weathering. Carefulinvestigation of stability aspects of previous excavationsand of natural slopes should be made. Foundations ofclay shales should be assumed to contain sufficient fis-sures so that the residual shear strength is applicableunless sufficient investigations are made to proveotherwise.

(5) Procedures for surface and subsurface geotechni-cal investigations and geophysical explorations are givenin EM 1110-1-1804 and EM 1110-1-1802, respectively.Soil sampling equipment and procedures are discussed inEM 1110-2-1907 (see also Hvorslev 1948). Foundationsbelieved to have a potential for liquefaction should bethoroughly investigated using in situ testing and dynamicresponse analysis techniques (see Sykora et al. 1991a,1991b; Sykora, Koester, and Hynes 1991a, 1991b; Sykoraand Wahl 1992; Farrar 1990).

b. Foundations.

(1) The foundation is the valley floor and terraceson which the embankment and appurtenant structures rest.Comprehensive field investigations and/or laboratorytesting are required where conditions such as those listedbelow are found in the foundation:

(a) Deposits that may liquefy under earthquakeshock or other stresses.

(b) Weak or sensitive clays.

(c) Dispersive soils.

(d) Varved clays.

(e) Organic soils.

(f) Expansive soils, especially soils containingmontmorillonite, vermiculite, and some mixed layerminerals.

(g) Collapsible soils, usually fine-grained soils oflow cohesion (silts and some clays) that have low naturaldensities and are susceptible to volume reductions whenloaded and wetted.

(h) Clay shales (compaction shales) that expand andlose strength upon unloading and/or exposure to weather-ing frequently have low in situ shear strengths. Althoughclay shales are most troublesome, all types of shales maypresent problems when they contain sheared and slicken-sided zones.

(i) Limestones or calcareous soil deposits contain-ing solution channels.

(j) Gypsiferous rocks or soils.

(k) Subsurface openings from abandoned mines.

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(l) Clay seams, shear zones, or mylonite seams inrock foundations.

(m) Rock formations in which the rock quality des-ignation (RQD) is low (less than 50 percent).

(2) Subsurface investigation for foundations shoulddevelop the following data:

(a) Subsurface profiles showing rock and soilmaterials and geological formations, including presence offaults, buried channels, and weak layers or zones. TheRQD is useful in the assessment of the engineering quali-ties of bedrock (see Deere and Deere 1989).

(b) Characteristics and properties of soils and theweaker types of rock.

(c) Piezometric levels of groundwater in variousstrata and their variation with time including artisan pres-sures in rock or soil.

(3) Exploratory adits in abutments, test pits, testtrenches, large-diameter calyx holes, and large-diametercore boring are often necessary to satisfactorily investigatefoundation and abutment conditions and to investigatereasons for core losses or rod droppings. Borehole pho-tography and borehole television may also be useful.Core losses and badly broken cores often indicate zonesthat control the stability of a foundation or excavationslope and indicate a need for additional exploration.

(4) Estimates of foundation permeability fromlaboratory tests are often misleading. It is difficult toobtain adequate subsurface data to evaluate permeabilityof gravelly strata in the foundation. Churn drilling hasoften proven satisfactory for this purpose. Pumping testsare required in pervious foundations to determine founda-tion permeability where seepage cutoffs are not providedor where deep foundation unwatering is required (seeEM 1110-2-1901).

c. Abutments. The abutments of a dam include thatportion of the valley sides to which the ends of the damjoin and also those portions beyond the dam which mightpresent seepage or stability problems affecting the dam.Right and left abutments are so designated looking in adownstream direction. Abutment areas require essentiallythe same investigations as foundation areas. Serious seep-age problems have developed in a number of casesbecause of inadequate investigations during design.

d. Valley walls close to dam. Underground riverchannels or porous seepage zones may pass around the

abutments. The valley walls immediately upstream anddownstream from the abutment may have steep naturalslopes and slide-prone areas that may be a hazard totunnel approach and outlet channels. Such areas shouldbe investigated sufficiently to determine if correctivemeasures are required.

e. Spillway and outlet channel locations. Theseareas require comprehensive investigations of the orienta-tion and quality of rock or firm foundation stratum.Explorations should provide sufficient information on theoverburden and rock to permit checking stability of exca-vated slopes and determining the best utilization of exca-vated material within the embankment. Where a spillwayis to be located close to the end of a dam, the rock orearth mass between the dam and spillway must be investi-gated carefully.

f. Saddle dams. The extent of foundation investi-gations required at saddle dams will depend upon theheights of the embankments and the foundation conditionsinvolved. Exploratory borings should be made at all suchstructures.

g. Reservoir crossings. The extent of foundationinvestigations required for highway and railway crossingof the reservoir depends on the type of structure, itsheight, and the foundation conditions. Such embankmentsmay be subjected to considerable wave action and requireslope protection. The slope protection will be designedfor the significant wave based on a wave hind cast analy-sis as described in Appendix C and the referenced designdocument. Select the design water level and wind speedbased on an analysis of the risk involved in failure of theembankment. For example, an evacuation route needs ahigher degree of protection, perhaps equal to the damface, than an access road to a recreational facility whichmay be cheaper to replace than to protect.

h. Reservoir investigations. The sides and bottomof a reservoir should be investigated to determine if thereservoir will hold water and if the side slopes willremain stable during reservoir filling, subsequent draw-downs, and when subjected to earthquake shocks.Detailed analyses of possible slide areas should be madesince large waves and overtopping can be caused byslides into the reservoir with possible serious conse-quences (see Hendron and Patton 1985a, 1985b). Watertable studies of reservoir walls and surrounding area areuseful, and should include, when available, data on localwater wells. In limestone regions, sinks, caverns, andother solution features in the reservoir walls should bestudied to determine if reservoir water will be lost through

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them. Areas containing old mines should be studied. Inareas where there are known oil fields, existing recordsshould be surveyed and reviewed to determine if pluggingold wells or other treatment is required.

i. Borrow areas and excavation areas. Borrowareas and areas of required excavation require investiga-tions to delineate usable materials as to type, gradation,depth, and extent; provide sufficient disturbed samples todetermine permeability, compaction characteristics, com-pacted shear strength, volume change characteristics, andnatural water contents; and provide undisturbed samplesto ascertain the natural densities and estimated yield ineach area. The organic content or near-surface borrowsoils should be investigated to establish stripping require-ments. It may be necessary to leave a natural imperviousblanket over pervious material in upstream borrow areasfor underseepage control. Of prime concern in consider-ing possible valley bottom areas upstream of the embank-ment is flooding of these bottom areas. The sequence ofconstruction and flooding must be studied to ensure thatsufficient borrow materials will be available from higherelevations or stockpiles to permit completion of the dam.Sufficient borrow must be in a nonflooding area to com-plete the embankment after final closure, or provisionmust be made to stockpile low-lying material at a higherelevation. The extent of explorations will be determinedlargely by the degree of uniformity of conditions found.Measurements to determine seasonal fluctuation of thegroundwater table and changes in water content should bemade. Test pits, dozer trenches, and large-diameter augerholes are particularly valuable in investigating borrowareas and have additional value when left open for inspec-tion by prospective bidders.

j. Test quarries. The purposes of test quarries areto assist in cut slope design, evaluate the controlling geo-logic structure, provide information on blasting techniquesand rock fragmentation, including size and shape of rocks,provide representative materials for test fills, give pro-spective bidders a better understanding of the drilling andblasting behavior of the rock, and determine if quarry-runrock is suitable or if grizzled rock-fill is required (seeEM 1110-2-2302).

k. Test fills. In the design of earth and rock-filldams, the construction of test embankments can often beof considerable value, and in some cases is absolutelynecessary. Factors involved in the design of earth androck-fill dams include the most effective type of compac-tion equipment, lift thickness, number of passes, andplacement water contents; the maximum particle sizeallowable; the amount of degradation or segregation

during handling and compaction; and physical propertiessuch as compacted density, permeability, grain-size distri-bution, and shear strength of proposed embankmentmaterials. Often this information is not available fromprevious experience with similar borrow materials and canbe obtained only by a combination of test fills and labora-tory tests. Test fills can provide a rough estimate ofpermeability through observations of the rate at whichwater drains from a drill hole or from a test pit in the fill.To measure the field permeability of test fills, use a dou-ble-ring infiltrometer with a sealed inner ring (describedin ASTM D 5093-90; see American Society for Testingand Materials 1990). It is important that test fills be per-formed on the same materials that will be used inconstruction of the embankment. The test fills shall beperformed with the same quarry or borrow area materialswhich will be developed during construction and shall becompacted with various types of equipment to determinethe most efficient type and required compaction effort. Itis imperative that as much as possible all materials whichmay be encountered during construction be included inthe test fills. Equipment known not to be acceptableshould be included in the test fill specifications so as notto leave any “gray areas” for possible disagreements as towhat will or will not be acceptable. Plans and specifica-tions for test quarries and test fills of both earth and rock-fill materials are to be submitted to the Headquarters,U.S. Army Corps of Engineers, for approval. Test fillscan often be included as part of access road constructionbut must be completed prior to completion of the embank-ment design. Summarized data from rock test fills forseveral Corps of Engineers projects are available (Ham-mer and Torrey 1973).

l. Retention of samples. Representative samplesfrom the foundation, abutment, spillway excavation, andborrow areas should be retained and stored under suitableconditions at least until construction has been completedand any claims settled. Samples should be available forexamination or testing in connection with unexpectedproblems or contractor claims.

3-2. Laboratory Testing

a. Presentation. A discussion of laboratory testsand presentation of test data for soils investigations inconnection with earth dams are contained in EM 1110-2-1906. Additional information concerning laboratory com-paction of earth-rock mixtures is given by Torrey andDonaghe (1991a, 1991b) and Torrey (1992). Applicabil-ity of the various types of shear tests to be used instability analyses for earth dams is given in EM 1110-2-1902. Rock testing methods are given in theRock Testing

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Handbook(U.S. Army Corps of Engineers 1990). Sinceshear strength tests are expensive and time-consuming,testing programs are generally limited to representativefoundation and borrow materials. Samples to be testedshould be selected only after careful analysis of boringlogs, including index property determinations. Mixing ofdifferent soil strata for test specimens should be avoidedunless it can be shown that mixing of different strataduring construction will produce a fill with characteristicsidentical to those of the laboratory specimens.

b. Procedure. Laboratory test procedures for deter-mining all of the properties of rock-fill and earth-rockmixtures have not been standardized (see Torrey andDonaghe 1991a, 1991b; Torrey 1992). A few division

laboratories have consolidation and triaxial compressionequipment capable of testing 12-in.-diam specimens.

c. Sample. For design purposes, shear strength ofrock-fill and earth-rock mixtures should be determined inthe laboratory on representative samples obtained fromtest fills. Triaxial tests should be performed on specimenscompacted to in-place densities and having grain-sizedistributions paralleling test fill gradations. Core samplescrushed in a jaw crusher or similar device should not beused because the resulting gradation, particle shape, andsoundness are not typical of quarry-run material. For12-in.-diameter specimens, maximum particle size shouldbe 2 in.

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Chapter 4General Design Considerations

4-1. Freeboard

a. Vertical distance. The term freeboard is appliedto the vertical distance of a dam crest above the maxi-mum reservoir water elevation adopted for the spillwaydesign flood. The freeboard must be sufficient to preventovertopping of the dam by wind setup, wave action, orearthquake effects. Initial freeboard must allow for subse-quent loss in height due to consolidation of embankmentand/or foundation. The crest of the dam will generallyinclude overbuild to allow for postconstruction settle-ments. The top of the core should also be overbuilt toensure that it does not settle below its intended elevation.Net freeboard requirements (exclusive of earthquake con-siderations) can be determined using the proceduresdescribed in Saville, McClendon, and Cochran (1962).

b. Elevation. In seismic zones 2, 3, and 4, as delin-eated in Figures A-1 through A-4 of ER 1110-2-1806, theelevation of the top of the dam should be the maximumdetermined by either maximum water surface plus con-ventional freeboard or flood control pool plus 3 percent ofthe height of the dam above streambed. This requirementapplies regardless of the type of spillway.

4-2. Top Width

The top width of an earth or rock-fill dam within conven-tional limits has little effect on stability and is governedby whatever functional purpose the top of the dam mustserve. Depending upon the height of the dam, the mini-mum top width should be between 25 and 40 ft. Wherethe top of the dam is to carry a public highway, road andshoulder widths should conform to highway requirementsin the locality with consideration given to requirementsfor future needs. The embankment zoning near the top issometimes simplified to reduce the number of zones, eachof which requires a minimum width to accommodatehauling and compaction equipment.

4-3. Alignment

Axes of embankments that are long with respect to theirheights may be straight or of the most economical align-ment fitting the topography and foundation conditions.Sharp changes in alignment should be avoided becausedownstream deformation at these locations would tend toproduce tension zones which could cause concentration ofseepage and possibly cracking and internal erosion. The

axes of high dams in narrow, steep-sided valleys shouldbe curved upstream so that downstream deflection underwater loads will tend to compress the impervious zoneslongitudinally, providing additional protection against theformation of transverse cracks in the impervious zones.The radius of curvature forming the upstream arching ofthe dam in narrow valleys generally ranges from 1,000 to3,000 ft.

4-4. Embankment

Embankment sections adjacent to abutments may be flaredto increase stability of sections founded on weak soils.Also, by flaring the core, a longer seepage path is devel-oped beneath and around the embankment.

4-5. Abutments

a. Alignments. Alignments should be avoided thattie into narrow ridges formed by hairpin bends in the riveror that tie into abutments that diverge in the downstreamdirection. Grouting may be required to decrease seepagethrough the abutment (see paragraph 3-1c). Zones ofstructurally weak materials in abutments, such as weath-ered overburden and talus deposits, are not uncommon. Itmay be more economical to flatten embankment slopes toattain the desired stability than to excavate weak materialsto a firm foundation. The horizontal permeability ofundisturbed strata in the abutment may be much greaterthan the permeability of the compacted fill in the embank-ment; therefore, it may be possible to derive considerablebenefit in seepage control from the blanketing effects offlared upstream embankment slopes. The design of atransition from the normal embankment slopes to flattenedslopes is influenced by stability of sections founded onthe weaker foundation materials, drainage provisions onthe slopes and within the embankment, and the desirabil-ity of making a gradual transition without abrupt changesof section. Adequate surface drainage to avoid erosionshould be provided at the juncture between the dam slopeand the abutment.

b. Abutment slopes. Where abutment slopes aresteep, the core, filter, and transition zones of an embank-ment should be widened at locations of possible tensionzones resulting from different settlements. Widening ofthe core may not be especially effective unless cracksdeveloping in it tend to close. Even if cracks remainopen, a wider core may tend to promote clogging. How-ever, materials in the filter and transition zones areusually more self-healing, and increased widths of thesezones are beneficial. Whenever possible, construction ofthe top 25 ft of an embankment adjacent to steep

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abutments should be delayed until significant embankmentand foundation settlement have occurred.

c. Settlement. Because large differential settlementnear abutments may result in transverse cracking withinthe embankment, it may be desirable to use higher place-ment water contents (see paragraph 7-8a) combined withflared sections.

4-6. Earthquake Effects

The embankment and critical appurtenant structuresshould be evaluated for seismic stability. The method ofanalysis is a function of the seismic zone as outlined inER 1110-2-1806. Damsites over active faults should beavoided if at all possible. For projects located near orover faults in earthquake areas, special geological andseismological studies should be performed. Defensivedesign features for the embankment and structures asoutlined in ER 1110-2-1806 should be used, regardless ofthe type of analyses performed. For projects in locationsof strong seismicity, it is desirable to locate the spillwayand outlet works on rock rather than in the embankmentor foundation overburden.

4-7. Coordination Between Design andConstruction

a. Introduction. Close coordination between designand construction personnel is necessary to thoroughlyorient the construction personnel as to the project designintent, ensure that new field information acquired duringconstruction is assimilated into the design, and ensure thatthe project is constructed according to the intent of thedesign. This is accomplished through the report on engi-neering considerations and instructions to field personnel,preconstruction orientation for the construction engineersby the designers, and required visits to the site by thedesigners.

b. Report on engineering considerations andinstructions to field personnel. To ensure that the fieldpersonnel are aware of the design assumptions regardingfield conditions, design personnel (geologists, geotechnicalengineers, structural engineers, etc.) will prepare a reportentitled, “Engineering Considerations and Instructions forField Personnel.” This report should explain the concepts,assumptions, and special details of the embankmentdesign as well as detailed explanations of critical sectionsof the contract documents. Instruction for the fieldinspection force should include the necessary guidance toprovide adequate Government Quality Assurance Testing.This report should be augmented by appropriate briefings,

instructional sessions, and laboratory testing sessions(ER 1110-2-1150).

c. Preconstruction orientation. Preconstructionorientation for the construction engineers by the designersis necessary for the construction engineers to be aware ofthe design philosophies and assumptions regarding siteconditions and function of project structures, and under-stand the design engineers’ intent concerning technicalprovisions in the P&S.

d. Construction milestones which require visit bydesigners. Visits to the site by design personnel arerequired to ensure the following (ER 1110-2-112,ER 1110-2-1150):

(1) Site conditions throughout the constructionperiod are in conformance with design assumptions andprinciples as well as contract P&S.

(2) Project personnel are given assistance in adapt-ing project designs to actual site conditions as they arerevealed during construction.

(3) Any engineering problems not fully assessed inthe original design are observed, evaluated, and appropri-ate action taken.

e. Specific visits. Specifically, site visits arerequired when the following occur (ER 1110-2-112):

(1) Excavation of cutoff trenches, foundations, andabutments for dams and appurtenant structures.

(2) Excavation of tunnels.

(3) Excavation of borrow areas and placement ofembankment dam materials early in the constructionperiod.

(4) Observation of field conditions that are signifi-cantly different from those assumed during design.

4-8. Value Engineering Proposals

The Corps of Engineers has several cost-saving programs.One of these programs, Value Engineering (VE), providesfor a multidiscipline team of engineers to develop alterna-tive designs for some portion of the project. The con-struction contractor can also submit VE proposals. AnyVE proposal affecting the design is to be evaluated bydesign personnel prior to implementation to determine thetechnical adequacy of the proposal. VE proposals must

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not adversely affect the long-term performance or condi-tion of the dam.

4-9. Partnering Between the Owner andContractor

Partnering is the creation of an owner-contractor relation-ship that promotes achievement of mutually beneficialgoals. By taking steps before construction begins tochange the adversarial mindset, to recognize commoninterests, and to establish an atmosphere of trust andcandor in communications, partnering helps to develop acooperative management team. Partnering is not a con-tractual agreement and does not create any legallyenforceable rights or duties. There are three basic stepsinvolved in establishing the partnering relationship:

a. Establish a new relationship through personalcontact.

b. Craft a joint statement of goals and establishcommon objectives in specific detail for reaching thegoals.

c. Identify specific disputes and prevention pro-cesses designed to head off problems, evaluate perfor-mance, and promote cooperation.

Partnering has been used by the Mobile District on OliverLock and Dam replacement and by the Portland Districton Bonneville Dam navigation lock. Detailed instructionsconcerning the partnering process are available inEdelman, Carr, and Lancaster (1991).

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Chapter 5Foundation and Abutment Preparation

5-1. Preparation

a. Earth foundations.

(1) The design of dams on earth foundations isbased on the in situ shear strength of the foundation soils.For weak foundations, use of stage construction, founda-tion strengthening, or excavation of undesirable materialmay be more economical than using flat slopes or stabilityberms.

(2) Foundation preparation usually consists ofclearing, grubbing to remove stumps and large roots inapproximately the top 3 ft, and stripping to remove sod,topsoil, boulders, organic materials, rubbish fills, andother undesirable materials. It is not generally necessaryto remove organic-stained soils. Highly compressiblesoils occurring in a thin surface layer or in isolatedpockets should be removed.

(3) After stripping, the foundation surface will bein a loose condition and should be compacted. However,if a silty or clayey foundation soil has a high water con-tent and high degree of saturation, attempts to compactthe surface with heavy sheepsfoot or rubber-tired rollerswill only remold the soil and disturb it, and only light-weight compaction equipment should be used. Wherepossible without disturbing the foundation soils, trafficover the foundation surface by the heaviest rollers orother construction equipment available is desirable toreveal compressible material that may have been over-looked in the stripping, such as pockets of soft materialburied beneath a shallow cover. Stump holes should befilled and compacted by power-driven hand tampers.

(4) For dams on impervious earth foundations notrequiring a cutoff, an inspection trench having a minimumdepth of 6 ft should be made. This will permit inspectionfor abandoned pipes, soft pockets, tile fields, perviouszones, or other undesirable features not discovered byearlier exploration.

(5) Differential settlement of an embankment maylead to tension zones along the upper portion of the damand to possible cracking along the longitudinal axis in thevicinity of steep abutment slopes at tie-ins or closuresections, or where thick deposits of unsuitable foundationsoils have been removed (since in the latter case, thecompacted fill may have different compressibility

characteristics than adjacent foundation soils). Differen-tial settlements along the dam axis may result in trans-verse cracks in the embankment which can lead to unde-sirable seepage conditions. To minimize this possibility,steep abutment slopes and foundation excavation slopesshould be flattened, if feasible, particularly beneath theimpervious zone of the embankment. This may be eco-nomically possible with earth abutments only. The por-tion of the abutment surface beneath the impervious zoneshould not slope steeply upstream or downstream, as sucha surface might provide a plane of weakness.

(6) The treatment of an earth foundation under arock-fill dam should be substantially the same as that foran earth dam. The surface layer of the foundationbeneath the downstream rock-fill section must meet filtergradation criteria, or a filter layer must be provided, sothat seepage from the foundation does not carry founda-tion material into the rock fill.

b. Rock foundations.

(1) Rock foundations should be cleaned of all loosefragments, including semidetached surface blocks of rockspanning relatively open crevices. Projecting knobs ofrock should be removed to facilitate operation of compac-tion equipment and to avoid differential settlement.Cracks, joints, and openings beneath the core and possiblyelsewhere (see below) should be filled with mortar or leanconcrete according to the width of opening. The treat-ment of rock defects should not result in layers of groutor gunite that cover surface areas of sound rock, sincethey might crack under fill placement and compactionoperations.

(2) The excavation of shallow exploration or coretrenches by blasting may damage the rock. Where thismay occur, exploration trenches are not recommended,unless they can be excavated without blasting. Wherecore trenches disclose cavities, large cracks, and joints,the core trench should be backfilled with concrete toprevent possible erosion of core materials by water seep-ing through joints or other openings in the rock.

