REMEDIATION OF SALUDA DAM

RCC AND ROCKFILL DAMS

Paul C. Rizzo1, Scott Newhouse2, Jeff Bair3

Abstract

Saluda Dam, part of the FERC regulated Saluda Hydroelectric Project located near Columbia, South Carolina, is being upgraded to resist a recurrence of the 1886 Charleston Earthquake. The existing, semi-hydraulic fill embankment Dam was completed in 1930 and, based on current technology, is viewed as being susceptible to liquefaction during the design seismic event. Several remediation options were considered with the selected approach being a back-up berm, essentially a “Dry Dam”, at the downstream toe of the existing Dam. The “Dry Dam” will consist of about 5500 feet of Rockfill and about 2300 feet of RCC. This Project is the largest active (year 2002) dam construction project in the United States and the final Project will involve the placement of 1.3 million cubic yards of RCC and 3.5 million cubic yards of Rock Fill. This paper discusses the design basis for the RCC Dam and the Rockfill Dam, with particular emphasis on the extensive laboratory and pre-construction test program for the RCC. We discuss the seismic design basis, loading conditions, finite element analysis, mix design parameters, drainage and joint design, facing considerations, thermal stress analysis and joint spacing, and the mix design testing programs. The mix design program addresses the use of aggregate from an on-site borrow area and the use of landfilled waste flyash as a constituent of the RCC.

Introduction

Paul C. Rizzo Associates is the engineer of record for the seismic upgrade of the Saluda Dam located in Columbia, South Carolina. The selected remediation consists of constructing a combination Roller Compacted Concrete (RCC) and Rock Fill Berms along the downstream toe of the existing Dam. The Project is the largest active (year 2003) Dam construction project in the United States. An extensive RCC testing program was developed to evaluate various RCC mix designs and to study the inclusion of landfill, waste ash as a constituent of the RCC. Utilizing the on-site waste ash made it possible to significantly reduce total project cots (through a reduced cement content) and provide for an increase in the available capacity of the existing ash landfill. 1President - Paul C. Rizzo Associates, 105 Mall Blvd. Suite 270E, Monroeville, Pennsylvania, 15146 USA 2 Project Supervisor - Paul C. Rizzo Associates, 105 Mall Blvd. Suite 270E, Monroeville, Pennsylvania, 15146 USA 3 Principal - Paul C. Rizzo Associates, 105 Mall Blvd. Suite 270E, Monroeville, Pennsylvania, 15146 USA

Both the Rockfill and the aggregate for the RCC will be obtained from an on-site quarry. Upon completion of the Dam remediation project, the on-site quarry will be converted to an ash landfill, which will provide 30 to 50 years worth of capacity for waste ash. The construction was bid in two packages. The first package included the installation of the dewatering system for construction. Construction of the dewatering system began in February 2002. The contract for the Dam remediation was awarded in August of 2002. Anticipated total project costs will be in excess of $200 million. Saluda Dam owned and operated by South Carolina Electric & Gas Company (SCE&G) impounds the Saluda River to form Lake Murray near Columbia, South Carolina, one of the largest manmade lakes in North America.

The Dam is a semi-hydraulic fill structure completed in 1930 following typical “puddle dam” construction technology popular in the early 1900’s. Table 1A is a summary of the main parameters describing the existing Dam and the impounded Lake.

Hydroelectric Plant

Lake Murray

Existing Dam Table 1 Summary - Main Parameters for Saluda Hydro

Lake Area 78 Square miles Lake Capacity 2,096,000 acre feet Dam Length 7,800 feet Max Dam Height 211feet Hydro Capacity 206 MW Original Construction Semi-Hydraulic Fill Original Completion 1930

The primary purpose of the Dam when originally constructed was for hydroelectric

generation by the Saluda Hydroelectric Plant located at the toe of the Dam. As such, the Dam is under the jurisdiction of the Federal Energy Regulatory Commission (FERC). Today, the Lake is a source of cooling water for the McMeekin Plant, drinking water for Columbia and adjacent communities, and a major recreation and residential community with statewide economic benefits.

Beginning in 1989, a series of geotechnical investigations were undertaken to assess the safety of the existing Dam, particularly under seismic loading. In this part of South Carolina, seismic design bases for critical facilities are, for all practical purposes, governed by a postulated re-occurrence of the 1886 Charleston Earthquake. The Charleston Earthquake is estimated to have had a Magnitude in the range of 7.1 to 7.3 with a recurrence interval in the range of 650 to 1000 years. This event has been established as the Design Seismic Event (DSE) for assessing the integrity of Saluda Dam.

