GR_23-18_MT_DOT_569(3)_Final_Geotechnical_Report.pdf

North of Moose Creek North October 2018

Table of Contents 1-i

Geotechnical Report No. GR 23-18

North of Moose Creek North

FINAL GEOTECHNICAL REPORT

MT DOT 569(3)

Deer Lodge County, Montana

October 2018

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Table of Contents i

TABLE OF CONTENTS

1 INTRODUCTION

1.1 Project Location

1.2 Scope of Project

1.3 Other Geotechnical Documentation

2 HIGHWAY COORIDOR SETTING

2.1 Topography, Drainage, and Vegetation

2.2 Climate

2.3 Geology

3 GEOLOGIC HAZARDS AND SITE SEISMICITY

3.1 Geologic Hazards

3.2 Site Seismicity

3.3 Liquefaction

3.4 Landslides

4 SITE CONDITIONS

4.1 Site ObservationS

4.2 Subsurface Investigation

4.3 Subsurface Profile

4.3.1 Road subgrade

4.3.2 California Creek Bridge

4.3.3 MSE Walls

4.3.4 Aquatic Organism Passage (AOP) Culverts and Embankment

ii Table of Contents

4.4 Groundwater

5 DESIGN RECOMMENDATIONS

5.1 Subgrade

5.2 Embankment Slopes

5.3 Cut Slopes

5.4 Embankment Suitibility

5.5 Subexcavation

5.6 Mechanically Stabilized Earth (MSE) Retaining Walls

5.7 AOP Culverts

6 CONSTRUCTION CONSIDERATIONS

6.1 Earth Work

6.2 Dewatering and shoring

6.3 California Creek Bridge Bypass

7 LIMITATIONS

8 REFERENCES

List of Figures iii

LIST OF FIGURES

Figure 1-1: Project Location Map

Figure 1-2: Vicinity Topographic Map

Figure 2-1: Excerpt from the Geologic Map of the Dillion 1°x 2°Quadrangle, Idaho and Montana

Figure 3-1: Quaternary Faults Map for the Site Vicinity

Figure 4-1: Aerial view of the landslide at Station 413+75

LIST OF TABLES

Table 2-1: Period of Record Monthly Climate Summary for Anaconda, Montana (240199)

Table 4-1: Boring Location Summary

Table 5-1: Approximate Relation Between Plasticity Index and Inherent Swelling Capacity (from Terzaghi, Peck, and Mesri (2009)) ........ Error! Bookmark not defined.

Table 5-2: MSE Wall Location and Design Summary

Table 5-3: Soil Parameters Used for MSE Wall Design

Table 5-4: Presumptive Bearing Resistance

APPENDICES

APPENDIX A

Site Photographs

APPENDIX B

Boring Location Plans

APPENDIX C

Descriptive Terminology for Boring Logs Boring Logs

APPENDIX D

Core Photographs

APPENDIX E

Laboratory Test Reports

Introduction 1

1 INTRODUCTION

This report provides the geotechnical investigation results, analysis, and final geotechnical recommendations for earthwork and retaining walls and construction considerations for the MT DOT 569(3) North of Moose Creek North project. Geotechnical recommendations in this report supersede previous recommendations from the Subsurface Investigation and Preliminary Geotechnical Recommendations, Geotechnical Memorandum GM 19-17, dated August 2017;

however, all geotechnical information regarding California Creek Bridge foundation is contained in California Creek, Final Foundation Recommendations Memorandum, GM 18-18, dated August 2018.

1.1 PROJECT LOCATION

This project is located on Montana State Highway 569, approximately 15 road miles south of Anaconda, Montana, in Deer Lodge County as shown in Figure 1-1 Project Location Map, and Figure 1-2 Vicinity Topographic Map. This project starts from the end of Montana Department of Transportation STPS-FLA 569-1(5)14 project constructed in 2014. The coordinates for the beginning and end of project are approximately 45.9636°, -113.0289° and 46.0027°, - 112.9869°, respectively (WGS84).

1.2 SCOPE OF PROJECT

The road provides access to the Beaverhead-Deer Lodge National Forest and Mount Haggin Wildlife Management Study area.

The proposed project includes reconstruction of existing paved surface to improve the driving surface, and improve vehicular safety by widening the roadway and improving horizontal and vertical curves. The anticipated design width is 26 feet, which includes two 12-foot lanes with 1-foot shoulders. The proposed plan includes areas of a vertical grade increase and decrease of up to 3 feet.

The project will also replace the existing bridge over California Creek that was built in 1940.

The existing bridge is 57 feet long with 3 spans on timber piles. The length of the proposed bridge is 83 feet and will accommodate two rows of closed end pipe piles are each abutment cap. The proposed bridge will be located on the same alignment but the grade will be raised by approximately 3 feet to allow for additional water flow with a riprap channel.

1.3 OTHER GEOTECHNICAL DOCUMENTATION

Geotechnical recommendations in this report supersede previous recommendations within GM19-17 when conflicts exist. Geotechnical information and foundation recommendations for California Creek Bridge are contained in GM 31-17 and GM 18-18. The following reports were previously prepared by WFLHD and are available by request:

2 Introduction

• Subsurface Investigation and Preliminary Geotechnical Recommendations Geotechnical, Memorandum, GM 19-17, dated November 2017. This report supersedes this memorandum for this project.

• California Creek, Preliminary Foundation Recommendations Memorandum, GM 31-17, dated December 2017.

• California Creek, Final Foundation Recommendations Memorandum, GM 18-18, dated August 2018.

Figure 1-1: Project Location Map

Figure 1-2: Vicinity Topographic Map

End of Project

Beginning of Project

Location of California Creek Bridge

Project Location

4 Highway Cooridor Setting

2 HIGHWAY COORIDOR SETTING

2.1 TOPOGRAPHY, DRAINAGE, AND VEGETATION

The general topography of the region consists of mountainous terrain between the Anaconda Range northwest of the project and Pioneer Mountain Range south of the project. The project is located in a relatively broad valley with the road generally traversing rolling terrain along the bottom of a U-shaped valley as it climbs from an elevation of about 6200 feet at the beginning of the project to about 6600 feet at the end of the project. Higher surrounding peaks extend to an elevation of more than 8000 feet.

