Geotechnical Section 2008 Annual Report MnDOT Office of Materials and Road Research

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Table of Contents Page Executive Summary 3 Purpose 4 Mission 4 Section Overview 4 Geotechnical Section Activities Foundations 8 Geology 12 Grading, Base and Aggregate 18 Section Highlights Foundations 19 Geology 45 Grading, Base and Aggregate 48 Cover photos clockwise from upper left Ariel view of TH 2 Landslide East of Crookston; L to R, Duane Hill, Bob Winter, Tom Sorel, Jason Richter and Mike Robinson at TH 169 in Chisholm; L to R, Kevin Wassen, Chuck Howe and Mike Novotny at I-90 near Nodine, Grading operation at TH 60 near Bigelow

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Executive Summary The Geotechnical Section continued to use new technology to improve our service to our customers in 2008. Each Unit within the Section is developing systems for the effective use of new technology. In general, each new system generates more accurate data in real-time. The following paragraphs give a brief description of what each unit has accomplished. Foundations The CPT has been a part of our geotechnical investigation program for several years. Expanded use of other tools such as the flat plate dilatometer, seismic, soil moisture resistivity, pore water pressure dissipation and push-in piezometers has made the CPT rigs much more effective. These tools enable engineers to collect valuable data that is used to design a variety of cost-effective solutions. In-place instrumentation reached a new level of sophistication this year on on a variety of projects including TH 2 East of Crookston. A shape-acceleration sensor array system (SAA) was installed to continuously monitor a potential unstable slope just a couple of months before its ultimate failure. Data from the SAA was used in the decision to close the road before the failure occurred. The decision most likely saved property damage to vehicles and probably personnel injury and lives. Geology Electrical Resistivity Imaging (ERI) was used extensively on a number of projects around the state. ERI is now a part of our routine geotechnical investigation process, directing the use of more precise tools such as CPT and SPT drilling. Grading, Base and Aggregate Intellegent Compaction (IC) and the Light Weight Deflectometer (LWD) were used on a number of projects across the state. For the first time in Minnesota, IC was also used on several pilot projects to monitor the compaction of hot-mixed asphalt. Work continues on refining the specifications and creating methods and policies for their use in our quality control and quality assurance processes.

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2008 Geotechnical Annual Report Report Purpose The purpose of this report is to describe the accomplishments and future direction of the Geotechnical Engineering Section of Mn/DOT’s Office of Materials and Road Research. It is also intended to help our customers gain a better understanding of what technical services are available for their use. Other benefits include:

1. Aid in effectively managing the section. 2. Tool to report to upper management. 3. Support strategic planning efforts. 4. Measure past accomplishments and set goals for the future.

Section Mission Support the Office of Materials and Road Research, Mn/DOT Districts, Policy, Safety and Strategic Initiatives Division and other agencies by providing geotechnical and geological engineering expertise. Section Overview The Section provides geotechnical engineering and geological services for:

• Structural foundations; • Engineered soil and rock slopes; • Aggregate durability, quality and availability; • Pavement subgrades and bases; • Geosynthetics; and • Vibrations.

These services are provided in the form of, surface and subsurface investigations, design recommendations, field assistance, laboratory testing, resource databases, specifications, design standards, and technical training. The section is comprised of three units, Foundations, Geology, and Grading, Base and Aggregate.

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The Foundations Unit duties include: • Subsurface investigations, sampling and testing of soil, rock, and

groundwater and measurement of in-situ engineering properties for foundations for bridges, retaining walls, high embankments and other structures.

• Design and review recommendations for bearing capacity, settlement, slope stability, and other foundation related problems.

• Design and review for engineered embankments and excavations of soil and rock, retaining walls and reinforced earth systems of all kinds on stable and unstable ground.

• Construction assistance and monitoring of geotechnical related functions such as pile driving (using the Pile Driving Analyzer), slope stability (using slope indicators), and pore water pressure (using piezometers).

• Expertise and training in geosynthetics, lightweight materials, alternate retaining walls/systems, geotechnical instrumentation, steepened slopes, swamp crossings, and failure investigations.

• Technical research liaison for geotechnical issues at local, regional, and national levels.

The Geology Unit duties include:

• Complete subsurface geophysical investigations using electrical resistivity for a variety of transportation infrastructure facilities.

• Lithological identification, rock mass classification and analysis of rock competence for recommendations including; rock slope and excavation design, foundation bearing capacities, blasting, vibrations, and rock fall management.

• Evaluation of groundwater problems and design of groundwater control systems; mitigation of dewatering impacts and prevention of moisture damage to pavement structures.

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• Guidance in the search for sound, durable aggregates for construction by identification of deleterious properties and recommendations for screening test procedures, and assessment of properties of native materials produced by the aggregate industry.

• Technical recommendations and guidance in the areas of engineering geology, vibrations, water wells, and aggregate quality by: providing training for technical certification; preparing manuals, standards, specifications and special provisions.

The Grading, Base and Aggregate Unit duties include:

• Provide aggregate source information to district soils, materials, and design engineers, and to the Office of Technical Support personnel.

• Maintain the Aggregate Source Information System (ASIS) computer database for aggregate sources and provide updates for district users, and others, as requested.

• Lead the implementation of new technology including Intelligent Compaction and Light Weight Deflectometers, for QC/QA of grading and base materials.

• Provide technical expertise regarding aggregate durability, availability, and specifications.

• Provide technical assistance and training to project personnel in matters related to excavation, embankment, and aggregate base construction items.

• Maintain the Grading & Base Manual and develop new specifications and/or modify existing specifications.

• Audit to ensure compliance with testing rates and specification requirements.

• Conduct and aid in research and implementation of research results relative to pavement design and subgrade soil properties and characteristics.

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Technical Classes As a specialty office one of our major functions is technical assistance. One way this is accomplished is through formal training. The Geotechnical Section was involved in teaching the following courses:

• Aggregate Production • Grading and Base I and 2 • Grading & Base Recertification • Construction Engineers Workshop • Materials Engineers Organization • Construction Inspectors Workshop • MSPE Inspector Workshop • Lab Chiefs Workshop • IAI Workshop • Soils Engineers Workshop • AGC Grading and Base Workshop

Web site The Geotechnical Engineering Section has a comprehensive web site on the Office of Materials web site at http://www.dot.state.mn.us/materials. The site is divided into four sections, Aggregate, Foundations, Geology, and Grading and Base. Each section contains information for our customers such as manuals, approved products, borings and CPT’s, pit maps, specifications, standard forms and staff contacts. Our intent is to eventually move all of our shared information to the site including all of our Mn/DOT manuals. Geotechnical Section Activities This section of the report details the various activities completed by each unit during 2008. This is the third time that most of this information was collected and comparisons with data from 2004 to 2008 are made. The data will be used as a baseline for future strategic planning efforts.

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Foundation Unit Activities Geotechnical Exploration Standard Penetration Test Borings The SPT is a major part of our geotechnical exploration program. Mn/DOT has three full-time crews assigned to the program. A fleet of three drill-rigs, each with its own unique capabilities, is used to complete drilling operations. The fleet size also allows for continuous operation in cases where mechanical break down occurs. The following borings were completed in 2008.

• 118 standard borings • 1690 moisture content/samples • 7563 linear feet of borings

020406080

100120140160

2004 2005 2006 2007 2008

Borings

0100020003000400050006000700080009000

2004 2005 2006 2007 2008

Lineal Feet

SPT borings showed a slight increase in 2008 and appears to be leveling off. This may be a sign that we have reached a balance with the SPT and CPT. Cone Penetration Test The CPT forms the other major part of our geotechnical investigation program. Mn/DOT had three full-time crews assigned to three rigs in 2008. In 2008 the CPT rigs were able to conduct 9 times as many soundings and five times the footage as the SPT crews. The following work was completed in 2008. There was a small decrease in the number and length of soundings primarily due to equipment and personnel issues.