A comprehensive liquefaction analysis and a post-earthquake stability analysis were conducted with the DSE yielding typical results as shown on Figure 1. This Figure shows that under certain assumptions, a major portion of the embankment will liquefy if the DSE occurs. Figure 1 - Existing Saluda Dam Factor of Safety Against Liquefaction -0.02 0.32 0.66 1.001.00 1.33 1.67 2.002.00 3.78 5.57 7.35

Should Saluda Dam fail, approximately 120,000 people would be in jeopardy, water

supplies for Columbia and surrounding communities would be lost, extreme environmental impacts would be realized and countless millions of dollars would be lost in the local economy. Consequently, a major remediation project has been developed for implementation in the 2002 to 2005 time period.

Remediation Concept

The Design Basis for the Remediation Concept has two major objectives and a corollary expected behavior criteria. The two major objectives are:

• Prevent catastrophic flooding downstream of the Dam and, • Assure Safe shutdown of the facilities, including lowering of

Lake Murray in a controlled manner. From a behavior perspective, the Owner and the FERC accept that some

remediation and repair may be required after the Design Earthquake, but catastrophic flooding is not acceptable. These major objectives were translated into loading cases and factors of safety by the authors with major over-riding input from the FERC.

After consideration, both technical and financial, the remediation concept was developed as a “Dry Dam” immediately downstream of the existing earth embankment. The existing Dam will remain in place and function as the primary impounding barrier for Lake Murray. The Dry Dam will become a water retention structure if Saluda Dam ever fails. Hence, the Dry Dam is designed for both dry and wet conditions with a series of loading cases that reflect hydrostatic pressures and uplift pressures in the wet case and

neither in the dry case. Both cases consider seismic forces acting both directions horizontally as well as vertical excitation. Additional design criteria to be implemented with the chosen remediation concept include the following:

• No excavation into the original sluiced Dam. Riprap placed after original dam construction will be removed to facilitate excavation.

• No excavation or construction into the Saluda River as defined by the maximum normal tailwater at El. 179.5 NAVD.

• The crest of the new Berm will be El. 372 NAVD1 (i.e., current minimum crest elevation of the existing Dam).

The Dry Dam concept is illustrated on Figures 2 and 3 below. Approximately 5500 feet of the total length of 7,800 feet is a Rockfill Berm (referred to as a berm rather than a dam as it does not retain water under normal conditions) and 2,600 feet of RCC Berm. (Also referred to as a berm rather than a dam for the same reason.) Figure 2 – Typical Section, Rockfill Berm Figure 3 - Typical Section, RCC Berm

In reply to the obvious question of, why not use a less expensive Rockfill Berm for the entire remediation. We refer the reader to the photo with Table 1 and Figure 4 where it may be seen that the existing Saluda Hydroelectric Powerhouse is at the toe of the existing Dam, thereby precluding a Rockfill Berm because of space limitations. It is in this zone behind (upstream) of the Powerhouse where we chose an RCC Berm as the primary remediation concept. 1 North American Vertical Datum of 1988

Figure 4 - Plan View of Saluda Remediation Rock Berms RCC Berms

Impact of the Remediation Concept on the McMeekin Steam Electric Plant

The McMeekin Steam Electric Plant is located at the toe of the existing Dam and

has several features directly associated with the Dam and the Remediation Project. The remediation of the dam has necessitated extensive modifications to the McMeekin major changes to the plant systems that are affected by the two berms as described below. Circulating Cooling Water Lines

Cooling water for the Steam Electric Plant is supplied from Lake Murray via two 90 inch diameter pipes which connect to Penstocks 1 and 3 at Saluda Hydro, directly West of the Hydro Powerhouse. The existing cooling lines which draw from Penstock Nos. 1 and 3 will remain operational until two new lines are constructed connecting to Penstocks 2 and 4. The new cooling water lines will be 72-inch diameter, and will be embedded in a new mass concrete foundation for the RCC Berm between the Hydro Powerhouse and the existing Dam.

The construction of the new cooling water lines will take place after the excavation of existing riprap from the area just west of the Saluda Hydro powerhouse. This riprap was placed in the early 1940’s as part of a program of modifications undertaken to increase the stability of the dam and the hydraulic capacity of the spillway. Once the riprap is removed and the toe of the existing dam stabilized with a temporary tieback wall, portions of the new cooling water lines will be constructed and connected to Penstocks 2 and 4. When this part of the cooling piping is complete, mass concrete will be placed around them and brought up to final elevation. This mass concrete will serve as the foundation for part of the RCC berm. The parts of the cooling system located outside of the new berm’s footprint

will be constructed, and final connection and commissioning of the new cooling water system will take place during an outage at McMeekin Plant in 2003. Ash Handling System-Pipelines

The existing Ash Handling System is a wet sluice system in which ash is removed from the boiler hoppers and pumped through two ash pipe lines that cross over the Saluda River on the downstream slope of the existing Dam to ash disposal ponds and a dedicated ash landfill. The ash sluice pipes directly interfere with the Remediation Concept as they lie partially in areas where the slope will eventually be covered with rock comprising the Rockfill Berm.