The highway crosses the Continental Divide just north of the end of the project. There are three known named creeks crossing the highway: American, California, and Oregon Creeks, while numerous smaller creeks also cross the road. These three creeks eventually flow in to Deep Creek and Big Hole River.

Vegetation within the project consists of wetlands, floodplains, grassy meadows, and forested areas. Vegetation primarily consists of grasses, conifer trees, and wetland vegetation such as willows. Streams exhibit numerous beaver dams which cause the streams to be braided.

2.2 CLIMATE

The climate of the project site is greatly influenced by the surrounding mountain ranges. Table 2-1 summarizes average temperature ranges, precipitation, and snow depth measurements from the Anaconda, Montana weather station, located approximately 15 miles from the project.

Table 2-1: Period of Record Monthly Climate Summary for Anaconda, Montana (240199)

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual Average Max.

Temperature (F) 35.1 38.1 45.3 54.3 62.7 71.6 81.1 80.1 69.2 57.2 43.1 34.2 56.0

Average Min.

Temperature(F) 14.6 15.9 21.7 28.3 35.6 42.2 47.5 45.9 38.6 31.0 21.5 14.3 29.8

Average Total Precipitation (in.) 0.78 0.67 1.02 1.21 2.19 2.46 1.43 1.27 1.31 0.94 1.00 0.80 15.07

Average Total Snow Fall (in) 10.0 9.1 11.3 7.7 2.4 0.3 0.0 0.1 1.3 4.4 10.5 11.0 67.9

Average Snow Depth (in) 4 3 2 0 0 0 0 0 0 0 2 4 1

Notes:

1. Period of Record: 6/1/1894 to 6/2/2016

2. Lat. 46.13139, Lon. -112.95694, Elevation 5280 feet

3. Percent of possible observations for period of record: Max: Temp. 98.6% Min. Temp.:

98.6% Precipitation: 98.5% Snowfall: 98.3% Snow Depth: 96.6%.

4. Data from Western Regional Climate Center, Western U.S. Climate Historical

Summaries, Anaconda, https://wrcc.dri.edu/cgi-bin/cliMAIN.pl?mt0199, accessed September 14,2018.

https://wrcc.dri.edu/cgi-bin/cliMAIN.pl?mt0199

Highway Cooridor Setting 5

2.3 GEOLOGY

The native soil along the project alignment consist of alluvial deposits. The alluvial deposits are associated with the numerous drainages in the area, including Oregon Creek, California Creek, and American Creek. The surface soils are mapped within the project limits as Holocene alluvium (Qa). The alluvium is described as channel, flood plain, and alluvial fan deposits consisting of silt, sand, and gravel. Material interpreted to be fill was encountered in borings on or near the existing roadway and associated embankments.

The mapped bedrock along the project alignment is primarily the Tertiary-aged Bozeman Group (Tbz) (Ruppel et al, 1993); which is undivided basin-fill deposits consisting of but not limited to indurated tuffaceous sandstone and siltstone, limestone, marl, and pebble and gravel conglomerates. Deposits may also include Tertiary landslide deposits. The Bozeman Group typically has a veneer of residual gravel or eolian silt, and ranges in thickness from less than 9800 feet to approximately 15,000 feet.

Other types of bedrock that are mapped in the in the project area include undivided Upper and Middle Cambrian-aged sedimentary rocks (Cu); including but not limited to dolomite, limestone, shale, and sandstone, and the Middle Proterozoic-aged Missoula Group (Ym) which consists of sedimentary rock and metamorphic rocks of sedimentary provenance, including but not limited to sandstone, argillite, and quartzite.

Figure 2-1 shows an excerpt from the Geologic Map of the Dillion 1°x 2°Quadrangle, Idaho and Montana.

6 Highway Cooridor Setting

Figure 2-1:Excerpt from the Geologic Map of the Dillion 1°x 2°Quadrangle, Idaho and Montana, (Ruppel et al, 1993)

Location of North of Moose Creek North Project

Geologic Hazards and Site Seismicity 7

3 GEOLOGIC HAZARDS AND SITE SEISMICITY

3.1 GEOLOGIC HAZARDS

Geologic hazards can include active faults, liquefaction and related phenomenon, soft or subsiding ground, strong ground shaking, and landslides, among other natural hazards. Our search did not discover a published geologic hazard map for the vicinity. Based on the geologic mapping and the subsurface conditions encountered in our borings (discussed later in this report), it is our opinion that the relevant geologic hazards in the site vicinity include: active faults, liquefaction/lateral spreading, and strong ground shaking. These hazards are discussed further in the Site Seismicity section below.

3.2 SITE SEISMICITY

Information from the USGS Quaternary Fault and Fold Database for the United States website was used to locate nearby active faults. The closest mapped active fault is located about 50 miles from the project site. The five closest active Quaternary-aged faults are listed below:

• Lost River fault located approximately 120 miles south, age of <150 years

• Hebgen fault located approximately 118 miles southeast, age < 150 years

• Georgia Gulch Fault located approximately 50 miles southeast from the project; age <

15,000 years

• Beaverhead fault, 87 miles south of the project, age <15,000 years

• Mission Fault (southern terminus) is located approximately 105 miles north- northwest of the project; age <15,000 years

An active fault is defined as a near surface or shallow fault whose location is known or can reasonable be inferred and which has exhibited evidence of displacement in Holocene (recent) time (in the past 11,000 years)

According to the website, the Georgia Gulch fault, runs north to south near the site vicinity, as shown in Figure 3-1 below. The normal fault is described as 69.5 kilometers (42.3 miles) in length with 0 degrees strike and a northwest dip direction. The slip rate is reported to be in the 0.2-1 millimeters per year category, and the age is reported to be in the less than 15,000 years category.

The dashed line of the mapping website indicates that the fault location is inferred and the southwestern mapped end stops on the east side of Highway 89. The map literature indicates that the sole source data for the fault is from detailed mapping and reconnaissance studies of scarp morphology. No detailed studies, such as trenching, have been conducted.

8 Geologic Hazards and Site Seismicity

Figure 3-1: Excerpt from the Quaternary Faults and Folds Database map for the Site Vicinity (USGS)

3.3 LIQUEFACTION

Soil liquefaction is a phenomenon in which cohesionless soil deposits below the groundwater table lose a substantial amount of strength due to pore pressure generation resulting from earthquake strong ground shaking (Kavazanjian, 2011). Soils that were encountered below the water table at the site were interpreted to be residual Tertiary-age bedrock that would not be susceptible to liquefaction.

