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Geotechnical Section 2010 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 Technical Classes 7 Web Site 7 Geotechnical Section Activities Foundations 8 Grading, Base and Aggregate 12 Geology 14 Section Highlights Geology 16 Foundations 32 Grading, Base and Aggregate 43 Case Study TH 67 Slide Repair 45 Cover photos clockwise from left; Joe Hudak at TH 13 in Mendota Heights, Mike Novotny, Tyler Lueck, and Joel Schleicher on TH 33 at TH 53, Chuck Howe at Gooseberry Park, and Dave Larson and Hannah Friedrich DNR in Kanabec County

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Executive Summary The Geotechnical Section continued to use new technology to improve our service to our customers in 2010. 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. We also continue to use automated Shape Accel Array (SAA) systems [similar to ‘in-place’ inclinometers] to monitor conditions in the field. This spring we began using GPS differential correction more routinely; the locations of our geotechnical assets are now routinely mapped to sub-foot precision. These tools enable engineers to collect valuable spatial and time-domain data that is used to design a variety of cost-effective solutions. 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. The Geology Unit also continued to expand the use of seismic geophysical methods with the acquisition of instrumentation and software with which to conduct surface wave seismic surveys. Grading, Base and Aggregate The Grading and Base unit provided both field and office technical assistance, training, and rewrote their specifications. Additionally they have led the evaluation of new technologies including LWD and Continuous Compaction Control (CCC). The Aggregate Unit maintained the Aggregate Source Information System (ASIS) computer database for aggregate sources and provide updates for district users, and others as requested.

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2010 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 Geotechnical Section provides geotechnical engineering and geological services for:

• Structural foundations; • Engineered soil and rock slopes; • Aggregate durability, quality and availability; • Roadway subgrade and base construction; • 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.

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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.

• 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 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 and/or modify existing specifications.

• Conduct construction site reviews to ensure compliance with testing rates and specification requirements.

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

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

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

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

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 • Midwest Geotechnical Conference

Web site The Geotechnical Engineering Section has a comprehensive web site on the Office of Materials web site at Uhttp://www.dot.state.mn.us/materialsU. 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.

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Geotechnical Section Activities This section of the report details the various activities completed by each unit during 2010. This is the third time that most of this information was collected and comparisons with data from 2004 to 2010 are made. The data will be used as a baseline for future strategic planning efforts. UFoundation 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 breakdowns occur. The following borings were completed in 2010.

• 130 standard borings • 7110 lf of borings

SPT borings showed a reduction in 2010 due primarily to the return of a “normal” bridge program. 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 2010. Unfortunately, one of our rigs was out of action for most of the year and will

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not be replaced until FY 2012. Still, in 2010 the CPT rigs were able to conduct 5.6 times as many soundings and 3.7 times the footage as the SPT crews. The following work was completed in 2010. The large decrease in the number and in the length of soundings was primarily due to the availability of only two rigs for most of the season.

• 723 CPT soundings • 26479 linear feet

The following non-standard tests were completed over the past year: 2007 2008 2009 2010 Seismic 58 33 18 6 SMR 45 22 21 11 PWP dissipation 9 1 13 1 Video 21 0 0 1 DMT 20 4 3 0 Geoprobe The Geoprobe was in its second full year of production work in 2010. It can do a variety work including SPT, CPT, coring, electrical conductivity, and continuous sampling. Its smaller size and tracked configuration make it great for use in tight spaces and soft soil conditions. To date it has primarily been used to obtain continuously sampled soils. The Geoprobe completed 88 borings last year for a total of 1635 lf.

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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. 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 2010. 64 Unconfined Compression - Soil 50 Consolidation 6 Direct Simple Shear 2 Triaxial Tests (3 or 4 to a test series) 32 Direct Shear Tests (3 or 4 to a test series) 8 Flexible Walled Permeability 5 Constant rate of strain consolidation The following chart compares the number of tests completed since 2002. The chart generally reflects the overall construction program seen over the past seven years.

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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. One hundred and one Foundation Reports were completed in CY 2011 in the following categories:

36 Bridge 16 Culverts 15 Retaining walls 9 Noise walls 3 Embankments 6 Cable median barriers 16 Other

The small increase in 2010 is primarily due to the larger construction program. The following two charts show the total number and type of reports completed over the past seven years.

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2004 2006 2008 2010

BridgesCulvertsRetaining WallsNoise WallsEmbankmentsCable MedianOther

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Consultant Contracts The Foundation Unit prepares and administers consultant contracts for the Office of Materials and Road Research. This past year our office did not write any consultant contracts for foundation borings. However, the Metro District wrote and funded two contracts for foundation borings. Both contracts totaled $180k. Consultants completed 145 borings for 6650 lf. 5BUGrading 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. Training Provided training agenda and materials for the Grading and Base Certification classes. Gave presentations at each of the Grading and Base II and recertification classes. Conferences Gave updates of projects, specifications, and new technologies at several conferences, meetings, and workshops.

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Specifications Revised all of the Grading and Base Specifications. Clarified language and reduced word count by 50%. Field Assistance Provided construction assistance to approximately one hundred state and local agency construction projects. Provided email, telephone and onsite field recommendations. The chart below shows items that were completed in the past year in the aggregate unit. The use of geosythetics continues to rise each year and the number of projects has more than doubled since 2005.

