GM 47-24 Custer Motorway Final Geotechnical Memorandum.pdf

DATE: December 23, 2024

TO: Wendy Schmidt Project Manager

FROM: Leah Wilmot Geotechnical Engineer

SUBJECT: Geotechnical Memo 4724 Final Geotechnical Recommendations Custer Motorway Stabilization Project

ID FLAP FS SC MULTI (1)

Custer County, Idaho

INTRODUCTION

This memorandum provides geotechnical investigation results, design, and construction recommendations for the Federal Lands Access Program (FLAP) Custer Motorway Stabilization Project being performed in Custer County, Idaho for Custer County and Salmon – Challis National Forest. The project stationing referenced in this memorandum is from the 70% Design Package, Dated November 6, 2024.

Scope and Purpose

The geotechnical scope of work for this project included a visual reconnaissance at Mile Post (MP) 24 and MP 25.3 sites and testing of samples taken from the project sites. Material testing was completed by Western Federal Lands Highway Division (WFL).

This memorandum was prepared to provide geotechnical recommendations for roadway rehabilitation, cut and fill slope angles, reinforced soil slope (RSS) engineering, design, and construction considerations.

This memorandum supersedes all other previous memorandums for this project.

PROJECT DESCRIPTION

The project is located in Custer County, Idaho along Forest Road 070 “Yankee Fork Road”, between Challis and Custer, Idaho as seen in Figure 1. The project consists of two shallow embankment failures located at MP 24 (Photographs A-1 through A-3) and the other at MP 25.3 (Photographs A-4 through A-5). The project includes fill slope stabilization consisting of in-stream toe stabilization, stream bank restoration, and fill side retaining structures. Photographs of the site are provided in Appendix A, Figure 1: Project Overview Map

Site MP 24 begins at station 00+00 and includes an approximate 254.5-foot-long RSS ending at station 2+45.52. Site MP 25.3 begins at station 00+00 and includes an approximate 175-foot-long RSS, ending at station 1+75.06. At both locations, seen in Figure 2 an RSS will be constructed overlying a riprap revetment with embedded root wads.

Figure 2: Vicinity Map

GEOLOGY

The project is located in the Challis Volcanics (Eocene period, 52 to 45 million years ago) physiographic province of Central Idaho. The Challis Volcanics include intrusive pink granite and lava flows ranging in composition from rhyolite to andesite deposits (Idaho State University, 2024). The project site is located in the southeastern section of the Salmon River Mountains, within a steep canyon along Mill Creek.

The geology of the area, according to Geologic Map of the Challis 1˚x 2˚ Quadrangle, Idaho (Fisher et al, 1992), is mapped as “Or” Ramshorn slate and is approximately 2,600 feet thick as shown in Figure 3. The Ramshorn slate (Or) unit is (Ordovician Period, 485.4 to 443.8 million years ago) and is described in color as being gray, greenish-gray, and/or purple with thin beds of sandstone near the ground surface. Thick conglomerate layers are observed in the base of this unit within outcrops west of Challis. At the project sites, the unit is thin-bedded, well-laminated, and locally phyllitic.

Yankee Fork Road

Figure 3: Geology Map (Fisher et al, 1992)

Seismicity

The project is located within a seismically active area. Central Idaho is vulnerable to shallow crustal earthquakes such as the magnitude 6.9 Borah Peak earthquake which occurred near Challis, Idaho in 1983 and the magnitude 7.3 Hebgen Lake, Montana earthquake which occurred in 1959. There are no known active faults within the project site.

However, four potentially active faults have been mapped within 50 miles of the project site.

These include: the Beaverhead Fault, the Lemhi Fault, the Lost River Fault, and the Sawtooth Fault (USGS, 2024).

Beaverhead Fault – A northwest trending fault located approximately 47 miles northeast of the project site. The total length of the fault is estimated to be 80 miles. Portions of this fault may have displaced in the last 15,000 years.

Lemhi Fault – A northwest trending fault located approximately 22 miles northeast of the project site. The total length of the fault is estimated to be 90 miles. This fault has ruptured in the last 10,000 years.