3.4 LANDSLIDES

The term landslide is often defined as the movement of rock, debris, or earth down a slope.

Landslides can also be further defined as flows, slides, falls, topples, and spread. Often landslides can be triggered by precipitation, groundwater, weathering, cuts in soil or rock, concentrated water sources, river erosion, reactivation of ancient landslides, and earthquakes. Their velocity of travel can occur very rapidly to extremely slow (less than 1-foot every 5 years) (Highland, 2008).

Project Area

Lost River Fault

Hebgen Fault

Site Conditions 9

4 SITE CONDITIONS

4.1 SITE OBSERVATIONS

Site observations were made during three site visits conducted between July 2016 and June 2017. At that time, the road surfacing appeared to be in good condition considering the age of the pavement structure. There are areas of recent pavement patching ranging in length between 30 feet to several hundred feet long. In a discussion with Mr. Wendt, Anaconda-Deer Lodge County Maintenance Supervisor, these areas of recent pavement patching are generally due to either pavement breaking up and requiring subexcavation or embankment slope failure.

Soil observed in cuts along the alignment consisted mostly of clay with sand and gravel with some cobbles and occasional boulders. Natural slopes surrounding the road, outside of the cut slopes and embankment slopes, are generally no steeper than about 12 degrees (about 1V:5H).

Towards the end of the project natural slopes are slightly steeper. Cut slopes within the project except for the cut slope starting at station 413+75, appear stable with a slope angle of about 26 degrees (about 1V:2H). Although some of these slopes are poorly vegetated.

Between stations 413+75 and 418+00 (gps coordinates on the road are respectively, 45.9841°N, -113.0083°W and 45.9859°N -113.0064°W [WGS84]) the road crosses a landslide.

Based on field observations, the landslide is interpreted to be slow-moving. The road surface is narrower in this section and the road centerline has a slight offset towards the right (downslope).

Mr. Wendt stated the Road Maintenance Department reestablishes the ditch line periodically in this section and adds asphalt patching to reestablish the roadway width. Tension cracks in the pavement were not seen. Pavement distress is somewhat more pronounced than average within this project.

During June 2017 site visit, a cursory field reconnaissance was conducted. The upper section of the suspected landslide was accessed from the quarry off Dry Creek Road. A head scarp was seen approximately 1700 horizontal feet up the slope from the road. A defined lateral scarp was also seen along the western edge the slide. At this time, the eastern extent of the landslide was not explored. Springs were noted along the western limits of the slide. The middle and lower (below the road) sections of the slide were accessed from the road. The terrain exhibits hummocky characteristics with shallow channels directing surface water flow towards each lateral extent. Figure 4-1 identifies Dry Creek Road running generally parallel to Highway 569.

It is interpreted that Dry Creek road is an abandon 14-foot wide gravel road constructed prior to Highway 569. Remnants of ditch lines and dry laid stone walls are present.

Figure 4-1 shows an aerial view of the landslide at Station 413+75. The top red line is the approximate location of the head scarp. The yellow dashed line is the interpreted limits of the active landslide and the orange dash-dot line is the interpreted limits of a larger mass, that extends beyond the aerial view, that may or may not be active. The blue circles represent area of springs noted during the June 2017 site visit.

10 Site Conditions

Figure 4-1: Aerial view of the landslide at Station 413+75

4.2 SUBSURFACE INVESTIGATION

The geotechnical investigation for this project consisted of a site reconnaissance, nine subgrade borings and six test borings at a proposed bridge, embankment widening, and wall locations.

The subgrade borings are generally located every ½-mile along the existing alignment, alternating in the center of each lane. Subgrade borings were advanced with a 12-inch outside diameter (O.D.) solid stem auger and a 14-inch flat profile auger bit to depths ranging between 4 to 10 feet. In all the subgrade borings except for SG17-09, a standard penetration test (SPT) was performed after the subgrade auger was removed. Subgrade boring SG17-07 was advanced with an 8.25-inch O.D. hollow stem auger between a depth of 5 feet and 10 feet.

Subgrade borings are denoted with the prefix, SG. Deeper test borings were advanced with an

Quarry off Dry Creek Road

Site Conditions 11

8.25-inch O.D. hollow stem auger and HQ3 wireline coring system. These test borings are denoted with the prefix, BH.

Bulk samples of subsurface materials were obtained in the subgrade borings from each soil layer. In the BH borings, a 2-inch O.D. and 3-inch O.D. split spoon sampler was used at regular intervals. Due to the proximity to BH17-01, regular split spoon sampling commenced in BH17- 01A at a depth of 20 feet.

The first phase of the subsurface drilling investigation was completed in May 2017 by SK Geotechnical from Billings, Montana. Diedrich D-120 truck-mounted drill rig advanced borings SG17-01 through SG17-08 and BH17-01. Haz-tech Drilling, Inc., from Meridian, Idaho, performed the second phase of the subsurface investigation in June 2017. A CME 85 truck-mounted drill rig advanced borings SG17-09 and BH17-01A through BH17-05. Table 4-1 shows the Boring Location Summary.

Table 4-1: Boring Location Summary

Boring No. Station Off-set (ft) Depth (ft.)

BH17-01 385+80 6.5 LT 44.5

BH17-01A 385+59 6.5 LT 100

BH17-02 386+55 6.5 RT 100

BH17-03 360+75 12 RT 51.5

BH17-04 387+75 12 RT 26.5

BH17-05 438+50 11.5 LT 50.5

SG17-01 316+00 6 LT 6.5

SG17-02 343+00 5 RT 6.5

SG17-03 364+75 4 RT 4.8

SG17-04 389+75 3 LT 6.5

SG17-05 417+00 4 RT 6.5

SG17-06 443+00 6.5 LT 6.5

SG17-07 471+50 6 RT 11.5

SG17-08 492+500 6 LT 6.5

SG17-09 395+00 6 RT 5

Selected soil samples from the test and subgrade borings were submitted to the Western Federal Lands Highway Division (WFLHD) Materials Laboratory for routine index testing. The following is a list of tests that were completed on the selected soil samples and the standards that were followed:

12 Site Conditions

• Particle Size Analysis - AASHTO T 88,

• Atterberg Limits - AASHTO T 89 /T 90,

• Soil classification -AASHTO M 145/ASTM D 2487,

• Apparent Specific Gravity – AASHTO T 100,

• Natural moisture content - AASHTO T 265,

• R-Value at 300 PSI Exudation (AASHTO T 190)

• Resistivity – AASHTO T 288,

• pH – AASHTO T289.