Other Items Completed in 2010 Revising the Grading and Base Manual Updating all the electronic forms and placing them on the G&B website LWD verification study data collection LWD pre-calibration testing

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Geology Unit Summary 2010 The Geology Unit consists of 4 geologists who provide statewide assistance and expertise with needs related to geophysics, groundwater, rock classification and strength testing, aggregate quality, rock slope recommendations, vibration monitoring, environmental assessments and other specialized geologic issues. The following is a summary of some of the tasks that the Geology Unit has worked on throughout 2010. Rock Core Description and Rock Strength Testing Bedrock retrieved from core drilling is subjected to qualitative and quantitative characterization. Information acquired from rock core descriptions is used to make recommendations on projects related to bridge foundations, slope stability, aggregate quality, to name a few. The graph to the right shows that amounts of rock core classification have been maintained at a steady and high level for the past 3 years. After rock core is classified, the Geology Unit prepares and tests rock core for unconfined compressive strength (UCS). Though the need for UCS data decreased in 2010 (see graph on right), the last 3 years of stats show that properties acquired from UCS testing are being used more frequently as a design input. 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 2009-

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2010 season, 14 Aggregate Production classes were taught. The 2010-2011 season is underway with 5 classes already taught. EAW’s, Water Well Recs, Aggregate Source Recs, Vibration Monitoring EAW, water well and new quarry source recommendations as well as vibration monitoring were all down in 2010. Assistance was provided to Metro District staff for an environmental review of SP8204-66 (TH36 at Hilton Trail) as well as a water well for the new MnDOT/Carver County-Chaska Truck Station on TH212. A summary of and recommendation for the Brown Quarry in Fillmore County was also performed. Vibrations were monitored during vibratory compaction of a new mill and overlay on TH95 in Stillwater adjacent to historic buildings. An oscillating compactor was used and generated very low peak particle velocities compared with conventional vibratory compactors. Rock Slopes/Rock Fall TH95-Stillwater 2010 saw a number of rock fall events along TH95, both north and south of Stillwater. These events began in the spring and continued into the fall. The rock slopes along this stretch of highway experience frequent rockfall, which is likely to continue in the future. After each rockfall event, the Geology Unit is called upon to make recommendations to Metro Maintenance crews. Several slope and ditch improvements were carried out this year. The Geology Unit is also monitoring a large dolostone block above TH95 south of Stillwater. Monitoring equipment will likely be installed in 2011.

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Section Highlights Geology Unit Pictured at right, Charles Howe with yet another scientific contribution to the North Shore- written description on a new plaque at Gooseberry Park describing engineering and geologic judgment applied toward the design and construction of Gooseberry River Bridge. Geophysics Geophysical information supplements other subsurface data sets created by conventional drilling techniques and cone penetration testing performed within the Geotechnical Engineering Section. In some cases, geophysical surveying provides the only information acquirable from a project site. The Geology Unit has instrumentation which allows for subsurface interpretations to be made based on electrical and seismic properties of soil, rock, and other targets within the subsurface. Electrical Resistivity Imaging/Induced Polarization (ERI/IP) is the most common method used by the Geology Unit. Seismic Refraction is also being used more to help decipher bedrock depths. With the recent addition of software and other accessories, Multi-Channel Analysis of Surface Waves (MASW) and Refraction Microtremor (ReMi) are currently being developed as an option in environments where Seismic Refraction is not effective. Using multiple methods on a single site is always desired to help bolster the subsurface data set.

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*Collectively, 56 geophysical surveys were performed in 2010 (see above figure). This equates to at least 1 full day per week in 2010’s 34-week ‘season’ being devoted to geophysical field surveying (excludes test surveys and office duties such as processing, interpretation and presentation).

1.) Electrical Resistivity/Induced Polarization Imaging (ERI/IP) The Geology Unit continued, in 2010, to utilize electrical geophysical methods on a wide variety of projects across the state. Warmer than normal spring temperatures allowed ERI/IP surveys to begin during the 4th week of March (some buried frost was encountered during the early spring at a couple of project sites but good data quality was preserved). ERI/IP surveying for 2010 came to completion around the 3rd week of November. *A total of 12,853 feet of ERI/IP surveying was performed during the 2010 geophysics season- a Geology Unit record. Additionally, the Geology Unit completed its 100th ERI/IP survey in 2010. 30 surveys (29 ERI, 1 IP) were conducted on 14 different projects (see above figure). 12 of the surveys incorporated a varying number of ‘roll-alongs’ which, individually, add quarter lengths to the survey line. No 3D surveys were performed in 2010. As visible in the graph on the previous

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page, the use of ERI/IP has increased almost every year since acquiring the capability despite performing more seismic surveying in recent years. The map to the right shows the locations where the Geology Unit has performed ERI/IP since 2005. Most usage continues to be conducted in the eastern half of the state, particularly in Districts 1, 3 and Metro. However, 2010 was a breakthrough year in terms of performing the first ERI surveys in District 2, 7 and 8. ERI/IP has now been utilized in every DOT district in Minnesota. Some of the projects where the Geology Unit used ERI/IP are described below, in chronological order: Norwood Young America- TH212 The Geology Unit started the year by fulfilling a scoping request from the Metro District. The site of interest was in the ‘Part B’ portion of TH212 where westward expansion of the new 4-lane divided highway is slated. As in previous scoping requests for the TH212 area, location and dimensions of potential organic deposits were of interest. To more efficiently survey at the site, the Geology Unit set up survey lines on both EB and WB centerlines of the proposed highway alignment and advanced eastward by ‘rolling-along’. Since the Geology Unit has two resistivity meters, data was collected by separate meters on an alternating basis.

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Collectively 2,300 feet at 3m spacing was covered in a single day via 9 roll-alongs. The resistivity model suggested that as much as 35 feet of organics may be present within a 130 foot swath on the east end of the survey. Ely- TH1 Much of TH1 south of Ely is slated for reconstruction or has been reconstructed to address geometric concerns. Subsurface information was requested for a portion which cuts through a swamp on the south side of Little Spring Lake. A rolling surcharge was possibly performed through the swamp during original road construction. Information about the lateral extent of the fill and underlying soil/rock was needed to help constrain a new roadway/embankment design. ERI was performed on the roadway (see photo) and within the water-filled ditches (see cover photo) which couldn’t be accessed by drill rigs. Ultimately, ERI, in conjuction with CPT info, identified thickness and dimensions of the fill as well as depths to native soil and bedrock. Waseca- TH13 & 14 In the spring of 2010, District 6 requested subsurface information for the TH13 & TH14 construction project near Waseca. Boulders were frequently encountered during pile driving for a bridge foundation. The Geology Unit conducted three ERI lines, two at the bridge foundation location and one to the north. It was discovered that the city had constructed a steel pipe casing for a future pipeline below the two ERI lines. The presence of the pipe casing influenced the profiles to such a degree that the soil stratigraphy could not be determined. A third ERI line was conducted to the north partially over another pipe casing beneath a ramp embankment (see profile). This profile showed the presence of clayey glacial soils over more granular soils.