In order to remove the existing ash sluice pipelines from the dam, a new ash handling system is being installed at McMeekin Plant in the fall of 2002. The new system will handle all of the plant’s ash in totally dry state, and will convey it to new silos adjacent to the plant. Ash Ponds and Landfill

The existing ash ponds and landfill will play a crucial role in the construction of the RCC berm. Once McMeekin Plant has been converted to the all-dry ash handling system described above, the two ash settling ponds will be emptied, capped, and graded to provide a 10 acres work area for aggregate processing and stockpiles, along with the RCC mixing plant. Although the existing landfill will continue to be used for ash storage during construction, the western end of the landfill will be excavated and the ash used in the RCC mix. This ash resides inside the excavation footprint of the south rock berm, and must be removed to allow construction.

RCC Berm Design

The RCC Berm, or Dam depending on one’s perspective, is one of the largest in the

world and the United States as indicated in Table 2.

Table 2 - RCC Dams Completed and Under Construction 1999

Name Country Owner Purpose River Dimensions

Volume

Height Length RCC (m) (m) (m3x103)

1. Beni Haroun Algeria Minister de’l Hydraulique, de’l Environment et des Forets

WI Kebir 121 710 1690

2. Miel I Colombia Hidromiel S.A. HFI LaMiel 188 345 1669 3. Miyagase Japan Ministry of Construction FWH Nakatsu 155 400 1537

4. Porce II Colombia Empresas Publicas de Medellin

H Porce 123 425 1300

5. Urayama Guanyinge

Japan W.R.D.P.C. FWH Urayama 156 372 1294

6. (Kwan-in-Temple)

China Benxi City, Liaoning Province HFI Taizhe 82 1040 1240

7. Bureya Russia RAO EDD ROSSI FH Bureya 140 1000 1200 8. Upper

Stillwater USA

Central Utah Water Conservancy District

WI Rock Creek

91 815 1125

9. Oliverhain Dam

USA San Diego County Water District

EW Colorado 94 772 1085

10. Saluda Dam

USA South Carolina Electric & Gas

FHRW Saluda 65 678 999

11. Jiangya China Lishui Hydropower Corporation HFIWN Loushui 128 336 990 12. Salto

Caxias Brazil COPEL H Iguacu 67 1083 912

It is noted that Olivenhain Dam is slightly larger and is being designed and

constructed contemporaneously with the RCC Berm at Saluda. Detailed design criteria for the Saluda RCC Berm include the following:

• The RCC Berm is founded on competent rock as defined by the commencement of coring operations and verified during construction.

• Uplift pressures for stability analyses are calculated assuming that the foundation drains will achieve a minimum drainage efficiency of 67 percent. The foundation drainage system consists of four-inch diameter drains installed at ten-foot spacing to a depth into the foundation rock equal to 30 percent of the total head.

• Usual (normal pool) and Extreme (earthquake) loading conditions include hydrostatic loads based on existing (i.e., pre-DSE) groundwater levels.

• Pseudo-static dynamic analyses are based on a horizontal seismic coefficient of 0.2g. Dynamic finite element analyses are used to determine the distribution of tensile and compressive stresses within the Berm using the DSE as input.

• Short-term, post-DSE loading conditions assume liquefied material (from the failure of the existing dam) on the upstream slope to El. 302 NAVD. For long-term, post-DSE loading conditions, the upstream-liquefied material has been assumed to be at El. 274 NAVD.

In the following paragraphs, we describe the following design topics. • Seismic Design Basis; • Loading Conditions; • Finite Element Analyses;

m; • RCC Mix Design Progran; • Joint and Drain Desig

• Facing Options; and

• Bedding Mix Application. Seismic Design Basis

The Design Seismic Event (DSE) at the Saluda Site used to develop the remedial design of the RCC Berm is defined in terms of the Newmark-Hall (NUREG-0098) median-based response spectra anchored to a horizontal peak ground acceleration (PGA) of 0.2g. These response spectra reflect a peak ground velocity of 7.2 in/sec and a peak ground displacement of 4.02 inches. The vertical response spectra are taken to be two-thirds the horizontal across the entire range of frequencies. Thus, the PGA in the vertical direction is 0.133g.

The seismic time history applied to the RCC Berm utilizes Artificial Time Histories (ATH) of acceleration. The artificial time histories are developed iteratively on the basis of the Design Response Spectra with consideration of the Power Spectral Density Function. The time envelope function defines a strong ground motion duration of about 16 seconds and a total duration of 30 seconds. Loading Conditions

The loading conditions (i.e., load cases) and associated factors of safety used for developing the remedial design were developed by PCRA in conjunction with comments received from the FERC. The FERC Engineering Guidelines (FERC, 1991), Draft Peer Review Chapter III of the FERC Engineering Guidelines (FERC, 2000), and generally accepted design methodologies have been used to develop the loading conditions. However, recognizing that the stability analyses used to develop the remedial design for the Dam present a unique case, engineering judgement and interpretation were utilized in the development of the appropriate loading conditions.