(3) Shale foundations should not be permitted to dryout before placing embankment fill, nor should they bepermitted to swell prior to fill placement. Consequently,it is desirable to defer removal of the last few feet ofshale until just before embankment fill placement begins.

(4) Where an earth dam is constructed on a jointedrock foundation, it is essential to prevent embankment fillfrom entering joints or other openings in the rock. This

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can be done in the core zone by extending the zone intosound rock and by treating the rock as discussed above.Where movement of shell materials into openings in therock foundation is possible, joints and other openingsshould be filled, as discussed, beneath both upstream anddownstream shells. An alternative is to provide filterlayers between the foundation and the shells of the dam.Such treatment will generally not be necessary beneathshells of rock-fill dams.

(5) Limestone rock foundation may contain solu-tion cavities and require detailed investigations, specialobservations when making borings (see EM 1110-1-1804),and careful study of aerial photographs, combined withsurface reconnaissance to establish if surface sinks arepresent. However, the absence of surface sinks cannot beaccepted as proof that a foundation does not contain solu-tion features. The need for removing soil or decomposedrock overlying jointed rock, beneath both upstream anddownstream shells, to expose the joints for treatment,should receive detailed study. If joints are not exposedfor treatment and are wide, material filling them may bewashed from the joints when the reservoir pool rises, orthe joint-filling material may consolidate. In either case,embankment fill may be carried into the joint, which mayresult in excessive reservoir seepage or possible piping.This consideration applies to both earth and rock-filldams.

(6) Where faults or wide joints occur in theembankment foundation, they should be dug out, cleanedand backfilled with lean concrete, or otherwise treated aspreviously discussed, to depths of at least three times theirwidths. This will provide a structural bridge over thefault or joint-filling materials and will prevent theembankment fill from being lost into the joint or fault. Inaddition, the space beneath the concrete plug should begrouted at various depths by grout holes drilled at anangle to intersect the space. This type of treatment isobviously required beneath cores of earth and rock-filldams and also beneath rock-fill shells.

c. Abutment treatment. The principal hazards thatexist on rock abutments are due to irregularities in thecleaned surfaces and to cracks or fissures in the rock.Cleaned areas of the abutments should include all surfacesbeneath the dam with particular attention given to areas incontact with the core and filters. It is good practice torequire both a preliminary and final cleanup of theseareas. The purpose of the preliminary cleanup is to facili-tate inspection to identify areas that require additionalpreparation and treatment. Within these areas, all irregu-larities should be removed or trimmed back to form a

reasonably uniform slope on the entire abutment. Over-hangs must be eliminated by use of concrete backfillbeneath the overhang or by barring and wedging toremove the overhanging rock. Concrete backfill mayhave to be placed by shotcrete, gunite, or similar methodsto fill corners beneath overhangs. Vertical rock surfacesbeneath the embankment should be avoided or, if per-mitted, should not be higher than 5 ft, and benchesbetween vertical surfaces should be of such width as toprovide a stepped slope comparable to the uniform slopeon adjacent areas. Relatively flat abutments are desirableto avoid possible tension zones and resultant cracking inthe embankment, but this may not be economically possi-ble where abutment slopes are steep. In some cases,however, it may be economically possible to flatten nearvertical rock abutments so they have a slope of 2 verticalon 1 horizontal or 1 vertical on 1 horizontal, therebyminimizing the possibility of cracking. Flattening of theabutment slope may reduce the effects of rebound crack-ing (i.e., stress relief cracking) that may have accompa-nied the development of steep valley walls. The cost ofabutment flattening may be offset by reductions in abut-ment grouting. The cost of foundation and abutmenttreatment may be large and should be considered whenselecting damsites and type of dam.

5-2. Strengthening the Foundation

a. Weak rock. A weak rock foundation requiresindividual investigation and study, and dams on suchfoundations usually require flatter slopes. The possibilityof artisan pressures developing in stratified rock mayrequire installation of pressure relief wells.

b. Liquefiable soil. Methods for improvement ofliquefiable soil foundation conditions include blasting,vibratory probe, vibro-compaction, compaction piles,heavy tamping (dynamic compaction), compaction (dis-placement) grouting, surcharge/buttress, drains, particulategrouting, chemical grouting, pressure-injected lime, elec-trokinetic injection, jet grouting, mix-in-place piles andwalls, insitu vitrification, and vibro-replacement stone andsand columns (Ledbetter 1985, Hausmann 1990, Moseley1993).

c. Foundations. Foundations of compressible fine-grained soils can be strengthened by use of wick drains,electroosmotic treatment, and slow construction and/orstage construction to allow time for consolidation tooccur. Because of its high cost, electroosmosis has beenused (but only rarely) to strengthen foundations. It wasused at West Branch Dam (now Michael J. Kirwan Dam),Wayland, Ohio, in 1966, where excessive foundation

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movements occurred during embankment construction(Fetzer 1967).

5-3. Dewatering the Working Area

a. Trenches. Where cutoff or drainage trenchesextend below the water table, a complete dewatering isnecessary to prepare properly the foundation and to com-pact the first lifts of embankment fill. This may also benecessary where materials sensitive to placement watercontent are placed on embankment foundations having agroundwater level close to the surface. This may occur,for example, in closure sections.

b. Excavation slopes. The contractor should beallowed a choice of excavation slopes and methods of

water control subject to approval of the ContractingOfficer (but this must not relieve the contractor of hisresponsibility for satisfactory construction). In establish-ing payment lines for excavations, such as cutoff or drain-age trenches below the water table, it is desirable tospecify that slope limits shown are for payment purposesonly and are not intended to depict stable excavationslopes. It is also desirable to indicate the need for watercontrol using wellpoints, deep wells, sheeted sumps, slurrytrench barriers, etc. Water control measures such as deepwells or other methods may have to be extended into rockto lower the groundwater level in rock foundations. If thegroundwater is to be lowered to a required depth belowthe base of the excavation, this requirement shall be statedin the specifications. Dewatering and groundwater controlare discussed in detail in TM 5-818-5.

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Chapter 6Seepage Control

6-1. General

All earth and rock-fill dams are subject to seepagethrough the embankment, foundation, and abutments.Seepage control is necessary to prevent excessive upliftpressures, instability of the downstream slope, pipingthrough the embankment and/or foundation, and erosionof material by migration into open joints in the foundationand abutments. The purpose of the project, i.e., long-termstorage, flood control, etc., may impose limitations on theallowable quantity of seepage. Detailed informationconcerning seepage analysis and control for dams is givenin EM 1110-2-1901.

6-2. Embankment

a. Methods for seepage control. The three methodsfor seepage control in embankments are flat slopes with-out drains, embankment zonation, and vertical (orinclined) and horizontal drains.

(1) Flat slopes without drains. For some damsconstructed with impervious soils having flat embankmentslopes and infrequent, short duration, high reservoir lev-els, the phreatic surface may be contained well within thedownstream slope and escape gradients may be suffi-ciently low to prevent piping failure. For these dams,when it can be ensured that variability in the characteris-tics of borrow materials will not result in adverse stratifi-cation in the embankment, no vertical or horizontal drainsare required to control seepage through the embankment.Examples of dams constructed with flat slopes withoutvertical or horizontal drains are Aquilla Dam, AubreyDam (now called Ray Roberts Dam), and Lakeview Dam.A horizontal drainage blanket under the downstreamembankment may still be required for control ofunderseepage.

(2) Embankment zonation. Embankments arezoned to use as much material as possible from requiredexcavation and from borrow areas with the shortest hauldistances, the least waste, the minimum essential process-ing and stockpiling, and at the same time maintainstability and control seepage. For most effective controlof through seepage and seepage during reservoir draw-down, the permeability should progressively increase fromthe core out toward each slope.

(3) Vertical (or inclined) and horizontal drains.Because of the often variable characteristics of borrowmaterials, vertical (or inclined) and horizontal drainswithin the downstream portion of the embankment areprovided to ensure satisfactory seepage control. Also, thevertical (or inclined) drain provides the primary line ofdefense to control concentrated leaks through the core ofan earth dam (see EM 1110-2-1901).

b. Collector pipes. Collector pipes should not beplaced within the embankment, except at the downstreamtoe, because of the danger of either breakage or separationof joints, resulting from fill placement and compactingoperations or settlement, which might result in eitherclogging or piping. However, a collector pipe at thedownstream toe can be placed within a small bermlocated at the toe, since this facilitates maintenance andrepair.

6-3. Earth Foundations

a. Introduction. All dams on earth foundations aresubject to underseepage. Seepage control is necessary toprevent excessive uplift pressures and piping through thefoundation. Generally, siltation of the reservoir with timewill tend to diminish underseepage. Conversely, the useof some underseepage control methods, such as reliefwells and toe drains, may increase the quantity of under-seepage. The methods of control of underseepage in damfoundations are horizontal drains, cutoffs (compactedbackfill trenches, slurry walls, and concrete walls),upstream impervious blankets, downstream seepageberms, relief wells, and trench drains. To select an under-seepage control method for a particular dam and founda-tion, the relative merits and efficiency of differentmethods should be evaluated by means of flow nets orapproximate methods (as described Chapter 4 and Appen-dix B, respectively, of EM 1110-2-1901). The changes inthe quantity of underseepage, factor of safety againstuplift, and uplift pressures at various locations should bedetermined for each particular dam and foundation vary-ing the anisotropy ratio of the permeability of thefoundation to cover the possible range of expected fieldconditions (see Table 9-1 of EM 1110-2-1901).

b. Horizontal drains. As mentioned previously,horizontal drains are used to control seepage through theembankment and to prevent excessive uplift pressures inthe foundation. The use of the horizontal drain signifi-cantly reduces the uplift pressure in the foundation underthe downstream portion of the dam. The use of the

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horizontal drain increases the quantity of seepage underthe dam (see Figure 9-1 of EM 1110-2-1901).

c. Cutoffs.

(1) Complete versus partial cutoff. When the damfoundation consists of a relatively thick deposit of pervi-ous alluvium, the designer must decide whether to make acomplete cutoff or allow a certain amount of underseep-age to occur under controlled conditions. It is necessaryfor a cutoff to penetrate a homogeneous isotropic founda-tion at least 95 percent of the full depth before there isany appreciable reduction in seepage beneath a dam. Theeffectiveness of the partial cutoff in reducing the quantityof seepage decreases as the ratio of the width of the damto the depth of penetration of the cutoff increases. Partialcutoffs are effective only when they extend down into anintermediate stratum of lower permeability. This stratummust be continuous across the valley foundation to ensurethat three-dimensional seepage around a discontinuousstratum does not negate the effectiveness of the partialcutoff.

(2) Compacted backfill trench. The most positivemethod for control of underseepage consists of excavatinga trench beneath the impervious zone of the embankmentthrough pervious foundation strata and backfilling it withcompacted impervious material. The compacted backfilltrench is the only method for control of underseepagewhich provides a full-scale exploration trench that allowsthe designer to see the actual natural conditions and toadjust the design accordingly, permits treatment ofexposed bedrock as necessary, provides access for instal-lation of filters to control seepage and prevent piping ofsoil at interfaces, and allows high quality backfillingoperations to be carried out. When constructing a com-plete cutoff, the trench must fully penetrate the perviousfoundation and be carried a short distance into unweath-ered and relatively impermeable foundation soil or rock.To ensure an adequate seepage cutoff, the width of thebase of the cutoff should be at least one-fourth the maxi-mum difference between the reservoir and tailwater eleva-tions but not less than 20 ft, and should be wider if thefoundation material under the cutoff is considered margi-nal in respect to imperviousness. If the gradation of theimpervious backfill is such that the pervious foundationmaterial does not provide protection against piping, anintervening filter layer between the impervious backfilland the foundation material is required on the downstreamside of the cutoff trench. The cutoff trench excavationmust be kept dry to permit proper placement and compac-tion of the impervious backfill. Dewatering systems ofwellpoints or deep wells are generally required during

excavation and backfill operations when below ground-water levels (TM 5-818-5). Because construction of anopen cutoff trench with dewatering is a costly procedure,the trend has been toward use of the slurry trench cutoff.

(3) Slurry trench. When the cost of dewateringand/or the depth of the pervious foundation render thecompacted backfill trench too costly and/or impractical,the slurry trench cutoff may be a viable method for con-trol of underseepage. Using this method, a trench isexcavated through the pervious foundation using a sodiumbentonite clay (or Attapulgite clay in saline water) andwater slurry to support the sides. The slurry-filled trenchis backfilled by displacing the slurry with a backfillmaterial that contains enough fines (material passing theNo. 200 sieve) to make the cutoff relatively imperviousbut sufficient coarse particles to minimize settlement ofthe trench forming the soil-bentonite cutoff. Alterna-tively, a cement may be introduced into the slurry-filledtrench which is left to set or harden forming a cement-bentonite cutoff. The slurry trench cutoff is not recom-mended when boulders, talus blocks on buried slopes, oropen jointed rock exist in the foundation due to difficul-ties in excavating through the rock and slurry loss throughthe open joints. When a slurry trench is relied upon forseepage control, the initial filling of the reservoir must becontrolled and piezometers located both upstream anddownstream of the cutoff must be read to determine if theslurry trench is performing as planned. If the cutoff isineffective, remedial seepage control measures must beinstalled prior to further raising of the reservoir pool.Normally, the slurry trench should be located under ornear the upstream toe of the dam. An upstream locationprovides access for future treatment provided the reservoircould be drawn down and facilitates stage construction bypermitting placement of a downstream shell followed byan upstream core tied into the slurry trench. For stabilityanalysis, a soil-bentonite slurry trench cutoff should beconsidered to have zero shear strength and exert only ahydrostatic force to resist failure of the embankment. Thedesign and construction of slurry trench cutoffs is coveredin Chapter 9 of EM 1110-2-1901. Guide specificationCW-03365 is available for soil-bentonite slurry trenchcutoffs.

(4) Concrete wall. When the depth of the perviousfoundation is excessive (>150 ft) and/or the foundationcontains cobbles, boulders, or cavernous limestone, theconcrete cutoff wall may be an effective method for con-trol of underseepage. Using this method, a cast-in-placecontinuous concrete wall is constructed by tremie place-ment of concrete in a bentonite-slurry supported trench.Two general types of concrete cutoff walls, the panel wall

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and the element wall, have been used. Since the wall inits simpler structural form is a rigid diaphragm,earthquakes could cause its rupture; therefore, concretecutoff walls should not be used at a site where strongearthquake shocks are likely. The design and constructionof concrete cutoff walls is covered in Chapter 9 ofEM 1110-2-1901. Guide specification CW-03365 isavailable for the concrete used in concrete cutoff walls.

d. Upstream impervious blanket.1 When a completecutoff is not required or is too costly, an upstream imper-vious blanket tied into the impervious core of the dammay be used to minimize underseepage. An example isshown in Figure 2-1f. Upstream impervious blanketsshould not be used when the reservoir head exceeds200 ft because the hydraulic gradient acting across theblanket may result in piping and serious leakage. Down-stream underseepage control measures (relief wells or toetrench drains) are generally required for use withupstream blankets to control underseepage and/or preventexcessive uplift pressures and piping through the founda-tion. Upstream impervious blankets are used in somecases to reinforce thin spots in natural blankets. Effec-tiveness of upstream impervious blankets depends upontheir length, thickness, and vertical permeability, and onthe stratification and permeability of soils on which theyare placed. The design and construction of upstreamblankets is given in EM 1110-2-1901.

e. Downstream seepage berm. When a completecutoff is not required or is too costly, and it is not feasi-ble to construct an upstream impervious blanket, a down-stream seepage berm may be used to reduce upliftpressures in the pervious foundation underlying an imper-vious top stratum at the downstream toe of the dam.Other downstream underseepage control measures (reliefwells or toe trench drains) are generally required for usewith downstream seepage berms. Downstream seepageberms can be used to control underseepage efficientlywhere the downstream top stratum is relatively thin anduniform or where no top stratum is present, but they arenot efficient where the top stratum is relatively thick andhigh uplift pressures develop. Downstream seepageberms may vary in type from impervious to completelyfree draining. The selection of the type of downstreamseepage berm to use is based upon the availability ofborrow materials and relative cost of each type. The

_____________________________1 The blanket may be impervious or semipervious (leaksin the vertical direction).

design and construction of downstream seepage berms isgiven in EM 1110-2-1901.

f. Relief wells. When a complete cutoff is notrequired or is too costly, relief wells installed along thedownstream toe of the dam may be used to prevent exces-sive uplift pressures and piping through the foundation.Relief wells increase the quantity of underseepage from20 to 40 percent, depending upon the foundation condi-tions. Relief wells may be used in combination withother underseepage control measures (upstream impervi-ous blanket or downstream seepage berm) to preventexcessive uplift pressures and piping through the founda-tion. Relief wells are applicable where the pervious foun-dation has a natural impervious cover. The well screensection, surrounded by a filter if necessary, should pene-trate into the principal pervious stratum to obtain pressurerelief, especially where the foundation is stratified. Thewells, including screen and riser pipe, should have adiameter which will permit the maximum design flowwithout excessive head losses but in no instance shouldthe inside diameter be less than 6 in. Geotextiles shouldnot be used in conjunction with relief wells. Relief wellsshould be located so that their tops are accessible forcleaning, sounding for sand, and pumping to determinedischarge capacity. Relief wells should discharge intoopen ditches or into collector systems outside of the dambase which are independent of toe drains or surface drain-age systems. Experience with relief wells indicates thatwith the passage of time the discharge of the wells willgradually decrease due to clogging of the well screenand/or reservoir siltation. Therefore, the amount of wellscreen area should be designed oversized and a piezome-ter system installed between the wells to measure theseepage pressure, and if necessary additional relief wellsshould be installed. The design, construction, and rehabil-itation of relief wells is given in EM 1110-2-1914.

g. Trench drain. When a complete cutoff is notrequired or is too costly, a trench drain may be used inconjunction with other underseepage control measures(upstream impervious blanket and/or relief wells) to con-trol underseepage. A trench drain is a trench generallycontaining a perforated collector pipe and backfilled withfilter material. Trench drains are applicable where the topstratum is thin and the pervious foundation is shallow sothat the trench can penetrate into the aquifer. The exis-tence of moderately impervious strata or even stratifiedfine sands between the bottom of the trench drain and theunderlying main sand aquifer will render the trench drainineffective. Where the pervious foundation is deep, atrench drain of practical depth would only attract a small

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portion of underseepage, and detrimental underseepagewould bypass the drain and emerge downstream of thedrain, thereby defeating its purpose. Trench drains maybe used in conjunction with relief well systems to collectseepage in the upper pervious foundation that the deeperrelief wells do not drain. If the volume of seepage issufficiently large, the trench drain is provided with aperforated pipe. A trench drain with a collector pipe alsoprovides a means of measuring seepage quantities and ofdetecting the location of any excessive seepage. Thedesign and construction of trench drains is given inEM 1110-2-1901.

h. Drainage galleries. Internal reinforced concretegalleries have been used in earth and rockfill dams builtin Europe for grouting, drainage, and monitoring ofbehavior. Galleries have not been constructed in embank-ment dams built by the Corps of Engineers to date. Somepossible benefits to be obtained from the use of galleriesin earth and rockfill dams are (Sherard et al. 1963):

(1) Construction of the embankment can be carriedout independently of the grouting schedule.

(2) Drain holes drilled in the rock foundationdownstream from the grout curtain can be discharged intothe gallery, and observations of the quantities of seepagein these drain holes will indicate where foundation leaksare occurring.

(3) Galleries provide access to the foundationduring and after reservoir filling so that additional grout-ing or drainage can be installed, if required, and theresults evaluated from direct observations.

(4) The additional weight of the overlyingembankment allows higher grout pressures to be used.

(5) Galleries can be used to house embankmentand foundation instrumentation outlets in a more conven-ient fashion than running them to the downstream toe ofthe dam.

(6) If the gallery is constructed in the form of atunnel below the rock surface along the longitudinal axisof the dam, it serves as an exploratory tunnel for the rockfoundation. The minimum size cross section recom-mended for galleries and access shafts is 8 ft by 8 ft toaccommodate drilling and grouting equipment. A gutterlocated along the upstream wall of the gallery along theline of grout holes will carry away cuttings from thedrilling operation and waste grout from the grouting oper-ation. A gutter and system of weirs located along the

downstream wall of the gallery will allow for determina-tion of separate flow rates for foundation drains.

6-4. Rock Foundations

a. General considerations. Seepage should be cutoff or controlled by drainage whenever economicallyfeasible. Safety must be the governing factor for selec-tion of a seepage control method (see EM 1110-2-1901).

b. Cutoff trenches. Cutoff trenches are normallyemployed when the character of the foundation is suchthat construction of a satisfactory grout curtain is notpractical. Cutoff trenches are normally backfilled withcompacted impervious material, bentonite slurry, or neatcement. Construction of trenches in rock foundationsnormally involves blasting using the presplit method withprimary holes deck-loaded according to actual foundationconditions. After blasting, excavation is normally accom-plished with a backhoe. Cutoff of seepage within thefoundation is obtained by connecting an impervious por-tion of the foundation to the impervious portion of thestructure by backfilling the trench with an imperviousmaterial. In rock foundations, as in earth foundations, theimpervious layer of the foundation may be sandwichedbetween an upper and a lower pervious layer, and a cutoffto such an impervious layer would reduce seepage onlythrough the upper pervious layer. However, when thethicknesses of the impervious and upper pervious layersare sufficient, the layers may be able to resist the upwardseepage pressures existing in the lower pervious layer andthus remain stable.

c. Upstream impervious blankets. Imperviousblankets may sometimes give adequate control of seepagewater for low head structures, but for high head structuresit is usually necessary to incorporate a downstream drain-age system as a part of the overall seepage control design.The benefits derived from the impervious blanket are dueto the dissipation of a part of the reservoir head throughthe blanket. The proportion of head dissipated is depen-dent upon the thickness, length, and effective permeabilityof the blanket in relation to the permeability of the foun-dation rock. A filter material is normally requiredbetween the blanket and foundation.

d. Grouting. Grouting of rock foundations is usedto control seepage. Seepage in rock foundations occursthrough cracks and joints, and effectiveness of groutingdepends on the nature of the jointing (crack width, spac-ing, filling, etc.) as well as on the grout mixtures, equip-ment, and procedures.