• 1034 CPT soundings • 924 lf CPT soil samples • 36756 linear feet

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0200400600800

100012001400

2004 2006 2008

Soundings

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2004 2006 2008

Linear Feet

Over the past year we have expanded our capabilities and tolls with the CPT. The following non-standard tests were completed over the past year: 2007 2008 Seismic 58 33 SMR 45 22 PWP dissipation 9 1 Video 21 0 DMT 20 4 Laboratory Testing Program The Foundations Unit has a very well equipped testing lab capable of performing tests on a variety of soils and rock to measure their engineering properties. Material testing is performed on a project basis as directed by the assigned geotechnical engineer. Each test result is used to aid in the design of a specific design feature. The following tests were performed in 2008. 97 Unconfined Compression - Soil 67 Consolidation 15 Direct Simple Shear 16 Triaxial Tests (3 or 4 to a test series) 19 Direct Shear Tests (3 or 4 to a test series) 34 Flexible Walled Permeability The following chart compares the number of tests completed since 2002. The chart generally reflects the overall construction program seen over the past six years.

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2002200320042005200620072008

Foundation Reports Foundation Reports are the primary product produced by the Foundations Unit. The reports are used as a guide to complete final designs for bridges, walls, culverts, embankments, and other features. Scheduling is driven by the current PPMS output. Ninety-six Foundation Reports were completed in CY 2008 in the following categories: Bridges – 36 Culverts – 12 Retaining Walls - 7 Noise Walls – 6 Embankments – 5 Roadway Settlement - 0 Guardrail –8 Overhead Signs - 1 Other - 21 The decrease in 2008 is primarily due to the reduction in the overall construction program. The following two charts show the total number and type of reports completed over the past five years.

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Consultant Contracts This section prepares and administers consultant contracts for the Office of Materials. There were 16 consultant drilling contracts totaling 1.43 million dollars in 2008. Consultants completed 80 borings for 6033 lf and collected 1493 samples.

020406080

100120140160180

2004 2005 2006 2007 2008

FoundationReports

0102030405060708090

100

2004 2005 2006 2007 2008

BridgesCulvertsRetaining WallsNoise WallsEmbankmentsOther

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Geology Unit Activities Geology Unit Activity Summary 2008 Aggregate Production Class Aggregate Production is a prerequisite for several courses in the Tech Certification Program. The Geology Unit teaches a half-day session on Minnesota geology and how it relates to aggregate quality. During the 2007-2008 season 22 Aggregate Production classes were taught. The 2008-2009 season is underway with 7 classes taught to date. Electrical Resistivity Imaging Electrical Resistivity Imaging or ERI, has been used increasingly in the past

three years by the Geology Unit to investigate the subsurface. The information provided by ERI assists in the interpretation of the subsurface stratigraphy. In 2008, ERI was used on 11 different projects adding up to 27 individual ERI investigations. The map on the left of the figure below shows in yellow the project locations where ERI was utilized, in 2005 (conducted with the assistance of the DNR), 2006, 2007 and 2008. In the three years since the Geology Unit purchased the instrument, the Unit has

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become proficient with its use, and has tested the capabilities in many challenging sites which much success. Several new types of surveys were conducted this year, including underwater surveys along a streambed, and 3D pole-pole surveys. A few of the projects where ERI was used are described in detail below. TH53 Miller Creek Along with the reconstruction of TH53 in Duluth, near the Miller Hill Mall, a wall was planned near Miller Creek. The district contacted the Geology Unit to help determine the subsurface stratigraphy, top of bedrock if shallow, as well as to determine the existence of obstacles to pile driving. The Geology Unit was able to utilize the underwater cables to obtain information in areas where both a land survey was not feasible and where drill rigs would have difficulty in accessing. Land ERI investigations were also conducted and correlated with the underwater surveys. TH23 Paynesville Bypass The Geology Unit was first called to investigate a proposed bypass for TH23 around the city Paynesville in the summer of 2008. The original bypass was planned to travel over an area that had the potential both for organic soils and for waste material; it was used historically as a dumping ground. In July, four 2-D ERI lines were conducted at the site, three along the alignment to the east of County Road 33 and one to the west. The line to the west did encounter resistivity values that showed the potential for organic soils. As work was being finished on interpreting the results from the ERI investigation, the Geology Unit was contacted by the district, notifying them of a change in alignment. The bypass alignment was moved to the north to avoid the problematic area. In November, the Geology Unit conducted three additional ERI lines along or near the new alignment. The new alignment is

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located over an area currently used by the city of Paynesville for the final pond in their system of settling ponds. Two-D ERI lines were conducted to the west of the pond along the east and the westbound centerlines and another roll-along line was conducted to the north of the pond. Each of the resistivity profiles matched well with nearby foundations borings. I-90 Nodine For the past 15 years, subsidence has been noted along the shoulder and backslope of westbound I-90 just west of the Nodine exit. District 6 contacted the Geology Unit to request assistance in recommendations for fixing the problem. The Geology Unit performed conducted three different ERI lines at the site. A variable bedrock surface, with possible voids and weathered rock zones at depth were revealed. District 6 is working with the Geology Unit to determine an appropriate repair for the site. Aggregate Source Investigations

Several investigations of new aggregate sources were conducted in 2008 and are listed in detail below. The table to the right shows how many investigations were conducted over the past four years. Red Rock Quarry: Rock type designation and assignment of aggregate class were conducted at the Red Rock Quarry found near Jeffers in Cottonwood County. The majority of rock in this quarry is quartzite from the Sioux Quartzite Formation. Two distinct argillite beds are also present and have contributed to marginal results during quality testing. Regardless, the prevalance of

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2005 2006 2007 2008

Number ofSources

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quartzite deemed aggregate produced from this quarry as Class A for both bituminous and concrete specifications. Jackson County Iron Mine Material being produced for aggregate from this source found near Black River Falls, WI is being derived from stripping piles created by past iron mining. The bulk of the riprap-sized stripping appears to be composed of a metadiorite. Other miscellaneous rock types are present such as mafic intrusives and iron formation. No class ratings have been assigned since rock type verification analyses and lithological summaries are ongoing. Weisenberger Quarry, WI Investigations at this quarry found near Marathon City, WI revealed mostly dioritic mineralogies with variation in texture and degree of alteration. Given the prevalance of igneous rock, aggregate produced from this quarry was deemed Class A for both bituminous and concrete applications. Selective blasting was recommended to ensure that undesirable aggregate produced from heavily altered zones would not exceed 4% of total mass. Koo Koo Club Quarry, WI Aggregate being produced from this quarry, also found near Marathon City, WI, appears to be quartz diorite. Rock type variation is present due to changes in texture as well as mineralogy which varies due to degree of alteration and/or deformation found within and near shear zones. An aggregate class rating has not been assigned to aggregate from this quarry since rock type verification analyses and lithological summaries are ongoing.