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Nodine- TH90 In the spring of 2010, the Geology Unit was summoned once again to Nodine where two years ago karst-related subsidence had taken place on the WB lane. Resistivity imaging was conducted in the right ditch adjacent to the EB lane where new subsidence was taking place and extending into the shoulder. The right driving lane, constructed of concrete with bituminous overlay, is likely bridging some underlying open space. Once again, ERI revealed a shallow bedrock surface with interspersed conductive zones indicative of past collapses and weak bedrock/filled voids as well as some potential void areas. Compaction grouting, which was used on WB in ’09, may need to be undertaken on the EB side. Mendota Heights- TH13 A new mainline sewer pipe is slated for placement within a stretch of TH13 west of I35E. Mn/DOT Metro District was interested in bedrock depth since shallow bedrock would require unwanted rock excavation prior to installation of the pipe. ERI profiles revealed shallow limestone bedrock (10’ or less) along the south ditch ofTH13. Consequently, an alternative route for the pipe was chosen near the toe of the WB inslope, adjacent and parallel to a bike path. ERI profiles in conjunction with some seismic refraction (see figure) revealed more acceptable subsurface conditions consisting of rippable sandstone bedrock between roughly 12’ and 30’ below surface. Some industrial fill was imaged on the west end. An anomalous feature within the sandstone may be related to an 1800’s vintage water well constructed by the old ‘Milwaukee Road’ railroad.

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Arden Hills- TH694 & 51 Two ERI surveys were performed on the west embankment toe for the ramp bringing 694 EB traffic on to SB TH51/Snelling Avenue. A portion of a new interchange is proposed in this area where organic soils could be present. Resistivity models revealed conductive soils related to dense clays but no appreciable thicknesses of compressible, organic soils. Mankato- TH22 ERI was requested where a Le Sueur River meander caused a slope failure in the ditch of NB TH22. Since continual river erosion could eventually undercut the roadway, sheet piling was recommended as a measure to maintain stability and control erosion. The resistivity survey was, therefore, needed to identify bedrock depth and boulder presence since both are obstacles during sheet pile installation. Inverted models suggested that a conductive overburden consisting of till overlying granular soils was present. Boulder presence was difficult to ascertain given the 3m electrode spacing, which was needed to infer potentially deep bedrock depths. Nonetheless, boulders were not observed during field recons of the meander cut nor in the slope failure.

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Mankato- TH66 ERI and seismic refraction were both utilized along a stretch of TH66 south of Mankato. In this location the roadway had been experiencing slope stability issues in recent years. Sheet piling and drainage improvements were planned. The variable bedrock topography in this area led to concerns that sheet piling may encounter bedrock before the desired depth. Electrical Resistivity Imaging was performed at this location to correlate with prior seismic refraction surveys. Both methods indicated that bedrock was unlikely to be encountered close to the surface, though boulders may be present. Gabions walls were proposed and constructed in the fall of 2010. Dresbach- TH90 Extensive subsurface information has been gathered for the construction of the new bridge along TH90 near Dresbach. In the summer of 2010 the Foundations Unit requested subsurface information at the location of a new bridge access to an existing rest area and boat launch. The bridge passes over a wet swampy area and foundations drill crews had difficulty accessing the site. Two intersecting ERI lines were performed orthogonal to each other. The profiles revealed a minor thickness of organic material present at surface and overlying granular soils and descending under a wedge of fill.

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Split Rock- TH61 A geophysical investigation was performed using ERI and seismic refraction to assist in the design of the rock/soil slope along TH61 to the south of the Split Rock River. One ERI line was located above the rock slope. Measurements were hampered by the presence of very dry air-filled soils which made current conduction through the soil difficult. Nonetheless, ERI results appeared to agree with the seismic refraction profiles which suggested that bedrock would not likely be encountered during construction of the slope (see project description under ‘Seismic Surveys’). Granite Falls- TH67 A 205 foot stretch of Trunk Highway 67 was subsiding into Hazel creek just a few miles South of Granite Falls. Site inspections revealed very saturated, low-permeability soils with standing water on the upslope side of the failure. These conditions combined with intermittent flooding of the creek likely constitute the mechanism for current and past failures. The Geology unit ran a 70 Meter, 2D ERI survey on the NB inslope and centered over the failure. The inverted resistivity section showed a 3 layer profile with sandy layers making up the upper most 5 feet, silt and clay for 20 to 25 feet ending in a dense Cretaceous aged regolith. The CPT data correlated very well with the ERI profile showing the denser/more resistive materials at depth. Information was needed quickly for this project to design a fix. The ERI data in conjunction with the CPT and SPT drilling was applied to design and construction of a Geopier-supported embankment with a reinforced steepened in-slope, rip-rapped bank and a modified sub-drain system.

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Ely- TH169 Poor geometrics and chronic winter icing are to blame for high traffic accident counts along a portion of TH169 in the Eagle’s Nest area between Soudan and Ely. The preferred new alignment crosses terrain comprised of various bedrock types with varying amounts of sulfide mineralization. Local residents have warned that exposing this material to air and water could create an environmental liability via acid rock drainage. An alternative route was suggested on the north side of TH169. However, geologic field mapping in the area suggests that greater amounts of sulfide bearing rock would be encountered north of TH169 in the bedrock as well as in some of the overlying soils. An ERI/IP survey was undertaken in a swamp north of the highway over the centerline of a potential alignment and revealed at least one IP anomaly underlying the organics (see profiles below). This suggests that chargeable sediments possibly consisting of sulfides may be present (borings are needed to verify). IP anomalies were found in bedrock strata interpreted from the ERI profile and are likely indicative of faults.

IP anamolies

Organics

Mixed Sand and Silt (saturated)

Fault?

Fault?

Chargeable Soil

Bedrock

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Oslo- TH1 For the Geology Unit’s first geophysical survey in the D2 District and North Dakota one ERI line was performed on both sides of the Red River along TH1 near Oslo. The new bridge and roadway alignment will be located just to the south of the current bridge. The profiles revealed upper silty soils and possible roadway fill overlying clayey soils. Buried metal structures were encountered on both profiles, likely a culvert and buried pipe. Aitkin County- DNR Aggregate Mapping Project A collaborative agreement between the DNR and Mn/DOT was made via Unfunded Needs at the division level to assist with the DNR’s county mapping program. Foundations drill crews would assist with auger sampling needs and Geology Unit personnel would supplement the information with ERI. Two subsurface profiles were acquired in October at a prospectable aggregate site on state-owned land near the town of Pliny in Aitkin County. Potential gravel-rich pockets were identified but will require verification via drilling.