The following load cases were used to analyze the stability of the proposed remedial design of the RCC Berm:

• Case I – Usual Loading Conditions (Normal Operating Conditions);

• Case II – Unusual Loading Conditions (Probable Maximum Flood Conditions);

• Case IIIA – Extreme Loading Conditions (Dry Dam with DSE earthquake forces);

• Case IIIB-1 – Post-Seismic Loading Conditions (Short-Term Operating Conditions after the postulated failure of the existing Dam); and

• Case IIIB-2 – Post-Seismic Loading Conditions (Long-Term Operating Conditions after the postulated failure of the existing Dam).

As the proposed Berm will be dry prior to the DSE and the existing Dam can pass

the PMF without overtopping, the results for Case II (Unusual loading Conditions) will be identical to Case I. For clarity, we have not included these results in the Summary Tables. The acceptable factors of safety for these loading conditions are presented in Table 3.

Table 3 - Acceptable Safety Factors RCC Berm

LOAD CONDITION FS Case I 3.0

Case IIIA 1.1 Case IIIB-1 1.1 Case IIIB-2 1.5

The critical load case occurs immediately following the DSE (i.e., Case IIIB-1) and

after the postulated failure of the existing Saluda Dam. Uncertainties associated with the probable loading for the RCC Berm during this particular load case are a function of the following factors:

• Height of silt (liquefied soil from the existing Dam against the upstream face of the RCC Berm.

• Residual shear strength (if any) of the liquefied embankment materials and Rockfill from the Highway Berm (i.e., combination of silt, rockfill, and water) which will be located against the upstream face of the RCC Berm.

• Buildup of uplift pressure beneath the RCC Berm and, specifically, whether the uplift pressure fully develops before the pore pressure dissipates from the potentially liquefied material on the upstream side of the RCC Berm.

To address these uncertainties, we analyzed the RCC Berm for a range of possibilities following the DSE. Our best estimate of the post-seismic loading conditions utilizes partial uplift (i.e., equal to uplift prior the DSE) beneath the RCC Berm and a best estimate strength for the combination of silt, rockfill, and water, which will be located along the upstream face of the Berm. Additionally, we have analyzed the Berm for worst-case post-seismic parameters which include full uplift beneath the foundation of the RCC Berm and a lower bound shear strength for the combination of silt, rockfill, and water which will be located along the upstream face of the RCC Berm. The results of these analyses have been used to design an RCC Berm that is stable under all postulated post-seismic design parameters. Finite Element Analyses

The RCC Berm has three basic cross sections—the Powerhouse section, which bears on a mass concrete foundation, and the South Section and the North Section which bear directly on rock. The mass concrete foundation behind the Powerhouse embeds the existing Penstocks and McMeekin Plant cooling water lines. These cross sections were analyzed using conventional finite element analyses (FEA) and we report in this paper the results for the Powerhouse section only. Also, while the FEA model for the Powerhouse section includes the mass concrete foundation, we discuss only the results in the RCC Berm, with particular emphasis on the tensile stresses as they control the RCC mix design.

The FEA performed for the RCC Berm assumes that the RCC Berm will be “dry” prior to the DSE. The evaluation combines the static stress state of the RCC Berm prior to the seismic event with the seismic stresses generated in the Berm due to seismic ground motions. Additionally, the evaluation addresses the stresses in the Berm for the post-

seismic loads. Both the static and seismic analyses utilize two-dimensional models of Powerhouse Section. Finite Element Models

The static analysis of the Powerhouse Section of the RCC Berm assumes plane stress conditions and uses a two-dimensional finite element model of the Planar Section shown in Figure 5. RISA-3D, a general-purpose finite element program suitable for the analysis of frame and panel structures, was used to evaluate the static stresses. Figure 5 - Finite Element Model (Powerhouse) Without Rockfill

111.7 FEET

40 FEET

The finite element model of the RCC Berm utilized in the static analysis includes panel elements representing the RCC Berm. Assigning a material density to the panels includes the dead load of the RCC. All other conditions existing on the RCC Berm prior to the seismic event are included as applied loads to the finite element model. For example, equivalent lateral loads on the Berm represent the retained rock-fill on the upstream face. Table 4 lists the properties used in the model.