Or

Lost River Fault – A northwest trending fault located approximately 20 miles southwest of the project site. The total length of the fault is estimated to be 90 miles. This fault ruptured during the 1983 Borah Peak earthquake, resulting in significant ground shaking and surface rupture forming a fault scarp.

Sawtooth Fault – A northwest trending fault located approximately 40 miles southwest of the project site. The total length of the fault is estimated to be 37 miles. Portions of this fault may have displaced in the last 15,000 years.

Based on the distances of the faults from the project sites, the risk of ground surface rupture is low.

The project area was considered for fill side retaining structure design. The scaled peak ground acceleration, As, for an earthquake with a return period of approximately 1,000 years was determined to be 0.274g using the USGS Seismic Design Maps website (2024). Seismic design for retaining structures is typically not required by AASHTO (2020) where the As is under 0.4g.

Therefore, additional seismic loads were not considered in the design of the retaining structures for the project. Embankment and cut slopes are generally not designed for earthquake loading for roadways except in close proximity to critical structures or facilities, like bridge abutments or commonly occupied buildings. No bridges are proposed for the project and no buildings exist immediately adjacent to the two sites.

SITE CONDITIONS

The project sites are located along the southern Salmon River Mountains and elevations range from approximately 6,940 feet at site MP 24 to 6,680 feet at site MP 25.3. The Salmon River Mountain range, where the projects sites are located, is in a steep sided valley that rises to an elevation of approximately 9,250 feet to the north at Corkscrew Mountain and approximately 9,830 feet to the south at Ramshorn Mountain.

Yankee Fork Road is an unpaved one lane road at MP 24 and MP 25.3 and runs generally west to east at the project sites along the north side of Mill Creek at the bottom of the steep valley slopes. Slopes are generally sloped at approximately 45 degrees and are moderately to mildly vegetated with grasses, sagebrush, and mixed conifer species.

At MP 24 and MP 25.3, Mill Creek has continued to scour the toe of the roadway fill slope as seen in photographs A-3 and A-6 of Appendix A. This has caused erosion and shallow slope failures as the embankment retrogresses at both sites. The near surface soils along the fill side embankments were observed to be coarse grained material with cobbles and boulders. Within the existing cuts we observed coarse grained materials with cobbles and at site MP 25.3, the near surface soils include boulders and potential bedrock outcroppings of slate.

Average Temperatures and Precipitation

The project site has a relatively mild climate. The winter months see cold temperatures with little snow that transitions into warmer springs and summers. Summer months are typically hot during the day and have cooler temperatures at night. The general area sees consistent amounts of light precipitation year-round. Table 1 shows the average maximum and minimum temperatures, average monthly precipitation, and the average monthly snowfall data for the period of 1895 to 1996 for the Challis, Idaho 101663 weather station (Western Region Climate Center, 2024).

Table 1. Climate Data Summary Challis, Idaho

Station: CHALLIS, IDAHO (101663)

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

Average Max.

Temperature (F)

30.3 37.7 47.5 58.3 67.5 75.8 85.3 83.6 73.8 61.1 43.9 32.1 58.1

Average Min.

Temperature (F)

8.7 14.9 22.5 30.1 37.9 44.7 50.3 48.2 40.2 31.3 20.8 11.3 30.1

Average Total Precipitation (in.)

0.5 0.41 0.43 0.56 1.06 1.1 0.63 0.59 0.67 0.47 0.41 0.54 7.38

Average Total Snow Fall (in.)

4.4 3.1 2.1 0.6 0.1 0 0 0 0 0.3 2.4 4.1 17.1

Average Snow Depth (in.)

2 1 0 0 0 0 0 0 0 0 0 1 0

Notes:

Percent of possible observations for period of record: 01/01/1895 to 06/30/1996 Max. Temp.: 98.1% Min. Temp.: 98.4% Precipitation: 98.8% Snowfall: 94.8% Snow Depth: 86%

SUBSURFACE CONDITIONS

No subsurface investigation was conducted for this project. We collected samples from Mill Creek Shale Pit east of the project alignment (location shown on Figure 4) and our WFL Construction staff also collected samples from the shoulder at the two sites (MP 24 and MP 25.3).