Selected samples were transported to Ag-Source Laboratories for sulfate and chloride testing.

The following list of tests that were completed and the standards that were followed:

• Water-Soluble Sulfate Ion Content Analysis in Soil - AASHTO T 290,

• Water-Soluble Chloride Ion Content Analysis in Soil - AASHTO T 291

The results of the soil index tests were used to classify the samples according to the Unified Soil Classification System (USCS). The USCS is reported on the laboratory test reports and boring logs.

Project boring logs, containing logs for both the subgrade borings and the deeper borings are contained in Appendix C. Appendix D contains the core photographs from borings BH17-01, BH17-01A, and BH17-02. Laboratory test reports are contained in Appendix E.

4.3 SUBSURFACE PROFILE

4.3.1 ROAD SUBGRADE

The subgrade (SG) borings encountered 3.5 to 7 inches of asphaltic concrete pavement.

Borings BH17-03 and BH17-05 encountered similar thicknesses of asphaltic pavement. Borings BH17-01, BH17-01A, and BH17-02, drilled behind the existing bridge abutments, encountered asphaltic pavement between 12-inches and 12.5-inches. This is interpreted due to maintenance patches that have been placed due to bridge approach settlement.

In general, the subgrade borings encountered poorly-graded sand with gravel, well-graded gravel with sand and cobbles, and clayey, silty sand with gravel ranging in depth between 1.2 to

4.8 feet below the pavement surface underlying the asphaltic pavement. This granular layer appears to be thicker in subgrade borings SG17-01, -02, -03, and -04 compared to the other subgrade borings. Underlying the granular layer includes clayey sand, clayey gravel, gravelly lean clay, fat clay, and organic clay.

4.3.2 CALIFORNIA CREEK BRIDGE

Borings BH17-01 and BH17-01A are located at the west end of California Creek Bridge and boring BH17-02 is located at the east end of the bridge. Soils encountered in the embankment

Site Conditions 13 include sand and sandy lean clay. Near stream elevation wet, loose, sand and medium dense silty gravel was encountered. Starting at about 12.5 feet in boring BH17-01 and 18 feet in BH17-02, highly to completely weathered interbedded shale and sandstone was encountered.

The residual soils from these materials consist of hard to stiff, fat clay and sandy fat clay, as well as medium dense to very dense silty sand with gravel, and clayey sand with gravel. Artesian groundwater conditions were observed in all three borings at about 38 feet below ground surface. Corrected (N1)60 values range from 12 to 94 blows per foot (bpf) in BH17-01, 21 to 49 bpf in BH17-01A, and 6 to 92 bpf in BH17-02.

4.3.3 MSE WALLS

Boring BH17-04 is located east of California Creek at station 387+75 for a proposed retaining wall location. From the ground surface to a depth of 7 feet the subsurface material consists of very loose clayey sand with organics. Medium dense to loose, sandy gravel underlies the clayey sand between the depths of 7 feet and 9.5 feet. Underlying the sandy gravel is a layer of loose to medium dense, clayey sand between the depths of 9.5 and 14.5 feet. Starting at about

14.5 feet, highly to completely weathered sandstone was encountered to termination depth of

26.5 feet. The residual soils from the completely weathered sandstone consist of medium dense to very dense clayey sand with gravel and sand with silt. Corrected (N1)60 values range from 4 to 100 blows per foot (bpf).

Boring BH17-05 is located at station 438+50. This boring was drilled for a MSE wall. Gravelly clay with sand was encountered between the bottom of the base course and a depth of 4.5 feet.

Underlying the gravelly clay is clayey sand with gravel between the depths of 4.5 feet and 9.5 feet. Clayey gravel with sand underlies the clayey sand to a depth of 17 feet. Highly to moderately weathered quartzite underlies the clayey gravel between the depths of 17 feet and

50.5 feet. Corrected (N1)60 values range from 7 blows per foot (bpf) to refusal.

4.3.4 AQUATIC ORGANISM PASSAGE (AOP) CULVERTS AND EMBANKMENT

Boring BH17-03 is located on an embankment slope that crosses American Creek at Station 360+75, where a 1-foot grade raise is proposed. This boring was terminated at a depth of 51.5 feet below ground surface. From the ground surface to a depth of 7 feet the subsurface material consists of loose to very loose clayey sand. Underlying the clayey sand is soft to firm, clay with sand between the depths of 7 feet and 16.3 feet. Wet organic clay underlies the clayey sand between 16.3 feet and 17 feet. Underlying the organic clay is dense gravel with sand, grading to sand with gravel between the depths of 17 feet to 22 feet. Interbedded layers of completely weathered to highly weathered claystone and siltstone underlie the gravel and sand layers between the depths of 22 feet and 51.5 feet. The residual soils from the completely weathered layers consist of medium dense to dense silty sand. Corrected (N1)60 values range from 6 to 65 blows per foot (bpf).

4.4 GROUNDWATER

Groundwater was encountered in all three borings at California Creek, BH17-01, BH17-01A, and BH17-02 between 7 and 8 feet below the ground surface, which is close to the elevation of

14 Site Conditions

California Creek. An artesian groundwater condition was also encountered in these three borings about approximately 39 feet below ground surface. At the end of drilling the artesian water reached about 2 feet above the ground surface with a rate of flow about 5.8 and 5.0 gallons per minute in borings BH17-01A and BH17-02, respectively. The rate of flow was not measured in boring BH17-01.

Groundwater was also encountered in boring BH17-03, BH17-04, and BH17-05 at approximately 16 feet, 7 feet, and 37.5 feet, respectively, below the roadway surface.

Active springs were noted near station 400+00 in the left ditch line, station 416+00 in the left cut slope, 472+00 in the left cut slope, and 493+00 left cut slope.

Design Recommendations 15

5 DESIGN RECOMMENDATIONS

The following are recommendations that were made to the design team for incorporation into this project. Please note that if there are any discrepancies between the recommendations listed within this report and the information presented in the plans, the information in the plans takes precedence. The signatories of this report should be contacted for any discussion/information of any discrepancies.