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(1) A grout curtain is constructed beneath theimpervious zone of an earth or rock-fill dam by drillinggrout holes and injecting a grout mix. A grout curtainconsisting of a single line of holes cannot be dependedupon to form a reliable seepage barrier; therefore, a mini-mum of three lines of grout holes should be used in arock foundation. Through a study of foundation condi-tions revealed by geologic investigations, the engineer andgeologist can establish the location of the grout curtain inplan, the depths of the grout holes, and grouting proce-dures. Once grouting has been initiated, the extent anddetails of the program should be adjusted, as drillingyields additional geological information and as observa-tions of grout take and other data become available.

(2) Careful study of grouting requirements isnecessary when the foundation is crossed by faults, partic-ularly when the shear zone of a fault consists of badlycrushed and fractured rock. It is desirable to seal off suchzones by area (consolidation) grouting. When such a faultcrosses the proposed dam axis, it may be advisable toexcavate along the fault and pour a wedge-shaped con-crete cap in which grout pipes are placed so that the faultzone can be grouted at depth between the upstream anddownstream toes of the dam. The direction of grout holesshould be oriented to optimize the intersection of jointsand other defects.

(3) Many limestone deposits contain solutioncavities. When these are suspected to exist in the founda-tion, one line (or more) of closely spaced explorationholes is appropriate, since piping may develop or theroofs of undetected cavities may collapse and becomefilled with embankment material, resulting in developmentof voids in the embankment. All solution cavities belowthe base of the embankment should be grouted with multi-ple lines of grout holes.

(4) The effectiveness of a grouting operation maybe evaluated by pre- and post-grouting pressure injectiontests for evaluating the water take and the foundationpermeability.

(5) Development of grouting specifications is adifficult task, and it is even more difficult to find experi-enced and reliable organizations to execute a groutingprogram so as to achieve satisfactory results. Groutingoperations must be supervised by engineers and geologistswith specialized experience. A compendium offoundation grouting practices at Corps of Engineers damsis available (Albritton, Jackson, and Bangert 1984). Acomprehensive coverage of drilling methods, as well asgrouting methods, is presented in EM 1110-2-3506.

6-5. Abutments

a. Through earth abutments. Earth and rock-filldams, particularly in glaciated regions, may have perviousmaterial, resulting from filling of the preglacial valleywith alluvial or morainal deposits followed by the down-cutting of the stream, in one or both abutments. Seepagecontrol through earth abutments is provided by extendingthe upstream impervious blanket in the lateral direction towrap around the abutment up to the maximum watersurface elevation, by placing a filter layer between thepervious abutment and the dam downstream of the imper-vious core section, and, if necessary, by installing reliefwells at the downstream toe of the pervious abutment.Examples of seepage control through earth abutments aregiven in EM 1110-2-1901.

b. Through rock abutments. Seepage should be cutoff or controlled by drainage whenever economicallypossible. When a cutoff trench is used, cutoff of seepagewithin the abutment is normally obtained by extending thecutoff from above the projected seepage line to an imper-vious layer within the abutment. Impervious blanketsoverlying the upstream face of pervious abutments areeffective in reducing the quantity of seepage and to someextent will reduce uplift pressures and gradients down-stream. A filter material is normally required at the inter-face between the impervious blanket and rock abutment.The design and construction of upstream imperviousblankets is given in EM 1110-2-1901.

6-6. Adjacent to Outlet Conduits

When the dam foundation consists of compressible soils,the outlet works tower and conduit should be foundedupon or in stronger abutment soils or rock. When con-duits are laid in excavated trenches in soil foundations,concrete seepage collars should not be provided solely forthe purpose of increasing seepage resistance since theirpresence often results in poorly compacted backfill aroundthe conduit. Collars should only be included as necessaryfor coupling of pipe sections or to accommodate differen-tial movement on yielding foundations. When needed forthese purposes, collars with a minimum projection fromthe pipe surface should be used. Excavations for outletconduits in soil foundations should be wide enough toallow for backfill compaction parallel to the conduit usingheavy rolling compaction equipment. Equipment used tocompact along the conduit should be free of framing thatprevents its load transferring wheels or drum from work-ing against the structure. Excavated slopes in soil forconduits should be no steeper than 1 vertical to 2

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horizontal to facilitate adequate compaction and bondingof backfill with the sides of the excavation. Drainagelayers should be provided around the conduit in the down-stream zone of embankments without pervious shells. Aconcrete plug should be used as backfill in rock cuts forcut-and-cover conduits within the core zone to ensure awatertight bond between the conduit and vertical rocksurfaces. The plug, which can be constructed of leanconcrete, should be at least 50 ft long and extend up tothe original rock surface. In embankments having a ran-dom or an impervious downstream shell, horizontal drain-age layers should be placed along the sides and over thetop of conduits downstream of the impervious core.

6-7. Beneath Spillways and Stilling Basins

Adequate drainage should be provided under floor slabsfor spillways and stilling basins to reduce uplift pressures.For soil foundations, a drainage blanket under the slabwith transverse perforated pipe drains discharging throughthe walls or floor is generally provided, supplemented inthe case of stratified foundations by deep well systems.Drainage of a slab on rock is usually accomplished bydrain holes drilled in the rock with formed holes or pipesthrough the slab. The drainage blanket is designed toconvey the seepage quickly and effectively to the trans-verse collector drains. It is designed as a graded reversefilter with coarse stones adjacent to the perforated drainpipe and finer material adjacent to the concrete structureto prevent the migration of fines into the drains. Outletsfor transverse drains in the spillway chute dischargethrough the walls or floor at as low an elevation as practi-cal to obtain maximum pressure reduction. Wall outletsshould be 1 ft minimum above the floor to prevent block-ing by debris. Cutoffs are provided at each transversecollector pipe to minimize buildup of head in case ofmalfunction of the pipe drain. Drains should be at least6 in. in diameter and have at least two outlets to minimize

the chance of plugging. Outlets should be provided withflat-type check valves to prevent surging and the entranceof foreign matter in the drainage system. For the stillingbasin floor slab, it may be advantageous to place a con-necting header along each wall and discharge all slabdrainage into the stilling basin just upstream from thehydraulic jump at the lowest practical elevation in orderto secure the maximum reduction of uplift for the down-stream portion of the slab. A closer spacing of drains isusually required than in the spillway chute because ofgreater head and considerable difference in water depth ina short distance through the hydraulic jump. Piezometersshould be installed in the drainage blanket and deeperstrata, if necessary, to monitor the performance of thedrainage system. If the drains or wells become pluggedor otherwise noneffective, uplift pressures will increasewhich could adversely affect the stability of the structure(EM 1110-2-1602, EM 1110-2-1603, andEM 1110-2-1901).

6-8. Seepage Control Against Earthquake Effects

For earth and rock-fill dams located where earthquakeeffects are likely, there are several considerations whichcan lead to increased seepage control and safety. Geo-metric considerations include using a vertical instead ofinclined core, wider dam crest, increased freeboard, flatterembankment slopes, and flaring the embankment at theabutments (Sherard 1966, 1967). The core materialshould have a high resistance to erosion (Arulanandan andPerry 1983). Relatively wide transition and filter zonesadjacent to the core and extending the full height of thedam can be used. Additional screening and compactionof outer zones or shells will increase permeability andshear strength, respectively. Because of the possibility ofmovement along existing or possibly new faults, it isdesirable to locate the spillway and outlet works on rockrather than in the embankment or foundation overburden.

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Chapter 7Embankment Design

7-1. Embankment Materials

a. Earth-fill materials.

(1) While most soils can be used for earth-fill con-struction as long as they are insoluble and substantiallyinorganic, typical rock flours and clays with liquid limitsabove 80 should generally be avoided. The term “soil” asused herein includes such materials as soft sandstone orother rocks that break down into soil during handling andcompaction.

(2) If a fine-grained soil can be brought readilywithin the range of water contents suitable for compactionand for operation of construction equipment, it can beused for embankment construction. Some slow-dryingimpervious soils may be unusable as embankment fillbecause of excessive moisture, and the reduction of mois-ture content would be impracticable in some climaticareas because of anticipated rainfall during construction.In other cases, soils may require additional water toapproach optimum water content for compaction. Evenponding or sprinkling in borrow areas may be necessary.The use of fine-grained soils having high water contentsmay cause high porewater pressures to develop in theembankment under its own weight. Moisture penetrationinto dry hard borrow material can be aided by ripping orplowing prior to sprinkling or ponding operations.

(3) As it is generally difficult to reduce substantiallythe water content of impervious soils, borrow areas con-taining impervious soils more than about 2 to 5 percentwet of optimum water content (depending upon theirplasticity characteristics) may be difficult to use in anembankment. However, this depends upon local climaticconditions and the size and layout of the work, and mustbe assessed for each project on an individual basis. Thecost of using drier material requiring a longer haul shouldbe compared with the cost of using wetter materials andflatter slopes. Other factors being equal, and if a choiceis possible, soils having a wide range of grain sizes (well-graded) are preferable to soils having relatively uniformparticle sizes, since the former usually are stronger, lesssusceptible to piping, erosion, and liquefaction, and lesscompressible. Cobbles and boulders in soils may add tothe cost of construction since stone with maximum dimen-sions greater than the thickness of the compacted layermust be removed to permit proper compaction. Embank-ment soils that undergo considerable shrinkage upon

drying should be protected by adequate thicknesses ofnonshrinking fine-grained soils to reduce evaporation.Clay soils should not be used as backfill in contact withconcrete or masonry structures, except in the imperviouszone of an embankment.

(4) Most earth materials suitable for the imperviouszone of an earth dam are also suitable for the imperviouszone of a rock-fill dam. When water loss must be kept toa minimum (i.e., when the reservoir is used for long-termstorage), and fine-grained material is in short supply,resulting in a thin zone, the material used in the coreshould have a low permeability. Where seepage loss isless important, as in some flood control dams not used forstorage, less impervious material may be used in theimpervious zone.

b. Rock-fill materials.

(1) Sound rock is ideal for compacted rock-fill, andsome weathered or weak rocks may be suitable, includingsandstones and cemented shales (but not clay shales).Rocks that break down to fine sizes during excavation,placement, or compaction are unsuitable as rock-fill, andsuch materials should be treated as soils. Processing bypassing rock-fill materials over a grizzly may be requiredto remove excess fine sizes or oversize material. If split-ting/processing is required, processing should be limitedto the minimum amount that will achieve required results.For guidance in producing satisfactory rock-fill materialand for test quarrying, reference should be made toEM 1110-2-3800 and EM 1110-2-2302.

(2) In climates where deep frost penetration occurs,a more durable rock is required in the outer layers than inmilder climates. Rock is unsuitable if it splits easily,crushes, or shatters into dust and small fragments. Thesuitability of rock may be judged by examination of theeffects of weathering action in outcrops. Rock-fill com-posed of a relatively wide gradation of angular, bulkfragment settles less than if composed of flat, elongatedfragments that tend to bridge and then break understresses imposed by overlying fill. If rounded cobblesand boulders are scattered throughout the mass, they neednot be picked out and placed in separate zones.

7-2. Zoning

The embankment should be zoned to use as much mater-ial as possible from required excavation and from borrowareas with the shortest haul distances and the least waste.Embankment zoning should provide an adequate impervi-ous zone, transition zones between the core and the shells,seepage control, and stability. Gradation of the materials

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in the transition zones should meet the filter criteria pre-sented in Appendix B.

a. Earth dams.

(1) In a common type of earth fill embankment, acentral impervious core is flanked by much more perviousshells that support the core (Figures 2-1b and 2-1c). Theupstream shell affords stability against end of construc-tion, rapid drawdown, earthquake, and other loading con-ditions. The downstream shell acts as a drain thatcontrols the line of seepage and provides stability underhigh reservoir levels and during earthquakes. For themost effective control of through seepage and seepageduring reservoir drawdown, the permeability shouldincrease progressively from the core out toward eachslope. Frequently suitable materials are not available forpervious downstream shells. In this event, control ofseepage through the embankment is provided by internaldrains as discussed in paragraph 6-2a(3).

(2) The core width for a central impervious core-type embankment should be established using seepage andpiping considerations, types of material available for thecore and shells, the filter design, and seismic consider-ations. In general, the width of the core at the base orcutoff should be equal to or greater than 25 percent of thedifference between the maximum reservoir and minimumtailwater elevations. The greater the width of the contactarea between the impervious fill and rock, the less likelythat a leak will develop along this contact surface. Wherea thin embankment core is selected, it is good engineeringto increase the width of the core at the rock juncture, toproduce a wider core contact area. Where the contactbetween the impervious core and rock is relatively nar-row, the downstream filter zone becomes more important.A core top width of 10 ft is considered to be the mini-mum for construction equipment. The maximum corewidth will usually be controlled by stability and availabil-ity of impervious materials.

(3) A dam with a core of moderate width andstrong, adequate pervious outer shells may have relativelysteep outer slopes, limited primarily by the strength of thefoundation and by maintenance considerations.

(4) Where considerable freezing takes place andsoils are susceptible to frost action, it is desirable to ter-minate the core at or slightly below the bottom of thefrost zone to avoid damage to the top of the dam.Methods for determination of depths of freeze and thaw insoils are given in TM 5-852-6. For design of road

pavements on the top of the dam under conditions of frostaction in the underlying core, see TM 5-818-2.

(5) Considerable volumes of soils of a randomnature or intermediate permeability are usually obtainedfrom required excavations and in excavating select imper-vious or pervious soils from borrow areas. It is generallyeconomical to design sections in which these materialscan be utilized, preferably without stockpiling. Whererandom zones are large, vertical (or inclined) and horizon-tal drainage layers within the downstream portion of theembankment can be used to control seepage and to isolatethe downstream zone from effects of through seepage.Random zones may need to be separated from pervious orimpervious zones by suitable transition zones. Homoge-neous embankment sections are considered satisfactoryonly when internal vertical (or inclined) and horizontaldrainage layers are provided to control through seepage.Such embankments are appropriate where available fillmaterials are predominantly of one soil type or whereavailable materials are so variable it is not feasible toseparate them as to soil type for placement in specificzones and when the height of the dam is relatively low.However, even though the embankment is unzoned, thespecifications should require that more pervious materialbe routed to the outer portions of the embankment.

b. Examples of earth dams.

(1) Examples of embankment sections of earthdams constructed by the Corps of Engineers are shown inFigures 7-1. Prompton Dam, a flood control project(Figure 7-1a), illustrates an unzoned embankment, exceptfor interior inclined and horizontal drainage layers tocontrol through seepage.

(2) Figure 7-1b, Alamo Dam, shows a zonedembankment with an inclined core of sandy clay andouter pervious shells of gravelly sand. The core extendsthrough the gravelly sand alluvium to the top of rock, andthe core trench is flanked on the downstream side by atransition layer of silty sand and a pervious layer ofgravelly sand.

(3) Where several distinctively different materialsare obtained from required excavation and borrow areas,more complex embankment zones are used, as illustratedby Figure 7-2a, Milford Dam, and Figure 7-2b, W. KerrScott Dam. The embankment for Milford Dam consistsof a central impervious core connected to an upstreamimpervious blanket, an upstream shell of shale and lime-stone from required excavation, an inclined and horizontal

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sand drainage layer downstream of the core, and down-stream random fill zone consisting of sand, silty sand, andclay. The embankment of W. Kerr Scott Dam consists ofan impervious zone of low plasticity silt, sloping upstreamfrom the centerline and flanked by zones of randommaterial (silty sands and gravels). Inclined and horizontaldrainage layers are provided in the downstream randomzone. Since impervious materials are generally weakerthan the more pervious and less cohesive soils used inother zones, their location in a central core flanked bystronger material permits steeper embankment slopes thanwould be possible with an upstream sloping imperviouszone. An inclined core near the upstream face may per-mit construction of pervious downstream zones during wetweather with later construction of the sloping imperviouszone during dry weather. This location often ensures abetter seepage pattern within the downstream portion ofthe embankment and permits a steeper downstream slopethan would a central core.

c. Rock-fill dams. Impervious zones, whetherinclined or central, should have sufficient thickness tocontrol through seepage, permit efficient placement withnormal hauling and compacting equipment, and minimizeeffect of differential settlement and possible cracking.The minimum horizontal thickness of core, filter, or tran-sition zones should be 10 ft. For design considerationswhere earthquakes are a factor, see paragraphs 4-6and 6-8.

d. Examples of rock-fill dams. Embankment sec-tions of four Corps of Engineers rock-fill dams are shownin Figures 7-3 and 7-4. Variations of the two principaltypes of embankment zoning (central impervious core andupstream inclined impervious zone) are illustrated in thesefigures.

7-3. Cracking

a. General. Cracking develops within zones oftensile stresses within earth dams due to differential settle-ment, filling of the reservoir, and seismic action. Sincecracking can not be prevented, the design must includeprovisions to minimize adverse effects. Cracks are offour general types: transverse, horizontal, longitudinal,and shrinkage. Shrinkage cracks are generally shallowand can be treated from the surface by removing thecracked material and backfilling (Walker 1984, Singh andSharma 1976, Jansen 1988).

b. Transverse cracking. Transverse cracking of theimpervious core is of primary concern because it creates

flow paths for concentrated seepage through the embank-ment. Transverse cracking may be caused by tensilestresses related to differential embankment and/or founda-tion settlement. Differential settlement may occur at steepabutments, at the junction of a closure section, at adjoin-ing structures where compaction is difficult, or over oldstream channels or meanders filled with compressiblesoils.

c. Horizontal cracking. Horizontal cracking of theimpervious core may occur when the core material ismuch more compressible than the adjacent transition orshell material so that the core material tends to archacross the less compressible adjacent zones resulting in areduction of the vertical stress in the core. The lowerportion of the core may separate out, resulting in a hori-zontal crack. Arching may also occur if the core rests onhighly compressible foundation material. Horizontalcracking is not visible from the outside and may result indamage to the dam before it is detected.

d. Longitudinal cracking. Longitudinal crackingmay result from settlement of upstream transition zone orshell due to initial saturation by the reservoir or due torapid drawdown. It may also be due to differential settle-ment in adjacent materials or seismic action. Longitudinalcracks do not provide continuous open seepage pathsacross the core of the dam, as do transverse and horizon-tal cracks, and therefore pose no threat with regard topiping through the embankment. However, longitudinalcracks may reduce the overall embankment stability lead-ing to slope failure, particularly if the cracks fill withwater.

e. Defensive measures. The primary line ofdefense against a concentrated leak through the dam coreis the downstream filter (filter design is covered inAppendix B). Since prevention of cracks cannot beensured, an adequate downstream filter must be provided(Sherard 1984). Other design measures to reduce thesusceptibility to cracking are of secondary importance.The susceptibility to cracking can be reduced by shapingthe foundation and structural interfaces to reduce differen-tial settlement, densely compacting the upstream shell toreduce settlement from saturation, compacting corematerials at water contents sufficiently high so that stress-strain behavior is relative plastic, i.e., low deformationmoduli, and shear strength, so that cracks cannot remainopen (pore pressure and stability must be considered), andstaged construction to lessen the effects of settlement ofthe foundation and the lower parts of the embankment.

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7-4. Filter Design

The filter design for the drainage layers and internal zon-ing of a dam is a critical part of the embankment design.It is essential that the individual particles in the founda-tion and embankment are held in place and do not moveas a result of seepage forces. This is accomplished byensuring that the zones of material meet “filter criteria”with respect to adjacent materials. The criteria for a filterdesign is presented in Appendix B. In a zoned embank-ment the coarseness between the fine and coarse zonesmay be such that an intermediate or transition section isrequired. Drainage layers should also meet these criteriato ensure free passage of water. All drainage or perviouszones should be well compacted. Where a large carryingcapacity is required, a multilayer drain should be pro-vided. Geotextiles (filter fabrics) should not be used in oron embankment dams.

7-5. Consolidation and Excess PorewaterPressures

a. Foundations.

(1) Foundation settlement should be considered inselecting a site since minimum foundation settlements aredesirable. Overbuilding of the embankment and of thecore is necessary to ensure a dependable freeboard. Stageconstruction or other measures may be required to dissi-pate high porewater pressures more rapidly. Wick drainsshould be considered except where installation would bedetrimental to seepage characteristics of the structure andfoundation. If a compressible foundation is encountered,consolidation tests should be performed on undisturbedsamples to provide data from which settlement analysescan be made for use in comparing sites and for finaldesign. Procedures for making settlement and bearingcapacity analyses are given in EM 1110-1-1904 andEM 1110-1-1905, respectively. Instrumentation requiredfor control purposes is discussed in Chapter 10.

(2) The shear strength of a soil is affected by itsconsolidation characteristics. If a foundation consolidatesslowly, relative to the rate of construction, a substantialportion of the applied load will be carried by the porewater, which has no shear strength, and the availableshearing resistance is limited to the in situ shear strengthas determined by undrained “Q” tests. Where the founda-tion shearing resistance is low, it may be necessary toflatten slopes, lengthen the time of construction, or accel-erate consolidation by drainage layers or wick drains.Analyses of foundation porewater pressures are covered

by Snyder (1968). Procedures for stability analyses arediscussed in EM 1110-2-1902 and Edris (1992).

(3) Although excess porewater pressures developedin pervious materials dissipate much more rapidly thanthose in impervious soils, their effect on stability is simi-lar. Excess pore pressures may temporarily build up,especially under earthquake loadings, and effectivestresses contributing to shearing resistance may bereduced to low values. In liquefaction of sand masses,the shearing resistance may temporarily drop to a fractionof its normal value.

b. Embankments. Factors affecting development ofexcess porewater pressures in embankments duringconstruction include placement water contents, weight ofoverlying fill, length of drainage path, rate of construction(including stoppages), characteristics of the core and otherfill materials, and drainage features such as inclined andhorizontal drainage layers, and pervious shells. Analysesof porewater pressures in embankments are presented byClough and Snyder (1966). Spaced vertical sand drainswithin the embankment should not be used in lieu ofcontinuous drainage layers because of the greater dangerof clogging by fines during construction.

7-6. Embankment Slopes and Berms

a. Stability. The stability of an embankmentdepends on the characteristics of foundation and fillmaterials and also on the geometry of the embankmentsection. Basic design considerations and procedures relat-ing to embankment stability are discussed in detail inEM 1110-2-1902 and Edris (1992).

b. Unrelated factors. Several factors not related toembankment stability influence selection of embankmentslopes. Flatter upstream slopes may be used at elevationswhere pool elevations are frequent (usually +4 ft of con-servation pool). In areas where mowing is required, thesteepest slope should be 1 vertical on 3 horizontal toensure the safety of maintenance personnel. Horizontalberms, once frequently used on the downstream slope,have been found undesirable because they tend to trap andconcentrate runoff from upper slope surfaces. The wateroften cannot be disposed of adequately, whereupon itspills over the berm and erodes the lower slopes. A hori-zontal upstream berm at the base of the principal riprapprotection has been found useful in placing and maintain-ing riprap.