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County Quarry, Spring Valley WI Material produced at the Spring Valley quarry is from the Prairie du Chien Group. Sandstone and dolostone were encountered in the quarry face, but dolostone was the predominant rock type once the material had been produced, due to the soft, friable nature of the sandstone. Investigations

were conducted to determine the quality of different beds. Following the investigation, it was recommended that unsound chert, shale, and siltstone should be minimized within the produced material to continue to meet quality specifications. Rock Strength Testing Rock strength testing has been conducted at Mn/DOT for many years. The Geology Unit performs unconfined compression testing on rock cores. The majority of tests are performed on rock cores taken for bridge projects. In 2008, the large increase in rock tests was due to the number of borings for the new Dresbach bridge over the Mississippi River as well as the use of RMR in the foundations design, which required a greater number of samples tested than in the past. Diamond drill core for two bridges, the Clementson and Dresbach, were tested to evaluate the uniaxial compressive strength of the rock for foundation evaluation. The rock type for the Clementson Bridge is greenstone, a dark altered basaltic rock. This is a very strong rock. Four out

01020304050607080

2005 2006 2007 2008

UnconfinedCompressionTests

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of the five samples easily withstood 12,000 psi of force. The Dresbach Bridge sits on top of sedimentary rock from the Eau Claire Formation. The rock mostly consists of Interbedded Sandstone and Shale layers. Nearly 70 UCS tests were made of this material to classify this variable rock type. Rock Fall/Rock Slopes 2008 was an eventful year for rock slopes in Minnesota. The Geology Unit assists in rock slope design recommendations and as conducts investigations when rockfall hazards exist or when rockfall occurs. Silver Creek Cliff In September of 2008, a large mass of rock fell from the southeastern side of the rock face before the Silver Creek Cliff Tunnel. The Geology Unit recommended that certain areas be removed to minimize hazards for the driving public. In October, one of these areas was removed with blasting. The ditch was also modified to minimize the chance of rockfall occurring on the roadway. The District is monitoring the area. The Arches Several recent and historic rockfalls have occurred at The Arches rock cut on TH14 in Winona County. Following the most recent rockfall in the spring of 2008, the district decided to cut back the slope to create a more stable rock cut. The cut was completed in the fall of 2008. The photo shows the rock cut in progress.

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Stillwater-TH95 In the fall of 2008, the Geology Unit began a large-scale rock slope recommendation project for TH95 near Stillwater. Each portion of the rock slopes from reference post 105 in the south to reference post 100 in the north, were described as to rock type, drainage, and condition. Recommendations concerning possible rockslope stability concerns were also given for each area. Grading, Base, and Aggregate Unit Activities The Grading, Base, and Aggregate Unit works with the Districts to construct high quality bases and subgrades. This is accomplished through technical assistance in the field by on-site visits and the development of specifications and technical manuals. The chart below shows the items that were completed during the past year.

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Other Items Completed in 2008

Technical support for drafting pilot specifications and modifying test methods

Maintained the Grading and Base Website Revising the Grading and Base Manual Updating electronic forms and placing them on the G&B website Revised the Grading and Base certification training manuals

The Grading and Base office joined the Associated General Contractors organization to present the first annual Grading Conference. The positive responses received include suggestions that aggregate production become a part of next year’s and agenda.

Section Highlights Foundations Unit Foundations Staffing

2008 has been the year for personnel changes in the Foundations Unit. Between moving, promotions, and new hires, there are at least ten people working in jobs new to them. A significant portion of 2008 was spent coming up with creative ways to keep the crews operating with reduced staff while working on hiring new people. It seemed like if you weren’t conducting interviews, you were getting ready to conduct interviews. The end result is that what used to be a well experienced workforce is now relatively new. The challenge for 2009 will be to train and support these new workers while delivering what appears will be a greater workload. Along with the challenges will be opportunities to optimize our site investigation capabilities. On the field investigation side, Jim Green has moved to Metro Soils and Dean Brady has moved to the office side of Foundations as the drill crew supervisor. Pat Faschingbauer, Tyler Lueck, Gerald Loher, Dave Larson, and Dave Malchow are new Transportation Generalists on the drill crews. A sixth Transportation Generalist will be hired in early 2009.

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Kevin Wassen and Dale Zerwas have been promoted to Transportation Specialist and will each be in charge of a drill crew. Richard Diemert, Pat O’Donell, and Bill Loher are now operating drill rigs as Transportation Generalist Seniors. On the office side, Julie Johnson accepted a position in The Bridge Office and has been replaced by Dean Brady as the drill crew supervisor. Dean brings a wealth of field experience having worked his way up through the ranks starting as a laborer, working as an operator, and eventually working as a crew chief. Hossana Teklyes rotated for six months as part of the Graduate Engineer program and is now a permanent part of the Foundations staff as a Graduate 2 Engineer. Stephanie Theriault has also been added to the Foundations staff as a geologist. Once the sixth Transportation Generalist has been hired, Foundations will have three standard penetration test crews and three cone penetration test crews. We will also have office staff to handle an increased workload and provide support for our joint venture with the Geology Unit to provide geophysical surveys on a more routine basis. Geophysics is playing a major role in expanding our site investigation capabilities. Surface resistivity (the primary geophysical method we are currently using) not only provides an overall view of a site, but can also be used as a guide for more detailed investigative tools.

Using modern subsurface investigation methods for spread footing settlement analysis Engineers in the Foundations Unit regularly recommend if bridges should be founded on deep (piles) or shallow (spread footing) foundations. While deep foundations provide a very sturdy foundation, spread footing foundations are often adequate enough to support bridge loads and they are much less costly and take only a fraction of the time to construct. However, often times in the past, spread footings were analyzed in foundation materials that appeared to be suitable for shallow foundations (i.e., medium dense sands), however, the calculated settlement was usually higher than structural engineers were comfortable with. This was due mostly to the fact that settlement calculations were based on Standard Penetration Test (SPT) N values (blow counts), which is considered a poor in-situ test because of its high variability. The settlement equations developed for the SPT N value reflected this high variability and produced very conservative settlement numbers.

Recently with the advent of more modern investigation techniques, Mn/DOT’s foundation engineers are better able characterize the compressible nature of the soils and provide more reliable settlement estimates. This in turn has translated into more recommendations for spread footing foundations for bridges and other structures. The Bridge Office has embraced these new techniques which has translated into many more spread footing foundations being constructed. These modern

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investigation techniques include the Seismic Cone Penetration Test (CPT) and Flat Plate Dilatometer Test (DMT). The Seismic CPT utilizes a special penetrometer, equipped with horizontal geophones, to determine the speed of a pressure wave through the foundation soils. This pressure wave is generated at the surface by special equipment attached to the push rig. As the normal CPT is advanced, a seismic test is performed at regular intervals (usually every meter). The test simply involves thumping the surface and recording the time it takes for the pressure wave to be heard by the geophone in the penetrometer. Afterwords, the raw data is processed to give the user a wave speed (Vs) with the units of feet per second. Wave speed in soils gives an indication of the density of soils (denser materials have higher wave speeds). In addition, wave speed can then be correlated to soil modulus values (soil stiffness) which aids in settlement calculations. The Flat Plate Dilatomer is a stainless steel instrumented blade that is pushed into the earth to determine the in-situ stiffness and strength of the soils. The equipment consists of a 2.5 in. diameter flexible steel membrane that is mounted on one side of a stainless steel blade having the dimensions of 4 in. wide, 8 in. long and 0.6 in. thick. The blade is advanced into the ground with push rods. At regualar intervals (usually every 1 or 2 ft.), penetration is stopped and the flexible steel membrane is inflated with nitrogen gas supplied through tubing extending to the surface. The gas pressure is governed by a control box at the surface where readings are taken to determine the pressure required to inflate the membrane into the soil. The raw data is then processed and translated into

t1

t2

V=dist/t

1 m

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engineering properties including stiffness parameters used to predict settlement. Example project TH 94 Ped Bridge In December, the Foundations Unit was asked to provide a foundations investigation and recommendations for an emergency bridge replacement project in St. Paul. An old ped bridge just west of Lexington Avenue was crumbling and had to be taken down fast and replaced in a short time frame. The Foundations Unit quickly mobilized its large CPT rig and had CPT soundings and DMT pushes taken at the proposed substructure locations. The soundings showed that the foundation soils were conducive to spread footing foundations at the abutments and pier locations. A settlement analysis was then performed using the following data:

1. interpreted SPT N values from CPT sounding 2. sheave wave velocity data from Seismic CPT sounding 3. soil elastic moduls data from DMT push

The results were then plotted on a graph depicting footing width versus nominal (unfactored) bearing pressure for a settlement value of one inch (accepted as maximum value for bridges).