5.1 SUBGRADE

Based on the subgrade borings the existing road surfacing section is supported on a layer of fill measuring 0.8 feet to 4.5 feet thick generally consisting of poorly-graded sand and well-graded gravel material with varying amounts of silt. Beneath this fill soft/loose, clay deposits were encountered in many of the borings. These fine-grained soils will not support construction earth moving equipment. Any excavation into the existing base section is perceived to have a very high risk of exposing weak subgrade soils that will not support construction equipment without costly subexcavation and replacement. Therefore, grades should be raised as recommended below to allow for construction of a stable embankment and surfacing section.

Due to the granular material encountered in subgrade borings BH18-01, 02, and 03, the Materials and Geotechnical Groups agreed to allowing the reduction of the road profile starting at the BOP to about Station 382+50 to improve vehicle sight distance. Soils encountered in subgrade borings were primarily granular to a depth of about 4 feet. Extreme care should be exercised during reconstruction of this section. If subgrade conditions change to a fine grain soil WFLHD Geotechnical Group should be contacted.

In areas where the alignment is over existing, the grade should be set so the new pavement section (asphaltic concrete and base course) is entirely above the existing surfacing section. In areas where the alignment is off existing alignment, the grade should be set so the bottom of the surfacing section is at least 18-inches above the existing ground elevation.

The existing roadway width varies from 21 to 24 feet throughout this project. The proposed plan is to construct a uniform roadway width of 26 feet. All six of the deeper borings (BH17-01 through 05) were drilled near the edge of the pavement. These borings indicate the existing pavement substructure (base materials) is potentially thinner than that same substructure encountered in the subgrade borings. The soils in the top 5 feet below the pavement surface and in the shoulder are very loose/soft. There is a risk that the proposed pavement section will be constructed on less than desirable subgrade materials. Risks include difficult earthwork conditions, differential settlement, and pavement distress in the pavement section construction off the existing pavement section. It is recommended to verify compaction requirements are met near the edge of the proposed road subgrade prior to placing the base coarse.

The liquidity index (LI) of fine-grained soil is an indicator of how the soil will behave upon disturbance. A LI value less than 0 indicate the material will behave as a semi-plastic or solid

16 Design Recommendations material. LI between 0 and 1 indicates the natural moisture content is between the plastic limit and liquid limit. LI values greater than 1.0 indicate the material will behave like a fluid when disturbed. LI values from the soil samples tested range from less than 0 to 0.2. In our experience, LI values greater than 0.3 result in rutting and pumping of subgrades when operating conventional earth moving equipment and trucks. If the material becomes wetted, such as with a rain event, the fine-grained soils present throughout the project are sensitive and may lose significant strength when disturbed.

There are numerous springs along the project alignment that can be seen within the cut slope and ditch line. Generally, in the areas of the springs and wet ditches the condition of the pavement exhibits more distress. Between Station 477+40 and the EOP exhibits a higher concentration of wet ditches and slopes. Some clays react to water ingress resulting in a seasonal volumetric increase of the soil. Volume increase within the subgrade can result in embankment failures and poor pavement performance. Using values obtained from Modified Activity Index, Am, and the clay fraction of a soil, Seed et al. (1962) developed a swell potential classification of clay soils. The classification rated the swell potential from low, medium, high, and very high with a swell potential of dividing line of 1.5 percent between low and medium, 5 percent between medium and high, and 25 percent between high to very high. Based on this classification method, samples from the borings BH17-01 through 05 fell into the range of low to very high swell potential.

Samples tested from the subgrade borings did not include a hydrometer gradation analysis;

therefore, a clay fraction was not determined for the subgrade samples. A relationship between plasticity index and inherent swelling capacity of clays, also from Seed et al. (1962), was included in Soil Mechanics in Engineering, Terzaghi, Peck, and Mesri (2009) and is shown in Table 5-1.. Based on this literature, soils tested from subgrade samples also exhibit swelling tendencies.

Table 5-1: Approximate Relation Between Plasticity Index and Inherent Swelling Capacity (from Terzaghi, Peck, and Mesri (2009))

Plasticity Index Inherent Swelling

Capacity 0 - 10 Low

10 - 20 Medium 20 - 35 High

35 - Very High

Discussions between WFL Materials, Geotechnical, Highway Design, and Project Management Groups determined it was beyond the scope of this project to increase the overburden pressure on the clay material. A class 1, non-woven, separation-stabilization geotextile is recommended to be placed between the subgrade and base course for the entire project. As stated previously the pavement exhibits more distress in areas near springs and wet ditches. A stabilization geogrid is recommended to be added on top of the separation-stabilization geotextile between Station 477+40 and the EOP.

Design Recommendations 17

5.2 EMBANKMENT SLOPES

Based on the March 2017 cross sections the design includes areas of embankment widening and/or grade raise. In general, the existing embankment slope ratios range between 1V:3H to 1V:4H with a few areas with embankment slope ratio of 1V:2H. embankment fills, up to 23 feet vertical measured from the proposed toe to the road surface, may exhibit post-construction cracking and settlement of the pavement on the outboard side. Embankment widening using sliver fills should be avoided. Minor alignment shifts to catch at the crest, or by adding sufficient width in combination with flatter fill slopes to allow embankment construction with conventional earthmoving and compaction equipment is recommended. Embankment slopes 1V:2H or flatter are recommended.

Subexcavate any soft or unsuitable material prior to placing embankment material. Class 1 separation-stabilization geotextile should be placed between the fill material and existing embankment material. Extend the geotextile on top of the subgrade towards centerline 5 feet beyond the transition of the existing embankment and the new embankment. Benches should be cut into the existing embankment slopes steeper than 1V:3H prior to placing the geotextile and new embankment material.

5.3 CUT SLOPES

Based on cross sections dated March 10, 2017 existing cut slopes ratios are generally range between 1V:5H to 1V:2H in soil and range between 3 and 20 feet high. The proposed cuts range in heights between 5 and 30 feet. Do not cut slope steeper than existing cut slopes within the same area.

It is interpreted that an active landslide crosses the road between stations 413+75 and 418+00 but historically the landslide has not caused significant damage or distortion of the road. The road appears to be located near the toe of the landslide. It is recommended to raise grade through this section and avoid any type of roadside cuts on the uphill (west) side of the road.