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c. Waste berms. Where required excavation orborrow area stripping produces material unsuitable for usein the embankment, waste berms can be used forupstream slope protection, or to contribute to the stabilityof upstream and downstream embankment slopes. Caremust be taken, however, not to block drainage in thedownstream area by placing unsuitable material, which isoften impervious, over natural drainage features. Thewaste berm must be stable against erosion or it will erodeand expose the upstream slope.

7-7. Embankment Reinforcement

The use of geosynthetics (geotextiles, geogrids, geonets,geomembranes, geocomposites, etc.) in civil engineeringhas been increasing since the 1970’s. However, their usein dam construction or repairs, especially in the UnitedStates, has been limited (Roth and Schneider 1991;Giroud 1989a, 1989b; Giroud 1990, Giroud 1992a,1992b). The Corps of Engineers pioneered the use geo-textiles to reinforce very soft foundation soils (Fowler andKoerner 1987, Napolitano 1991). The Huntington Districtof the Corps of Engineers used a welded wire fabricgeogrid for reconstruction of Mohicanville Dike No. 2(Fowler et al. 1986; Franks, Duncan, and Collins 1991).The Bureau of Reclamation has used geogrid reinforce-ment to steepen the upper portion of the downstreamslope of Davis Creek Dam, Nebraska (Engemoen andHensley 1989, Dewey 1989).

7-8. Compaction Requirements

a. Impervious and semi-impervious fill.

(l) General considerations.

(a) The density, permeability, compressibility, andstrength of impervious and semi-impervious fill materialsare dependent upon water content at the time of compac-tion. Consequently, the design of an embankment isstrongly influenced by the natural water content of borrowmaterials and by drying or wetting that may be practicableeither before or after delivery to the fill. While naturalwater contents can be decreased to some extent, someborrow soils are so wet they cannot be used in anembankment unless slopes are flattened. However, watercontents cannot be so high that hauling and compactionequipment cannot operate satisfactorily. The design andanalysis of an embankment section require that shearstrength and other engineering properties of fill materialbe determined at the densities and water contents that willbe obtained during construction. In general, placementwater contents for most projects will fall within the range

of 2 percent dry to 3 percent wet of optimum water con-tent as determined by the standard compaction test(EM 1110-2-1906). A narrower range will be requiredfor soils having compaction curves with sharp peaks.

(b) While use of water contents that are practicallyobtainable is a principal construction requirement, theeffect of water content on engineering properties of acompacted fill is of paramount design interest. Soils thatare compacted wet of optimum water content exhibit asomewhat plastic type of stress-strain behavior (in thesense that deformation moduli are relatively low andstress-strain curves are rounded) and may develop low“Q” strengths and high porewater pressures during con-struction. Alternatively, soils that are compacted dry ofoptimum water content exhibit a more rigid stress-strainbehavior (high deformation moduli), develop high “Q”strengths and low porewater pressures during construction,and consolidate less than soils compacted wet of optimumwater content. However, soils compacted substantiallydry of optimum water content may undergo undesirablesettlements upon saturation. Cracks in an embankmentwould tend to be shallower and more self-healing if com-pacting is on the wet side of optimum water content thanif on the dry side. This results from the lower shearstrength, which cannot support deep open cracks, andfrom lower deformation moduli.

(c) Stability during construction is determinedlargely by “Q” strengths at compacted water contents anddensities. Since “Q” strengths are a maximum for watercontents dry of optimum and decrease with increasingwater content, construction stability is determined (apartfrom foundation influences) by the water contents atwhich fill material is compacted. This is equivalent tosaying that porewater pressures are a controlling factor onstability during construction. “Q” strengths, and pore-water pressures during construction are of more impor-tance for high dams than for low dams.

(d) Stability during reservoir operating conditions isdetermined largely by “R” strengths for compacted mater-ial that has become saturated. Since “R” strengths are amaximum at about optimum water content, shear strengthsfor fill water contents both dry and wet of optimum mustbe established in determining the allowable range ofplacement water contents. In addition, the limiting watercontent on the dry side of optimum must be selected toavoid excessive settlement due to saturation. Preferablyno settlement on saturation should occur.

(2) Dams on weak, compressible foundations.Where dams are constructed on weak, compressible

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foundations, the embankment and foundation materialsshould have stress-strain characteristics as nearly similaras possible. Embankments can be made more plastic andwill adjust more readily to settlements if they are com-pacted wet of the optimum water content. Differences inthe stress-strain characteristics of the embankment andfoundation may result in progressive failure. To preventthis from occurring, the embankment is designed so thatneither the embankment nor the foundation will bestrained beyond the peak strength so that the stage whereprogressive failure begins will not be reached. Strengthreduction factors for the embankment and foundation aregiven in Figure 7-5 (Duncan and Buchignani 1975,Chirapuntu and Duncan 1976).

(3) Dams on strong, incompressible foundations.Where the shear strength of the embankment is lower thanthat of the foundation, such as the case where there is astrong, relatively incompressible foundation, the strengthof the fill controls the slope design. The “Q” strength ofthe fill will be increased by compacting it at water con-tents at or slightly below optimum water contents and theporewater pressures developed during construction will bereduced. Soils compacted slightly dry of optimum watercontent generally have higher permeability values andlower “R” strengths than those wet of optimum watercontent. Further, many soils will consolidate upon satura-tion if they are compacted dry of optimum water content.All of these factors must be considered in the selection ofthe range of allowable field compaction water contents.

(4) Abutment areas. In abutment areas, large differ-ential settlements may take place within the embankmentif the abutment slopes are steep or contain discontinuitiessuch as benches or vertical faces. This may inducetension zones and cracking in the upper part of theembankment. It may be necessary to compact soils wetof optimum water content in the upper portion of embank-ment to eliminate cracking due to differential settlements.Again, shear strength must be taken into account.

(5) Field densities. Densities obtained from fieldcompaction using conventional tamping or pneumaticrollers and the standard number of passes of lift thicknessare about equal to or slightly less than maximum densitiesfor the standard compaction test. This has established thepractice of using a range of densities for performance oflaboratory tests for design. Selection of design densities,while a matter of judgment, should be based on theresults of test fills or past experience with similar soilsand field compaction equipment. The usual assumption isthat field densities will not exceed the maximum densitiesobtained from the standard compaction test nor be less

than 95 percent of the maximum densities derived fromthis test.

(6) Design water contents and densities. A basicconcept for both earth and rock-fill dams is that of a coresurrounded by strong shells providing stability. Thisconcept is obvious for rock-fill dams and can be appliedeven to internally drained homogeneous dams. In thelatter case, the core may be compacted at or wet ofoptimum while the outer zones are compacted dry of opti-mum. The selection of design ranges of water contentsand densities requires judgment and experience to balancethe interaction of the many factors involved. Theseinclude:

(a) Borrow area water contents and the extent ofdrying or wetting that may be practicable.

(b) The relative significance on embankment designof “Q” versus “R” strengths (i.e., construction versusoperating conditions).

(c) Climatic conditions.

(d) The relative importance of foundation strengthon stability.

(e) The need to design for cracking and develop-ment of tension zones in the upper part of the embank-ment, especially in impervious zones.

(f) Settlement of compacted materials on saturation.

(g) The type and height of dam.

(h) The influence on construction cost of variousranges of design water contents and densities.

(7) Field compaction.

(a) While it is generally impracticable to considerpossible differences between field and laboratory compac-tion when selecting design water contents and densities,such differences do exist and result in a different behaviorfrom that predicted using procedures discussed in preced-ing paragraphs. Despite these limitations, the proceduresdescribed generally result in satisfactory embankments,but the designer must verify that this is true as early aspossible during embankment construction. This can oftenbe done by incorporating a test section within theembankment. When field test section investigations areperformed, field compaction curves should be developedfor the equipment used.

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Figure 7-5. Peak strength correction factors for both embankment and foundation to prevent progressive failure inthe foundation for embankments on soft clay foundations (Duncan and Buchignani 1975)

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(b) Proper compaction at the contact between theembankment and the abutments is important. Sloping thefill surface up on a 10 percent grade toward a steep abut-ment facilitates compaction where heavy equipment is tobe used. Where compaction equipment cannot be usedagainst an abutment, thin lifts tamped with hand-operatedpowered tampers should be used, but tamping of soilunder overhangs in lieu of removal or backfilling withconcrete should not be permitted.

(c) Specific guidance on acceptable characteristicsand operating procedures of tamping rollers, rubber-tiredrollers, and vibratory rollers is given in guide specificationCW-02212, including dimensions, weights, and speed ofrolling; also see EM 1110-2-1911.

b. Pervious materials (excluding rock-fill).

(l) The average in-place relative density of zonescontaining cohesionless soils should be at least 85 percent,and no portion of the fill should have a relative densityless than 80 percent. This requirement applies to drainageand filter layers as well as to larger zones of perviousmaterials, but not to bedding layers beneath dumped rip-rap slope protection. The requirement also applies tofilter layers and pervious backfill beneath and/or behindspillway structures. The relative density test is generallysatisfactory for pervious materials containing only a fewpercent finer than the No. 200 sieve. For some materials,however, field compaction results equal to 100 percent ormore of the standard compaction test maximum densitycan be readily obtained and may be higher than 85 per-cent relative density. If 98 percent of the maximum den-sity from the standard compaction test is higher than85 percent relative density, the standard compaction testshould be used. The design should provide that clean,free-draining pervious materials be compacted in as nearlya saturated condition as possible. Otherwise compactionat bulking water contents might result in settlement uponsaturation.

(2) It is possible to place pervious fill such asfree-draining gravel or fine to coarse sand, into a lift 3 to4 ft thick in shallow water and to obtain good compactionby rolling the emerged surface of the lift with heavycrawler tractors. However, less pervious soils cannot becompacted if placed in this manner or even on a wetsubgrade. In general, sand containing more than 8 to10 percent finer than the No. 200 sieve cannot be placedsatisfactorily underwater, and well graded sand-gravelmixtures must contain even fewer fines. The ability toplace pervious soils in shallow water after stripping

simplifies construction and makes it possible to constructcofferdams of pervious material by adding a temporaryimpervious blanket on the outer face and thus permitunwatering for the impervious cutoff section. The coffer-dams subsequently become part of the pervious shells ofthe embankment.

c. Rock-fill.

(l) It is often desirable, especially where rocks aresoft, for procedures to be used in compacting rock-fillmaterials to be selected on the basis of test fills, in whichlift thicknesses, numbers of passes, and types of compac-tion equipment (i.e., different vibratory rollers) are inves-tigated (paragraph 3-1k). Many test fills have beenconstructed by the Corps of Engineers and other agencies,and the results should be reviewed for possible applicabil-ity before constructing test fills. Rock-fill should not beplaced in layers thicker than 24 in. unless the results oftest fills show that adequate compaction can be obtainedusing thicker lifts. As the maximum particle size of rock-fill decreases, the lift thickness should be decreased. Inno case should the maximum particle size exceed 0.9 ofthe lift thickness. Smooth-wheeled vibratory rollers hav-ing static weights of 10 to 15 tons are effective in achiev-ing high densities for hard durable rock if the speed,cycles per minute, amplitude, and number of passes arecorrect. Quarry-run rock having an excess of fines can bepassed over a grizzly, and the fines placed next to thecore. Fine rock zones should be placed in 12- to 18-in.lift thicknesses.

(2) There is no need to scarify the surfaces of com-pacted lifts of hard rock-fill. Soft rocks, such as somesandstones and shales, often break down to fine materialson the surface of the lift. Other sandstones may be com-pacted in the same manner as other hard rocks. Scarify-ing has been used on soft sandstone layers to move finesdown into the fill. If breaking down of the upper part ofthe layer cannot be prevented, it may be necessary to usevery thin lifts to break the sandstone so that the largerparticles are surrounded with sand. Ten-ton vibratoryrollers and tracked equipment break the rock more thanrubber-tired equipment. If soft material breaks downuniformly, vibratory or other equipment can be used, butthe dam should be designed as an earth dam. Specifica-tions should prohibit the practice often used by contrac-tors of placing a cover of fine quarry waste on completedlifts of larger rock to facilitate hauling and to reduce tirewear. If such a cover of fines were extensive, it couldhave a detrimental effect on drainage and strength charac-teristics of the outer rock zones.

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7-9. Slope Protection

Adequate slope protection must be provided for all earthand rock-fill dams to protect against wind and waveerosion, weathering, ice damage, and potential damagefrom floating debris. Methods of protecting slopesinclude dumped riprap, precast and cast-in-place concretepavements, soil cement, bituminous soil stabilization,

sodding, and planting. The type of protection provided isgoverned by available materials and economics. Slopeprotection should be designed in accordance with theprocedures presented in Appendix C. Due to the highcost, the initial slope protection design should be accom-plished during the survey studies to establish a reliablecost estimate. The final design should be presented in theappropriate feature design memorandum.

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Chapter 8Appurtenant Structures

8-1. Outlet Works

a. Foundation. If the dam’s foundation consists ofcompressible soils, the outlet works tower and conduitshould be founded upon or in stronger abutment soils orrock where less settlement and horizontal spreading willoccur and where the embankment is lower. Seepagecollars should not be used because adequate compaction israrely achieved around the collars and because their pres-ence may increase the separation of conduit sectionsshould the embankment tend to spread. A drainage layershould be provided around the conduit in the downstreamzone of embankments. Excavation slopes in earth forconduits should be no steeper than 1 vertical on 2 hori-zontal to facilitate adequate compaction and bonding ofbackfill with the sides of the excavation.

b. Concrete plug. A concrete plug should be usedas backfill in rock cuts for cut-and-cover conduits withinthe core area to ensure a watertight bond between thestructure and vertical rock surface. The plug, which canbe constructed of lean concrete, should be provided overthe length of the core contact area and extend up to theoriginal rock surface. The substitution of hand-tampedearth fill is not considered an acceptable substitute for thelean concrete. Seepage collars should not be used exceptwhere they function for alignment control. In embank-ments having a random or an impervious downstreamshell, horizontal drainage layers should be placed alongthe sides and over the top of conduits downstream of theimpervious core.

c. Basins. Intake structure towers and outlet head-walls at stilling basins are often recessed into the embank-ment to reduce the length of conduit. Since the tolerablehorizontal movements of these features are very small,they should be designed for earth pressure at rest, takinginto account the surcharge effect of the sloping embank-ment and water table considerations. Sidewalls shouldalso be designed for at rest earth pressures, consideringsurface effects from the sloping embankment whereapplicable.

d. Piers. When service bridge piers have beenconstructed concurrently with placement of the embank-ment fill, they have often suffered large horizontal move-ments. Construction of such piers should be delayed untilafter the embankment has been brought to grade, or at

least until a large part of the embankment fill has beenplaced.

e. Outlet structures. Where outlet structures are tobe located in active seismic areas, special attention mustbe given to the possibility of movement along existing orpossibly new faults.

8-2. Spillway

a. Excavations. Excavations for spillways oftenrequire high side slopes cut into deposits of variablematerials, often below groundwater table. If materialfrom the spillway excavation is suitable for embankmentfill, the stability of spillway slopes may be increasedwithout increasing construction costs by excavating toflatter slopes. The stability of slopes excavated into natu-ral materials is much more difficult to assess than that ofslopes of properly constructed embankment. For excava-tion into natural soil deposits, detailed subsurface explora-tion including groundwater observations and appropriatelaboratory tests on representative soils supply the informa-tion needed for slope stability analyses. When requiredexcavation is in rock, the influence of structural discon-tinuities such as joints, faults, and bedding planes over-shadows the properties of the intact rock as determined bytests on core samples. Consequently, detailed geologicstudies and subsurface investigations, together with empir-ical data on natural and man-made slopes in the vicinity,are used for determining excavation slopes in rock and inclay shales.

b. Grout curtains. It is often necessary to extendgrout curtains beyond the dam axis to include the abut-ment between the dam and spillway, as well as beneathand across the spillway structure. If the rock is of poorquality, it may be necessary to build concrete walls orprovide revetment to protect against erosion toward thespillway.

8-3. Miscellaneous Considerations

a. Temporary slopes. Temporary excavation slopesbehind training walls are commonly shown on contractplans as 1 vertical on 1 horizontal for pay purposes; how-ever, for major cuts and for cuts in weak materials, theslopes should be designed for adequate stability and therequired slopes shown on the contract drawings. Drainageof the backfill must be provided to reduce pressuresagainst the walls to a minimum. The backfill shouldeither consist entirely of free-draining material or have azone of free-draining material adjacent to the wall

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containing a collecting pipe drain along the lower part ofthe backfill near the wall. Where there is room to do so,the most effective way to control drainage within the soilbackfill is an inclined drainage blanket with a longitudinaldrain (see EM 1110-2-2502, paragraph 6-6).

b. Channel slopes. Channel slopes adjacent to spill-way and outlet structures must be designed to provideadequate factors of safety against slope failure. For somedistance below stilling basins, the channel slopes and bedmust be protected against scour with derrick stone and/orriprap; guidance on the design of such protection is fur-nished in EM 1110-2-1602 and EM 1110-2-1603.

c. Embankments. Special attention must be given tothe junction of embankments with concrete structures suchas outlet works, spillway walls, lock walls, and power-houses to avoid piping along the zone. An embankmentabutting a high concrete wall creates a tension zone in thetop of the embankment similar to that occurring next tosteep abutments. Horizontal joints should not be cham-fered in the contact areas between embankment and

concrete. A 10 vertical on 1 horizontal batter on the con-crete contact surfaces will ensure that the fill will becompressed against the wall as consolidation takes place.The interface of an earth embankment abutting a highconcrete wall should be aligned at such an angle that thewater load will force the embankment against the wall.The best juncture of a concrete dam with flanking earthembankments is by means of wraparounds. Internaldrainage provided beneath the downstream portion of theembankment should be carried around to the downstreamcontact with the concrete structure. Compaction contigu-ous to walls may be improved by sloping the fill awayfrom the wall to increase roller clearances. Where rollerscannot be used because of limited clearance or wherespecifications restrict the use of rollers near walls, powertamping of thinner layers should be used to obtain densi-ties equal to the remainder of the embankment. It may bedesirable to place material at higher water contents toensure a more plastic material which can adjust withoutcracking, but then the effects of increased porewater pres-sures must be considered.

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Chapter 9General Construction Considerations

9-1. General

The design of an earth or rock-fill dam is a process con-tinued until construction is completed. Much additionalinformation on the characteristics of foundations andabutments is obtained during clearing, stripping, andtrenching operations, which may confirm or contradictdesign assumptions based on earlier geologic studies andsubsurface exploration by drill holes and test pits. Opera-tions in the borrow areas and in required excavations alsoprovide much data pertinent to characteristics of fillmaterial and of excavated slopes. Weather and ground-water conditions during construction may significantlyalter water contents of proposed fill material, or createseepage and/or hydraulic conditions, necessitating modifi-cations in design. Projects must be continuously evalu-ated and “re-engineered,” as required, during construction,to ensure that the final design is compatible with condi-tions encountered during construction. Design and designreview personnel will make construction site visits todetermine whether design modifications are required tomeet actual field conditions (see ER 1110-2-112). Envi-ronmental considerations discussed in paragraph 2-5 mustbe given attention in construction operations.

9-2. Obtaining Quality Construction

a. Definitions (ER 1180-1-6).

(1) Quality is conformance to properly developedrequirements. In the case of construction contracts, theserequirements are established by the contract specificationsand drawings.

(2) Quality management is all control and assur-ance activities instituted to achieve the product qualityestablished by the contract requirements.

(3) Contractor quality control (CQC) is the con-struction contractor’s system to manage, control, anddocument his own, his supplier’s, and his subcontractor’sactivities to comply with contract requirements.1

_____________________________1 Additional information is given in EP 715-1-2 andInternational Commission on Large Dams Bulletin 56“Quality Control for Fill Dams” (International Commis-sion on Large Dams 1986).

(4) Quality assurance (QA) is the procedure bywhich the Government fulfills its responsibility to becertain the CQC is functioning and the specified endproduct is realized.

b. Policy. Obtaining quality construction is a com-bined responsibility of the construction contractor and theGovernment. The contract documents establish the levelof quality required in the project to be constructed. Incontracts of $1 million or greater, detailed CQC will beapplied and a special CQC Section will be included in thecontract. CEGS-01440 is to be used in preparation of theCQC Section. QA is required on all construction con-tracts. The extent of assurance is commensurate with thevalue and complexity of the contracts involved. QAtesting is required (ER 1180-1-6).

c. Contractor responsibility. Contractors shall beresponsible for all activities necessary to manage, control,and document work so as to ensure compliance with thecontract P&S. The contractor’s responsibility includesensuring adequate quality control services are provided forwork accomplished by his organization, suppliers, subcon-tractors, technical laboratories, and consultants. For con-tracts of $1 million or greater, contractors will be requiredto prepare a quality control plan (ER 1180-1-6).

d. Government responsibility. QA is the processby which the Government ensures end product quality.This process starts well before construction and includesreviews of the P&S for biddability and constructibility,plan-in-hand site reviews, coordination with using agen-cies or local interests, establishment of performanceperiods and quality control requirements, field office plan-ning, preparation of QA plans, reviews of quality controlplans, enforcement of contract clauses, and acceptance ofcompleted construction (ER 1180-1-6).

e. QA for procedural specifications. Some QAtesting in the case of earthwork embankment and concretedam structures must be conducted continuously. A com-prehensive QA testing program by the Government isnecessary when specifications limit the contractor to pre-scriptive procedures leaving the responsibility for endproduct quality to the Government (ER 1180-1-6).

9-3. Stage Construction

a. The term “stage construction” is limited here toconstruction of an embankment over a period of time withsubstantial intervals between stages, during which little or

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no fill is placed. Where a foundation is weak and com-pressible, or where impervious fill is on the wet side ofnormally acceptable placement water contents, it may bedesirable to restrict the rate of fill placement or to ceasefill placement for periods of time to permit excess pore-water pressures in the foundation and/or the fill to dissi-pate. Another beneficial effect of periods of inactivity isthat rates of pore-pressure buildup in partially saturatedsoils upon resumption to fill placement may be reduced(see Clough and Snyder (1966) and Plate VIII-3 ofEM 1110-2-1902).

b. High embankments. Where high embankmentsare constructed in narrow valleys, it may be possible toplace fill rapidly, which will increase pore-pressurebuildup in the embankment and/or foundation. Ratherthan reduce the rate of fill placement unduly, it may bedesirable to use flatter slopes, add stabilizing berms, orbuild the embankment in stages.