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The results clearly shows that for SPT N value data, the allowable bearing pressure for one inch of settle is significantly lower than that of the other two more modern methods. Moreover, national geotechnical research has found that DMT and Seismic CPT data more closely match the settlements of large scale spread footing load tests and that SPT data is very conservative. For this example, for a 10 ft. wide footing, the Foundations Unit would recommend the following nominal bearing pressures to keep the settlement under one inch. Seismic CPT 7000 psf DMT data 6000 psf SPT N values 1900 psf In this case, the Foundations Unit felt the most comfortable with the DMT data and recommended a bearing pressure value of 6000 psf for one inch of settlement. If SPT data alone were used, the spread footing would have to be constructed about three times larger than if the other more modern methods were used. TH 2 Landslide Projects of note in 2008 should include the massive landslide the occurred just east of Crookston, MN that took out the westbound lanes of USTH 2. The problem area started out as a dip in the road that the District Materials Engineer had been keeping his eye on and Maintenance had patched to level the roadway up. Foundations was called in the Fall of 2007 to take a look at the situation. Some cosmetic things were then recommended and implemented as an easy less expensive way to see if the

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situation healed up and went away. One of the mitigation things done was to install perforated pipe drains along the north inslope of the WB lanes to dry out the clay soils. The District reported heavy flow in the drains from the moment they were installed. Numerous shallow inslope sloughs could be found in the area, some newer looking and some older. The Red Lake River flows near the bottom of the slope and makes a sharp bend at the location of the problems. Just to the east of the area and mostly off the ROW is the site of a large landslide from decades ago that some of the oldest employees in the District may remember. Mud waves from that slide can still be found along the banks of the Red Lake River and an old brick column that marked the gate into a religious building still stands. Survey control points were established to monitor the area periodically along with the observational method of control. The patch in the roadway looked to be more of a dip in the pavement rather than any lateral movement or shear cracking. Dips (settlement) in roadways where there is soft clay soils, organics or high moisture content are common across the state and too numerous to all be repaired. Movements were noticed in 2008 and at least several patches had to be made on the WB lanes. Late Sept. 2008 saw a more rapid rate of movement and cracks forming. The WB roadway was then closed and within a week later a massive landslide occurred taking out both WB lanes of TH 2. One face scarp of the slide exhibited over 10’ of vertical movement. The Foundations Unit assisted the District with borings, installing inclinometers and reviewing the data. Through communications within the District between Maintenance, Materials and others along with Central Office Foundations a serious human disaster was avoided. The disaster was confined to the highway infrastructure. The next phase was to decide what needed to be done to restore the traffic capacity of USTH 2. Options included repair of the failed area, bridging the site or moving the roadway. A new type of inclinometer called a shape array (see more on this device later in the report) was used to help gather data for the decision. Cost, and more importantly, safety issues made the repair option unattractive. A new alignment was chosen to restore TH 2.

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MN/DOT’S EXPLORATION OF

GEOTHERMAL WELLS In 2008, the Foundations Unit was solicited by Mn/DOT to investigate the subsurface conditions at two state owned locations; Paynesville truck stop on TH 23 and Central Shop in the Twin Cities. Both of these locations are considering the addition of a geothermal well system to efficiently and effectively heat and cool their buildings. However when one thinks of Minnesota, especially our winters, the last thing to come to mind is deriving warm air from the ground to heat and cool homes. Yet geothermal heating and cooling systems for residential and commercial buildings have become increasingly popular in Minnesota. The Minnesota Department of Health notes that in the past 25 years over 2,000 vertical heat loop permits have been issued and the number of systems installed between 2006 and 2008 has more than doubled. Of the over 2,000 permits issued, about 75% were for smaller (10 ton or less) systems, which includes those for residential homes. A necessity of a successful geothermal system is a thorough understanding of the groundwater, soil, and bedrock. Although geothermal systems can be used almost anywhere, it is imperative to know the subsurface conditions of a given area in order to choose the proper system for installation. This is where the Foundations Unit comes into play. By utilizing our highly capable fleet of drill crews as well as past boring and sounding logs, we can generate an interpreted subsurface conditions report, outlining the soil and bedrock stratigraphy and sometimes determine the groundwater elevation. In the essence of saving time and money, we utilized the CPT to produce information regarding the subsurface conditions at each location. Reports

GEOTHERMAL WELL INSTALLATION IS BEING EXPLORED FOR

MNDOT’S CENTRAL SHOP NEAR THE C01 MARK.

GEOTHERMAL WELL INSTALLATION IS ALSO

BEING INVESTIGATED FOR PAYNESVILLE’S

TRUCK STATION NEAR THE T01 MARK.

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for both of these sites have been completed by the Foundations Unit and sent off to Facilities Management Services for further review. HOW DOES GEOTHERMAL WORK? Although we, on the surface, experience many shifts in temperature throughout the year, subsurface temperatures are fairly stable. In Minnesota, subsurface temperatures range between 50-55 degrees Fahrenheit. Other places in the world, especially those with more prominent subsurface heating sources, such as volcanism or tectonics, can have much higher temperatures. Essentially, geothermal heat pumps capitalize on earth’s naturally regulated and constant temperature to heat or cool the air in a building as well as in certain circumstances act as a water heater.

As mentioned, when deciding the type of system to install several important factors including bedrock geology, soil types, groundwater, and size of home or business must be considered. There are two main types of geothermal heat pumps: open loop or closed loop, and these systems can run horizontally or vertically. Open loop heat systems utilize groundwater to heat and cool the air. The closed loop heat systems run food-grade antifreeze through closed piping which will absorb and disperse heat. The closed loop system is far more popular than the open loop because it does not need to use a groundwater source or special permitting from the DNR.

OPEN LOOP HEAT PUMP SYSTEMS CONSIST OF VERTICAL

PIPES THAT TRANSPORT WATER, WHICH HAS A GROUND

REGULATED TEMPERATURE, INTO THE HOME TO AID IN

HEATING & COOLING. PICTURE COURTESY OF THE U.S. DEPARTMENT OF ENERGY.

CLOSED LOOP VERTICAL HEAT PUMPS CONSIST OF A SERIES

OF VERTICAL U SHAPED PIPES THAT CARRY A FOOD GRADE

ANTI-FREEZE WHICH EASILY HEATS UP OR COOLS DOWN

WITH THE SURROUNDING TEMPERATURES. PICTURE

COURTESY OF THE U.S. DEPARTMENT OF ENERGY.

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ECONOMIC & ENERGY INCENTIVES So why are we seeing an increase in interest and installation of geothermal systems in Minnesota? With much political debate surrounding it, on October 3, 2008 President George W. Bush signed the Emergency Economic Stabilization Act of 2008 into law which not only provided financial relief for many businesses across the United States but also included important extensions to the Energy Policy Act of 2005. The credits outlined in both bills include a tax break of 30% of the cost, or up to $2,000, for home owners who install an ENERGY STAR labeled geothermal heat pumps between January 1, 2008 and December 31, 2016. Another important factor in the switch from the standard oil or natural gas furnaces and central air systems to geothermal heat pumps is the overall financial savings and energy efficiency. The U.S. Department of Energy noted that geothermal pumps save an average of 30-60% on energy.