Figure 4: Mill Creek Shale Pit Location

Laboratory Materials Testing

Laboratory tests results were completed for the select soil samples obtained from the project sites and the Mill Creek Shale Pit location. Laboratory tests consisted of pH and resistivity testing, and soil testing to characterize the near-surface materials and characterize engineering properties of the soils for potential use in reinforced soil slope backfill. A summary of laboratory testing can be found in Table A-1 in Appendix B followed by individual sample laboratory test results.

The following index and electrochemical tests were performed on selected soil samples:

Liquid Limit, Plastic Limit, and Plasticity Index – AASHTO T89/90 Natural Moisture – AASHTO T265 Soil Classification – AASHTO M145 Sieve Analysis – AASHTO T11/27 pH of Soil for Corrosion Testing – AASHTO T 89 Standard Proctor – AASHTO T99

Direct Shear – AASHTO T236 Resistivity – AASHTO T288 R-Value test – AASHTO T190 Apparent Specific Gravity – AASHTO T 100 Particle Size Analysis – AASHTO T88

All laboratory testing was conducted at the WFL Materials Laboratory in accordance with appropriate American Association of State Highway and Transportation Officials (AASHTO) and American Society of Testing and Materials (ASTM) test methods.

DISCUSSION, RECOMMENDATIONS, AND CONSTRUCTION CONSIDERATIONS

Our site observations combined with the above information was analyzed and our geotechnical design recommendations for earthwork cut and fill slope angles, reinforced soil slope (RSS) mitigations, and material and aggregate sources are discussed in the following sections.

Earthwork Slopes

Temporary cut slopes are expected along the project alignment. It is the responsibility of the contractor to slope these cuts in accordance with OSHA requirements.

Fill slope areas are expected along the project alignment. Fill slopes are anticipated to vary and will depend on the means and methods of the contractor and how the contractor constructs the construction access to reach the bottom of the fill slope near the creek for the riprap revetment with embedded root wads work. We understand that the fill slopes will be blended at the edges of the RSS to match existing slopes and will vary depending on the surrounding terrain.

Reinforced Soils Slopes (RSS)

Reinforced soil slopes are proposed at both the MP 24 and MP 25.3 locations to protect the roadway from further erosion and undermining from Mill Creek. Based on the roadside samples obtained from each site, we have designed the RSSs to use the roadway excavation materials as RSS backfill. The near surface material within the excavation is expected to be silty Gravel with sand.

We have modeled the RSS’s using Slide2 software by Rocscience. The RSSs will be constructed overlying a riprap revetment at each location, as illustrated in Figure 5. The proposed RSSs are a welded wire face with reinforcement geogrid, type 3. At both sites, we propose a minimum length of reinforcement, L, of 12 feet and a maximum reinforcement spacing of 1.5 feet. At site MP 24, the current RSS profile shows a maximum height of approximately

21.5 feet with a face angle of 1.25V:1H, while at the MP 25.3 site, the RSS profile shows a maximum height of approximately 15.5 feet with a face angle of 1.5V:1H. At both sites, we are proposing a 12 to 16 inches pocket of topsoil at the face to construct a vegetated face on the

RSS.

Drilling is outside the scope of this work so the depth to bedrock is uncertain. If unsuitable material is encountered during the riprap revetment excavation, remove and replace with suitable material. The geology above is mapped as Ramshorn slate (Or) with thin beds of sandstone near the ground surface. It is not anticipated that strong rock will be encountered, but if strong bedrock is encountered that cannot be excavated with heavy equipment (e.g., a CAT 200-series excavator with a bucket equipped with rock teeth), then the geogrid reinforcement length can potentially be reduced. These changes during construction will require approval through the Contracting Officer (CO).