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2.) Seismic Surveys As with other geophysical methods, data from seismic methods are used by the Geology Unit to complement other forms of subsurface information. Preferably, seismic methods are applied in conjunction with ERI, particularly where bedrock presence is anticipated. In some parts of the state soil conditions are unfavorable to ERI (e.g., boulder and gravel laden ground moraine typical of much of District 1) but pose less of an obstacle to seismic data acquisition. Seismic refraction, in particular, is a valuable tool which is quick and fairly simple to conduct and provides accurate determinations of bedrock topography and depth. Development and initial application of seismic refraction took place in 2009 with full implementation in 2010. Surface wave methods, such as Multichannel Analysis of Surface Waves (MASW) and Refraction Microtremor (ReMi) have been applied over the past 2 years by the Geology Unit but are still being developed (new software and field equipment was/is being acquired in 2010 which should increase the use of surface wave methods in 2011). Surface wave methods are relatively new in geotechnical engineering, but are becoming more common in site characterization. Like seismic refraction, MASW uses an active source, such as a sledge hammer, to create a seismic signal whereas ReMi uses a passive source, such as road traffic. MASW and ReMi measure Rayleigh wave propagation which is considered ‘noise’ on other forms of seismic surveying (refraction measures P-wave propagation). Therefore, surface wave methods can provide subsurface information in areas where seismic refraction is not possible, such as in urban settings. Also, unlike seismic refraction, surface wave methods are less sensitive to ‘velocity inversions’ which occur where high density material overlies low density material in the subsurface. Consequently, alternating soil/rock densities can be imaged and surveying can be performed on rigid surface layers, such as pavement. Data

Seismic survey locations to date

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acquisition in the field is similar to that of seismic refraction although lower frequency geophones, 4Hz instead of 14.5Hz, are used with longer recording times. Surface wave methods provide a shear wave velocity profile of the subsurface. Shear wave velocities are a measure of soil stiffness and, thus, can identify stratigraphic soil/rock changes and potential void areas. Setting up the land-streamer for MASW surveys Some of the projects where the Geology Unit used seismic methods are described below: Mendota Heights- TH13 Seismic refraction was performed to verify bedrock depth interpretations acquired from previous ERI surveying (see project description under ERI portion). Surveying took place over a portion of the ERI line adjacent and north of the bike trail. Processed data revealed rippable sandstone bedrock at depths within the range established by ERI. TH61- Split Rock River Project In the late summer of 2010 District 1 personnel requested assistance with determination of bedrock depth in an area southwest of the Split Rock River and on the northwest side of TH61. The investigation was conducted above a rock slope area that was excavated during recent construction. As construction approached the northeast end of the rock cut, bedrock was no longer present in the cut slope. This left an unstable area in the backslope.

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The District desired to know if and where bedrock would be encountered as construction proceeded. Two seismic refraction surveys and one ERI survey were conducted (see ERI project description above). The profiles revealed that bedrock was unlikely to be encountered during the construction of a soil slope to the northeast of the rockslope. In early October 2010 the soil slope was constructed at a 1:2.7 slope and did not encounter any rock. TH66 Slope Failure Seismic refraction was conducted in conjunction with ERI along a stretch of TH66 south of Mankato. Both methods indicated that bedrock was unlikely to be encountered close to the surface, though boulders may be present. Gabion walls were proposed and constructed in the fall of 2010.

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TH66 Seismic Refraction Preliminary Results

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or possible top of wx bedrock

or possible top of wx bedrock

Approximate location of Line 2

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TH1 Ely Continuing from 2009, seismic refraction was used extensively in the spring and summer of 2010 along TH1 east of Ely. The U.S. Forest Service and District 1 have been addressing poor geometrics in this area by realigning certain portions and constructing wider ditches. Due to difficult site access, district augering could not be performed along some of the stretches. Alternatively, the Geology Unit conducted several refraction surveys to determine depth to bedrock. As in 2009, velocity models revealed boulder laden glacial soils that overlie a variable bedrock surface. In the early spring Foundations crews were able to conduct two SPT borings which better constrained velocities and subsurface interpretations.

TH247- Plainview The Geology Unit was approached by personnel from Mn/DOT Research Services inquiring about the possibility of using surface wave methods to estimate soil volume loss in road embankments where culvert failures have created or have the potential of creating subsidence issues on the roadway. Petitions to district hydraulics engineers were made to identify preferred sites for an MASW pilot test. Two sites on TH47 west of Plainview were chosen: one, consisting of a large ‘cattle pass’ style culvert about 15 feet below a bituminous roadway and exhibiting no surface failure and, two, consisting of a 48” RCP about 5’ below bituminous pavement with history of

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MASW profile from RP9 Culvert Site (Line 2) inducing roadway failure. Three surveys were conducted at each site on the pavement and parallel to the roadway. Processed data provided profiles which delineated large scale features, such as possible bedrock presence, but not smaller targets such as culverts or void space (see profile below). Further study and application of alternate field and processing approaches may provide more model detail which could provide information useful for site remediation. TH210 Carlton Bridge Top of bedrock information for foundation analyses was requested from the Foundations Unit for a proposed steel-arch bridge replacement over the St. Louis River. Seismic refraction was applied at and east of the northeast abutment and encountered fairly level bedrock about 12 feet below surface. Refraction data was also collected at the southwest abutment but was noisy due to pounding river currents created by the upstream release of dammed water from the Thomson Dam flood gates. MASW was also conducted using

Pavement/Base/Fill Influence

Possible Top of Bedrock

Glacial Soils?

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various shot configurations on and off the roadway at the southwest and southeast abutments. Profiles appear to suggest that the bedrock surface slopes downward to the west away from the southwest abutment but is generally level, around 12 feet below surface, at and east of the southeast abutment. Seismic surveying was not performed at the northwest abutment due to site restrictions. Rock core drilling was performed at the abutments and appears to corroborate the seismic profiles.

U

Bedrock

Stiff Fill?