9-4. Stream Diversion

a. Requirements. Requirements for diversion ofstreamflow during construction and the relative ease andcost of stream control measures may govern site selection.Since river diversion is a critical operation in constructinga dam, the method and time schedules for diversion areimportant elements of design.

b. Methods of stream control.

(1) The principal factors that determine methodsof stream control are the hydrology of the stream, thetopography and geology of the site, and the constructionschedule. A common diversion method is to construct thepermanent outlet works and a portion of the embankmentadjacent to an abutment in the initial construction period.During the next construction period, at a time when floodpossibility is low and favorable embankment placementconditions are likely, a cofferdam is constructed to divertriverflow through the outlet works (guidance on planning,design, and construction of cofferdams is given inER 1110-2-2901 and EM 1110-2-2503). A downstreamcofferdam may also be required until the embankment hasbeen completed above tailwater elevation. In the periodfollowing diversion, the closure section is first brought upto a level with the remainder of the dam, after which theembankment is completed to a given height as rapidly aspossible in preparation for high water. In the final period,the entire dam is brought up to full height. Simultaneousclosure of upstream and downstream cofferdams mayfacilitate a difficult closure. The downstream cofferdam

puts a back head on the construction area and reduceserosion of the downstream slope and adjacent foundation.

(2) Cofferdams are often constructed in two stages:first, a small diversion cofferdam is constructed upstreamof the main embankment, and second, the main cofferdamis constructed. The cofferdam may form a permanent partof the embankment wherever suitable strength and perme-ability characteristics of the fill can be obtained. Gravelfill is particularly suitable for cofferdam constructionsince it readily compacts under water. If seepage consid-erations require an upstream impervious blanket on acofferdam built of pervious soil, the blanket should beremoved later if it restricts drainage during drawdown.

c. Cofferdam design. Major cofferdams are thosecellular or embankment cofferdams, which, upon failure,would cause major damage downstream and/or consider-able damage to the permanent work. Minor cofferdamsare those which would result in only minor flooding ofthe construction work. All major cofferdams should beplanned, designed, and constructed to the same level ofengineering competency as for main dams. Design con-siderations should include minimum required top eleva-tion, hydrologic records, hydrographic and topographicinformation, subsurface exploration, slope protection,seepage control, stability and settlement analyses, andsources of construction materials. The rate of construc-tion and fill placement must be such to prevent over-topping during initial closure of the cofferdam. Thecofferdam for Cerrillos Dam, Puerto Rico, was unique inthat it was designed to handle being overtopped. Theovertopping protection consisted of anchoring weldedsteel rebar/wire mesh to the downstream face. Crestprotection was provided by gabions with asphalt paving(U.S. Army Engineer District, Jacksonville 1983). Minorcofferdams can be the responsibility of the contractor.Excavations for permanent structures should be made soas not to undermine the cofferdam foundation or other-wise lead to instability. Adequate space should be pro-vided between the cofferdam and structural excavation toaccommodate remedial work such as berms, toe but-tresses, and foundation anchors should they be necessary.

d. Protection of embankment.

(1) Where hydrologic conditions require, emergencyoutlets should be provided to avoid possible overtoppingof the incomplete embankment by floods that exceed thecapacity of the outlet works. As the dam is raised, theprobability of overtopping gradually decreases as a resultof increased discharge capacity and reservoir storage.

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Should overtopping occur, however, damage to the par-tially completed structure and to downstream propertyincreases with increased embankment heights. It is pru-dent to provide emergency outlets by leaving gaps or lowareas in the concrete spillway or gate structure, or in theembankment during wintering over periods. Excavationof portions of the spillway approach and discharge chan-nels, combined with maintaining low concrete weir sec-tions, may provide protection for the later phases ofembankment construction during which the potential dam-age is greatest.

(2) When a portion of the embankment is con-structed before diversion of the river, temporary riprap orother erosion protection may be required for the toe of theembankment adjacent to the channel. This temporaryprotection must be removed before placement of fill forthe closure section.

(3) In some cases the cost of providing sufficientflow capacity to avoid overtopping becomes excessive,and it is more appropriate to provide protection for possi-ble overflow during high water conditions, as was done atBlakely Mountain Dam (U.S. Army Engineer WaterwaysExperiment Station 1956).

(4) Within the past 10 years innovative methodsfor providing overtopping protection of embankmentshave been developed. These include roller-compactedconcrete and articulated concrete blocks tied together bycables and anchored in place (see Hansen 1992;Powledge, Rhone, and Clopper 1991; Wooten, Powledge,and Whiteside 1992; and Powledge and Pravdivets 1992).

9-5. Closure Section

a. Introduction. Because closure sections of earthdams are usually short in length and are rapidly broughtto grade, two problems are inherent in their construction.First, the development of high excess porewater pressuresin the foundation and/or embankment is accentuated, andsecond, transverse cracks may develop at the juncture ofthe closure section with the adjacent already constructedembankment as a result of differential settlement. Whenthe construction schedule permits, excess porewater pres-sures in the embankment may be minimized by providinginclined drainage layers adjacent to the impervious coreand by placing gently sloping drainage layers at verticalintervals within semi-impervious random zones. How-ever, acceleration of foundation consolidation by means ofsand blankets and vertical wick drains or reduction ofembankment pore pressures by stage construction isgenerally impracticable in a closure section. A more

suitable procedure is to use flatter slopes or stabilizingberms. Cracking because of differential settlement maybe minimized by making the end slopes of previouslycompleted embankment sections no steeper than 1 verticalon 4 horizontal. The soil on the end slopes of previouslycompleted embankment sections should be cut back towell-compacted material that has not been affected bywetting, drying, or frost action. It may be desirable toplace core material at higher water contents than else-where to ensure a more plastic material which can adjustwithout cracking, but the closure section design must thenconsider the effects of increased porewater pressureswithin the fill. The stability of temporary end slopes ofembankment sections should be checked.

b. Limit. If specifications limit the rate of fillplacement, piezometers must be installed with tips in thefoundation and in the embankment to monitor porewaterpressures. Conduits should not be built in closure sec-tions or near enough to closure sections to be influencedby the induced loads.

c. Closure section. Closure sections, with founda-tion cutoff trenches if required, are generally constructedin the dry, behind diversion cofferdams. In a few cases,the lower portions of rock-fill closure sections with“impervious” zones of cohesionless sands and gravelshave been successfully constructed under water (see Pope1960). Hydraulic aspects of river diversion and closuresare presented in EM 1110-2-1602.

9-6. Construction/Design Interface

It is essential that all of the construction personnel associ-ated with an earth or rock-fill dam be familiar with thedesign criteria, performance requirements, and any specialdetails of the project. As discussed in paragraph 4-7,coordination between design and construction is accom-plished through the report on engineering considerationsand instructions to field personnel, preconstruction orien-tation for construction engineers by the designers, andrequired visits to the site by the designers.

9-7. Visual Observations

Visual observations during all phases of constructionprovide one of the most useful means for controllingconstruction and assessing validity of design assumptions.It is not practical, for economic reasons, to performenough field density control tests, to install enoughinstrumentation, and to obtain enough data from pre-construction subsurface explorations to ensure that alltroublesome conditions are detected and that satisfactory

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construction is being achieved. While test data andinstrument observations provide more detailed and quanti-tative information than visual observations, they serveprincipally to strengthen and supplement visual observa-tions of the embankment and foundation as the variousconstruction activities are going on. Field forces shouldbe constantly on the alert for conditions not anticipated inthe design, such as excessively soft areas in the founda-tion; jointing, faulting, and fracturing in rock foundations;unusual seepage; bulging and slumping of embankmentslopes; excavation movements; cracks in slopes; and thelike. It is particularly important to make observationsduring the first filling of the reservoir as weaknesses in acompleted dam often show up at this time. For this rea-son, each reservoir project is required to have an “InitialFilling Plan” (discussed in paragraph 9-8). Visual obser-vations of possible distress such as cracking, the appear-ance of turbid water in downstream toe drainage systems,erosion of riprap, soft wet spots downstream of the abut-ments or at the downstream toe or on the downstreamslope, and other observations are important. Observationsof instrumentation also yield valuable data in this respect.

9-8. Compaction Control

a. Principal compaction. Principal compactioncontrol is achieved by enforcement of specifications relat-ing to placement water content, lift thickness, compactingequipment, and number of passes for the various types offill being placed. Experienced inspectors can quicklylearn to distinguish visually whether the various contentsare within the specified range for compaction, and toassess whether satisfactory compaction is being achieved.This ability is gained by closely observing the behavior ofthe materials during spreading and compacting operations.

b. Field compaction. A systematic program of fieldcompaction control should be established and executed,involving determinations of in-place densities and watercontents, and relating the results to specified or desiredlimits of densities and water contents. Special emphasismust be placed in the compaction program on the need toobtain sufficient densities in each lift along the impervi-ous core contact area on the abutments, and in each lifton either side of the outlet conduit along the backfill-conduit contact to verify adequate compaction in theseand other critical zones. If good correlations can beobtained between direct methods and nuclear moisture-density meters, the latter may be used to increase thenumber of determinations with a minimum increase intime and effort, but nuclear measurements cannot be usedto replace direct determinations. A more reliable method

for determination of field water content is available usingthe microwave oven (see below).

c. Oven system. A computer-controlled microwaveoven system (CCMOS) is useful for rapid determinationof water content for compaction control. The principle ofoperation of the system is that water content specimensare weighed continuously while being heated by micro-wave energy, and a computer monitors change in watercontent with time and terminates drying when all freewater has been removed. A water content test in theCCMOS requires 10 to 15 min, and the system has beenfield tested at Yatesville Lake and Gallipolis Lock pro-jects. Test results indicated that CCMOS produces watercontents within 0.5 percent of conventional oven watercontent. Special procedures must be used when dryingmaterials which burst from internal steam pressure duringmicrowave drying (which includes some gravel particlesand shales) and highly organic material, which requires aspecial drying cycle. Gypsum-rich soils are dehydratedby the microwave oven system giving erroneous resultsand should not be analyzed by this method. However, itshould be noted that a special drying procedure isrequired to dry gypsum-rich soils in the conventional oven(Gilbert 1990, Gilbert 1991).

d. Compaction. In order to check the adequacy ofcompaction in the various embankment zones and toconfirm the validity of the design shear strengths andother engineering parameters, a systematic schedule forobtaining 1-cu-ft test pit samples at various elevations andlocations in the embankment should be established. Sam-ples so obtained will be suitably packed and shipped todivision laboratories for performance of appropriate tests.

9-9. Initial Reservoir Filling

a. General. The initial reservoir filling is definedas a deliberate impoundment to meet project purposes andis a continuing process as successively higher pools areattained for flood control projects. The initial reservoirfilling is the first test of the dam to perform the functionfor which it was designed. In order to monitor this per-formance, the rate of filling should be controlled to theextent feasible, to allow as much time as needed for apredetermined surveillance program including the observa-tion and analysis of instrumentation data (Duscha andJansen 1988). A design memorandum (DM) on initialreservoir filling is required for all new reservoir projects.1

_____________________________1 Additional information is given in ETL 1110-2-231.

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b. Design memorandum. As a minimum, the DMon initial reservoir filling will include the following(EM 1110-2-3600):

(1) Reservoir regulations during project construc-tion stage(s).

(2) Water control plan.

(3) Project surveillance.

(4) Cultural site surveillance.

(5) Flood emergency plan.

(6) Public affairs.

(7) Safety plan.

(8) Transportation and communications.

9-10. Construction Records and Reports

a. General. Engineering data relating to projectstructures will be collected and permanently retained atthe project site (see Appendix A of ER 1110-2-100).This information has many uses such as determining thevalidity of claims made by construction contractors,designing future alterations and additions to the structure,familiarizing new personnel with the project, and provid-ing guidance for designing comparable future projects.These documents will include as many detailed photo-graphs as necessary. This information provides the basisfor analysis and remedial action in the event of futuredistress.

b. Field control data. Records including field con-trol data on methods of compaction, in-place unit weightand moisture content, piezometers, surface monuments,and inclinometers are kept for use in construction, opera-tion, and maintenance of the project. Instructions regard-ing specific forms to use for field data control are givenin ER 1110-2-1925.

c. As-constructed drawings. As construction of aproject progresses, plans will be prepared showing thework as actually constructed. Changes may be indicatedin ink on prints of the construction drawings or the trac-ings may be revised and new prints made to show thework as constructed, as specified in ER 1110-2-1200.

d. Embankment criteria and foundation report.Earth and earth-rock-fill dams require an embankment

criteria and foundation report to provide a summary ofsignificant design assumptions and computations, specifi-cation requirements, construction procedures, field controland record control test data, and embankment perfor-mance as monitored by instrumentation during construc-tion and during initial reservoir filling. This report isusually written by persons with first-hand knowledge ofthe project design and construction. The written text isbrief with the main presentation consisting of a set ofidentified construction photographs, data summary tables,and as-constructed drawings. This report provides in onevolume the significant information needed by engineers tofamiliarize themselves with the project and to re-evaluatethe embankment in the event unsatisfactory performanceoccurs (see ER 1110-2-1901).

e. Construction foundation report. In addition toan embankment criteria and foundation report, all majorand unique dams require a construction foundation reportto be completed within 6 months after completion of theproject or part of the project for which the report iswritten (see Appendix A of ER 1110-1-1801 for a sug-gested outline for foundation reports). This report docu-ments observations of subsurface conditions encounteredin all excavations and provides the most complete recordof subsurface conditions and treatment of the foundation.The foundation report should be complete with suchdetails as dip and strike of rock, faults, artisan conditions,and other characteristics of foundation materials. A com-plete history of the project in narrative form should bewritten, giving the schedule of starting and completing thevarious phases of the work, describing construction meth-ods and equipment, summarizing quantities of materialsinvolved, and other pertinent data. An accurate recordshould be maintained as to the extent and removal of alltemporary riprap or stockpiled rock such as that used fordiversion channel protection. The construction foundationreport saves valuable time by eliminating the need tosearch through voluminous construction records of thedam to find needed information to use in planning reme-dial action should failure or partial failure of a structureoccur as a result of foundation deficiencies.

f. Photographs and video tape taken during con-struction. Embankment criteria and foundation and con-struction foundation reports should be supplemented byphotographs that clearly depict conditions existing duringembankment and foundation construction. Routine photo-graphs should be taken at regular intervals, and additionalpictures should be taken of items of specific interest, suchas the preparation of foundations and dam abutments. Forthese items, color photographs should be taken. Thecaptions of all photographs should contain the name of

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the project, the date on which the photograph was taken,the identity of the feature being photographed, and thelocation of the camera. In reports containing a number ofphotographs, an alternative would be an index map with acircle indicating the location of the camera with an arrow

pointing in the direction the camera was pointing, witheach location keyed to the numbers on the accompanyingphotographs (EM 1110-2-1911). Consideration should begiven to using video tape where possible to documentconstruction of the dam.

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Chapter 10Instrumentation

10-1. General

a. Dam safety. In view of concerns for dam safety,it has become increasingly important to provide sufficientinstrumentation in earth and rock-fill dams for monitoringthe performance of the structure during construction, andfor all anticipated stress conditions throughout the opera-tional life of the project. Visual observations and theinterpretation of instrumentation data from the embank-ment, foundations, abutments, and appurtenant featuresprovide the primary means for engineers to evaluate damsafety. In recent years, technology of devices for measur-ing seepage, stresses, and movements in dams hasimproved significantly with respect to accuracy, reliabil-ity, and economics. Guidance on the selection and use ofvarious types of instrumentation is presented inEM 1100-2-1908, Parts 1 and 2.

b. Instrumentation. Once instrumentation has beeninstalled, a program must be developed to collect data onan appropriate schedule established for each project. Aminimum collection schedule is described in ER 1110-2-100. Data must be promptly plotted, summarized, andcritically reviewed and evaluated by competent personnel.It is important to realize that installation of instrumenta-tion, without appropriate collection and review of data,does not accomplish the desired end result of evaluatingthe performance and safety of the structure. Data tabula-tions and evaluation summaries should be presented forrecord in periodic inspection reports throughout the opera-tional life of the project.

10-2. Instrumentation Plan and Records

A separate design memorandum should be prepared out-lining the proposed instrumentation. This should includea presentation of the following items:

a. The number, location, and type of piezometers,inclinometers, surface movement markers, settlementgages, or other types of instrumentation.

b. A separate plan of each feature of the projectwith the instrumentation clearly located.

c. A general schedule of installation and frequencyof observation.

d. An explanatory discussion of the purpose of thedevices to be installed.

e. Threshold limits, along with the predicted per-formance levels, should be given.

ER 1110-2-1925 prescribes the forms to be used inrecording instrumentation observations.

10-3. Types of Instrumentation

The type, number, and location of required instrumenta-tion depend on the complexity of the project. Devicesmay consist of the following: piezometers (open tube,such as the Casagrande type, electrical, vibrating wire, oroccasionally closed systems) located in the foundationabutment and/or embankment, surface monuments, settle-ment plates within the embankment, inclinometers withtelescoping casing, movement indicators (at conduit joints,outlet works, and intake tower), internal vertical and hori-zontal movement and strain indicators, earth pressurecells, and accelerographs (in areas of seismic activity).

10-4. Discussion of Devices

a. Piezometers. The safety of a dam is affected byhydrostatic pressures that develop in the embankment,foundation, and abutments. Periodic piezometer observa-tions furnish data on porewater pressures within theembankment, foundation, and abutments, which provide acheck on seepage conditions and performance of thedrainage system. The installation should consist of sev-eral groups of piezometers placed in vertical planes per-pendicular to the axis of the dam so that porewaterpressures and/or seepage pressures may be accuratelydetermined for several cross sections. At each crosssection where piezometers are placed, some should extendinto the foundation and abutments and be located at inter-vals between the upstream toe and the downstream toe, aswell as being placed at selected depths in the embank-ment. In addition to the groups of piezometers at selectedcross sections, occasional piezometers at intermediatestations will provide a check on the uniformity of condi-tions between sections. Each piezometer should be placedwith its tip in pervious material. If pervious material isnot present in the natural deposit of foundation material,or if the tip is in an impervious zone of the embankment,a pocket of pervious material should be provided. Two ofthe more important items in piezometer installation are theprovision of a proper seal above the screen tip and thewater tightness of the joints and connections of the riserpipe or leads.

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b. Surface monuments. Permanent surface monu-ments to measure both vertical and horizontal alignmentshould be placed in the crest of the dam and on theupstream and downstream slopes. Survey control shouldbe maintained from reference monuments located in stablematerial outside of the limits of influence from the con-struction. Monuments should be embedded in theembankment by means of a brass or steel rod encased inconcrete to a depth appropriate for regional frost action.All monuments must be protected against disturbance byconstruction and maintenance equipment. Guidance onspacing is as follows: 50-ft intervals for crest lengths upto 500 ft, l00-ft intervals for crest lengths to 1,000 ft, and200- to 400-ft intervals for longer embankments. Thesemonuments should be installed as early as possible duringconstruction and readings obtained on a regular basis.

c. Inclinometers. Inclinometers should be installedin one or more cross sections of high dams, dams onweak deformable foundations, and dams composed atleast in part of relatively wet, fine-grained soils. Inclino-meters should be installed particularly where dams arelocated in deep and narrow valleys where embankmentmovements are both parallel and perpendicular to the damaxis. It is essential that these devices be installed andobserved during construction as well as during the opera-tional life of the project.

d. Miscellaneous movement indicators. Varioustypes of instrumentation may be installed to measurehorizontal spreading of the embankment (particularlywhen the foundation is compressible), movements adja-cent to buried structures, foundation settlement, andinternal strains. Strain measurements are particularlysignificant adjacent to abutments and below the crest todetect cracking of the core. Where there is a possibilityof axial extension, as near steep abutments, surface monu-ments should be placed on the crest at 50-ft intervals topermit measurement of deformations along the axis.

e. Pressure cells. The need for reliable pressurecells for measuring earth pressures in embankments haslong been recognized, and much research has been donetoward their development. Although many pressure cellsnow installed in earth dams have not proved to be entirelysatisfactory, newer types are proving to be satisfactoryand increased usage is recommended. Some types ofpressure cells installed at the interface of concretestructures and earth fill have performed very well.

f. Accelerographs. For important structures in areasof seismic activity, it is desirable to install strong-motion,self-triggering recording accelerographs to record the

response of the embankment to the earthquake motion.ER 1110-2-103 provides requirements and guidance forinstallation and servicing of strong-motion instruments.EM 1110-2-1908 discusses types of devices and factorscontrolling their location and use. Digital accelerographsare recommended as replacements for existing analogfilm-type accelerographs. A status report on Corps ofEngineers strong-motion instrumentation for measurementof earthquake motions on civil works structures is pro-vided annually. As of September 1993, the Corps ofEngineers has installed 431 accelerographs, 56 peak accel-erograph recorders, and 36 seismic alarm devices at124 projects located in 33 states and the Commonwealthof Puerto Rico.

10-5. Measurements of Seepage Quantities

The seepage flow through and under a dam produces bothsurface and subsurface flow downstream from the dam.The portion of the total seepage that emerges from theground, or is discharged from drains in the dam, its foun-dation, or abutments, is the only part that can be mea-sured directly. An estimate of the quantity of subsurfaceflow from flow net studies may be based on assumedvalues of permeability. The portion of the seepage thatappears at the ground surface may be collected by ditchesor pipe drains and measured by means of weirs or otherdevices (monitoring performance of seepage controlmeasures is discussed in detail in Chapter 13 ofEM 1110-2-1901).

10-6. Automatic Data Acquisition

a. Electronics. Developments in the field of elec-tronics have now made it possible to install and operateautomated instrumentation systems that provide cost-effective real time data collection from earth and rockfilldams. Installation of these computer-based automatic dataacquisition systems (ADAS) satisfies the growing demandfor more accurate and timely acquisition, reduction, pro-cessing, and presentation of instrumentation data forreview and evaluation by geotechnical engineers. Consid-eration should be given to providing an ADAS for all newdam projects. General guidance for developing an ADASis presented in Appendix D. A database for automatedgeotechnical and some structural instrumentation at Fed-eral and non-Federal projects is maintained under theCorps of Engineers Computer Applications in Geotechni-cal Engineering (CAGE) Program.1

____________________________1 Additional information is given in ETL 1110-2-316,Data Base for Automated Geotechnical Instrumentation.

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b. Automatic data acquisition systems. It is alsoadvantageous to retrofit existing projects with an ADAS ifone or more of the following conditions exist:

(1) The project is located in a remote area, farfrom the District office where instrumentation data wouldbe difficult to obtain during critical operating conditions.