The subsurface drainage system for the RSS consists of partial coverage of the temporary cut slope with a geocomposite sheet drain meeting FP24 Standard Specification 714.02 and install as shown in Figure 5. This partial coverage is intended to reduce hydrostatic pressure should incidental groundwater be encountered after construction. If areas of active seepage are encountered or identified during construction, these seepage areas should include additional coverage with the geocomposite sheet drains. There is no perforated pipe system within the RSS because of the riprap revetment underlying the RSS. We are anticipating that groundwater will flow through the geocomposite sheet drain and filter through the riprap revetment in sections directly overlying the revetment or flow towards the revetment in areas bearing in soil or bedrock at the ends of the RSS.

Table 2 summarizes the factor of safety results for the Slide2 analysis in Appendix C. The results indicate adequate factors of safety above 1.3 for static conditions.

Table 2: Slide 2 Results Summary

Analysis Method

Site MP 24 Site MP 25.3

Analysis Method

Static Factor of Safety (Rip Rap

Foundation)

Static Factor of Safety (Soil Foundation)

Analysis Method

Static Factor of Safety (Rip Rap

Foundation) Spencer 1.4 1.7 Spencer 1.3

Bishop Simplified 1.4 1.7 Bishop Simplified 1.3

Figure 5: Typical Section of RSS overlying riprap revetment

Material and Aggregate Sources

We anticipate that the excavation material will be suitable to be reused as RSS backfill, fill and road building material. Imported fill materials are anticipated for riprap, streambed material, and topsoil. There is no Government provided material source for this project. A Bureau of Land Management (BLM) source, known as the Morgan Creek Community Rip-Rap Pits along Morgan Creek Road, has been identified as a possible local source. It is the Contractor’s responsibility to locate an approved material source from an available commercial or private source for all construction materials that meet the requirements of the contract.

Excavation

As noted above, based on the samples obtained from each site, we have designed the RSSs to use the excavation materials as RSS backfill. However, if encountered, unsuitable materials, such as wood, organics, and other debris, should be segregated and hauled offsite. As of the preparation of this memorandum, one waste site has been provided as the Mill Creek Shale Pit location identified in Figure 4 at coordinates 44°30'42.1"N 114°22'21.1"W. This site is approximately 25 feet wide by 200 feet long and is located on the cut side of the roadway (Photograph A-7).

Temporary slopes for the excavation of the RSS foundations and the revetments are the responsibility of the contractor. Temporary slope angles will be determined based OSHA requirements and on the conditions encountered, anticipated traffic/equipment loading above the temporary cut, and other factors under the control of the Contractor during construction.

LIMITATIONS

This memorandum was prepared to provide geotechnical recommendations for the design and construction of the Federal Lands Access Program (FLAP) Custer Motorway Project being performed in Custer County, Idaho for Custer County and Salmon – Challis National Forest.

Professional judgments and recommendations are presented in this memorandum. 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.

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

REFERENCES

AASHTO LRFD Bridge Design Specifications, 9th Edition, American Association of State Highway and Transportation Officials, 2020.

Fisher, F., McIntyre D., and Johnson K., 1992, Geologic Map of the Challis 1˚ X 2˚ Quadrangle. Idaho, United States Geologic Survey, Miscellaneous Investigations Series Map I-1819.

Idaho State University “Digital Geology of Idaho.”, www.isu.edu/digitalgeologyidaho. (Accessed August 2024).

USGS Seismic Design Web Service, earthquake.usgs.gov/ws/designmaps/aashto- 2009.json?latitude=44.500997&longitude=-114.395544&siteClass=B&title=ID FLAP FS SC MULTI (1) (accessed August 2024).

U.S. Geological Survey’s Interactive Quaternary Faults Database: U.S. Quaternary Faults (arcgis.com) (accessed August 2024).

Western Regional Climate Center, 2024, Cooperative Climatological data summaries:

CHALLIS, IDAHO (101663), CHALLIS, IDAHO - Climate Summary (accessed August 2024).