372.0 FEET

Location of ATH Input to model

200 FEET

-124.3

578.1 FEET

165.5 FEET

Table 4 - Material Properties for Static Finite Element Model

Material Compressive strength – f’c

(psi)

Elastic modulus

(ksi) Poisson’s

ratio Density

(kcf)

Roller compacted concrete 2,300 2,734 0.2 0.146

Conventional concrete facing 3,000 3,122 0.2 0.150

Mass concrete base 3,000 3,122 0.2 0.150 Existing concrete 4,000 3,606 0.2 0.150

Rock foundation Not applicable 1,742 0.3 Not applicable

Table 5 shows the material properties for the “structural portion” of the model. The

dynamic elastic modulus for the various types of concrete is calculated by multiplying the static modulus by 1.15. The soil and rock-fill area retained by the upstream portion of the RCC Berm is treated in the analysis as part of the structure. Table 5 - Material Properties for Seismic Finite Element Model

Material Description Density (kcf)

Shear wave

velocity (fps)

Compression wave

velocity (fps)

Shear wave

damping ratio

Compression wave

damping ratio

Shear modulus (ksf)

1 Existing concrete 0.150 7,307 11,930 0.05 0.05 248,800

2 Mass concrete 0.150 6,800 11,100 0.05 0.05 215,400

3 Conventional

concrete facing

0.150 6,800 11,100 0.05 0.05 215,400

4 Roller

compacted concrete

0.146 6,452 10,540 0.05 0.05 188,800

5 Soil 0.120 1,099 1,794 0.05 0.05 45,00

6-10 Rock-fill (bottom) 0.130 877

to 1,709 1433

to 2,791 0.05 0.05 3,108 to 11,790

Stress Results in the RCC

Table 6 presents the maximum principal tension stresses at the upstream and downstream locations of the RCC Berm Section at the Powerhouse. These stresses are presented for the static loads and the seismic loads resulting from the Artificial Time Histories matching the Design Response Spectra.

Table 6 - Maximum Principal Tension Stress in RCC (psi) powerhouse section

Location

Pre-seismic Design Response Spectra Post-seismic

1.4*Dead + 1.7*Live

Without Rockfill

With Rockfill

Unlimited cohesion at

base

No cohesion at base

RCC -

downstream face

5 296 359 3 2

Upstream concrete

facing 5 12 28 2 0

As seen from Table 6, the Maximum Principal tension ranges from 5 to 359 psi

(based on use of the ground Design Response Spectrum). The stresses “with rock-fill” on the upstream face are somewhat higher than the stresses “without rock-fill”. The maximum tension occurs on the downstream face at the interface of the RCC and the underlying mass concrete. Please note that the seismic analysis described herein assumes linear material behavior and allows, as much tension in the RCC and RCC/rock interface as the loads will generate. In reality, the material may sustain cracking at locations where the tension stress exceeds the material tension strength. For example, the tension at the RCC/rock interface will be limited by the cohesion mobilized at this interface. Therefore, the tension stresses reported in Table 6, are an upper bound to the actual tension stresses in the RCC. Limit Equilibrium Analyses and Bedding Mix Requirements

The results of a post-DSE Limit Equilibrium Analysis (LEA) were used to determine interface friction angle necessary to achieve a sliding factor of safety of 1.1. The analysis assumes that cohesion is zero and that the lift joint considered is fully cracked along the entire width of the Berm. Based on the results of the dynamic analyses, we do not expect appreciable cracking between the RCC lift joints. However, we have conservatively assumed that cracking does occur along the entire length of the RCC lift line and have performed static sliding stability analysis along these planes.

A sensitivity analysis was performed to determine the minimum shear strength parameters at the lift joints and within parent RCC. Two limiting cases were considered in each Section; cohesion with no friction and friction with no cohesion. The results indicate bedding mortar should be placed up to El. 215 NAVD to assure a sliding factor of safety in excess of 1.1 along the RCC lift lines.

Bedding mix will also be applied along a 22-foot wide zone at the upstream face of the RCC, full-height, for seepage control. At El. 215 NAVD, the interface friction angle to achieve a minimum sliding factor of safety of 1.1 is equal to or less than 35 degrees for both lower bound and best-estimate parameters. RCC Mix Design Program

We have established the Minimum Design Strength for the Final RCC mix based on Phase I and II laboratory testing conducted on various RCC mixes. The final RCC mix

design will meet or exceed these minimum strengths. A Dynamic Increase Factor (DIF) of 1.5 is applied to the static tensile strength to compute the dynamic tensile strength. A summary of the Minimum Design Strengths for the final RCC mix are provided in Table 7. Table 7 - Minimum Design Strength Final RCC Mix

Property

Minimum Design Strength At One Year

Static Compressive Strength 2,300 psi

Static Direct Tensile Strength Parent RCC and bedded

lift joints Unbedded Lift Joints

239 psi

115 psi

Dynamic Direct Tensile

Strength Parent RCC and bedded

lift joints Unbedded Lift Joints

359 psi

173 psi

Note: Dynamic Direct Tensile Strengths are calculated utilizing a DIF of 1.5

Direct tensile strength criteria used for design were correlated with a compressive

strength of 2,300 psi. The relationship between the compressive strength and the direct tensile strength was extrapolated from the project-specific RCC laboratory test results. Thermal Analysis and Joint Spacing

A Simplified Thermal Analysis (STA) or Level I Thermal analysis has been completed to evaluate the potential for thermal cracking of the RCC during placement. A more rigorous thermal analysis, i.e., a Level II Analysis, which utilizes detailed finite element analyses and placement schedules, was being performed while this paper was in preparation.