(2) Because of a shortage of manpower at the pro-ject, it would be difficult to obtain a sufficient number ofmanual instrumentation readings when extreme loadingconditions exist.

(3) Where geotechnical engineers have a need foreither more accurate and/or more frequent readings thanoperations personnel can supply.

(4) If rapid data processing and presentation ofinstrumentation data for review and evaluation is neces-sary. For example, it is now possible with the use ofADAS to force readings at any time, see those readingsimmediately in the District office, and within an hour,have the data plotted for presentation.

(5) Where it is economically cheaper to purchase,install, and maintain an ADAS.

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Appendix AReferences

A-1. Required Publications 1

Public Law 91-190National Environmental Policy Act of 1969

TM 5-818-2Pavement Design for Seasonal Frost Conditions

TM 5-818-5Dewatering and Groundwater Control

TM 5-852-6Calculation Methods for Determination of Depths ofFreeze and Thaw in Soils

ER 5-7-1(FR)Project Management

ER 415-2-100Staffing for Civil Works Projects

ER 1110-1-1801Construction Foundation Report

ER 1110-2-100Periodic Inspection and Continuing Evaluation of Com-pleted Civil Works Structures

ER 1110-2-103Strong Motion Instrument for Recording EarthquakeMotions on Dams

ER 1110-2-110Instrumentation for Safety Evaluations of Civil WorksProjects

ER 1110-2-112Required Visits to Construction Sites by Design Personnel

ER 1110-2-1150Engineering After Feasibility Studies

_________________________1 References published by the Department of the Armyare available through USACE Command InformationManagement Office Sources.

ER 1110-2-1156Dam Safety - Organization, Responsibilities, andActivities

ER 1110-2-1200Plans and Specifications

ER 1110-2-1806Earthquake Design & Analysis for Corps of EngineersProjects

ER 1110-2-1901Embankment Criteria and Performance Report

ER 1110-2-1925Field Control Data for Earth and Rockfill Dams

ER 1110-2-2901Construction Cofferdams

ER 1130-2-417Major Rehabilitation Program and Dam Safety AssuranceProgram

ER 1130-2-419Dam Operations Management Policy

ER 1165-2-119Modifications to Completed Projects

ER 1180-1-6Construction Quality Management

EPEP 715-1-2715-1-2A Guide to Effective Contractor Quality Control (CQC)

EM 1110-1-1802Geophysical Exploration

EM 1110-1-1804Geotechnical Investigations

EM 1110-1-1904Settlement Analysis

EM 1110-1-1905Bearing Capacity of Soils

EM 1110-2-1414Water Levels and Wave Heights for Coastal EngineeringDesign

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EM 1110-2-1601Hydraulic Design of Flood Control Channels

EM 1110-2-1602Hydraulic Design of Reservoir Outlet Works

EM 1110-2-1603Hydraulic Design of Spillways

EM 1110-2-1901Seepage Analysis and Control for Dams

EM 1110-2-1902Stability of Earth and Rock-Fill Dams

EM 1110-2-1906Laboratory Soils Testing

EM 1110-2-1907Soil Sampling

EM 1110-2-1908Instrumentation of Earth and Rock-Fill Dams -Parts 1 and 2

EM 1110-2-1911Construction Control for Earth and Rock-Fill Dams

EM 1110-2-1913Design & Construction of Levees

EM 1110-2-1914Design, Construction, and Maintenance of Relief Wells

EM 1110-2-2202Dam Safety Preparedness

EM 1110-2-2300Earth and Rock-Fill Dams General Design and Construc-tion Considerations

EM 1110-2-2302Construction with Large Stone

EM 1110-2-2502Retaining and Flood Walls

EM 1110-2-2503Design of Sheet Pile Cellular Structures Cofferdams andRetaining Structures

EM 1110-2-3506Grouting Technology

EM 1110-2-3600Management of Water Control Systems

EM 1110-2-3800Systematic Drilling and Blasting for Surface Excavations

ETL 1110-2-231Initial Reservoir Filling Plan. (ETL’s are temporary doc-uments and subject to change.)

ETL 1110-2-316Date Base for Automated Geotechnical Instrumentation

CEGS-01440Contractor Quality Control

CW-02212Embankment (For Earth Dams)

CW-02214Soil-Bentonite Slurry Trench Cutoffs

CW-03365Concrete for Cutoff Walls

A-2. Related Publications 2

ACI Committee 230 1990ACI Committee 230. 1990 (Jul-Aug). “State-of-the-ArtReport on Soil Cement,”ACI Materials Journal, Vol 87,No. 4, American Concrete Institute, Detroit, MI.

Albritton, Jackson, and Bangert 1984Albritton, J., Jackson, L., and Bangert, R. 1984 (Oct).“Foundation Grouting Practices at Corps of EngineersDams,” Technical Report GL-84-13, U.S. Army EngineerWaterways Experiment Station, Vicksburg, MS.

American Society for Testing and Materials 1990American Society for Testing and Materials. 1990 (Aug).“Field Measurement of Infiltration Rate Using a Double-Ring Infiltrometer with a Sealed-Inner Ring,” ASTMD 5093-90, Philadelphia, PA.

________________________2 References available on interlibrary loan from theResearch Library, U.S. Army Engineer Waterways Exper-iment Station, ATTN: CEWES-IM-MI-R, 3909 HallsFerry Road, Vicksburg, MS 39180-6199.

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EM 1110-2-230031 Jul 94

Arulanandan and Perry 1983Arulanandan, K., and Perry, E. B. 1983 (May). “Erosionin Relation to Filter Design Criteria for Earth Dams,”Journal of the Geotechnical Engineering Division,American Society of Civil Engineers, Vol 109, No. 5,pp 682-698.

Beene and Pritchett 1985Beene, R. R. W., and Pritchett, E. C. 1985. “The R. D.Bailey Dam - A Concrete-Faced, Earth-Rockfill,”Concrete Face Rockfill Dams - Design, Construction, andPerformance, J. B. Cooke and J. L. Sherard, eds., Ameri-can Society of Civil Engineers, New York, pp 163-172.

Bureau of Reclamation 1984Bureau of Reclamation. 1984 (15 Oct). “General DesignStandards,” Chapter 1,Embankment Dams, Engineeringand Research Center, Denver, CO.

Bureau of Reclamation 1986Bureau of Reclamation. 1986 (14 Apr). “Soil-CementSlope Protection,” Chapter 17, Draft Design StandardsNo. 13, Embankment Dams, Engineering and ResearchCenter, Denver, CO.

Casias and Howard 1984Casias, T. J., and Howard, A. K. 1984 (Sep). “Perfor-mance of Soil-Cement Dam Facings - 20-Year Report,”Report No. REC-ERC-84-25, U.S. Department of theInterior, Bureau of Reclamation, Denver, CO.

Chirapuntu and Duncan 1976Chirapuntu, S., and Duncan, J. M. 1976 (Jun). “TheRole of Fill Strength in the Stability of Embankments onSoft Clay Foundations,” Contract Report No. S-76-6,U.S. Army Engineer Waterways Experiment Station,Vicksburg, MS.

Clough and Snyder 1966Clough, G. W., and Snyder, J. W. 1966 (May).“Embankment Pore Pressures During Construction,” Tech-nical Report No. 3-722, U.S. Army Engineer WaterwaysExperiment Station, CE, Vicksburg, MS.

Davidson, Levallois, and Graybeal 1992Davidson, R. R., Levallois, J., and Graybeal, K. 1992(Sep). “Seepage Cutoff Wall for Mud Mountain Dam,”Slurry Walls: Design, Construction, and Quality Control,D. B. Paul, R. R. Davidson, and N. J. Cavalli, eds.,American Society for Testing and Materials, Philadelphia,PA, STP 1129, pp 309-323.

Deere and Deere 1989Deere, D. U., and Deere, D. W. 1989 (Feb). “Rock Qual-ity Designation (RQD) After Twenty Years,” ContractReport GL-89-1, U.S. Army Engineer Waterways Experi-ment Station, Vicksburg, MS.

DeGroot 1971DeGroot, G. 1971 (May). “Soil-Cement Slope Protectionon Bureau of Reclamation Features,” Report No. REC-ERC-71-20, U.S. Department of the Interior, Bureau ofReclamation, Denver, CO.

Denson, Husbands, and Loyd 1986Denson, R. H., Husbands, T., and Loyd, O. K. 1986(Aug). “Soil-Cement Study, Truscott Brine Dam,”Miscellaneous Paper SL-86-10, U.S. Army EngineerWaterways Experiment Station, Vicksburg, MS.

Dewey 1989Dewey, R. L. 1989 (Jun). “The Bureau of ReclamationUses Geosynthetics,”Geotechnical News, Vol 7, No. 2,pp 39-42.

Duncan and Buchignani 1975Duncan, J. M., and Buchignani, A. L. 1975 (Mar). “AnEngineering Manual for Slope Stability Studies,” Depart-ment of Civil Engineering, University of California,Berkeley, CA.

Duscha and Jansen 1988Duscha, L. A., and Jansen, R. B. 1988. “Surveillance,”Jansen, R. B., ed.,Advanced Dam Engineering, forDesign, Construction, and Rehabilitation, Van NostrandReinhold, New York, pp 777-797.

Edelman, Carr, and Lancaster 1991Edelman, L., Carr, F., and Lancaster, C. L. 1991 (Dec).“Partnering,” Institute for Water Resources Pamphlet-91-ADR-P-4, Ft. Belvoir, VA.

Edris 1992Edris, E. V., Jr. 1992 (Nov). “User’s Guide: UTEXAS3Slope-Stability Package, Vol IV: User’s Manual,”Instruction Report GL-87-1, U.S. Army Engineer Water-ways Experiment Station, Vicksburg, MS.

Engemoen and Hensley 1989Engemoen, W. O., and Hensley, P. J. 1989 (Feb).“Geogrid Steepened Slope at Davis Creek Dam,”Pro-ceedings, Geosynthetics ’89, San Diego, CA, Vol 2,pp 255-268.

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EM 1110-2-230031 Jul 94

Farrar 1990Farrar, J. A. 1990 (Mar). “Study of In Situ Testing forEvaluation of Liquefaction Resistance,” Report No.R-90-06, U.S. Department of the Interior, Bureau ofReclamation, Denver, CO.

Federal Emergency Management Agency 1979Federal Emergency Management Agency. 1979 (Jul).“Federal Guidelines for Dam Safety,” FEMA 93 (Pre-pared by the Ad Hoc Interagency Committee on DamSafety of the Federal Coordinating Council for Science,Engineering and Technology), Washington, DC.

Federal Emergency Management Agency 1988Federal Emergency Management Agency. 1988.“National Dam Safety Program - 1986 and 1987, AProgress Report,” Washington, DC.

Federal Emergency Management Agency 1992Federal Emergency Management Agency. 1992 (Sep).“National Dam Safety Program, 1990 & 1991, A ProgressReport,” Vol 2, FEMA 236, Washington, DC.

Fetzer 1967Fetzer, C. A. 1967 (Jul). “Electro-Osmotic Stabilizationof West Branch Dam,”Journal of the Soil Mechanics andFoundations Division,American Society of Civil Engi-neers, Vol 93, No. SM4, pp 85-106.

Fowler and Koerner 1987Fowler, J., and Koerner, R. M. 1987 (Feb). “Stabil-ization of Very Soft Soils Using Geotynthethics,”Pro-ceedings, Geosynthetics ’87, New Orleans, LA, Vol 1,pp 289-300.

Fowler et al. 1986Fowler, J., Leach, R. E., Peters, J. F., and Horz, R. C.1986 (Aug). “Mohicanville Reinforced Dike No. 2Design Memorandum,” Miscellaneous Paper GL-86-25,U.S. Army Engineer Waterways Experiment Station,Vicksburg, MS.

Franks, Duncan, and Collins 1991Franks, L. W., Duncan, J. M., and Collins, S. A. 1991(Apr). “Design and Construction of Mohicanville DikeNo. 2,” Use of Geosynthetics in Dams, Eleventh AnnualUSCOLD Lecture Series, White Plains, NY, United StatesCommittee on Large Dams.

Gilbert 1990Gilbert, P. A. 1990 (Dec). “Computer-Controlled Micro-wave Drying of Potentially Difficult Organic and

Inorganic Soils,” Technical Report GL-90-26, U.S. ArmyEngineer Waterways Experiment Station, Vicksburg, MS.

Gilbert 1991Gilbert, P. A. 1991 (Jan). “Rapid Water Content byComputer-Controlled Microwave Drying,”Journal of theGeotechnical Engineering Division, American Society ofCivil Engineers, Vol 117, No. 1, pp 118-138.

Giroud 1989aGiroud, J. P. 1989a (Feb). “Are Geosynthetics DurableEnough to be Used in Dams?,”Water Power and DamConstruction, Vol 41, No. 2, pp 12-13.

Giroud 1989bGiroud, J. P. 1989b. “Review of Geotextile Filter Cri-teria,” Reinforced Soil and Geotextiles, A. A. Balkema,Rotterdam, Netherlands, pp 1-6.

Giroud 1990Giroud, J. P. 1990 (Jun). “Functions and Applications ofGeosynthetics in Dams,”Water Power and Dam Con-struction, Vol 42, No. 6, pp 16-23.

Giroud 1992aGiroud, J. P. 1992a (Jul/Aug). “Geosynthetics in Dams:Two Decades of Experience,”Geotechnical FabricsReport, Vol 10, No. 5, pp 6-9.

Giroud 1992bGiroud, J. P. 1992b (Sep). “Geosynthetics in Dams:Two Decades of Experience,”Geotechnical FabricsReport, Vol 10, No. 6, pp 22- 28.

Goldin and Rasskazov 1992Goldin, A. L., and Rasskazov, L. N. 1992.Design ofEarth Dams, A. A. Balkema, Rotterdam, Netherlands.

Golze 1977Golze, A. R. 1977. Handbook of Dam Engineering, VanNostrand Reinhold Company, New York.

Hammer and Torrey 1973Hammer, D. P., and Torrey, V. H. 1973 (Mar). “TestFills for Rock-fill Dams,” Miscellaneous Paper S-73-7,U.S. Army Waterways Experiment Station, Vicksburg,MS.

Hansen 1986Hansen, K. D. 1986. Soil-Cement for EmbankmentDams, ICOLD Bulletin 54, International Commission onLarge Dams, Paris, France.

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EM 1110-2-230031 Jul 94

Hansen 1992Hansen, K. D. 1992. “Roller-Compacted Concrete forOvertopping Protection of Embankment Dams,”Modifica-tion of Dams to Accommodate Major Floods, TwelfthAnnual USCOLD Lecture Series, Fort Worth, TX, UnitedStates Committee on Large Dams.

Hausmann 1990Hausmann, M. R. 1990. Engineering Principles ofGround Modification, McGraw-Hill, New York.

Hendron and Patton 1985aHendron, A. J., Jr., and Patton, F. D. 1985a (Jun). “TheVaiont Slide, a Geotechnical Analysis Based on NewGeologic Observations of the Failure Surface, Vol I, MainText,” Technical Report GL-85-5, U.S. Army EngineerWaterways Experiment Station, Vicksburg, MS.

Hendron and Patton 1985bHendron, A. J., Jr., and Patton, F. D. 1985b (Jun). “TheVaiont Slide, a Geotechnical Analysis Based on NewGeologic Observations of the Failure Surface, Vol II,Appendices A through G,” Technical Report GL-85-5,U.S. Army Engineer Waterways Experiment Station,Vicksburg, MS.

Holtz and Walker 1962Holtz, W. G., and Walker, F. C. 1962 (Dec). “Soil-Cement as Slope Protection for Earth Dams,”Journal ofthe Soil Mechanics and Foundations Division, AmericanSociety fo Civil Engineers, Vol 88, No. SM6, pp 107-134.

Hvorslev 1948Hvorslev, M. J. 1948 (Nov). “Subsurface Explorationand Sampling of Soils for Civil Engineering Purposes,”U.S. Army Engineer Waterways Experiment Station,Vicksburg, MS.

Jansen 1988Jansen, R. B., ed. 1988.Advanced Dam Engineering forDesign, Construction, and Rehabilitation, Van NostrandReinhold, New York.

Ledbetter 1985Ledbetter, R. L. 1985 (Aug). “Improvement of Liquefi-able Foundation Conditions Beneath Existing Structures,”Technical Report REMR-GT-2, U.S. Army EngineerWaterways Experiment Station, Vicksburg, MS.

Leenknecht, Szuwalski, and Sherlock 1992Leenknecht, D. A., Szuwalski, A., and Sherlock, A. R.

1992 (Sep). “Automated Coastal Engineering System,”Version 1.07, U.S. Army Engineer Waterways ExperimentStation, Vicksburg, MS.

Mitchell 1983Mitchell, R. J. 1983. Earth Structures Engineering,Allen & Unwin, Inc., Boston.

Moseley 1993Moseley, M. P., ed. 1993.Ground Improvement, CRCPress, Boca Raton, FL.

Napolitano 1991Napolitano, P. J. 1991 (Apr). “Geotextiles in Embank-ments on Soft Foundations,”Use of Geosynthetics inDams, Eleventh Annual USCOLD Lecture Series, WhitePlains, NY, United States Committee on Large Dams.

Perry 1987Perry, E. B. 1987 (Aug). “Laboratory Tests on GranularFilters for Embankment Dams,” Technical ReportGL-87-22, U.S. Army Engineer Waterways ExperimentStation, Vicksburg, MS.

Pope 1960Pope, R. J. 1960. “Rockfill Dams: Dalles ClosureDam,” Transactions, American Society of Civil Engineers,Vol 125, Pt. 2, pp 473-487.

Portland Cement Association 1986Portland Cement Association. 1986. “Suggested Specifi-cations for Soil-Cement for Embankments (Central-Plant-Mixing Method,” Skokie, IL.

Portland Cement Association 1988Portland Cement Association. 1988. “Soil-Cement SlopeProtection for Embankments: Construction,” Skokie, IL.

Portland Cement Association 1991Portland Cement Association. 1991. “Soil-Cement SlopeProtection for Embankments: Planning and Design,”Skokie, IL.

Portland Cement Association 1992aPortland Cement Association. 1992a. “Soil-CementLaboratory Handbook,” Skokie, IL.

Portland Cement Association 1992bPortland Cement Association. 1992b. “Soil-Cement forFacing Slopes, Lining Reservoirs, Channels, andLagoons,” Skokie, IL.

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Powledge and Pravdivets 1992Powledge, G. R., and Pravdivets, Y. P. 1992. “Overtop-ping of Embankments to Accommodate Large FloodEvents - An Overview,”Modification of Dams to Accom-modate Major Floods, Twelfth Annual USCOLD LectureSeries, Fort Worth, TX, United States Committee onLarge Dams.

Powledge, Rhone, and Clopper 1991Powledge, G. R., Rhone, T. J., and Clopper, P. E. 1991.“Accommodating Rare Floods over Embankments andSteep Reinforced Channels,”The Embankment Dam,Proceedings of the Sixth Conference of the British DamSociety held in Nottingham, 12-15 September 1990,pp 165-176.

Roth and Schneider 1991Roth, L. H., and Schneider, J. R. 1991 (Apr). “Consider-ations for Use of Geosynthetics in Dams,”Use of Geo-synthetics in Dams, Eleventh Annual USCOLD LectureSeries, White Plains, NY, United States Committee onLarge Dams.

Saville, McClendon, and Cochran 1962Saville, T., McClendon, E. W., and Cochran, A. L. 1962(May). “Freeboard Allowances for Waves in InlandReservoirs,”Journal of the Waterways and Harbors Divi-sion, Journal, American Society of Civil Engineers,Vol 88, Paper 3138, No. WW2, pp 93-124.

Sherard 1966Sherard, J. L. 1966 (Jul).A Study of the Influence of theEarthquake Hazard on the Design of Embankment Dams,Woodward, Clyde, Sherard and Associates, Oakland, CA.

Sherard 1967Sherard, J. L. 1967 (Jul). “Earthquake Considerations inEarth Dam Design,”Journal of the Geotechnical Engi-neering Division, American Society of Civil Engineers,Vol 93, No. SM4, pp 377-401.

Sherard 1979Sherard, J. L. 1979. “Sinkholes in Dams of Coarse,Broadly Graded Soils,”Transactions, Thirteenth Interna-tional Congress on Large Dams, Vol 2, pp 25-34.

Sherard 1984Sherard, J. L. 1984 (Dec). “Trends and DebatableAspects in Embankment Dam Engineering,”Water Powerand Dam Construction, Vol 36, No. 12, pp 26-32.

Sherard and Dunnigan 1985Sherard, J. L., and Dunnigan, L. P. 1985. “Filters andLeakage Control in Embankment Dams,”Seepage andLeakage from Dams and Impoundments, R. L. Volpe andW. E. Kelly, eds., American Society of Civil Engineers,New York, pp 1-30.

Sherard et al. 1963Sherard, J. L., Woodward, R. J., Gizienski, S. F., andClevenges, W. A. 1963.Earth and Earth-Rock Dams,John Wiley & Sons, New York.

Singh and Sharma 1976Singh, B., and Sharma, H. D. 1976.Earth and RockfillDams, Sarita Prakashan, Meerut, India.

Snyder 1968Snyder, J. W. 1968 (Jul). “Pore Pressures in Embank-ment Foundations,” Technical Report S-68-2, U.S. ArmyEngineer Waterways Experiment Station, CE, Vicksburg,MS.

Soil Conservation Service 1986Soil Conservation Service. 1986 (15 Jan). “Guide forDetermining the Gradation of Sand and Gravel Filters,”Soil Mechanics Note No. 1, Washington, DC.

Sykora and Wahl 1992Sykora, D. W. and Wahl, R. E. 1992 (Sep). “USACEGeotechnical Earthquake Engineering Software, Report 1,WESHAKE For Personal Computers,” U.S. Army Engi-neer Waterways Experiment Station, Vicksburg, MS.

Sykora et al. 1991aSykora, D. W., Koester, J. P., Hynes, M. E., Wahl, R. E.,and Yule, D. E. 1991a (Sep). “Seismic Stability Evalua-tion of Ririe Dam and Reservoir Project, Report 1, Con-struction History and Field and Laboratory Studies, Vol I,Main Text,” Technical Report GL-91-22, U.S. ArmyEngineer Waterways Experiment Station, Vicksburg, MS.