CLOSING

Questions regarding this memorandum should be addressed to Leah Wilmot, WFL Geotechnical Engineer, at (360) 619-7697, or Leah.Wilmot@dot.gov and/or Evan Garich, Geotechnical Team Lead, at (360) 619-7824, or Evan.Garich@dot.gov.

LW

CC: Evan Garich, Geotechnical Engineer Team Lead Eric Lim, Senior Geotechnical Engineer

Douglas A. Anderson, GEO Team Functional Manager Katie Alexander, Highway Designer

Geotechnical File

Attachments:

Appendix A: Photographs Appendix B: Lab Test Results Appendix C: Slide2 Analysis

APPENDIX A

Photographs

Photograph A-1: Site MP 24 looking west. Shallow slope failure on the fill side of the roadway.

Photograph A-2: Site MP 24 looking north upslope towards the roadway.

Shallow slope failure

Slope failure

Photograph A-3: Site MP 24 looking west. Toe erosion along Mill Creek at the bottom of the fill slope.

Erosion along the toe of the slope

Photograph A-4: Site MP 25.3 looking west. Shallow slope failure on the fill side of the roadway.

Photograph A-5: Site MP 25.3 looking east. Shallow slope failure on the fill side of the roadway.

Shallow slope failure

Potential bedrock outcropping

Photograph A-6: Site MP25.3 looking west. Toe erosion along Mill Creak at the bottom of the fill slope.

Photograph A-7: Mill Creek Shale Pit location, looking east.

Erosion along the toe of the slope

Waste Site

APPENDIX B

Table B‐1: Laboratory Testing Summary Table Laboratory Testing Results

Table B-1 : Laboratory Testing Summary

SAMPLE

DEPTH

LL PL PI pH Direct Shear

ft. - - - -

MP 24.0 0-2 57.0 27.0 30.0 7

MP 25.3 0-2 30.0 22.0 8.0 7.6

Shale Pit 1.0 23.0 18.0 5.0 - -

76.2mm 50mm 37.5mm 25.0mm 19.0mm 12.5mm 9.5mm 4.75mm 2.00mm 425µm 150µm 75µm 20µm 10μm 5µm 2µm 3" 2" 1.5" 1" 3/4" 1/2" 3/8" #4 #10 #40 #100 #200 20µm 10μm 5µm 2µm

ft. % % % % % % % % % % % % % % % % % % % % MP 24.0 0-2 100.0 100.0 97.0 93.0 86.0 76.0 69.0 56.0 43.0 30.0 22.0 17.3 57.0 13.0 12.7 17.3 MP 25.3 0-2 100.0 98.0 96.0 93.0 89.0 81.0 73.0 53.0 37.0 23.0 19.0 15.6 63.0 14.0 7.4 15.6 Shale Pit 1.0 100.0 99.7 98.8 96.0 88.0 79.7 53.6 29.0 17.4 12.0 10.1 9.2 7.3 4.7 71.0 11.6 5.4 12.0

- 632.812-

Density @ R Value pcf

-4250

UNIFIED SOIL CLASSIFICATION SYSTEM (USCS)

Silty GRAVEL with sand (GM) Silty GRAVEL with sand (GM)6.7 - -

Moisture @ R Value

AASHTO

CLASSIFICATION

131.1 A-2-4 (0) A-2-7 (0)

Grab Sample Location

Moisture

R Value by Exudation

@ 300 psi

Specific Gravity

@ 20˚ C

Resistiviety

Ω-cm 1500 -

SILT-CLAY

SAMPLE

DEPTH

Grab Sample Location

FINE

SAND

Gravel

COARSE

SAND

PARTICLE SIZE AASHTO FRACTIONS

Poorly graded GRAVEL with silt and sand (GP-GM)12.6 A-1-a (0)

Western Federal Lands

Project No.: ID FLAP FS SC MULTI(1) Sample ID: W-23-1642-GS

Materials Laboratory

ISO/IEC 17025:2017 Accredited Date Distributed: 10/10/2023

Table of Contents

Station:

Material Description: SO-PS

MilePost:

Offset:

Intended Use:

Remarks:

Source Name:

Source Location:

Sample Location: Pit

Submitted By: T Hansen

Quantity Represented:

Item No.:

Field Sample No.: 1

Lot No.:

Date Sampled: 9/13/2023

Depth: 1 Hole No.: Shale Pit

Project Name: CUSTER MOTORWAY AND

YANKEE FORK ROAD

IMPROVEMENTS

W-23-1642-GS _________________________________________________________________ 2

W-23-1642-GS _________________________________________________________________ 7

Station:

Project No.: ID FLAP FS SC MULTI(1) Sample ID: W-23-1642-GS

Materials Laboratory

ISO/IEC 17025:2017 Accredited Date Distributed: 10/10/2023

Material Description: SO-PS

MilePost:

Offset:

Intended Use:

Remarks:

Source Name:

Source Location:

Sample Location: Pit

Submitted By: T Hansen

Quantity Represented:

Item No.:

Field Sample No.: 1

Lot No.:

Date Sampled: 9/13/2023

Depth: 1 Hole No.: Shale Pit

Project Name: CUSTER MOTORWAY AND

YANKEE FORK ROAD

IMPROVEMENTS

Unit of MeasureResult

R value by Exudation @ 300 psi 63

Density @ R Value 131.1 pcf

Moisture @ R Value 12.6 %

Methods: T 190 AASHTO Test Date: 10/2/2023 Tested By: Rob Lange

Comments:

Test Validated By: Rob Lange Validated Date: 10/4/2023

Version 1

Unit of MeasureResult

Specific Gravity @ 20°C 2.812

Methods: AASHTO T 100 - Specific Gravity of Soils Test Date: 10/3/2023 Tested By: Rob Lange

Comments:

Test Validated By: Rob Lange Validated Date: 10/4/2023

Version 1

Unit of MeasureResult

Liquid Limit From T 89 23

Plastic Limit from T 90 18

Plasticity Index 5

Methods: AASHTO T 89 & T 90 - Atterberg Limits Test Date: 9/29/2023 Tested By: Rob LangeVersion 1

All reported results apply to the sample as received.

Page 2 of 5Sample ID: W-23-1642-GS

Con tro lle d C op y

Comments:

Test Validated By: Rob Lange Validated Date: 10/5/2023

Unit of MeasureResult

6"sieve (152.4 mm) % Passing - %

5" sieve (127.0 mm) % Passing - %

4" sieve (101.6 mm) % Passing - %

3.5" sieve (88.9 mm) % Passing - %

3" sieve(76.2 mm) % Passing - %

2.5" sieve (63.5 mm) % Passing - %

2" sieve (50.0 mm) % Passing 100 %

1.5" sieve (37.5 mm) % Passing 100 %

1" sieve (25.0 mm) % Passing 99 %

3/4" sieve (19.0 mm) % Passing 96 %

1/2" sieve (12.5 mm) % Passing 88 %

3/8" sieve (9.5 mm) % Passing 80 %

No. 4 sieve (4.75 mm) % Passing 54 %

No. 8 sieve (2.36 mm) % Passing - %

No. 10 sieve (2.0mm) % Passing - %

No. 16 sieve (1.18 mm) % Passing - %

No. 20 sieve (0.841 mm) % Passing - %

No. 30 sieve (0.600 mm) % Passing - %

No. 40 sieve (0.425 mm) % Passing - %

No. 50 sieve (0.300 mm) % Passing - %

No. 60 sieve (0.250 mm) % Passing - %

No. 80 sieve (0.177 mm) % Passing - %

No. 100 sieve (0.150 mm) % Passing - %

No. 200 sieve (0.075 mm) % Passing - %

AASHTO T11 (% finer than No. 200 sieve) N/A

Methods: AASHTO T 11 & T 27 - Sieve Analysis of Aggregate & Minus No.