The actual temperature rise in the RCC Berm depends on the heat generating characteristics of the RCC mix and accompanying thermal properties, environmental conditions, geometry of the section, and construction conditions. Peak temperatures are reached a few days or weeks after placement. For massive structures, the temperature of the RCC slowly decreases until it reaches the average annual temperature of the site. As the RCC cools, the volume of the RCC decreases. Since this volume reduction is constrained by the bedrock foundation, sufficient strain can develop to cause a tensile failure or crack of the RCC. To prevent excessive cracking of the RCC, transverse contraction joints are placed into the RCC mass at a prescribed interval. A thermal analysis is used to justify the selection of the contraction joint spacing.

The methodology followed for this Project is described in the American Society of Civil Engineers publication entitled “Roller Compacted Concrete III” (Tatro and Schrader, 1992).

The results of this analysis are summarized in Table 8. Please note that the analysis assumes that aggregate production and stockpiling commences two months before RCC placement.

Table 8 - Summary of Results Simplified Thermal Analysis

Placement Schedule (Month)

Placing Temperature

(°F)

ΔL (in)

Number of Cracks (Assuming 0.05 width)

Avg. Crack Spacing (ft c/c)

February 1 51.2 0 0 Infinite

May 1 68.7 0.88 18 75 August 1 79.3 1.76 35 38

November 1 61.8 0.31 6 212

As shown on Table 8, RCC placement in the summer months (i.e., August) significantly increases the thermal displacements in the RCC mass.

The results of this analysis, for the proposed transverse contraction joint spacing of 60 feet center-to-center (c/c), indicate that RCC construction stockpiling and aggregate production should be limited to the Fall and Winter months and that placement and/or stockpiling of RCC in the spring and summer months may require some form of pre-cooling to minimize cracking. Mix Design Testing Program

The Mix Design Testing Program was established in the early project as a four Phase Program summarized in the following Table 9.

Table 9 – Summary of RCC Mix Design Phases

Phase No. Description ScheduleStarted May 2000 Status: Complete

Started December 2000 Status: Complete

Started August 2001 Status: Ongoing

Status: Future Work after RCC Berm Contractor Selection

I

II

III

IV

Initial Lab Program (13 Mixes)

Final Lab Program (5 Verification Mixes)

On-Site, Full-Scale Design RCC Test Pads with Aggregate from On-Site

Borrow Area

Pre-Construction Test Pad for Verification of Contactor

Methodology

As seen on the table, we began with an “exploratory” Phase I laboratory testing program to determine if sluiced, landfilled flyash from the adjacent McMeekin Steam Electric Plant operations could be utilized. Offsite aggregate was used in Phase I as well as in Phase II. The ash is disposed in an on-site landfill located at the toe of the existing Dam and a portion of it has to be moved in any event. Phase I yielded positive results and Phase II was used to refine the mix options and to hone in on a final mix design. We then proceeded with a full-scale test pads using aggregate from our on-site borrow area, fully processed in accordance with a plan for crushing and screening.

Phase III consists of three main test pads, each with a different mix with the cement content being the primary differing constituent as shown on Table 10. In addition to the three main pads, a series of smaller pads were constructed to allow for variation of placement parameters, testing procedures and the like. Phase III is currently in the “curing” stage (April 2002). Table 10 - Phase III RCC Mixes

Cem

ent Pozzolan

(McMeekinFly Ash)

Waterin

excessof SSD

b

BlendedAggregate

(Fine +Coarse) D

esig

nD

ensi

ty @

3% A

ir

Mix Designation a(lb

s / y

d3 )

(lbs /

yd3 )

(lbs /

yd3 )

Mod

. VB

Tim

e (s

ec)

(lbs /

yd3 )

(lbs /

ft3 )

Primary RCC Mix Design125 150 252 30 3,467 146

Secondary RCC Mix Design175 150 270 30 3,364 146

Tertiary Mix150 150 259 30 3,423 146

RCC Berm Drainage Design

The design of the drainage system for the RCC Berm as shown on Figure 6 consists of three primary elements as follows:

• A Drainage Gallery 14 feet from the Upstream Face just above Tailwater;

• Bedrock Drains (4” dia.) from the Gallery drilled to a depth equal to 30% of normal headwater; and

• Crest-to-Gallery Drains (6” dia.) to intercept drainage through cracks on the upstream face.

Figure 6 – Typical RCC Section

6” FILLET OF BEDDING MIX

3/8” THICK BEDDING MIX

RCC FACE OF TEMPORARY FORMWORK

2’ LIF

T

(TYP

.)

Upstream and Downstream Facing Upstream and Downstream Facing Upstream and downstream facing considerations include constructability, aesthetics, economics and, in the case of the upstream face, watertightness. Final decisions will be based on cost as quoted by bidders, but options for the downstream face include (a) formed RCC Steps, and (b) precast concrete panels, with the former illustrated on Figure 7.