ENVIRONMENTAL & ECONOMIC DISADVANTAGES There are, however, some debatable disadvantages to a geothermal heating system, both economically and environmentally. Economically speaking, the systems are generally not cheap to install and, depending upon usage, may take several years to make up the difference in the cost of the system through energy savings. Environmentally speaking, although geothermal heat pumps utilize a natural energy source, the pump itself runs on electricity. Some people believe this may actually increase the output of CO2 into the atmosphere than would a typical natural gas or oil powered furnace. Also, open loop systems have the potential to use up a lot of groundwater that could otherwise be saved for clean water drinking purposes. Finally, as mentioned before the geology, soil types, and groundwater dictates which systems can be used and depending on the system installed, it may cause some temporary aesthetics issues with the property. For example, a horizontal system may require up to 100 to 300 foot trenches, which would involve excavating some of the land near the home or business. WHY MN/DOT? Fortunately for Mn/DOT, it seems the advantages far outweigh any possible disadvantages. In correspondence with Clayton Gore, an Engineering Specialist with Mn/DOT’s Facilities Management Services, he noted that some of the motivations behind Mn/DOT looking into geothermal not only

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were dictated by a legislative requirement to investigate feasibility using bonded money but also to promote the state’s advancement in green technology. Mn/DOT already uses in-floor radiant heat systems, and geothermal would be complimentary to that, as well as save money and increase energy efficiency. Clayton also stated that Mn/DOT is trying to incorporate geothermal systems into all new building plans where conditions are favorable because of the savings incentives. Perhaps with time and progress, the Foundations Unit will continue to help and promote money savings through the use of green technology at Mn/DOT. Information collected from the U.S. Department of Energy, ENERGY STAR, and the Minnesota Department of Natural Resources. Pizometer Use in the Construction of an Embankment The Metro District wanted to widen TH 284 NB, located 1.2 miles south junction of TH 5, to add a turn lane and a full shoulder. After a request from the district for a soil investigation and recommendation, an extensive subsurface investigation was performed by the Foundations unit. Our investigation in this area revealed the presence of relatively deep organic and clayey soil deposits. Based on our analysis of the borings at this site, it was apparent that the organic and clay soil deposits would create foundation problems for the proposed embankment widening. A preliminary slope stability analysis showed that the proposed embankment widening would result in slopes with a safety factor close to 1.1. Apart from slope stability problems, 3ft-14 ft. fills would create unsafe differential settlement conditions between the new and old embankment. To provide for stable embankments with minimal settlement concerns, the following options were analyzed:

1- Dig out the organic soils and replace with granular backfill. (This idea was quickly ruled out because of cost.)

2- Support the embankment widening with a pile supported

embankment and use lightweight fill over the existing roadway. (This idea was also ruled out because of cost.)

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3- Reduce the width of fill using a reinforced soil slope (RSS) and to use staged construction methods to place the fill. This staged construction method has been used successfully on similar projects. The idea is to remove the majority of the settlement by adding fill in thin lifts (1-3 ft.) with a one to two week waiting period between lifts. This waiting period will be adjusted based on the results from settlement plates and piezometers.

Based on review of all the options listed above and conferring with the District, it was decided that the best option for constructing the widened highway embankment was to use a combination of excavation, reinforced steepened slopes, staged construction and instrumentation.

When constructing an embankment on a clay or organic soil it is very important to monitor the pore water pressure and the settlement. These types of soils dissipate pore water pressure very slowly unlike granular soils. Excess pore water pressures are created when each additional lift of fill is placed. If the embankment were to be constructed too rapidly, with out a waiting period for each 1-3 ft. of additional lift of RSS, it is possible that the undrained shear strength of the foundation soil might be exceeded and soil failure would result. For the soil to regain its strength, the built up pore water pressure has to dissipate. To mitigate this problem, staged

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construction, installation of piezometers and settlement plates were implemented by Foundations unit. After partial excavation of the organic and clayey soil and construction of Load Transfer Platform (LTP), the Foundations unit pushed six Geokon Piezometers 15 to 30 ft. deep into the ground. Each piezometer has a transducer located inside a housing with a drill rod and a removable point nose cone which will monitor the pore water pressure during the staged construction of the embankment. The piezometer is then connected to a datalogger placed outside the construction zone. The datalogger was set up to read the pore pressure in 90 minute intervals. The datalogger stores the data until all the data is transferred to one of our laptops.

During the three month time span, the Foundations unit was able to download data from the dataloggers. From the data we were able to predict the pore water pressure trend as shown in Fig-4 below. The data from the piezometers were then compared to data from the settlement plates. From this correlation we were able to predict waiting periods for each 1-3 ft. lift of RSS.

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The different colors represent five piezometers showing the pore water pressure expressed in terms of elevation of water. The spikes in the graph indicates the increase of pore water pressure right after additional soil lift being placed during the staged construction of the embankment Conclusion The consolidation behavior of organic and clay soil is hard to predict. This is mainly due to high compressibility, rapid change of permeability and occurrence of creep behavior during the consolidation process. Due to these reasons, instrumentation is usually recommended to monitor pore water pressure and settlement of structures built in these types of soil. In this particular project five of the six piezometers functioned well throughout the staged construction. We were able to download data from the datalogger throughout the completion of the project in a consistent manner. The Metro District were in a tight construction schedule because of the approaching winter and were seeking ways of speeding the construction without compromising the quality of the project. By using the piezometers and settlement plates, the Foundations unit was able to predict the shortest waiting period which helped speed-up the staged construction. The result of the instrumentation was successful and we expect to use them on similar projects in the future. The result validated our belief that implementing new technologies increases safety and quality of projects by decreasing construction cost.

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Instrumentation and Monitoring Highlights of 2008 This year there were a number of geotechnical projects where instrumentation was used to monitor the behavior of foundations, slopes, walls, and bridges. Each of the monitoring programs provided valuable information- in one case it allowed the design to be revised saving project cost, in another it confirmed design assumptions as part of a QC/QA program, and in a third case the monitoring program possibly prevented significant property damage and possibly the loss of life. Monitoring Spread Footing Foundation Performance at New US 212 and CR 110 The bridge at county road 110 in Chaska was originally to be supported on driven piling. Due to compressible clay soils underlying the site, and very large embankment fills associated with the new construction, significant drag-load on the abutment piling was anticipated. The down-drag computations indicated that the piling would need to be significantly more robust than originally anticipated or extraordinary countermeasures to prevent down-drag would need to be employed, such as pre-boring, or coating the piles. American Engineering and Testing (AET), the geotechnical consultant for ZRC (the design build contractor) and Mn/DOT collaboratively worked to develop a spread footing design at the abutments that was acceptable to all the involved parties. An extensive QC/QA program was adopted which included optical survey targets, inclinometers, tilt-meters, and earth pressure cells. The data was used to show that the footings were carrying the anticipated loads and not rotating more than assumed in the design computations. The results of the monitoring program were very interesting and are published in the proceedings of the 57th Annual University of Minnesota Geotechnical Conference as one of the case histories. Of interest was the earth pressure behavior with time as the embankments were constructed and the tilt data. The measurements suggest that the abutments rotate back toward the backfill, possibly due to consolidation settlement of soils below (and in) the embankment backfill. This rotation is somewhat offset by some relative outward rotation of the abutment stem due to lateral earth pressure. This monitoring project resulted in two awards for AET and

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Mn/DOT; an Honor Award from the American Council of Engineering Companies of Minnesota and a merit award from the Minnesota Society of Professional Engineers.