Any cuts in to the left slope may accelerate the landslide and result in roadway damage. In addition, a riprap lined ditch along the left side may help hold the ditch open. At a minimum, the current grade raise and existing cut is expected to result in the cut slope moving toward the road at is current rate and the continuing loss of the ditch line.

Landslide mitigation is outside of the scope of this project; therefore, a mitigation design is not provided for this project. However, based on discussions with Maintenance personnel the landslide is not currently causing significant roadway damage. Following our recommendation to raise grade will reduce the risk of future landslide movement impacting the road.

5.4 EMBANKMENT SUITIBILITY

The soils from the cut areas will be a mixture of clayey sand, silty sand, sandy clay, and fat clay soils with AASHTO Classifications of A-2-7 and A-6/A-7. Excavation is expected to consist of mostly these soils. These soils do not meet the specification for unclassified borrow as stated in Section 704.06 of the Standard Specifications for Construction of Roads and Bridges on Federal Highway Projects, FP14. It is highly likely that these soils will not be suitable for embankment at

18 Design Recommendations the in-situ moisture contents. The soil from the cuts are anticipated to require time, favorable weather conditions (dry and hot), and a significant amount of disking, windrowing, and working of the soil to adequately dry it to a moisture content suitable for compaction. Tracked equipment should be considered by the contractor. The soils will rut and shove under conventional rubber-tired construction equipment when moisture contents are above optimum and the potential to get stuck is perceived to be high.

5.5 SUBEXCAVATION

In order to match existing grade at the end of the project and to remove unsuitable subgrade material a subexcavation is recommended between Station 493+00 and 495+00. Excavate 2 feet below the planned top of subgrade daylighting the excavation on the side. Place Class 1 Type C, non-woven, separation-stabilization geotextile along the bottom and sides of the excavation. Install stabilization geogrid on top of the geotextile and backfill with select borrow.

Do not excavate below the ditch elevation. Decrease the depth of the subexcavation so it is above the bottom of the ditch. Grade bottom of subexcavation to drain.

5.6 MECHANICALLY STABILIZED EARTH (MSE) RETAINING WALLS

A retaining wall is necessary between Stations 386+69 and 389+81 to avoid impacting California Creek. A retaining wall is necessary between Stations 437+50 and 443+10 due to right of way clearances. MSE walls for this project will utilize typical welded wire fabric (WWF) facing elements with 18-inch vertical lifts. The WWF facing elements will have a gabion rock backfill with no hardware cloth or geogrid allowed at the face. Install galvanized wire facing elements treated with a weathering agent to reduce the brightness of the galvanization for reduced visual impact. Long-term stability of the WWF facing will be mitigated by the internal wrap of the geogrid reinforcement. Table 5-2 shows the approximate MSE wall locations.

The design software MSEW 3.0 by ADAMA Engineering, Inc. was used with the AASHTO LRFD Bridge Design Specifications analysis method for external, internal, and global stability analysis of the MSE walls as wrapped face geogrid walls. Each current MSE wall location was analyzed for the estimated grid length that would satisfy global stability of the retaining structure. A summary of the soil parameters used for the MSE wall design are shown in Table 5-3. The design was completed assuming the geogrid reinforcements with a nominal long-term design tensile strength of at least 4000 lb./ft.

Table 5-2: MSE Wall Location and Design Summary

Wall No. Station Start Station End Approx.

Length

(ft.)

Approx. Max.

Height (ft.)

1 386+69 389+82 313 10.5 2 438+00 442+92 492 10.5

Design Recommendations 19

Table 5-3: Soil Parameters Used for MSE Wall Design

Property Units Foundation Soil

Retained Soil

Reinforced Soil

Effective Unit Weight - Wall 1 pcf 63 125 115

Friction Angle – Wall 1 deg 34 34 34

Cohesion – Wall 1 pcf 0 0 0

Effective Unit Weight – Wall 2 pcf 125 125 125

Friction Angle – Wall 2 deg 34 34 34

Cohesion -Wall2 pcf 0 0 0

Wall 1 does not include an underdrain system at the heel of the wall due to the elevation of the bottom of the wall relative to the creek elevation. The bottom two layers of the reinforcement will be backfilled with open-graded backfill material. This will allow the material to drain quickly.

Start Wall 1 so the facing basket is butted against the end of the concrete wing wall. Provide reinforcement wraps similar to the facing wraps along the full reinforcement length perpendicular to the wall facing at the beginning of the wall. The facing wraps may need to extend back station, behind the wingwall, to reduce the possibility of uncontained wingwall backfill soil from piping out between the two walls.

Wall 2 will utilize a geocomposite underdrain system at the heel of the wall. The geocomposite sheet drain should be placed with 40 percent coverage of the wall excavation cut slope. If areas of active seepage are encountered during construction, these seepage areas should be modified to include 100 percent coverage with the geocomposite sheet drains.

Provide returns at ends of walls where they terminate into a fill slope and extending perpendicular into the wall a minimum of 4 feet. Embed the returns so at least 2 feet of return is below the surface of the slope.

5.7 AOP CULVERTS

AOP culverts are located at Station 360+19 and Station 421+98. The AOP culvert at Station 360+19 will replace two 48-inch culverts with one precast reinforced concrete box with dimensions of 14 feet span and 8 feet rise. The AOP culvert at Station 421+98 will replace two 48-inch culverts with one 120-inch diameter pipe culvert. OSHA Type C soils will be encountered in the excavations at both culvert locations. The excavations at these locations will be in excess of 20-feet in depth from the existing grade, making the extent of temporary cuts very large. Temporary shoring may be necessary. Groundwater was encountered in BH17-03 at American Creek above the foundation elevation; however, a subsurface investigation was not performed for the culvert at Oregon Creek. Dewatering is anticipated to be required for both culvert replacements. Factored presumptive bearing resistances for the soil at of each AOP were taken from Table C10.6.2.6.1-1 (AASHTO) are listed below in Table 5-4.