Less Stiff Fill?

Pavement/Base Influence

MASW profile from southwest abutment

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UFoundations Unit Wet cast gravity retaining walls Wet cast gravity retaining walls now available for use. Due to durability concerns with dry-cat retaining wall blocks a durable modular wall alternative was needed in the salt splash zones next to our highways. Gabions have been in use many years at MN/DOT but another option with a different look was desired so wet-cast blocks were investigated. It was discovered that a few different types were on the market and available for use. The New Retaining Wall Committee (NRC) developed some standards and an approved products list. The list may be found at: http://www.dot.state.mn.us/products/walls/pmgbw_9-3-10.pdf Not many have been built to date by MN/DOT but with each one new lessons are learned. One notable wall built during the 2010 construction season was along T.H. 25 in the city of Belle Plaine. This was a short wall of about five feet in height. The site has an existing masonry block and mortar wall that has areas of intense deterioration. Behind the wall lies trees and private property so it was desired that the existing wall not be removed. The new wall was simply set directly in front of the old wall to cover it up and the old wall would act as sort of a construction form eliminating the need for a backslope excavation or temporary easement agreements. One detail that happened to slip through the review process was for sight distance from autos pulling up to a stop sign and trying to cross or enter T.H. 25. The new wall in front of the old wall blocked the safe sight distance it was discovered during the construction process. The nice thing about this type of modular wall is that field adjustments can be made by simply moving the blocks. In this case a few blocks near the corner of the side street were removed until it was determined that a safe sight distance had been attained. The remaining slope on top and behind the removed blocks was simply regraded to match into the existing backslope. What would have been a major problem and costly teardown with a conventional cast in place wall was now just a minor field adjustment.

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Not only can modular retaining walls be adjusted to fit special field conditions but they can be reused for other walls in the future. If utility or similar work needs to be done behind or under them they can be removed, the work performed and the wall blocks restacked without having to make a patch that will match the existing wall color and texture. This new class of retaining walls now available for use should be an economical alternative for the Designer’s tool box. Instrumentation of Spread Footings for Settlement Hwy 610 in Metro Area: In 2009, Minnesota was awarded federal funding stemming from an economic stimulus bill. One of the Design-Build projects that were funded under this bill was the construction of a new 4-lane freeway in the City of Maple Grove Minnesota. The project extends from County Road 81 to TH169 and includes the construction of five new bridges and an expansion of an existing bridge

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at TH169. All five Bridges in this project are supported by spread footings. Fig 1: A map from Google showing the locations of the five Bridges in Maple Grove. Sub-surface Investigation: A minimum of one SPT boring was taken per substructure of each bridge. From the SPT borings, the predominant soil type at this site is loose to dense sandy soil and some clay soil. The blow counts (SPT N60 values) ranged from 4 (loose) to 100 (very dense). The blow counts for the clay soil ranged from 8 (medium stiff) to 36 (very stiff) Shallow vs. Deep Foundation: For many years the use of a pile foundation has meant security to many designers. The temptation to use piles under every facility is great; detailing of plans is routine, quantity estimate is neat, and safe structural support apparently assured. Unfortunately, the rationale behind pile type selection, length, and allowable load, is usually based on peripheral factors such as local availability, outdated dynamic formulas or previous usage of certain pile types. Shallow Foundations represent the simplest form of load transfer from a structure to the ground beneath. They are typically constructed with generally small excavations into the ground, do not require specialized construction equipment or tools, and are relatively inexpensive. In most cases, shallow foundations are the most cost-effective choice for support of a structure. Some cost analysis show that spread footings are 50 to 65 percent cheaper than the alternate choice of pile foundation. Shallow Foundations (Spread Footing): Foundation movement studies in the past have shown that Spread Footings can easily tolerate differential settlements of 1 to 3 inches without serious distress. Recent studies have also shown that majority of settlement at bridge abutments occur during the construction of the foundations and placement of the soil backfill. Due to these facts geotechnical engineers usually tend to over-predict settlement of spread footings. This leads to the unnecessary use of a deep foundation instead of a spread footing.

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Fig 1: Spread Footing With Cantilever Stem wall at Bridge Abutment (Typical of TH610 construction) Instrumentation: Targets were mounted on footing and stem of spread footings. Mn/DOT surveyors took survey shots of targets during and after the construction process. Table 1, below, shows the comparison of predicted settlement and actual settlement from survey shots. The predicted settlement is based on Hough method and average value of Boussinesq and Westergaard, which utilizes the standard penetration test (SPT) values from the soil borings.

Fig 2: Seen here to the right, inside the red circle shapes, two Survey target points located on the stem of one of the abutments of pedestrian bridge.

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Table 1: Settlement prediction and surveyed data:

BRIDGE

Predicted Settlement Actual Settlement* Over -Prediction Of Settlement (Yes or No)

N. Abut (inches)

Pier (inches)

S. Abut (inches)

N. ABUT (inches)

PIER (inches)

S. ABUT (inches)

Pedestrian 2 1.5 2 < 0.25 < 0.25 < 0.25 YES Hemlock Lane

1.5 1 1.5 < 0.25 < 0.25 < 0.25 YES

Zacahary Lane**

1.5 1.5 1.75 < 0.25 < 0.25 < 0.25 YES

Revere Lane

2 1.5 2 < 1 < 1 < 1 YES

Jefferson** 1.5 1.5 1.75 < 0.25 < 0.25 < 0.25 YES *Settlement experienced by the beams and decks will be smaller than the indicated values; studies in the past have shown about 50% of settlement occurs before the beam and deck are set. **Construction of these brides is not complete and final settlement might be a little bit higher As shown in table 1, all the predicted settlement values are higher than the actual settlement measured at the site. It is also important to note that almost 50 to 60 % settlement occurs during the construction process before the beams are placed and deck is cast. Conclusion: More instrumentation programs should be implemented in the future to monitor settlement of spread footings in different types of soils. These results will be helpful in the future in the determination of foundation types. From the few instrumentation programs that Foundations unit implemented to date, it is evident that this will increase the use of spread footings in the future. As a result, this will reduce cost of some projects without compromising the standards of the structures.