Upstream and downstream facing considerations include constructability, aesthetics, economics and, in the case of the upstream face, watertightness. Final decisions will be based on cost as quoted by bidders, but options for the downstream face include (a) formed RCC Steps, and (b) precast concrete panels, with the former illustrated on Figure 7. Figure 7 – Formed RCC Face Figure 7 – Formed RCC Face For the Upstream face, we are currently considering (a) conventional concrete, (b) grout enriched RCC against forms, and (c) precast panels. Figure 8 illustrates the conventional concrete and the treatment of the top of the Berm.

For the Upstream face, we are currently considering (a) conventional concrete, (b) grout enriched RCC against forms, and (c) precast panels. Figure 8 illustrates the conventional concrete and the treatment of the top of the Berm.

UPSTREAM FACING

DRAINAGE GALLERY

RCC BERM

CREST TO GALLERY DRAINS

NORMAL POOL

SILT / ROCK MIXTURE

GROUND SURFACE

RESIDUAL SOIL

FOUNDATION COMPETENT ROCK DRAINS

Figure 8 – Upstream Facing

Rockfill Berm Design

As mentioned above, the Rockfill Berm portion of the Remediation Concept will be

approximately 5500 lineal feet of rockfill dam comprising of approximately four million cubic yards. The Design Cross section shown on Figure 9 includes upstream filters against a transition zone, essentially a low permeability core, downstream blanket drain and founded on residual soil.

Figure 9 – Typical Rockfill Berm Design Section

Basic Design Criteria for the Rockfill Berm The basic design criteria utilized to design the Rockfill Berm is summarized as

follows: • The design has minimized the volume of embankment

material required by aligning the crest of the new Rockfill Berm as far upstream as practical. In this way, the amount of new Rockfill placed to create the upstream shell of the new Berm has been minimized.

• Avoid excavation of the sluiced embankment material. • The toe of the existing Dam defines the start of the

excavation of the residual soil. The excavation proceeds downstream from this point to the foundation elevation.

• The transition zone is founded completely on dense residual soil or weathered rock.

• The foundation of the Rockfill Berm will be excavated to a depth to preclude piping and limit seepage. The Transition Zone (i.e., the core) of the new Rockfill Berm will be founded below “pipeable” materials.

• The gradation of the Rockfill has been specified such that the outer slopes of the final structure can be constructed at 1.5H to 1V.

Toe of the Existing Dam

Determination of the location of the toe of the original Dam in the field is not straightforward. The toe has been covered with riprap and the area has been generally disturbed and vegetated. We have used two methods to estimate the position of the toe of the existing Dam and enveloped the results in a conservative manner. First, the as-built cross section drawings provided every 50 feet along the longitudinal axis of the dam were reviewed and the distance from the centerline of the Dam to the downstream toe of the Dam was measured and recorded for each as-built cross section. Second, we projected a 2.5H to 1V slope (design slope of the original Dam) from the edge of the upstream crest down to the residual soil (as noted on the as-built drawings). This was done for each 250-foot Design Cross Section and the results were combined to develop a set of design cross section drawings. Foundation Excavation Depth The required depth of excavation beneath the Filter/Transition Zone of the proposed Rockfill Berm has been an item of discussion between all of the concerned parties. It was finally agreed that the excavation would be extended to a depth where (N1)60 is greater than 25. Proof rolling of the foundation will be conducted to identify and remediate soft zones, if any. Other features related to the depth of excavation include the following:

• The Transition Zone will be constructed utilizing on-site residual soil.

• Piping will be controlled through a combination of internal filters and a downstream drainage blanket.

Rockfill Berm Alignment The alignment of the Rockfill Berm has been determined based on the location of

the toe and the required depth of excavation with the following considerations. • There shall be no excavation into the original embankment

Dam. However, a portion of the subsequently placed riprap may be excavated.

• At least 25 percent of the upstream shell, measured laterally, shall be founded on residual soil with an SPT value greater than 5 to 7.

• The entire Transition Zone and downstream shell of the Rockfill Berm shall be founded on material meeting the depth of excavation requirements discussed above.

Embankment Design

The following paragraphs describe the design rationale and proposed gradation for the materials comprising the Rockfill Berm (i.e., transition zone, filters, and rockfill). Transition Zone Gradation

The purpose of the Transition Zone is to control seepage through the Rockfill Berm. To prevent piping of the Transition Zone material, a graded filter, consisting of fine and coarse zones, will be placed on the upstream and downstream sides of the Transition Zone. Similarly, to prevent piping of the foundation material, both fine and coarse filters will be placed between the downstream shell and the foundation.

The embankment design includes a vertical upstream face of the Filter/Transition Zone to minimize the footprint of the Rockfill Berm. The Filter/Transition Zone will be located completely on a stable foundation of residual soil. A vertical upstream side of the Filter/Transition Zone keeps the Rockfill Berm Crest as close as possible to the crest of the existing Dam, thereby minimizing earthwork quantities and the impact on downstream land without sacrificing other design criteria.