Sykora et al. 1991bSykora, D. W., Koester, J. P., Hynes, M. E., Wahl, R. E.,and Yule, D. E. 1991b (Sep). “Seismic Stability Evalua-tion of Ririe Dam and Reservoir Project, Report 1, Con-struction History and Field and Laboratory Studies, VolII, Appendices A through J,” Technical Report GL-91-22,U.S. Army Engineer Waterways Experiment Station,Vicksburg, MS.

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Sykora et al. 1992Sykora, D. W., Koester, J. P., Wahl, R. E., and Hynes,M. E. 1992. “Post-Earthquake Slope Stability of TwoDams with Liquefied Gravel Foundations,”Stability andPerformance of Slopes and Embankments-II, R. B. Seedand R. W. Boulanger, eds., American Society of CivilEngineers, New York, pp 990-1005.

Sykora, Koester, and Hynes 1991aSykora, D. W., Koester, J. P., and Hynes, M. E. 1991a(Sep). “Seismic Stability Evaluation of Ririe Dam andReservoir Project, Report 2, Stability Calculations, Anal-ysis and Evaluations, Vol I, Main Text,” Technical ReportGL-91-22, U.S. Army Engineer Waterways ExperimentStation, Vicksburg, MS.

Sykora, Koester, and Hynes 1991bSykora, D. W., Koester, J. P., and Hynes, M. E. 1991b(Sep). “Seismic Stability Evaluation of Ririe Dam andReservoir Project, Report 2, Stability Calculations, Analy-sis and Evaluations, Vol II, Appendices A through J,”Technical Report GL-91-22, U.S. Army Engineer Water-ways Experiment Station, Vicksburg, MS.

Torrey 1992Torrey, V. H., III 1992 (Apr). “Compaction Control ofEarth-Rock Mixtures: How to Develop and Use DensityInterference Coefficients and Optimum Water ContentFactors,” Instruction Report GL-92-1, U.S. Army Engi-neer Waterways Experiment Station, Vicksburg, MS.

Torrey and Donaghe 1991aTorrey, V. H., III, and Donaghe, R. T. 1991a (Aug).“Compaction Characteristics of Earth-Rock Mixtures,”Miscellaneous Paper GL-91-16, U.S. Army EngineerWaterways Experiment Station, Vicksburg, MS.

Torrey and Donaghe 1991bTorrey, V. H., III, and Donaghe, R. T. 1991b (Aug).“Compaction Control of Earth-Rock Mixtures,” TechnicalReport GL-91-16, U.S. Army Engineer Waterways Exper-iment Station, Vicksburg, MS.

United States Committee on Large Dams 1993United States Committee on Large Dams. 1993 (May).“General Guidelines and Current U.S. Practice in Auto-mated Performance Monitoring of Dams,” Denver, CO.

U.S. Army Corps of Engineers 1984U.S. Army Corps of Engineers. 1984. “Shore ProtectionManual,” 2 Vols, Washington, DC.

U.S. Army Corps of Engineers 1990U.S. Army Corps of Engineers. 1990. “Rock TestingHandbook,” U.S. Army Engineer Waterways ExperimentStation, Vicksburg, MS.

U.S. Army Corps of Engineers, Hydrologic Engineer-ing Center 1980U.S. Army Corps of Engineers, Hydrologic EngineeringCenter. 1980 (Jun). “Flood Emergency Plans Guidelinesfor Corps Dams,” Research Document No. 13, Davis, CA.

U.S. Army Corps of Engineers, Hydrologic Engineer-ing Center 1982U.S. Army Corps of Engineers, Hydrologic EngineeringCenter. 1982 (Jan). “Emergency Planning for Dams,Bibliography and Abstracts of Selected Publications,”Davis, CA.

U.S. Army Corps of Engineers, Hydrologic Engineer-ing Center 1983aU.S. Army Corps of Engineers, Hydrologic EngineeringCenter. 1983a (Aug). “Example Emergency Plan forBlue Marsh Dam and Lake,” Research Document No. 19,Davis, CA.

U.S. Army Corps of Engineers, Hydrologic Engineer-ing Center 1983bU.S. Army Corps of Engineers, Hydrologic EngineeringCenter. 1983b (Aug). “Example Plan for Evacuation ofReading, Pennsylvania, in the Event of Emergencies atBlue Marsh Dam and Lake,” Research Document No. 20,Davis, CA.

U.S. Army Engineer District, Jacksonville 1983U.S. Army Engineer District, Jacksonville. 1983(30 Jun). “Cerrillos Dam and Spillway,” Design Memo-randum No. 17, Vol 1, Report, Jacksonville, FL.

U.S. Army Engineer Waterways Experiment Station1949U.S. Army Engineer Waterways Experiment Station.1949 (Mar). ”Slope Protection for Earth Dams,” Prelimi-nary Report, Vicksburg, MS.

U.S. Army Engineer Waterways Experiment Station1956U.S. Army Engineer Waterways Experiment Station 1956(Oct). “Review of Soils Design, Construction, and Proto-type Analysis, Blakely Mountain Dam, Arkansas,” Tech-nical Report No. 3-439, Vicksburg, MS.

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Veesaert 1990Veesaert, C. J. 1990 (Jun). “Standardizing the Approachto Dam Safety Training,”Hydro Review, Vol 9, No. 3,pp 46-50.

Walker 1984Walker, W. L. 1984 (Dec). Earth Dams: GeotechnicalConsiderations in Design and Construction, Ph.D. Disser-tation, Oklahoma State University, Stillwater, OK.

Wooten, Powledge, and Whiteside 1992Wooten, R. L., Powledge, G. R., and Whiteside, S. L.1992 (Jan). “Dams Going Safely Over the Top,”CivilEngineering, American Society of Civil Engineers,Vol 62, No. 1, pp 52-54.

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Appendix BFilter Design

B-1. General

The objective of filters and drains used as seepage controlmeasures for embankments is to efficiently control themovement of water within and about the embankment. Inorder to meet this objective, filters and drains must, forthe project life and with minimum maintenance, retain theprotected materials, allow relatively free movement ofwater, and have sufficient discharge capacity. For design,these three necessities are termed piping or stabilityrequirement, permeability requirement, and dischargecapacity, respectively. This appendix explains how theserequirements are met for cohesionless and cohesive mater-ials, and provides general construction guidance for instal-lation of filters and drains. The terms filters and drainsare sometimes used interchangeably. Some definitionsclassify filters and drains by function. In this case, filtersmust retain the protected soil and have a permeabilitygreater than the protected soil but do not need to have aparticular flow or drainage capacity since flow will beperpendicular to the interface between the protected soiland filter. Drains, however, while meeting the require-ments of filters, must have an adequate discharge capacitysince drains collect seepage and conduct it to a dischargepoint or area. In practice, the critical element is not defi-nition, but recognition, by the designer, when a drain mustcollect and conduct water. In this case the drain must beproperly designed for the expected flows. Where it is notpossible to meet the criteria of this appendix, the designmust be cautiously done and based on carefully controlledlaboratory filter tests (Perry 1987).

B-2. Stability

Filters and drains1 allow seepage to move out of a pro-tected soil more quickly than the seepage moves withinthe protected soil. Thus, the filter material must be moreopen and have a larger grain size than the protected soil.Seepage from the finer soil to the filter can cause move-ment of the finer soil particles from the protected soil intoand through the filter. This movement will endanger the

_____________________________1 In paragraphs B-2 and B-3 the criteria apply to drainsand filters; for brevity, only the word filter will be used.

embankment.2 Destruction of the protected soil structuremay occur due to the loss of material. Also, clogging ofthe filter may occur causing loss of the filter’s ability toremove water from the protected soil. Criteria developedby many years of experience are used to design filters anddrains which will prevent the movement of protected soilinto the filter. This criterion, called piping or stabilitycriterion, is based on the grain-size relationship betweenthe protected soil and the filter. In the following para-graphs, the lower case “d” is used to represent the grainsize for the protected (or base) material and the uppercase “D” the grain size for the filter material. Determinefilter gradation limits using the following steps (Soil Con-servation Service 1986):

a. Determine the gradation curve (grain-size distri-bution) of the base soil material. Use enough samples todefine the range of grain size for the base soil or soils anddesign the filter gradation based on the base soil thatrequires the smallest D15 size.

b. Proceed to stepd if the base soil contains nogravel (material larger than No. 4 (4.75 mm) sieve).

c. Prepare adjusted gradation curves for base soilswith particles larger than the No. 4 (4.75 mm) sieve:

(1) Obtain a correction factor by dividing 100 bythe percent passing the No. 4 (4.75 mm) sieve.

(2) Multiply the percentage passing each sieve sizeof the base soil smaller than No. 4 (4.75 mm) by thecorrection factor from stepc(1).

(3) Plot these adjusted percentages to obtain a newgradation curve.

(4) Use the adjusted curve to determine the percentpassing the No. 200 (0.075 mm) sieve in stepd.

d. Place the base soil in a category based on thepercent passing the No. 200 (0.075 mm) sieve in accor-dance with Table B-1.

_____________________________2 In practice, it is normal for a small amount of protectedsoil to move into the filter upon initiation of seepage. Thisaction should quickly stop and may not be observed whenseepage first occurs. This is one reason that initial opera-tion of embankment seepage control measures should beclosely observed by qualified personnel.

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EM 1110-2-230031 Jul 94

Table B-1Categories of Base Soil Materials

Percent finer than the No. 200Category (0.075 mm) sieve

1 852 40-853 15-394 15

e. Determine the maximum D15 size for the filter inaccordance with Table B-2. Note that the maximum D15

is not required to be smaller than 0.20 mm.

Table B-2Criteria for Filters

Base Base soil description, and Filter criteria insoil percent finer than No. 200 terms of maximumcategory (0.075 mm) sieve1 D15 size2 Note

1 Fine silts and clays; D15 < 9 x d85 (1)more than 85% finer

2 Sands, silts, clays, D15 < 0.7 mmand silty and clayeysands; 40 to 85% finer.

3 Silty and clayey D15 <40-A

(2),(3)sands and gravels;

40-15

15 to 39% finer {(4 x d85)- 0.7 mm}+ 0.7 mm

4 Sands and gravels; less D15 < 4 to 5 x d85 (4)than 15% finer.

1 Category designation for soil containing particles larger than4.75 mm is determined from a gradation curve of the base soilwhich has been adjusted to 100% passing the No. 4 (4.75 mm)sieve.2 Filters are to have a maximum particle size of 3 in. (75 mm) anda maximum of 5% passing the No. 200 (0.075 mm) sieve with theplasticity index (PI) of the fines equal to zero. PI is determined onthe material passing the No. 40 (0.425 mm) sieve in accordancewith EM 1110-2-1906. To ensure sufficient permeability, filters areto have a D15 size equal to or greater than 4 x d15 but no smallerthan 0.1 mm.

NOTES: (1) When 9 x d85 is less than 0.2 mm, use 0.2 mm.(2) A = percent passing the No. 200 (0.075 mm) sieve

after any regrading.(3) When 4 x d85 is less than 0.7 mm, use 0.7 mm.(4) In category 4, the d85 can be based on the total base

soil before regrading. In category 4, the D15 < 4 xd85 criterion should be used in the case of filtersbeneath riprap subject to wave action and drainswhich may be subject to violent surging and/orvibration.

f. To ensure sufficient permeability, set the mini-mum D15 greater than or equal to 3 to 5 × maximum d15

of the base soil before regrading, but no less than0.1 mm.

g. Set the maximum particle size at 3 in. (75 mm)and the maximum passing the No. 200 (0.075 mm) sieveat 5 percent. The portion of the filter material passing theNo. 40 (0.425 mm) sieve must have plasticity index (PI)of zero when tested in accordance with EM 1110-2-1906.

h. Design the filter limits within the maximum andminimum values determined in stepse, f, andg. Standardgradations may be used if desired. Plot the limit valuesand connect all the minimum and maximum points withstraight lines. To minimize segregation and relatedeffects, filters should have relatively uniform grain-sizedistribution curves, without “gap grading”--sharp breaks incurvature indicating absence of certain particle sizes.This may require setting limits that reduce the broadnessof filters within the maximum and minimum values deter-mined. Sand filters with D90 less than about 20 mmgenerally do not need limitations on filter broadness toprevent segregation. For coarser filters and gravel zonesthat serve both as filters and drains, the ratio D90/D10

should decrease rapidly with increasing D10 size. Thelimits in Table B-3 are suggested for preventing segrega-tion during construction of these coarser filters.

Table B-3D10 and D 90 Limits for Preventing Segregation

If minimum D10 Then maximum D90

mm mm

<0.5 20.5 - 1.0 251.0 - 2.0 302.0 - 5.0 405.0 - 10 5010 - 50 60

B-3. Permeability

The requirement that seepage move more quickly throughthe filter than through the protected soil (called the per-meability criterion) is again met by a grain-size relation-ship criterion based on experience:

Permeability

15 percent size of filter material> 3 to 5 (B-1)15 percent size of protected soil

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Permeability of a granular soil is roughly proportional tothe square of the 10 to 15 percent size material. Thus,the permeability criterion ensures that filter materials haveapproximately 9 to 25 or more times the permeability ofthe protected soil. Generally, a permeability ratio of atleast 5 is preferred; however, in the case of a wide bandof uniform base material gradations, a permeability ratioas low as 3 may be used with respect to the maximum15 percent size of the base material. There may be situa-tions, particularly where the filter is not part of a drain,where the permeability of the filter is not important. Inthose situations, this criterion may be ignored.

B-4. Applicability

The filter criteria in Table B-2 and Equation B-1 areapplicable for all soils (cohesionless or cohesive soils)including dispersive soils (Sherard and Dunnigan 1985).However, laboratory filter tests are recommended fordispersive soils, very fine silt, and very fine cohesive soilswith high plastic limits.

B-5. Perforated Pipe 3

The following criteria are applicable for preventing infil-tration of filter material into perforated pipe, screens,etc.):

minimum 50 percent size of filter material> 1.0 (B-2)hole diameter or slot width

In many instances a filter material meeting the criteriagiven by Table B-2 and Equation B-1 relative to thematerial being drained is too fine to meet the criteriagiven by Equation B-2. In these instances, multilayeredor “graded” filters are required. In a graded filter eachlayer meets the requirements given by Table B-2 andEquation B-1 with respect to the pervious layer with thefinal layer in which a collector pipe is bedded also meet-ing the requirements given by Equation B-2. Gradedfilter systems may also be needed when transitioning fromfine to coarse materials in a zoned embankment or wherecoarse material is required for improving the water carry-ing capacity of the system.

_____________________________3 EM 1110-2-2300 states, “Collector pipe should not beplaced within the embankment, except at the downstreamtoe, because of the danger of either breakage or separationof joints, resulting from fill placement and compactionoperations, or settlement, which might result in eitherclogging and/or piping.”

B-6. Gap-Graded Base

The preceding criteria cannot, in most instances, beapplied directly to protect severely gap- or skip-gradedsoils. In a gap-graded soil such as that shown in Fig-ure B-1 the coarse material simply floats in the matrix offines. Consequently, the scattered coarse particles willnot deter the migration of fines as they do in a well-graded material. For such gap-graded soils, the filtershould be designed to protect the fine matrix rather thanthe total range of particle sizes. This is illustrated inFigure B-1. The 85 percent size of the total sample is5.2 mm. Considering only the matrix material, the85 percent size would be 0.1 mm resulting in a muchfiner filter material being required. This procedure mayalso be followed in some instances where the materialbeing drained has a very wide range of particle sizes (e.g.,materials graded from coarse gravels to significant per-centages of silt or clay). For major structures such adesign should be checked with filter tests.

B-7. Gap-Graded Filter

A gap-graded filter material must never be specified orallowed since it will consist of either the coarse particlesfloating in the finer material or the fine material havingno stability within the voids produced by the coarsematerial. In the former case the material may not bepermeable enough to provide adequate drainage. Thelatter case is particularly dangerous since piping of theprotected material can easily occur through the relativelylarge, loosely filled voids provided by the coarse material.

B-8. Broadly Graded Base

One of the more common soils used for embankmentdams is a broadly graded material with particle sizesranging from clay sizes to coarse gravels and including allintermediate sizes. These soils may be of glacial, allu-vial-colluvial, or weathered rock origin. As noted bySherard, since the 85 percent size of the soil is commonlyon the order of 20 to 30 mm, a direct application of thestability criteria D15/d85 < 4 to 5 would allow very coarseuniform gravel without sand sizes as a downstream filter,which would not be satisfactory (Sherard 1979). Thetypical broadly graded soils fall in Soil Category 2 inTable B-2 and require a sand or gravelly filter with D15 <0.7 mm.

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B-9. Example of Graded Filter Design for Drain

Seldom, if ever, is a single gradation curve representativeof a given material. A material is generally representedby a gradation band which encompasses all the individualgradation curves. Likewise, the required gradation for thefilter material is also given as a band. The design of agraded filter which shows the application of the filtercriteria where the gradations are represented by bands isillustrated in Figure B-2. A typical two-layer filter forprotecting an impervious core of a dam is illustrated. Theimpervious core is a fat clay (CH) with a trace of sandwhich falls in Category 1 soil in Table B-2. The criterionD15 < 9 × d85 is applied and point “a” is established inFigure B-2. Filter material graded within a band such asthat shown for filter material A in Figure B-2 is accepta-ble based on the stability criteria. The fine limit of theband was arbitrarily drawn and in this example isintended to represent the gradation of a readily availablematerial. A check is then made to ensure that the 15 per-cent size of the fine limit of the filter material band(point b) is equal to or greater than 3 to 5 times the15 percent size of the coarse limit of the drained materialband (point c). Filter A has a minimum D10 size and amaximum D90 size such that, based on Table B-3, segre-gation during placement can be prevented. Filter materialA meets both the stability and permeability requirementsand is a suitable filter material for protecting the impervi-ous core material. The second filter, filter material B,usually is needed to transition from a fine filter (filtermaterial A) to coarse materials in a zoned embankmentdam. Filter material B must meet the criteria given byTable B-2 with respect to filter material A. For stability,the 15 percent size of the coarse limit of the gradationband for the second filter (point d) cannot be greater than4 to 5 times the 85 percent size of the fine limit of thegradation band for filter material A (point e). For per-meability, the 15 percent size of the fine limit (point f)must be at least 3 to 5 times greater than the 15 percentsize of the coarse limit for filter material A (point a).With points d and f established, the fine and coarse limitsfor filter material B may be established by drawing curvesthrough the points approximately parallel to the respectivelimits for filter material A. A check is then made to seethat the ratio of maximum D90/minimum D10 size of filtermaterial B is approximately in the range as indicated inTable B-3. A well-graded filter which usually would notmeet the requirements in Table B-3 may be used if segre-gation can be controlled during placement. Figure B-2 isintended to show only the principles of filter design. Thedesign of thickness of a filter for sufficient seepage dis-charge capacity is done by applying Darcy’s Law,

Q = kia (an example is presented in Chapter 8 ofEM 1110-2-1901).

B-10. Construction

EM 1110-2-1911 provides guidance for construction.Major concerns during construction include:

a. Prevention of contamination of drains and filtersby runoff containing sediment, dust, construction traffic,and mixing with nearby fine-grained materials duringplacement and compaction. Drain and filter material maybe kept at an elevation higher than the surrounding fine-grained materials during construction to prevent contami-nation by sediment-carrying runoff.

b. Prevention of segregation, particularly well-graded filters, during handling and placement.

c. Proper in-place density is usually required to bean average of 85 percent relative density with no area lessthan 80 percent relative density. Granular materials con-taining little or no fines should be saturated during com-paction to prevent “bulking” (low density) which canresult in settlement when overburden materials are placedand the drain is subsequently saturated by seepage flows.

d. Gradation should be monitored closely so thatdesigned filter criteria are met.

e. Thickness of layers should be monitored toensure designed discharge capacity and continuity of thefilter.

Thus, quality control/assurance is very important duringfilter construction because of the critical function of thisrelatively small part of the embankment.

B-11. Monitoring

Monitoring of seepage quantity and quality (see Chap-ter 13 of EM 1110-2-1901 for methods of monitoringseepage) once the filter is functioning is very important tothe safety of the embankment. An increase in seepageflow may be due to a higher reservoir level or may becaused by cracking or piping. The source of the addi-tional seepage should be determined and action taken asrequired (see Chapters 12, 13, and 14 of EM 1110-2-1901). Decreases in seepage flows may also signal dan-gers such as clogging of the drain(s) with piped material,iron oxide, calcareous material, effects of remedial grout-ing, etc. Again, the cause should be determined and

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appropriate remedial measures taken. Drain outletsshould be kept free of sediment and vegetation. In coldclimates, design or maintenance measures should be takento prevent clogging of drain outlets by ice.

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Appendix CSlope Protection

C-l. General

a. Upstream slopes. Upstream slopes require moreextensive treatment than downstream slopes because theyare exposed to wave action. The required upstream slopeprotection depends on the expected wind velocities andduration, the size and configuration of the reservoir, thepermanent water-surface elevation, and the frequency ofthe pool elevation. Where a permanent pool exists, elabo-rate protection below the minimum water surface is sel-dom needed since erosive action would be negligiblebelow that level, and a selected gravel will afford suffi-cient protection. Above the permanent pool elevation,protection against wave action is required. On the down-stream slope, only erosion from rainfall and surface runoffand/or wind erosion must be considered except for sec-tions that may be affected by wave action in the tailwaterpool. A performance survey was made in 1946 coveringslope protection for a number of major earth dams(largely Corps of Engineers) in the United States (theresults are reported in U.S. Army Engineer WaterwaysExperiment Station 1949).

b. Probability evaluation. An evaluation of theprobability for erosion damage should be made for eachslope protection design. The evaluation should considerthe effects of each type of erosion: wave, rainfall andsurface runoff, and wind erosion. The influence of seep-age, freezing and thawing, and ice buildup should beconsidered, as appropriate. Due to the high cost of slopeprotection, this evaluation should be accomplished duringthe survey studies to establish a reliable cost estimate.The final design should be presented in the appropriatefeature design memoranda.

c. Bedding layers. Bedding layers beneath riprapshould be designed to provide for retention of beddingparticles for the overlying riprap and for retention of thematerial underlying the bedding layer. To satisfy theserequirements, multiple bedding layers may be required.The minimum bedding layer thickness should be 9 in.Geotextiles (filter fabrics) should not be used beneathriprap on embankment dams.