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Hastings Design Build Bridge Load Testing

In the Summer and Fall of 2010, the Foundations Unit played an important role in the design and construction of the Hastings Design Build (DB) Bridge Project. As a key member of Mn/DOT’s oversight team, Rich Lamb participated in design reviews and general guidance for the new gateway structure into historic Hastings. In the Fall, the DB contractor (Ames-Lunda), performed a series of pile load tests to provide for a safe and economical foundation design and to meet the requirements of the contract. The tests were performed on two foundation

piles consisting of 42 in. open- ended steel pipe pile (with a 1 in. and 7/8 in. wall thickness) driven for the river piers. The contractor designed the pipe piles to be driven through loose to dense alluvial deposits (sands, silty sands and silty clays) to the top of bedrock, located at a depth of approximately 180 ft. below the river

Proposed Hastings Bridge

Soil/Rock Stratigraphy

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bottom. While bearing resistance for piles driven to rock is not typically a problem, pile load tests typically allow the foundation designer to prove out a higher capacity and thereby reduce the total number of foundation piles. In addition, load testing reduces the overall risk for the foundation system and allows the designer to use a smaller safety factor or in the case of Load and Resistance Factor Design, a higher resistance factor.

During pile driving (piles were driven with an APE D125 single action diesel hammer), the Contractor monitored the piles with the Pile Driving Analyzer (PDA) to assure the pile driving hammer was not overstressing the steel shells. Restrike tests were also performed to determine the redistribution of skin and toe resistance. Surprisingly, after only 1-2 days, both test piles showed a significant amount of setup, with a doubling of the skin resistance. Overall, the piles ended up with the following resistance distribution: Side Resistance 41-47% End Bearing 53-59%

After completing the driving of the test piles, the DB Contractor performed two axial and one lateral load tests utilizing the Statanamic load test method. Unlike conventional static load tests, the Statnamic method delivers a sudden force to the pile by launching a mass above the pile, effectively pushing down with enough force to move the pile. Utilizing Newtons 2nd and 3rd Laws of Motion, the pile moves downward with the same force as the mass moves upward; the force being defined as mass times acceleration (F=ma). To force the mass upwards, a special fuel is burned to generate gas pressure in a cylinder and ram. The

fuel type produces a smooth increasing force with venting. One can think of the load produced by this method as in impulse load that occurs over a time frame of ½ second or less. During the test, a data acquisition system records readings from a series gages

Driving Pier 6 Test Pile

Statnamic Test

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including a load cell, displacement transducers, accelerometers and embedded strain gages, and allows engineers to produce a load displacement curve. The main advantages of the Statnamic method is that the test can be performed quickly and does not require massive load frames and reaction pile to resist the loads. Statnamic tests are especially economical for river applications, where driving reaction piles and load frames is much more costly than for land applications. For our test piles on the Hastings Project, the contractor used a 5000 ton system with a 140 ton mass. The first axial test occurred on Friday, December 10 at the proposed Pier 10 (near north abutment). The gages measured a maximum load of 4100 kips (2050 tons) and a final vertical displacement of ½ in. This result exceeded the design load requirement of 2935 kips. The second test pile was driven at Pier 6, the western main span pier. This test pile was tested with the Statnamic

Pier 10 Statnamic Test

Pier 10 Statnamic Load-Displacement Graph

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method in both the axial and lateral direction. The axial test was performed on Friday, December 17th, again in the evening. The results for this test were very similar to the first one, with a maximum load of 4600 kips and a final displacement (set) of 0.25 inches. By comparison, the PDA with subsequent CAPWAP analysis showed significantly lower resistances for both test piles. The main reason for this is that the pile driving hammer did not have enough energy to mobilize the pile enough to realize a higher capacity. As one analogy, it is like hitting a big nail with a tiny hammer. The resistance of the material the nail is going through is limited to a certain extent by the energy put into the nail by the hammer. Testing Summary Pier 6 (1 in. wall) Pier 10 (7/8 in. wall) Pile Design Capacity (factored) 2640 kips (1320 tons) 2320 kips (1160 tons) LRFD Resistance Factor 0.8 0.8 Target Pile Design Capacity (nominal) 3300 kips 2900 kips PDA Capwap Initial Drive resistance (nominal) 3476 kips (blow #302) 3384 kips (blow #911) PDA Capwap Restrike resistance (nominal) (1-2 day setup)

3455 kips (blow #5) 3146 kips (blow #2) 3628 kips (blow #115)

Statnamic maximum resistance (nominal) 4650 kips* (1/4 in. displacement)

4100 kips* (1/2 in. displacement)

Structural capacity of pile 5220 kips 4580 kips

*Geotechnical nominal resistance greater than demonstrated with Statnamic axial load test. Based on equivalent static load-settlement curve, the nominal resitance of the structural section would likely govern. While the Statnamic tests showed that there is significantly more resistance available when driving these piles, the pile design capacities were limited by the allowable driving stresses associated with the contractor’s pile driving system. In other words, to avoid damaging the piles during installation, the piles had to be designed for somewhat lower capacities. The lateral load test was intended to simulate a vessel impact and help the designers determine soil properties for their design. For this test, the contractor used the same

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loading device, but in a horizontal application. The ram and piston were placed on a barge on a track system that would allow the system to recoil after the charge was set off. For this test, four different horizontal loads were applied to the top of the foundation pile, starting with 50 kips and ending with a maximum horizontal load of 125 kips. The pile top deflected from 3-12 in. during the tests.

Continued GIS Legacy Data Updating and GPS Process Improvement: Updating of older boring logs to electronic format, including computing UTM coordinates from historic stationing, continues as an on-going effort. We are also improving our GPS operations. CPT crews are now using higher precision antennas and we are now routinely using post processing and differential correction to provide sub-foot spatial precision (horizontal and vertical) for CPT sounding locations where possible.