20 Design Recommendations

Table 5-4: AOP Culverts Factored Presumptive Bearing Resistance

AOP Culvert Factored Presumptive Bearing

Resistance (ksf) American Creek 5.0

Oregon Creek 5.0

Construction Considerations 21

6 CONSTRUCTION CONSIDERATIONS

6.1 EARTH WORK

Based on the subgrade borings the existing road surfacing section is supported on a layer of fill measuring 0.8 feet to 4.5 feet thick generally consisting of poorly-graded sand and well-graded gravel material with varying amounts of silt. Beneath this fill soft/loose, clay deposits were encountered in many of the borings. These fine-grained soils will not support construction earth moving equipment. Any excavation into the existing base section is perceived to have a very high risk of exposing weak subgrade soils that will not support construction equipment.

6.2 DEWATERING AND SHORING

Groundwater is likely to be encountered in the MSE wall excavations and in the excavations for the culvert replacements at American and Oregon Creeks. A major challenge for this project will be the constructability of MSE wall in close proximity of California Creek and deep excavation for the culvert replacements below surface water elevation. The wall foundation at California Creek is expected to be founded on clayey sand and gravel. The wall foundation at Station 438 is expected to be founded on clayey sand and gravel. The culvert at American Creek is expected to be founded on gravel and sand. There is no subsurface information the culvert replacement at Oregon Creek but may be similar to American Creek.

In addition, right of way is not sufficient to divert traffic around the culvert replacement;

therefore, shoring may be needed to pass traffic at American and Oregon Creeks culvert replacement sites and at the wall starting at Station 438+00. Temporary slope angles and/or the need for shoring for excavation of the MSE wall foundations is the responsibility of the Contractor based on the conditions encountered, traffic/equipment loading above the temporary cut, and other factors under their control during construction.

6.3 CALIFORNIA CREEK BRIDGE BYPASS

A temporary bypass is required during construction of the bridge at California Creek. Cut the vegetation flush with the ground surface and place a Class 1, woven, separation-stabilization geotextile prior to embankment construction. The geotextile should extend to the proposed edge of embankment toe.

22 Limitations

7 LIMITATIONS

This report was prepared to provide subsurface investigation results and geotechnical recommendations for the proposed highway project. Professional judgments and recommendations are presented in this report. They are based partly on evaluation of the technical information gathered and partly on the Geotechnical Team’s general experience with subsurface conditions in the area. It should be noted the borings might not represent potentially unfavorable subsurface conditions away from the borings. The observed water levels and/or conditions indicated on the logs are as recorded at the time of the exploration. The water levels and/or conditions may vary considerably, with season/time, changes in climate, rainfall, and other factors and are otherwise dependent on the duration of, and methods used in, and interpretations made from the exploration program.

If soil conditions are encountered during construction that vary from those discussed in this report, or if design loads, project stationing, and/or configurations change, the WFLHD Geotechnical Team should be notified immediately in order to evaluate what effects, if any, the changes have on the recommendations contained in this report. The recommendations presented in this report are applicable only to this specific site. These data are not to be used for other purposes.

Questions regarding this report should be addressed to Diann Morehouse, WFLHD Geotechnical Engineer, at (360) 619-7609, or diann.morehouse@dot.gov.

mailto:diann.morehouse@dot.gov

Limitations 23

GEOTECHNICAL REPORT NO. 23-18

FINAL GEOTECHNICAL REPORT

North of Moose Creek North

MT DOT 569(3)

Deer Lodge County, Montana

Prepared by: _________________________________________ Diann Morehouse, Geotechnical Engineer

Reviewed by: _________________________________________ Brian Collins, Sr. Geotechnical Engineer

Approved by: _________________________________________ Nathan Jenks, Supervisory Geotechnical Engineer

24 References

8 REFERENCES

AASHTO LRFD Bridge Design Specifications, Seventh Edition (2014 with 2015 and 2016 interim revisions) American Association of State Highway and Transportation Officials, Washington, D.C.

Highland, L.M. and Bobrowsky, P., (2008) The Landslide Handbook- A Guide to Understanding Landslides, Circular 1325, U.S. Geological Survey, Reston, Virginia

Ruppel, E.T., O’Neill, J.M., Lopez, D.A., Geologic Map of the Dillion 1°x2° Quadrangle, Idaho and Montana, Miscellaneous Investigation Series, Map I-1803-H, U.S. Geologic Survey and U.S. Department of the Interior.

Kavazanjian, and others (2011), LRFD Seismic Analysis and Design of Transportation Geotechnical Features and Structural Foundations, GEC No. 3, FHWA-NHI-032, National Highway Institute, U.S. Department of Transportation, Washington, D.C.

Samtani, N.C., Nowatzki, E.A., (2006), Soils and Foundations Reference Manual, FHWA-NHI-06- 088, National Highway Institute, U.S. Department of Transportation, Washington, D.C.

Terzaghi, Peck, and Mesri, (2009), Soil Mechanics in Engineering, 3rd Edition, John Wiley & Sons, Inc. New York.

U.S. Geological Survey, USGS Earthquake Hazards Program website, 2008 Interactive Deaggregations, http://geohazards.usgs.gov/deaggint/2008/, accessed December 2014

U.S. Geological Survey, Quaternary Fault and Fold Database for the United States, accessed September 14, 2018, from USGS web site: https://earthquake.usgs.gov/hazards/qfaults/

Western Regional Climate Center (2018), Cooperative Climatological Data Summaries, Anaconda, Montana (240199): https://wrcc.dri.edu/cgi-bin/cliMAIN.pl?mt0199, accessed September 14, 2018.

https://earthquake.usgs.gov/hazards/qfaults/ https://wrcc.dri.edu/cgi-bin/cliMAIN.pl?mt0199

APPENDIX A

Project Pictures

Picture A-1: SG17-01

Final Geotechnical Recommendations Page A 2

Picture A-2: SG17-02

Picture A-3: SG17-02

Final Geotechnical Recommendations Page A 3

Picture A-4: SG17-03

Picture A-5: SG17-03

Final Geotechnical Recommendations Page A 4 October 2018

Picture A-6: SG17-04

Picture A-7: SG17-04

Final Geotechnical Recommendations Page A 5 October 2018

Picture A-8: SG17-05

Picture A-9: SG17-05

Final Geotechnical Recommendations Page A 6 October 2018

Picture A-10: SG17-06

Picture A-11: SG17-06

Final Geotechnical Recommendations Page A 7 October 2018

Picture A-12: SG17-07

Picture A-13: SG17-07

Final Geotechnical Recommendations Page A 8

Picture A-14: SG17-08

Picture A-15: SG17-08

Final Geotechnical Recommendations Page A 9 October 2018

Picture A-16: SG17-09

Picture A-17: SG17-09

APPENDIX B

Boring Location Plan View

P O

T

.1

O f f s e t= 0

.0

R T

S ta .= 3

+0

.9

+3.5

3%

,2

.8

,2

.7

+3.8

0%

200' VC

K = 695

,2

.9

500' VC

K = 167

SSD = 610'