C-2. Design Considerations

Slope protection should be provided for the range offrequent and extended reservoir elevations. The slope ofthe flood hydrograph determines the length of time the

pool resides at each elevation. If the response timebetween the storm and the resulting flood pool isrelatively short, the high winds associated with the stormmay not have subsided and must be considered in theselection of the design wind. The steepness of theembankment slope, ease of access for maintenance, natureof the embankment materials to be protected, and avail-ability of materials for use as slope protection should beconsidered in the design. Slopes flatter than 1 vertical on15 horizontal seldom require slope protection. Embank-ment slopes of 1 vertical on 6 horizontal and flatter canbe traversed easily by construction and maintenanceequipment.

a. Classification of embankment slopes for proba-bility of damage. The possibility of damage to the slopevaries with the steepness of the slope, nature of theembankment materials, wind speed, fetch, and exposuretime to the wave attach. Guidelines for slope classifica-tion based on this exposure concept are as follows:

(l) Upstream slope.

(a) Class I: The zone of an embankment slope withmaximum exposure to pool elevations during normalproject operation. Generally, the Class 1 zone will extendfrom an upper pool elevation determined by an annualchance of exceedence of 10 percent plus the appropriatewave runup down to a drawdown pool elevation deter-mined by 10 percent chance of occurrence. The embank-ment elevations in the multipurpose operating range havea near constant exposure and should be Class I.

(b) Class II: The zone of an embankment slopewith infrequent exposure to pools. Generally, this is thezone immediately above or below the Class I zone, anddamage to the slopes in this zone is usually a result ofrainfall and surface runoff, floods during construction,wave attack during the initial reservoir filling, or erosiondue to currents. For embankment dams with gated outletworks, the zone and below the top of spillway gates pluswave runup or uncontrolled spillway crest plus waverunup, should be Class II. For embankment dams withungated outlet works, the zone and below the lower ofelevation of the uncontrolled spillway crest plus waverunup or elevation obtained by rounding on the top ofmultipurpose pool the standard project flood and addingwave runup, should be Class II.

(c) Class III: The zone of an embankment slopewith rare exposure to pools. The occurrence of poolsabove the Class II embankment zone is very infrequentand the duration of these pools is usually short. However,

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the potential for wave erosion to result in a safety hazardincreases as the width of embankment narrows. Allembankment slopes above the Class II elevations shouldbe Class III, except at the top of embankment where thesafety of the dam during a spillway design flood becomesa primary concern, and a lower class category may beappropriate. Special design considerations for theembankment crest are discussed in paragraph C-2d.

(2) Downstream slopes. The embankment slopebelow the maximum tailwater elevation for the spillwaydesign flood will usually be classified as Class II. Inmany projects the geographic relationship between theembankment and spillway preclude the necessity forextensive tailwater protection. For projects where largespillway flows discharge near the embankment toe, ahydraulic model test is required to establish the flowvelocities and wave heights for which slope protectionshould be designed.

b. Riprap. Dumped riprap is the preferred type ofupstream slope protection. While the term “dumped rip-rap” is traditionally used, it is not completely descriptivesince some reworking of dumped rocks is generally neces-sary to obtain good distribution of rock sizes. For riprapup to 24 in. thick, the rock should be well graded fromspalls to the maximum size required. For thicker riprapprotection, a grizzly should be used to eliminate rockfragments lighter than 50 lb. Riprap sizes and thicknessesare determined based on the significant wave height(design wave). The design wave and wave runup willchange for different pool levels as a result of variations inthe effective fetch distance and applied wind velocity.Riprap in the upstream slope should have a minimumthickness of 12 in. The selection of design water leveland wave height should follow the procedures outlined inEM 1110-2-1414. Actual wind, wave, fetch, and stonesize will be computed in accordance with algorithmsand/or figures in EM 1110-2-1414, “Automated CoastalEngineering System” (Leenknecht, Szuwalski, andSherlock 1992), and the “Shore Protection Manual”(U.S. Army Corps of Engineers 1984).

(l) Design wind. Use of the actual wind record fromthe site is the preferred method for establishing the windspeed-duration curve (see paragraph 5-7 of EM 1110-2-1414). For riprap in Class I zone, select the 1 percentwind. For riprap in Class II zone, select a wind betweenthe 10 percent chance and 2 percent chance based on arisk analysis. For riprap in Class III zone, select a windbetween 50 percent chance and 10 percent chance basedon a risk analysis.

(2) Effective fetch. Compute the effective fetch, inmiles, using the procedure explained in paragraph 5-7 ofEM 1110-2-1414. Using the Automated Coastal Engi-neering System (ACES) software (see Leenknecht,Szuwalski, and Sherlock 1992), especially the desktopcomputer routine for wind wave hindcasting in restrictedfetches, will simplify and standardize the computations inconjunction with the methodology described in EM 1110-2-1414. As an alternative, the restricted fetch computa-tions from the “Shore Protection Manual” (U.S. ArmyCorps of Engineers 1984) can also be used. For design ofriprap in a Class I zone, compute the effective fetch for apool elevation with a 10 percent chance of exceedence.For design of riprap in the Class II zone, compute theeffective fetch for the applicable pool elevation (i.e., topof gates, uncontrolled spillway crest, etc.). If anotherpool level is used to define the elevation Class I or ClassII zones, compute the effective fetch for the higher of thetwo elevations. Riprap will seldom be required for slopesin the Class III zone, but when riprap is selected for aband along the embankment crest, compute the effectivefetch for the maximum surcharge pool.

(3) Design wave. Computation of the design waveis explained in EM 1110-2-1414 and “Automated CoastalEngineering System.” By using the algorithm in ACES(see Leenknecht, Szuwalski, and Sherlock 1992) for wind-speed adjustment and wave height design, restricted fetchoption, the wave height, and period are computed at thesame time the effective fetch is determined. For designof riprap, use the significant wave height (average of theone-third highest waves in a given group). If a verticalwall is part of the design, use a higher wave, i.e., average1 percent or 10 percent, depending on structure rigidity.

(4) Riprap design. Determine the size of the riprapand the layer thickness using the rubble-mound revetmentdesign in ACES (see Leenknecht, Szuwalski, and Sher-lock 1992). This algorithm will give the stone size, layerthickness, and compute wave runup on a riprap slope withan impervious foundation. Use this computed runup inparagraph C-2b(2) to check the embankment height.

c. Bedding layers. The gradation of the beddingmaterial should provide for the retention of bedding parti-cles by the overlying riprap layer and for the retention ofthe material underlying the bedding layer. If the underly-ing material has low plasticity, the gradation of the bed-ding material should conform with the following filtercriteria.

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D15B > 5D15E (C-1)

D15B < 5D85E (C-2)

D85B > D15R/5 (C-3)

D15B = the 15 percent passing the size of the bedding

D85B = the 85 percent passing the size of the bedding

D15E = the 15 percent passing the size of the material tobe protected

D85E= the 85 percent passing the size of the material tobe protected

D15R = the 15 percent passing the size of the riprap

An intermediate filter layer may be required between thebedding and riprap to prevent washout of the bedding.Bedding layers over erosion-resistant clay materials neednot be designed to meet the criteria of Equation C-1 orEquation C-2 but must still satisfy Equation C-3. Eachdesign should produce a specification that defines materialsources, gradations, and layer thickness to economicallyprovide the riprap and bedding layers required to protectthe embankment.

d. Embankment crest. The top of dam elevation isusually selected much earlier in the design process than isthe slope protection. When the slope protection designhas been selected, the top of dam elevation should bereviewed to ensure that runup computations (from para-graph C-2b(4)) are consistent with the type of protectionto be provided. The slope protection near the top of thedam must ensure embankment safety and security todownstream areas. Each embankment dam should bereviewed to determine the needed crest elevations of theupstream slope. Intermittent overtopping by wave runupmay be acceptable where access to the top of the dam isnot necessary during occurrence of the maximum sur-charge pool and when the crest and downstream slopeconsist of material that will not experience damagingerosion. The slope protection provided at the near crestelevations of the upstream slope may vary for differentreaches but must be stable for the design wave used toestablish the top of dam elevation.

e. Downstream slope protection.

(l) Where an adequate growth of grass can be main-tained, vegetative cover is usually the most desirable type

of downstream slope protection. A slope of approxi-mately 1 vertical on 3 horizontal is about the steepest onwhich mowing and fertilizing equipment can operateefficiently. In arid or semiarid regions where adequateturf protection cannot be maintained, outer embankmentzones composed of soils susceptible to erosion (silts andsands) may be protected with gravel or rock spall blanketsat least 12 in. thick, have berms with collector ditchesprovided, and have collector ditches at the embankmenttoe.

(2) Where the downstream slope is exposed totailwater, criteria used to establish the required upstreamprotection should be used for that portion of the slopeexposed to wave action. Alternatively, a rock toe may beprovided, extending above the maximum tailwaterelevation.

f. Alternative slope protection. Alternative slopeprotection designs that are functional and cost effectivemay be used. Factors that influence the selection of slopeprotection are embankment damage, materials fromrequired excavation, availability and quality of offsitequarries, and turfs. A greater thickness of quarry-runstone may be an option to relatively expensive gradedriprap. Some designers consider the quarry-run stone tohave another advantage: its gravel- and sand-size compo-nents serve as a filter. The gravel and sand sizes shouldbe less by volume than the voids among the larger stone.Not all quarry-run stone can be used as riprap; stone thatis gap graded or has a large range in maximum to mini-mum size is unsuitable. Quarry-run stone for riprapshould be limited to D85/D15 < 7. Additional informationis available in EM 1110-2-1601. A careful analysisshould be made to demonstrate the economics of usingthe alternative.

(l) Upstream slope.

(a) Class I zone. One alternative to riprap is to useriprap-quality, quarry-run stone dumped in a designatedzone within, but not at, the outer slope of the embank-ment. The dumped rock is spread and then processed bya rock rake operating in a direction perpendicular to thestrike of the exterior slope. Rock raking will move thelarger stones in the zone contingent to the exterior slopeof the embankment. The quarry-run stone that remains inthe dumped zone serves as a bedding. The size of thestone in the outer layer can be partially controlled by theblasting techniques, quarry handling of material, and bythe tooth spacing on the rock rake. The outer zone oflarge stone should produce a thickness (normal to the

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slope) greater than the thickness of required layers ofriprap protection. Another alternative is to use a welldesigned and properly controlled plant-mix, soil-cementlayer placed with established and acceptable techniques.The Bureau of Reclamation pioneered in the developmentand use of soil-cement for upstream slope protection ofdams (Holtz and Walker 1962, Bureau of Reclamation1986, DeGroot 1971, Casias and Howard 1984, Adaskaet al. 1990). Details concerning design and constructionare available (Bureau of Reclamation 1986; Hansen 1986;Portland Cement Association 1986, 1988, 1991, 1992a,1992b). The Tulsa District has used soil cement asupstream slope protection at Optima Dam, OK, ArcadiaDam, OK, and Truscott Brine Dam, TX (Denson,Husbands, and Loyd 1986).

(b) Class II zone. An alternative to riprap isquarry-run stone consisting of stones that may be of lessthan riprap quality. The quarry-run stone layer thicknessis dependent on material quality and size, but shouldalways be greater than the thickness of required layers ofriprap protection.

(c) Class III zone. An alternative to riprap islayers of quarry-run materials or erosion-resistant mater-ials in thicknesses greater than those designed for riprap.Slopes between 1 vertical on 8 horizontal and 1 verticalon 15 horizontal with a maintenance access to the slopemay be protected by an erosion-resistant material withminimum thickness of 1 ft normal to the slope.

(2) Downstream slopes. The slope is usually pro-tected by a layer of locally available, erosion-resistantmaterial from required excavation or by turf. Designedintercepter ditches across the slope would be provided,where long unbroken surfaces exist or where the intersec-tion of slopes steepen in a downslope direction. Sheetflow of surface runoff without the beginning of erosiongullies is seldom possible for distances greater than200 ft. This is especially true in regions with semiaridclimates. Because failure of an inadequately sized inter-cepter ditch or an improperly constructed ditch and dikecan create serious erosion, it is important that intercepterditches be carefully planned.

g. Erosion-resistant granular materials. Gravelsand combination gravel and soft clay are resistant toerosion under many conditions. The resistance of gravelsis dependent on the severity of erosion, steepness of theslope, size and shape of the gravels, and quantity andplasticity of fines. Compaction may be required to ensuresatisfactory performance of some of these materials.

h. Erosion-resistant clays. The performance of aclay is hard to predict, but experience has shown someclays to be very resistant to erosive forces (Arulanandanand Perry 1983). Clay materials with a liquid limit above40 percent and that plot above the “A” line would norm-ally qualify as “erosion resistant.” When clay is used asan erosion-resistant material, an upper liquid limit shouldbe specified. An upper liquid limit is selected to limit thelow, long-term shear strength characteristics and changesin volume, expansion, and shrinkage, with changes inclimate. Clays can also be used as underlayers for mar-ginal slope protection at little additional cost. Erosion-resistant clays employed for slope protection should becompacted as specified for impervious fill.

i. Turfs. Turfs consisting of grasses suitable tolocal climate and tolerant to some inundation often pro-vide sufficient resistance to erosion, including upstreamClass III zones. A turf protection requires a soil layerthat is capable of supporting vegetation. The topsoil andseeding operations should be performed during the grow-ing season as the embankment construction proceeds.This procedure will minimize surface erosion on theunprotected embankment surface and will establish muchof the surface turfing prior to the contractor’s departurefrom the site. To facilitate establishment of a turf andmowing the embankment, slopes should not be steeperthan 1 vertical on 3 horizontal. In some climatic regions,turfs are not suitable alternatives for slope protection.

C-3. Stone Quality

Riprap protection requires good quality rock and beddingof sufficient size to meet the design requirements. Con-sideration should be given to materials available fromrequired excavations as well as from the nearby quarrysources. Freeze-thaw, wet-dry, specific gravity, absorp-tion, sodium sulphate soundness, and Los Angeles abra-sion tests should be formed to determine the durability ofthe material under the anticipated field conditions(detailed test procedures are given in EM 1110-2-2302).Service records for proposed materials should be studiedto evaluate how they have performed under fieldconditions.

C-4. Construction

Performance of riprap can only be realized by properspecifications and government inspection to ensure adher-ence to the specifications. The contract documents shouldidentify sources and geologic formations that can produce

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acceptable material, provide controlled quarry blasting andproduction techniques, define gradation ranges and per-missible percentages of undesirable materials, definepermissible ratio of maximum to minimum particledimensions, describe required particle quality, define layerthickness and allowable tolerances, describe required layercondition and restrictions to placement techniques, and

define the quality control testing procedures and frequen-cies of performance. The control of blasting technique isimportant to prevent the development of closely spacedincipient fractures that open shortly after the weatheringprocesses begin. Government inspectors should confirmthat the slope protection materials meet the specificationsand produce stable layers of interlocking particles.

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Appendix DAutomatic Data Acquisition Systems

D-1. Introduction

Computer-based automated data acquisition systems havebecome a valuable means of collecting geotechnicalinstrumentation data. Developments in the field of elec-tronics have made it possible to install and operate remotedata acquisition systems that provide accurate, reliable,and effective real time data collection. With the increasedemphasis on dam safety and the continued decrease inavailable manpower, the advantages of providing auto-matic systems are numerous. Many tasks that are tradi-tionally done by instrumentation personnel are betteraccomplished by machines since the machine will takemeasurements in the same manner at each reading.Human error can cause minor variations in reading andinterpreting data. Automation also permits a greater vol-ume of data to be collected in a given period of time, anddata can be collected during significant events at remotesites when personnel may not be available or able toaccess the site. The automated system must not relieve orreplace the normal visual inspection schedule of projectfeatures. The cost of instrumentation and computers tomonitor instrumentation has decreased so that in manycases it is now more economical, in terms of overall costand more consistent data, to automate the reading ofinstruments than to continue reading them manually.Since automation is a new technology, efforts to standard-ize sensors, communications, and software should bemade in each FOA.1 A database for automated geotech-nical and some structural instrumentation at Federal andnon-Federal projects is maintained under the Corps ofEngineers Computer Applications in Geotechnical Engi-neering (CAGE) Program.2

D-2. Requirements of an Automatic DataAcquisition System

Considerable thought must be given in the design of asystem for each individual project to ensure that the sys-tem produces the desired information in a meaningful,dependable, and reliable manner. While much flexibilityin system design is available, each system should includethe following basic requirements.

_____________________________1 Additional information is given in United States Com-mittee on Large Dams (1993).2 Additional information is given in ETL 1110-2-316.

a. The ability to manually read each instrumentmust be maintained.

b. Each instrument should have the capability to beread automatically at the site.

c. The system should utilize microcomputers tocollect and process data which can be accessed at anytime at the project, at the District office, or at other desig-nated locations. The system should also be capable ofperforming a quality control check of instrument readings,respond to preset threshold levels, and interface withexisting District hardware and software applications.

d. A backup communication link to the Districtoffice should be provided for data transmission.

e. Considerations should also be given to a backuppower supply, maintenance, vandalism protection, systemdiagnosis, and software versatility. Because of theamount of electrical circuits, lightning protection isessential.

D-3. System Configuration

A rendering of a typical project automation plan is shownin Figure D-1. A photo showing a remote monitor unit isin Figure D-2. Components of such a system wouldtypically consist of the following:

a. Sensors. Sensors should be selected based ondesired function, data required, and economics. Types ofgeotechnical and related instrumentation which can beautomated are shown in Table D-1. Some considerationsin the selection of sensors are provided below.

(1) Accuracy. Only the required level of accuracyshould be specified since special sensors, extra documen-tation, and more expensive transmission lines required forthe higher accuracy can significantly add to project cost.

(2) Range. A flexible range and an over-rangewhich prevents sensor damage should be chosen.

(3) Temperature compensation. Temperature com-pensation should be eliminated unless required.

(4) Material. Sensor composition must be compat-ible with the media in which it is located.

(5) Shock, vibration, acoustic bombardment.Remotely locating the sensor can reduce shock which may

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Table D-1List of Dam Safety Instruments and Measurement Devices

Can Be Not EasilyInstrument or Measurement Device Automated Automated

Piezometers:Standpipe XElectrical XVibrating wire XPneumatic XHydraulic twin tube (USBR) XUplift (standpipe with gage) X

Inclinometers X (1)Borehole extensometers XPlumblines XTiltmeters XTemperature (concrete or fluid) XJoint and deformation meters XStress and strain (strain gages) XWeirs XStaff gages XSurface monuments XSettlement plates X (2)Soil pressure meter XChannel scour survey data X

NOTES: (1) Can be automated using a series of sensors.(2) Certain methods of settlement sensing exist that can

be automated.

permit selection of less expensive sensors, simpler mount-ings, and less expensive cable.

(6) Electrical characteristics. Sensitivity, impedance,and excitation should be selected to match the needs ofthe system.

b. Project computers. Computers at the site must becapable of monitoring geotechnical parameters, processingall data into meaningful terms, and communicating data tothe District office. While commercially available systemshave various configurations, each system basically con-sists of remote monitoring units located around a projectsite and a central network monitor located in the projectoffice. Individual sensors are hard wired to the remotemonitor units, which are capable of obtaining measure-ments from a number of sensors. Remote monitor unitscommunicate with the central network monitor either byhard wire or by ultra-high-frequency radio link. The unitsare networked together so that they can automatically takemeasurements in a programmed sequence and store thedata until they are interrogated from either the projectoffice or the District office. The project microprocessorsmust also respond to measurement and data transfer com-mands from the project or District office at any time.General requirements for the remote monitor units andcentral network monitor are as follows:

(1) Full user programmability of all measurementand control functions.

(2) Operate stand-alone with a portable computer,independent of being connected to a hard wire or radio-based network.

(3) Store or buffer at least 16KB of data, withoptions to accept additional memory.

(4) Perform both linear and nonlinear engineeringunit conversions on measured data.

(5) Perform alarm limits checking (both on amax/min and rate of change basis) in engineering units onmeasured data values.

(6) Capability of programming measurement cyclesand frequency on an individual channel basis for allinstrument channels.

c. Cabling. Individual sensors must be hard wiredto the remote monitor unit. All cables should be placedin trenches to a sufficient depth for satisfactory and safeoperation. In critical areas such as beneath roadways orslope protection, the cables should be placed in protectivepolyvinyl chloride conduits.

d. Power source. The monitoring units shouldhave low power design such that solar panel capacity willbe sufficient to keep the batteries in the units adequatelycharged. The units should be equipped with a nonswitchover (on line) uninterruptible power supply with a sealedinternal battery. The power unit should provide power toall remote units including sensor inputs and communica-tions devices.

e. District microcomputer. The central networkmonitor at the project office must be accessible by amicrocomputer located in the District office. Basic com-munication between the project and the District is usuallythrough telephone line modems. Backup communicationssuch as by satellite link should be provided for emergencysituations. Instrumentation data stored at the site must beaccessible by the District computer at any time, and thesystem at the project site must also be capable of beingqueried for readings from the District at any time. Datashould be presented in such a manner that it can be easilyand rapidly evaluated and recorded for presentation inperiodic inspection reports.

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D-4. Retrofitting

Instrumentation automation retrofitting represents anyeffort to modify existing instruments so that they may bemonitored completely under automated control, or suchthat the modification will aid instrumentation personnel incollecting the instrument data. Since the Corps has alarge investment in structural safety-related instrumentsinstalled in dams throughout the country and since mostof these instruments are still in working condition and stillserving a useful purpose, keeping these instruments work-ing rather than replacing them is in the best interest of theoverall economy. Before considering a retrofitting opera-tion, an analysis of whether the instrument retrofittingwould be more cost-effective than purchasing new equip-ment should be made. Cost factors such as age of equip-ment to be retrofitted, cost of peripheral equipment whichmust be purchased to make the retrofit possible, as wellas installation costs, must be weighed against the cost ofnew equipment and their installation costs before a wisedecision regarding automation can be made. It is alsoimportant to consider accuracy and resolution of the olderinstruments, frequency of the data collection operations,

information which is needed about the structure, accessi-bility of the site, and availability of personnel to makemanual readings before making the decision on how toproceed.

D-5. Cost-Effectiveness and Priority ofAutomation

A review of all costs associated with automation of newdams and retrofitting existing dams by other agencies andinitial test programs within the Corps of Engineers indi-cates that automation is cost-effective in making timelydam evaluations. The cost-effectiveness increases atprojects or locations where access is limited due to terrainand/or weather, and at projects that experience consider-able pool and/or tailwater fluctuations. Automation ofexisting projects within an FOA should be accomplishedover a several year period and be based on priority ofneed. When determining priority of projects, consider-ation should be given to the consequences of failure, lifeof the structural features, nature of the structure withrespect to the foundation and external loading, past perfor-mance, and remedial measures.

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