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Pile Research Continues The second phase of the pile research is in full swing. Sam Paikowsky and Aaron Budge are working on assessing numerous dynamic pile driving formulas to determine which best fits Mn/DOT pile driving practices. Sam will analyze several formulas and determine a suitable phi factor based on reliability criteria. He is using a database of pile driving records from tests run all over the world. He is also using PDA/CAPWAP results from piles driven in Minnesota. The one element missing is static load testing from piles driven in Minnesota. Historically, Mn/DOT has not conducted many static load tests. Minnesota is not the only state interested in calibrating their dynamic pile driving formula. Neighboring states were contacted to discuss what we are each doing and determine if efforts could be shared. We held conference calls with Illinois, Iowa, and Wisconsin. These three states use dynamic formulas to control pile driving that are different from the one used by Mn/DOT and will be looked at as part of Mn/DOT’s research. A fourth state that was contacted, Ohio DOT, rarely uses a dynamic formula. Nearly all of their pile driving is controlled using PDA/CAPWEAP. Iowa is the only state that has conducted a significant number of static load tests. Sam’s database includes the pile load tests from Iowa, unfortunately most of those tests are on H-Pile, the predominant pile type used in Iowa. Mn/Dot drives mostly pipe pile. In order to provide more data from Minnesota and to provide valuable design data, several load tests have been performed or are planned for the Lafayette Bridge, Hastings Bridge, and Dresbach Bridge. We are also pursuing implementation dollars for conducting several load tests around the state to provide valuable data for further calibration of the Mn/DOT pile driving formula. We have a contract to design and construct a load frame that can be used and reused for conducting static load tests to help save on costs associated with future load tests.

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Grading Base and Aggregate Unit Light Weight Deflectometer In 2010, the LWD was placed into approximately 10 project proposals for acceptance of grading materials. While it appeared to be successful on a couple projects, it was removed from the requirements on most projects, because it provided inconsistent results. An evaluation project was started in 2010 to gather field data with the purpose of ascertaining whether a useable model could be developed for QA applications. The Grading and Base Unit are in the process of validating these models. Evaluation of the future implementation of the device will continue in 2011. Sonic Test Roller A research project to develop the Sonic Test Roller for grading acceptance is currently ongoing by Minnesota State University Mankato. In the future, the Sonic Test Roller may augment and/or replace the current test roller. The device attaches to the front axle of a conventional dump truck and continuously measures the deflection of the wheels into the grade. The data is stored and available for viewing on software currently under development. The software, when completed in 2011, will allow inspectors to view the deflection data collected in a plan view. The Sonic test Roller will be used on a variety of pilot projects around the state in 2011. The Grading and Base Unit is optimistic of its potential successful implementation.

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Continuous Compaction Control (CCC) MnlDOT had the following 2 new grading projects with CCC during 2010:

• SP 2801-80 TH16 (emulsion stabilized FDR) • SP 2771-38 (TH10 – ATC, in-place granular materials)

These projects, as well as previous projects, show the potential of CCC as a QC tool; however, additional examination is ongoing to evaluate QA implementation, as previous projects have not proven successful in this area. A TH 23 project (near Paynesville) will use CCC in 2011. A 2010 project, in Olmsted County, was specified for CCC but the equipment was pulled from the project because the system was not operable. Timely data management and analysis has been a significant obstacle to reaching the full potential with CCC since the construction of the initial projects in Minnesota. Each CCC compactor manufacturer has their unique software and generally it is not capable of completing the needed analyses. In addition, on-site inspectors need output that is easy to read and understand. To fill this need, MnDOT has partnered with the FHWA to fund a $150,000 consultant contract with The Transtec Group of Austin, Texas. Development of the software is currently underway with completion due in early 2011. We expect this tool to be a breakthrough development in the implementation of CCC.

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A Case Study: TH 67 “Granite Falls” Landslide- Emergency Remediation In the summer of 1998, pavement distress was noticed along TH 67, 1.1 miles east of the JCT with county road 44; the District contacted the Foundations Unit to have an inclinometer installed to monitor an embankment adjacent to Hazel Creek just west of an Indian Casino. The principal distress was to the roadway shoulder and half of the NW driving lane. Boring, T-100, was advanced in middle of the distressed area, and an inclinometer installed. A second boring, T101, was advanced nearby. The boring samples showed a mix of granular and soft plastic materials overlying mudstone. The slope displayed minor movements in subsequent years, but not enough to warrant designing a large scale construction project to remediate the highway embankment. The monitoring program continued through the fall of 2010 when a heavy rainfall swept across the southern portion of the state. Figure 1 shows the project area. Some erosion is evident in the photo on the outside bend of the meander between the creek and the highway. Figure 2 shows the pavement distress in 1999 when the inclinometer was installed and the distress in 2007 after the roadway had been patched several times. Fig 1: Hazel Creek runs just north of TH67; at the project location a meander in the stream has been slowly eroding the hillside below the highway.

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Fig 2: The pavement distress in 1999 continued to appear in roughly the same location in subsequent years (as seen in the photo from 2007, at right) after maintenance crews patched and overlaid the roadway. The distress always appeared limited to part of the NW driving lane. On September 23, 2010, many counties in SW Minnesota received three to eight inches of heavy rainfall. On October 3rd new roadway cracks were found by the District. These new cracks were generally further east than the cracks seen previously- in addition they extended across the entire roadway and encompassed a much larger area of pavement. Additional readings were taken on the inclinometer at T-100 and the Foundations Unit mobilized a CPT rig to the site to advance several lines of soundings across the distressed area. Figure 3 shows some of the slope scarping and the temporary one-lane traffic set-up around the distressed pavement.

Fig 3: The pavement distress was severe enough to restrict travel to one lane for a time until the roadway could be patched. Several significant scarps, fissures, and other failure features were observed in the slope.

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Fig 4: Several lines of CPT soundings were advanced to gain a better understanding of the site soils below the distressed area of the embankment. The soundings showed that the embankment material was very loose and had very low strength. The soils were also highly mixed and the stratigraphy was highly variable. Following the CPT investigation, a Geoprobe rig was mobilized to the site to sample at 3 specific locations in order to recover thin-walled (TW) samples for laboratory direct shear testing. In addition, an electrical resistivity geophysical survey was conducted along the north roadway shoulder to gain additional insight into the soil density, depth to bedrock, and site variability.

Fig 5: The electrical resistivity survey confirmed the CPT data: the embankment soils were generally silty and clayey and less dense than the roadway subgrade or underlying weathered rock materials.

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The inclinometer data showed that there had been an increase in movement in early 2009, but that a more significant amount of deformation occurred between September 9, 2010 and September 29 2010 at two depths along the inclinometer. A small movement was seen at a depth of about 26 feet, while a larger movement of about 1.5 inches was seen at a depth of 17feet.