The bridge pier is founded on piling while both abutments are on large spread footings. The spread footing behavior was monitored by optical survey targets, inclinometers, earth pressure cells, and tiltmeters. The instrumentation validated the design assumptions and provided important performance information as part of the QC/QA program. Osterberg Cell (O-Cell) Testing of Post –Grouted Drilled Shafts in Soil This project was a continuation of an earlier project where the pier foundations for Bridges 27405 and 27406 (I-35W crossing Minnehaha Creek and Parkway) were evaluated after post grouting the bases of the shafts. The first set of testing was performed on the NB bridge widening in August of 2007. The second test, described here, was performed in March of 2008. The O-cell, which is a large hydraulic jack, was placed near the base of the shaft and 5 sets of strain gauges were placed at intervals along the length of the 61 ft. shaft. The test monitors the pressure in the jack, the strain in the gages, and the displacement at the top of the shaft. The test was conducted until the top of the O-cell (in interval 1L-9) deflected 0.3 inches. Based on data from the test, the load distribution was interpreted and side-shear and end-bearing capacities were determined.

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Based on this information, the production shafts were shortened and will now be installed to an elevation of 774 ft. (an elevation of 668 ft. was originally called for in the plans).

The top of the drilled shaft being tested with the O-cell can be seen in the right of the left-hand photo. Data is monitored and recorded using a notebook computer. Pile Downdrag Study on BR 27V74 (Crosstown Commons) In an effort to better determine the physical significance of downdrag and its impact on driven piling, a research project was developed and a contract was awarded to Professor Aaron Budge at Mankato State University. Three research piles were instrumented with strain gages and driven as part of the foundation for BR 27V74 over a railroad track near Lyndale Avenue in the I-35W/MN 62 crosstown commons area. A horizontal inclinometer was also installed in the backfill behind the abutment heel. Although a number of measures were taken to protect the gages from damage during installation, a large number of them appear to have been lost. This may be due to significant problems in protecting the wiring connecting the gages, as opposed to the gages themselves. It is hoped that information from the few gages that are still reading properly can be used in conjunction with the inclinometer data to make some rough analysis of the behavior of the bridge piles and how the stresses change with time. The site has an automated data collection system which has been in-place since shortly after the piles were driven. This study is still ongoing.

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The gages were attached at the contractors staging facility to save time on-site. Several problems during construction may have resulted in gage and gage wire damage. Wall H (on MN HWY 41, just south of New US 212) During construction, before the completion of “Wall H,” a heavy rainstorm occurred and a significant amount of water flooded into the backfill and around the north end of the wall. This resulted in some loss-of-ground and disturbance to a number of the concrete facing panels. Crack monitoring and an ongoing wall survey began last year and continued through 2008. In the summer of 2008 a comprehensive wall condition survey was performed to quantify those aspects of the wall which were out of tolerance based on the contract documents. The measurements included the tilt of the wall, gap sizes between adjacent panels, the elevations of selected leveling pads, the size of gaps between the mainline paving and the wall moment slab, and other details. The condition survey was completed and an independent consultant was retained to assess the impact of these deficiencies on the future performance of the wall. After the evaluation, it was concluded that the factor of safety may have been impacted somewhat reducing it from 1.5 to 1.4 and that the wall system may be susceptible to additional adverse impacts during heavy rain events. A solution is still in development by the contractor, with input from Mn/DOT.

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Larger than acceptable gaps are present between many of the wall panels on the north end of wall H. This summer, the Foundations Unit completed a condition survey measuring the various ways the wall did not meet contract specifications. A bulge in the wall can be seen by looking along the coping from the north end. East of Crookston, just east of MN 9 on US HWY 2. Two SAA systems (described in the previous section) were installed in the summer of 2008 to monitor an area of roadway on US 2 just east of Crookston. Within 3 months the area with the ‘maintenance headache’ of some minor roadway subsidence and patching had turned into the largest landslide impacting a Minnesota highway in recent memory, completely destroying half of a four-lane divided highway.

Over a three day period in late September of 2008, a landslide occurred taking the two westbound lanes of US 2 with it. The roadway subsided over

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10 feet. Traffic had been detoured several days earlier based on observations at the site and the data from the two SAA sensors installed at the site. The problem area started out as a dip in the westbound roadway that the District had been watching; District Maintenance had patched the area to re-level the roadway. The Foundations Unit was called in the fall of 2007 to take a look at the situation.

The site as it appeared in October of 2007. Some (mostly cosmetic) fixes were recommended and implemented as a less expensive way to see if the situation healed, without major activities. One of the mitigation strategies was to install perforated pipe drains along the north inslope of the westbound lanes to dry out the roadway embankment soils. The District reported heavy flow in the drains from the moment they were installed. Numerous shallow inslope sloughs could be found in the area, some newer looking and some older. The Red Lake River flows near the bottom of the slope and makes a sharp bend at the location of the problems. The site is just west of a large former landslide (1980) area that impacted the roadway and entrance to a religious school. Survey control points were established to monitor the area periodically along with the observational method of control. The deformations in the roadway patches appeared to be more like a dip in the pavement rather than any lateral movement or shear cracking. Dips (settlement) in roadways where there are soft clay soils or soils with organic materials or high moisture content are common across the state and too numerous to all be repaired. Movements were noticed in 2008 and several

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patches had to be made on the WB lanes during our involvement with the project area.

A roadway patch as seen in April of 2008

Another roadway patch as seen in September of 2008. In September of 2008 the rate of movement of the slope was increasing, both as observed on the SAA sensors and by visual inspection of the site. Cracks were forming faster than previously and over a larger area. Some engineers with the Foundations Unit met with staff from the NW District on site on September 10, 2008 to discuss the site and the probable need for a traffic detour in the very near future. Over the weekend of September 13th additional cracking was noticed after a weekend of rain. The decision was then made to detour traffic and westbound traffic was detoured to the north of the city on September 15, 2008. By Friday, September 19th some pavement cracking with gaps and drops of an inch or more were apparent at

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multiple locations. By Tuesday, September 23rd drops and gaps of several inches had formed especially at pavement joints.

The failure was relatively slow, spanning several days. This photo shows the onset of ‘significant distress.’ On Friday, September 26th the pavement over several hundred feet of mainline westbound US 2 had dropped several feet, and would continue to drop by over 10 feet over the next several days.

Understandably, the site was of significant interest after the failure. In expectation of the slide, it was decided that the eastbound lanes would carry both EB and WB US 2 traffic. Temporary crossovers were constructed (an emergency contract had been let at the time of the traffic

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detour). A semi-permanent site repair was made by removing the pavement from the failed area, grading the slope, and establishing turf. Several new inclinometers were installed to monitor the EB lanes, now carrying all US 2 traffic. Three are in the median of the (former) divided highway and one is located on the far side of the roadway from the slide area. Two are being monitored with traditional inclinometers and two have new SAA systems installed in them. Data suggests that the site is still moving somewhat as a result of the slide, however the rates and magnitudes are very small. It is anticipated that traffic can safely continue to be routed on the EB lanes until a 4 lane section can be rebuilt.