+3.8

0%

GPS

F4909

CP

E4909

BEGIN PROJECT

N

Line to be constructed Slopes stake limits

Slopes stake limits

Existing ground

Profile grade

Profile grade

Existing ground

El=6218.84

E=1071735.55

N=645336.14

314+75.00

MT DOT 569(3)

LEGEND:

Terminal section type tangentT

LEGEND:

Do Not Disturb / Do Not Drill

50 10002550

Scale in feet

SG17-01

BH

Location pre-approaved for drilling

Offset= 6.00 RT

Sta.= 316+00.00

E= 1071738.55

N= 645461.25

BH-SG17-01

CUYD

EXC.

CUYD

EMB.

325+00322+50320+00317+50315+00312+50

6200 6230

6205 6235

6210 6240

6215 6245

6220 6250

6225 6255

6230 6260

6235 6265

6240 6270

Z.1

STATE PROJECT

NUMBER

SHEET

I n t_ ft

D c m y fi le s p w p r o d u c ti o n d m t-z a .d g n

MT DOT 569(3)

A

M

M a r c h

K

H a r r is o n

M il le r

C h e c k e d b y

D e s ig n e d b y

314+75 to 325+00

PLAN AND PROFILE

PLANS TO BE USED FOR GEOTECH DRILLING OPERTATIONS ONLY

Diann.Morehouse Rectangle

62556255

6255 6255

6255 6255

62556255

P C

.5

+0.8000%

+0.8000%

N

Line to be constructed

Existing ground

Profile grade

CP

CP

16101

16102

Slope stake limits

Slope stake limits

Curve= C1001

D

R= 1,800.00'

T= 592.44' e= 0.046

L= 1,144.68'

325+00 to 340+00

PLAN AND PROFILE

50 10002550

Scale in feet

LEGEND:

Do Not Disturb / Do Not Drill

CUYD

EXC.

CUYD

EMB.

340+00337+50335+00332+50330+00327+50325+00

6235 6235

6240 6240

6245 6245

6250 6250

6255 6255

6260 6260

6265 6265

6270 6270

6275 6275

Z.2

STATE PROJECT

NUMBER

SHEET

I n t_ ft m y fi le s p w p r o d u c ti o n d m t-z b .d g n

MT DOT 569(3)

M a r c h

H a r r is

M il

C h e c k e d b y

D e s ig n e d b y

PLANS TO BE USED FOR GEOTECH DRILLING OPERTATIONS ONLY

62656265

62656265

627062706270

62706270

62706270

62706270

P T

.2

IR

IR

+0.8000%

N

Line to be constructed

Slope stake limits

Slope stake limits

CP

16103

GPS

A4909

Existing ground

Profile grade

R T

50 10002550

Scale in feet

LEGEND:

Do Not Disturb / Do Not Drill

340+00 to 355+00

PLAN AND PROFILE

SG17-02

BH

Offset= 6.00 RT

Sta.= 343+00.00

E= 1072121.99

N= 648060.69

BH-SG17-02

CUYD

EXC.

CUYD

EMB.

355+00352+50350+00347+50345+00342+50340+00

6245 6245

6250 6250

6255 6255

6260 6260

6265 6265

6270 6270

6275 6275

6280 6280

6285 6285

Z.3

STATE PROJECT

NUMBER

SHEET

I n t_ ft m y fi le s p w p r o d u c ti o n d m t-z c .d g n

MT DOT 569(3)

M a r c h

H a r r is

M il

C h e c k e d b y

D e s ig n e d b y

PLANS TO BE USED FOR GEOTECH DRILLING OPERTATIONS ONLY

6255 6255

62556255

P C

.9

,2

.6

-3.5000%

506' VC

K = 118

SSD = 504'

,2

.3

+1.500 0%

600' VC

K = 120

,2

.5

+3.4

0%

300' VC

K = 158

N

GPS

16104

CP

16105

CP

16106

Line to be constructed

Slope stake limits

Slope stake limits , R

T

L T

, R

T

, L

T concrete box culvert precasted reinforced

12 feet span, 8 feet rise

360+15

Profile grade

Existing ground

Curve= C1002

D

R= 2,850.00'

T= 668.10' e= 0.034

L= 1,312.51'

LEGEND:

Do Not Disturb / Do Not Drill

50 10002550

Scale in feet

355+00 to 370+00

PLAN AND PROFILE

SG17-03

BH

Offset= 11.00 RT

Sta.= 364+50.00

E= 1073400.26

N= 649783.61

BH-SG17-03

CUYD

EXC.

CUYD

EMB.

370+00367+50365+00362+50360+00357+50355+00

6240 6240

6245 6245

6250 6250

6255 6255

6260 6260

6265 6265

6270 6270

6275 6275

6280 6280

Z.4

STATE PROJECT

NUMBER

SHEET

I n t_ ft m y fi le s p w p r o d u c ti o n d m t-z d .d g n

MT DOT 569(3)

M a r c h

H a r r is

M il

C h e c k e d b y

D e s ig n e d b y

PLANS TO BE USED FOR GEOTECH DRILLING OPERTATIONS ONLY

Diann.Morehouse Oval

Diann.Morehouse Text Box

BH17-03

Diann.Morehouse Line

628062806280

62856285

P T

.4

,2

.8

+3.4

0% -4.6000%

920' VC

K = 115

SSD = 498'

+3.4

0%

-4.6000%

N

CP

16107

Line to be constructedSlope stake limits

Slope stake limits

Profile grade

Existing ground

370+00 to 380+00

PLAN AND PROFILE

50 10002550

Scale in feet

LEGEND:

Do Not Disturb / Do Not Drill

CUYD

EXC.

CUYD

EMB.

380+00377+50375+00372+50370+00

6260 6260

6265 6265

6270 6270

627…