The gradation band of the Transition Zone was designed by considering the gradations of core and transition zones for existing rockfill dams. An extensive Bulk Sampling Program (borings and test pits) and laboratory analyses were conducted to determine if the on-site residual soil would be acceptable for use in the Transition Zone and laboratory testing program.

Filter Material Gradation

Filters consisting of cohesionless material will be placed both upstream and downstream of the Transition Zone and between the foundation and the downstream Rockfill Shell. Due to the large difference in gradation between the Transition Zone and the Rockfill, a two-layer graded filter will be used. Upstream Filters between the Transition Zone and Rockfill Shell will be 4-feet thick and Downstream Filters will be 6-feet thick to minimize the impact of material segregation during construction and to assure filter integrity. Two, 4-foot-thick filter layers are adequate to withstand lateral deformations of the Rockfill Berm up to 2 feet.

Rockfill Gradation The Rockfill Shell will be composed of reasonably well graded, angular rock

fragments with less than 10 percent fines passing the No. 200 sieve to assure adequate shear strength. To assure proper compaction, the maximum rock particle size will not exceed the thickness of the lift. We plan to place and compact rock fill in 3-foot-thick lifts, hence the maximum particle size of 30 inches will be adequate. The gradation band for the Rockfill is shown on Figure 10. Figure 10 – Rockfill Gradation Band

Material Properties

The material properties used in the stability analysis of the proposed Rockfill Berm consisting of unit weights, effective friction angles, and effective cohesions are summarized on Table 11.

Table 11 - Material Properties for Rockfill Berm

Embankment Material

Unit Weight (pcf)

Effective Friction Angle

(degrees)

Normal Stress (psf)

Effective Cohesion

(psf)

Rockfill 130 50 <2,800 0 Rockfill 130 43 >2,880 864

Transition Zone 127.8 29.9 - 648 Filter Zone 115.0 37 - 0

Residual Soil 120.5 33.1 - 200 Existing Dam

(Unwashed Fill) 123.1 32.6 - 100

Failed Material (short-term)

120 0 - 200

Failed Material (long-term)

120 32.6 - 100

A two-stage bi-linear shear strength envelope has been used to model the shear

strength of the rockfill. An effective friction angle of 50 degrees was selected for the lower normal stress range (i.e., less than 2,880 psf) and an effective friction angle of 43 degrees and an effective cohesion of 864 psf was used for the higher normal stress range (i.e., greater than 2,880 psf). A unit weight of 130 pounds per cubic foot was used as the unit weight of the Rockfill.

The material properties used for the transition zone are based on the results of the bulk soil sampling program which included a series of Direct Shear tests on recompacted samples compacted to 95 percent of the maximum dry density within + 2 percent of the optimum moisture content as determined from Modified Proctor Compaction Tests. The Average shear strength parameters from the laboratory testing program were used to represent the shear strength for the transition zone material. The material properties used for the residual soil and existing Dam material are based on the results of Consolidated Undrained Triaxial Compressive Strength Tests (with pore pressure measurements) performed on undisturbed samples of both the residual soil and unwashed fill material. An effective friction angle of 37 degrees was used to represent the shear strength for the filter materials (i.e., compacted sand or gravel). Stability Analysis

Slope stability analyses have been conducted for six representative cross sections of the proposed Rockfill Berm. These stability analyses have been conducted in general accordance with the FERC Engineering Guidelines and the SLOPE/W Computer program (GEO-SLOPE, 1998). This program has been selected for the analysis because of its ability to develop different slope stability models at a rapid pace due to its compatibility with the Windows environment. SLOPE/W also has the ability to handle pore water pressures specified as either a phreatic line or imported pore water pressures from a flow net or finite element analysis. Typical results are shown on Table 12.

Table 12 - Rockfill Berm Stability Analysis Results Section 25+00

LOADING CONDITION (1)

FS

FSreq (2) Upstream Downstream

Circle Wedge

Circle Wedge

I NA NA 1.81 2.21 1.5 IIIA NA NA 1.21 1.62 1.1

IIIB-1 (normal pool) 1.70 1.39 1.74 1.82 1.1 IIIB-1 (lowered pool) 1.60 1.36 1.74 1.82 1.1 IIIB-2B (normal pool) 1.93 2.60 1.74 1.82 1.5

CLOSING REMARKS

The Saluda Dam Remediation Project is one of the largest, active dam remediation

projects in the world and will be one of the top ten largest RCC Dams in the world. The Project includes practically all of the complicating factors that a dam engineer can face in remediating an existing dam, including deep toe excavations under near-full head, variable soil and rock conditions and exceptionally difficult space constraints. The use of RCC aided significantly to solving the space constraints, but involved a great deal of up front testing and verification analysis. We still have to complete testing on the Phase III samples to finalize the mix design and we still have to complete a Phase IV testing program.