The westbound section of US 2 has been transformed into a slope. Note that the equipment cabinet with the instrumentation for the SAA systems is still vertical, having traveled with the slide several feet to the north and down in elevation. Long term solutions included repair and regarding of the failed area using lightweight fills or ground improvement, spanning the failure area with a bridge, or moving the roadway. After consideration of cost, constructability, long-term performance, and safety, a new alignment about 450 feet to the south was chosen as the preferred alternative to restore US 2. The new roadway section is currently being designed. In a true collaborative effort, the Foundations Unit assisted the NW District with borings, inclinometer and SAA installation and reviewing the data. Through active investigation, monitoring, and communication among

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District Maintenance, Construction, Surveys, and the Geotechnical Section, what could have been a serious disaster, was avoided. As a result of the prudent traffic detour nearly a week earlier the event was confined to the highway infrastructure and there was harm to the driving public. The project also captured the interest of the media and numerous print and television stations carried stories about the slide. Plots of the slope movement prior to the major slide (top) and just after the slide (bottom) in late September of 2008 are shown here. The SAA systems [incredibly] recorded over 10 feet of lateral displacement before breaking.

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Downtown Crookston on US HWY 2 In the summer of 2007, three new ShapeAccelArray (SAA) systems [similar to in-place inclinometers] were installed in Crookston along the Red Lake River at the site of a landslide that occurred in 2003 (and at other times in the past in the immediate area). This site was selected as a test site to determine how well this new instrumentation worked and to find out if there were any bugs that would need to be worked out before deployment on a critical project. Several ‘traditional’ inclinometers were located in the immediate area, which would provide valuable information for correlation purposes. The SAA system uses MEMS (Micro Electro Mechanical Systems) sensors to detect the orientation of each sensor (installed every foot along the length of the array). The shape of the array with respect to gravity is then determined and the deflections are presented graphically in a wide variety of formats useful for the engineering analysis of the area. The new instrumentation has been successfully monitoring the site since late June of 2007. The SAA systems are much more ductile than traditional inclinometer casing and have been able to measure (and survive) relatively large earth movements, not previously possible with traditional systems. One of the three arrays is located relatively close to US 2 and shows no significant movements. The other two arrays are located within the previous landslide area and show clearly that the landslide continues to creep at a more-or-less uniform rate, subject to some event-based changes. The rate of movement appears to have significantly increased since some grading work was performed by the city in the autumn of 2008. As a result of the successful monitoring of this area, the NW District elected to install the new sensors at another area with instability just to the east of Crookston, described in the following section.

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Installation #2 is located in the middle of the slope and is showing a distinct slip-plane at a depth of about 35 feet. There appears to be somewhat more movement at depth than on the surface, which could indicate the potential for an abrupt slip or break at the ground surface at some point in the future. About 10 inches of movement has occurred since July of 2007 (about 18 months).

Installation #3 is located further down the slope closer to the river. This array is showing a distinct slip-plane at a depth of about 45 feet, with nearly 15 inches of movement observed since July of 2007. The plot at the right shows the rate of movement; a clear increase in the rate occurred in the autumn of 2007 and it has not slowed even after the work was complete (or over the winter months).

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Geology Unit New Seismic Equipment The Geology Unit has recently acquired new geophysical equipment. Seismic methods have been used for shallow subsurface investigation for many years in the transportation industry. Mn/DOT has utilized seismic geophysical methods in the recent past; however, these were always done by consultants. As the Unit researches ways to increase the quantity and quality of geologic information, seismic methods were chosen to add to the geophysical tools available. Seismic geophysical methods use the seismic velocities of earth materials to interpret subsurface stratigraphy, elevation of water table, and bedrock topography just to name a few. Seismic refraction and reflection both work similarly; a seismic signal is generated at a known time, the signal is reflected and refracted back to detectors at the surface. The time between the signal being imparted to the ground and being detected is used to interpret information about the subsurface. Seismic refraction makes use of the compressional P-wave. Refracted rays travel from the seismic source; travel along the boundary between layers, and are then critically refracted and detected by geophones. The method assumes an increase of seismic velocity with layers at increasing depths. After the data is collected in the field, the first arrivals and the geophone locations are used to create a velocity profile of the subsurface. From the seismic

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velocities, properties about the subsurface can be inferred. The Geology Unit currently makes use of a hammer and a strike plate for the seismic source. This method is generally of most use when target depths are shallow (<50ft). Seismic methods are best suited for investigations in the subsurface containing large seismic velocity contrasts. The Geode from Geometrics Inc was purchased in the summer of 2008. The Geology Unit expects that the Geode will be used for applications such as: determining bedrock topography, subsurface stratigraphy, depth to water table, void detection, and estimation of rock competence and rock type. Rock Mass Rating (RMR) The Rock Mass Rating system (RMR), or also called Geomechanics Classification was developed in the early 1970’s by Bieniawski. This classification system has been modified some over the years, but has been a widely used and economical way for classifying rock strength. Over the past year, some of Mn/Dot’s drill cores for larger bridge projects have been evaluated using the RMR system, adapting it for foundation evaluation. There are six parameters, each individually rated and summed for a generalized rock mass rating. The first parameter is the strength of the intact rock, where point load strength or uniaxial compressive strength tests can be used. The other parameters include: Rock quality designation, RQD (%), spacing of discontinuities, condition of discontinuities, ground water, and strike and dip orientations. These parameters are used to sum up a total RMR value up to one hundred. Based on the range of the rating the RMR value can be given a class number from one to five and a generalized description, such as “Very good rock”.

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Mn/Dot’s most recent project using RMR to rate the rock strength was for the Dresbach Bridge on TH-I90. One of the problems encountered assigning drill core with an RMR method is rating the last two tested parameters. RMR was primarily developed for tunneling applications. Ground water conditions can be tested along with the strike and dip of joints and discontinuities in a tunneling situation, but is not directly suited for drill core. The Geology and Foundations units are interested in using the RMR value as an input for the LRFD’s Hoek and Brown shear strength criteria. For the Dresbach bridge core we decided to assume that the ground water conditions were wet, giving it a mid range value, being that it was below the water table. As for the strike and dip orientations, that was given a mid range value of fair. These two parameter values cancel each other out making the summed RMR values solely based of the first four parameters measured directly from the drill core. For the nine diamond drill holes that Mn/Dot drilled on the Dresbach Bridge project, there were approximately seventy uniaxial compressive strength tests for the varying lithologies. In doing our UCS tests, we decided it would be better to test as the lithology changes rather than per core run to characterize the strength of each lithology. We might have done more UCS tests than we needed for this area, but there were a lot of small variations in the core in regards to the visual amounts of sand, the grain size of the sand, silt layers etc. Computing the RMR for each UCS test has made a more detailed investigation of the drill core. We plan on doing RMR on the larger projects that require it. Most of the data to compute RMR is already included on the gINT logs.

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Grading, Base and Aggregate Deflection Method (Light Weight Deflectometer) Update The Minnesota Department of Transportation is continuing efforts towards the implementation of the Light Weight Deflectometer (LWD) as a Deflection Method to the compaction requirements in Specification 2105. This test method is a type of plate-bearing test, where the load is a force pulse generated by a falling weight (mass). The falling weight is dropped on a buffer system that transmits the load pulse through a plate resting on the material to be tested. The weight is raised to a height, that when dropped, will impart the desired force pulse. The weight is dropped and the resulting vertical movement or deflection of the surface is measured using suitable instrumentation. The peak deflection and estimated modulus resulting from the force pulse at each location is recorded. (ASTM E2583-07) Mn/DOT currently supports the ZFG2000 model manufactured by Zorn (a total of 27 LWDs have been purchased to date). A pilot LWD quality compaction specification was used during 2007/2008 and will be used during the 2009 construction season. The main change in this pilot specification is the use of deflection values instead of modulus of elasticity as acceptance criteria. Efforts continue to be expended towards the development of target values for varying soil and moisture conditions, in lieu of using control strips for development of these values. Data collected by the Districts and the data / findings resulting from the following investigations will be utilized:

• “Implementation of Intelligent compaction Performance Based Specifications in Minnesota” – Dr. White (Iowa State University), Final Report Due: February 28, 2009

• “Compaction Specifications for Unbound Materials” – John Siekmeier, End Date: February 28, 2009.