Fig 6: T-100 inclinometer plots for the past 1.5 years

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Expedited Reporting and Recommendations: Based on the inclinometer data, lab testing, CPT soundings, and ER geophysical survey, it appeared that the highway embankment was in severe distress and that an inexpensive solution would not be cost effective in stabilizing the area until a more significant solution could be undertaken. The significant erosion along the slope made additional disturbance highly likely; during the investigation it appeared that the temporary pavement patch was undergoing new distress. The Foundations Unit prepared a report with 3 possible solutions and a general description of the costs/benefits/risks of each. A shallow reinforced earth ground improvement strategy, a lightweight fill option, and an aggregate column supported embankment [CSE] were proposed. Special attention was paid to the desire for a solution that was designable and constructible in the late fall- early winter of 2010. Column Supported Embankment Strategy: After several meetings and consideration, a aggregate column supported embankment and stabilization system (ACSESS) plan was adopted and a ‘performance specification’ design was developed collaboratively by the Willmar District and the Foundations Unit. The plan called for the roadway embankment to be supported by relatively tall columns, which in turn, would support a reinforced roadway embankment. At a pre-bid meeting and subsequent on-site discussions with interested contractors and the specialty ground improvement contractor, several concerns were raised and the special provisions were revised. After bids for the work were received, and further design work was conducted by the ground improvement contractor, Geopier, it was determined that there would be significant difficulty achieving the required factor of safety for long-term slope stability. The original bids were determined to be non-compliant (none met the required FS for the performance specification) and the District did not award the contract based on this design. After a review of the problems with the first design, new design was developed by the Foundations Unit (after the several original options and original CSE/ACSESS designs, the newest was denoted “Plan E”). This

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revision called for the aggregate columns to be shorter and moved from under the roadway embankment to the north where they would support a reinforced steepened slope (to be built using the Mn/DOT standard RSS plan). The reinforcement for the RSS was extended further back than required for slope stability to aid in the reinforcement and stiffening of the roadway embankment. Diagrams of the typical profile for the original design and the final design, “Plan E,” are shown in Figure 7, next page. Expedited Design, Plan Development, and Contracting: The project was fast-tracked at every step of the way; investigations, testing, reporting, and post-report discussions all came in quick succession. The foundations report was issued on October 12, 2010. The contract documents were prepared (including the project plans and special provisions) and then subsequently revised over the next month. After the second issue of the plans was sent out for bids, two contractors bid for the work. Notice to proceed was given for the Emergency Slide Repair SP 8707-89 on November 12, 2010. The price for the remediation was $847,146 with $350,000 for the aggregate column supported stabilization system (the columns), $117,000 for the RSS and the remainder for the excavation, roadway work, channel protection, mobilization, etc… Figure 8 shows the area after the pre-con meeting on November 16, 2010.

Fig 8: The roadway distress and temporary patch can be seen in this photo, just prior to the road closure for the construction work.

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Fig 7: Typical section 1 (top) shows the original plan where the roadway was to be supported on compacted aggregate columns. This plan was later determined not to have sufficient detail along the slope to ensure the columns and roadway would have adequate long-term stability. A new plan (typical section 2, bottom) was developed. The columns were relocated to a lower elevation and would now support the base of a reinforced steepened slope (RSS) which would provide improved slope stability and highway embankment support.

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Due to the exceptionally tight timeline a number of assumptions were made in the design process that needed to be validated by lab testing. Two additional borings were taken at the embankment toe once access to that area was available. Tests on the new samples were conducted as quickly as possible; some adjustments were needed during construction based on the new geotechnical information that was becoming available. Modifications were required to flatten the channel protection slopes in front of the RSS and the reinforcing within the RSS was doubled to accommodate for exceptionally high variability observed in the lab tests. The extra reinforcement ensures that an appropriate long-term factor of safety against compound failure (where a failure would occur both through the RSS and through native soils) is provided. The embankment was removed as soon as a telephone utility could be relocated. Shortly after the embankment excavation began, a slide occurred in the backslope; given the poor quality of the site soils this was not unexpected. Luckily, after this initial movement the site was generally stable. By early December, the installation of the rammed aggregate columns had begun and the base of the future RSS was being slowly and steadily improved. The contractor had just finished work on a RSS for the Paynesville Bypass project on TH 23, so they had familiarity with the construction, which likely provided a significant advantage in meeting the tight construction timeline. Figure 9 shows the installation of the columns through the poor site soils to the underlying weathered bedrock. The weather generally deteriorated as construction progressed. The contractor finished work in mid-December, just prior to a weekend of very cold temperatures and snow. The Foundations Unit made a significant effort to install two new inclinometers at the site (at the base of the RSS), working around scheduling and contractor conflicts. Lights were procured so that work could continue into the night on a Friday (the crews normally work 4 ten hour days, M-Th).

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Fig 9: The Geopier company equipment is seen here installing the rammed aggregate columns. The columns provide increased stiffness, shear reinforcing, and drainage.

Fig10: The aggregate columns have been installed and construction is now underway on the reinforced steepened slope (RSS). The river can be seen at left. A large portion of the project included channel protection. Although the slope in this area had been monitored for over a decade, the vast majority of the work to assess, design, plan, contract, and complete the site remediation occurred in less than 3 months- an astoundingly ambitious schedule, especially just before winter. This project was an extensive partnering effort between the Foundations Unit and a number of partners in District 8 (Willmar). Several graduate engineers on rotation in our office

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[who, unusually, were able to see a slope stability project from beginning to end] and field crew members on our staff deserve acknowledgement, as well as key District individuals for their contributions to SP 8707-89. Although the failure was sudden and severe, a good (although expensive) solution was developed using a variety of our latest geotechnical site investigation tools and tests. The final design addressed the exceptionally poor and variable site soils, site geometry and stratigraphy (making use of the relatively close weathered bedrock), hydraulic considerations, tight design and construction timelines, constructability, and the desire for a long-term solution at the site.

Fig11: The two new inclinometers, successfully installed to provide verification that the new design and construction has stabilized the slope and provides adequate roadway support. Hazel Creek and the (snow covered) channel protection can be seen at left, and the RSS at the center-right).