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• “Mn/ROAD 2008 Reconstruction” – Field data collection is complete and data has been organized. Laboratory testing is currently being completed.

The needed deflection target value analysis is anticipated to be completed by March 2009. Other means for establishing target values, in lieu of a “table”, are still be considered and investigated. An updated test procedure and data collection form is available on the Grading and Base Website (http://www.dot.state.mn.us/materials/gradingandbase.html). Please note that in addition to some minor changes, an LWD Test Depth table (see table 1) was also incorporated into the test procedure. Lines for LWD Target Value, Test Depth, Test Number on the Smart Card, Standard Optimum Moisture Content and Relative Moisture were added to the data collection form.

Table 1. LWD Test Depths1

Material Type LWD Test Depth1

Granular Soils ≤ one-half lift thickness2 (see Figure 1 [a])

Granular Base / Stabilization Layer

0 mm (compaction surface)

Compacted with Padfoot Roller: Bottom of deepest indentation of the padfoot penetration. (see Figure 1 [b])Non-Granular Soils Compacted with Smooth-Drum Roller: Compaction Surface (0 mm)

Note 1— Perform tests at a uniform depth, representative of the compaction state. Ensure consistent test depths are used, throughout the project, for given material types. Note 2— The influence depth is approximately 1 to 1.5 times the plate diameter, consequently, deflection measurements obtained for lifts less than this depth are a composite deflection measurement.

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Note 3— Complete test at compaction surface (0 mm) for cases where disturbance effects exist (i.e., deflection measurements increase, due to disturbance caused by the test, from that observed at the surface).

(a) Test depth at one-half the lift thickness. (b) Test depth at bottom of padfoot penetration.

Repeatability testing continues to be completed on an annual basis (starting in December), after the purchase of new devices, prior to re-commissioning after calibration by a Test Institute and when measurements are no longer repeatable or are questionable. This testing is completed to verify that deflection measurements are repeatable and meet the deflection value for a given pad configuration. Please ensure new LWDs are submitted for this testing prior to commissioning. This allows baseline values to be established, along with ensuring the device was adequately calibrated. An Intelligent Compaction and Light Weight Deflectometer User Group meeting was held December 2 at the St. Cloud Conference Center. District, County and Contractor personnel were invited to participate in the discussions. Discussions were focused on what worked in the field, problems encountered and recommendations. The following are reminders for those using the LWD (please contact the Grading and Base Office with any questions):

• Periodically check the release assembly for slippage. • Ensure the calibration height is used during testing. During

repeatability testing, it was noted that some of the LWD drop heights were incorrect.

• Transport the LWD with the falling weight in the locked position. • Ensure the guide rod is vertical during testing.

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• Districts are now responsible for purchasing, maintenance and calibration costs.

Intelligent Compaction (IC) The Grading & Base Office considers the IC roller a valuable tool to measure the uniformity of grading materials and to provide an incentive to the contractors when they meet a certain level of subgrade uniformity. A couple of research papers indicate that when the subgrade is uniform, the life of the roadway doubles. The IC method is a cost effective method to increase the life of the roadway. Examining IC data from past projects and following other IC research projects in the United States, we are finding that there is more than one factor that affects uniformity. The factors that affect uniformity are: material consistency, moisture content, compaction, and the soil strength below the subgrade. Therefore, the Grading & Base Office will use the IC roller as the contractor quality control testing devise and Mn/DOT will use a separate test method for quality assurance. The contractor will develop their own test QC method using the IC roller and the data will be given to Mn/DOT. The Grading & Base Office will develop a revised specification this spring to be used on future granular projects. 2010 Standard Construction Specifications The specifications will have a new look when they are rewritten for the 2010 spec book. The 2010 specifications will be written in active voice and use positive outcome based requirements presented in simple English using the least number of words possible. The NHI Specification Writing Course provided excellent guidelines that will be used throughout the effort. The spec should be about 60% shorter and most of the “do not” items will be deleted from the spec. This means that if it is not in the specification, the contractor cannot do it.

The Grading & Base Office will be deleting the testing rates from their specifications, and incorporating the rates into the Schedule of

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Materials Control. The only exceptions are pilot specifications like the LWD & IC specifications. These testing rates will be incorporated into the Schedule of Materials Control after standardization. Portions of some specifications will be re-arranged to make it easier to understand by construction personnel. Pay Reductions During the 2008 construction program, it was discovered that a few construction engineers were using pay reductions that were not in the specification 2211 pay reduction tables. The reason given for this action was that “There were no pay reductions in the spec book that covered that item”. The intent of the Grading & Base Office is to handle pay reductions not covered in the specifications on a case-by-case basis. Our reasoning is that often several factors must be considered in determining the pay reduction. Some of the questions that need to be answered include:

1) Was the Certification of Aggregate Materials given to the project personnel before the material was delivered to the project?

2) Is the material going to perform as intended by the specification? 3) How this material is going to perform during the projected

roadway life? 4) How is this material going to perform during freeze-thaw cycles? 5) Did the material meet the aggregate quality tests?

The intent of the Grading & Base Office is that failing materials should not be used on a construction project, but we also know this is not always practical. Consequently, in these unique cases, pay reductions are issued. Certification of Aggregate Materials Through the audit process, and when pay reductions are requested, we have discovered that some construction personnel are not requiring the contractor provide the Certification of Aggregate Materials before the material is placed on the project. When this occurs construction personnel are required to follow the following specification: 2211.F1 Gradation Control, 1st paragraph, last sentence

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“All payments for aggregate base materials shall be withheld until the Project Engineer receives and accepts the Contractor’s Certification and quality control testing results.”

The contractor is required to take ownership of the materials they deliver to the project. The owner needs to test the materials before the next layer is placed, to determine if the materials meet specifications. If the material does not meet specifications, the contractor has the option to correct the material, before a pay reduction is issued, unless the failure is in the corrective action category. The Grading & Base Office will issue pay reductions when the material falls in the corrective action category on a case-by-case basis.

Field Reviews More effort was focused on office related activities because we had fewer and smaller grading projects in 2008. Favorable weather promoted accelerated grading efforts with few problems. Twenty projects were formally reviewed during the 2008 construction season. Seven of these projects needed advice or recommendations to resolve a major problem. The rest of the reviews were for random checks of construction compliance or assisting with the collection of research test data. A common centerline culvert replacement plan on TH 218 near Blooming Prairie is a good example of unexpected site conditions requiring innovative changes to successfully complete the restoration of the roadway. The contract required excavating a subcut 2’ to 4’ deep; filling it with variable depth select granular borrow, 9” of class 5 and 4” of bituminous pavement and then opening it to traffic on the same day. Excess moisture in the unstable subgrade caused

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the new pavement to rut 6 to 9 inches deep and fail within 24 hours of completion. The new pavement, base and granular were then removed and the section was rebuilt with an 18” layer of crushed rock (100% -3” and +3/4”), a 6” layer of crushed rock (100% -1” and +#4) and 4” of bituminous pavement. The contractor asked and we allowed the complete substitution of crushed bituminous and concrete for the crushed rock at a significant cost reduction for the reconstruction. See picture above. The new design successfully returned the road to full traffic loads the same day. The number of projects and the quantity of aggregate base failing to meet quality requirements escalated in 2008. This issue is compounded because more than half of the projects reviewed by audit failed to comply with their project inspection requirements. As a response we are currently revising our testing and acceptance standards. We have also made teaching the requirements and the problems caused by failures our highest priority in the certification training.