200 Wash

Test Date: 9/27/2023

Tested By: Chuck Miller

Comments:

Test Validated By: Chuck Miller Validated Date: 9/27/2023

Version 1

Unit of MeasureResult

6" sieve (152.4 mm) % Passing - %

5" sieve (127 mm) % Passing - %

4" sieve (101.6 mm) % Passing - %

3 1/2" sieve (88.9 mm) % Passing - %

3" sieve sieve (76 mm) % Passing - %

2 1/2" sieve (63.5 mm) % Passing - %

2" sieve (50.0 mm) % Passing 100.0 %

Methods: AASHTO T 88 - Particle Size Analysis of Soils Test Date: 10/2/2023 Tested By: Rob LangeVersion 1

All reported results apply to the sample as received.

Page 3 of 5Sample ID: W-23-1642-GS

Con tro lle d C

Unit of MeasureResult

1 1/2" sieve (37.5 mm) % Passing 99.7 %

1" sieve (25.0 mm) % Passing 98.8 %

3/4" sieve (19.0 mm) % Passing 96.0 %

1/2" sieve (12.5 mm) % Passing 88.0 %

3/8" sieve (9.5 mm) % Passing 79.7 %

No. 4 sieve (4.75 mm) % Passing 53.6 %

No. 10 sieve (2.0 mm) % Passing 29.0 %

No. 40 Sieve (0.425 mm) % Passing 17.4 %

No. 200 Sieve (0.075 mm) % Passing 12.0 %

Interpolated 0.020 mm % Passing 10.1 %

Interpolated 0.010 mm % Passing 9.2 %

Interpolated 0.005 mm % Passing 7.3 %

Interpolated 0.002 mm % Passing 4.7 %

Interpolated 0.001 mm % Passing 4.5 %

D10 0.0183 mm

D30 2.0696 mm

D50 4.1833 mm

D60 5.6279 mm

CU 308.169

CC 41.673

Comments:

Test Validated By: Rob Lange Validated Date: 10/5/2023

Unit of MeasureResult

Classification A-1-a (0)

Gravel (2.00 mm and larger) 71.0 %

Coarse sand (2.0 to 0.42 mm) 11.6 %

Fine Sand (0.42 to 0.074 mm) 5.4 %

Silt-clay (0.075mm and smaller) 12.0 %

Methods: AASHTO M 145 - Classification (AASHTO M 145 is not an AAP accredited test)

Test Date: 10/5/2023

Tested By: Rob Lange

Comments:

Test Validated By: Rob Lange Validated Date: 10/5/2023

Version 1

Unit of MeasureResult

Classification GP-GM, Poorly graded gravel with silt with sand

Cobbles 0 %

Coarse Gravel 4 %

Methods: ASTM D2487 - (Unified Soils Classification System) Test Date: 10/5/2023 Tested By: Rob LangeVersion 1

All reported results apply to the sample as received.

Page 4 of 5Sample ID: W-23-1642-GS

Con tro lle d C

Fine Gravel 42 %

Coarse Sand 25 %

Medium Sand 12 %

Fine Sand 5 %

D10 0.019 mm

D30 2.072 mm

D50 4.185 mm

D60 5.630 mm

CU 301.2580

CC 0.7622

Comments:

Test Validated By: Rob Lange Validated Date: 10/5/2023

All reported results apply to the sample as received.

Page 5 of 5Sample ID: W-23-1642-GS

Con tro lle d C

Name Units Value

➖➖➖ Results ➖➖➖

Plotting Method Curved

R Value by exudation @ 300 psi [none] 62.66

Density at R Value PCF 131.1

Moisture at R Value % 12.6

Sample ID: W-24-0477-GS

Materials Laboratory

ISO/IEC 17025:2017 Accredited Date Distributed: 08/15/2024

Table of Contents

Station:

Material Description: SO-SIM

MilePost:

Offset:

Intended Use:

Remarks:

Source Name:

Source Location:

Sample Location: Other

Submitted By: Eric Lim

Quantity Represented:

Item No.:

Field Sample No.: Grab

Lot No.:

Date Sampled: 5/22/2024

Depth: 0-2' Hole No.: MP24.0

Project Name: CUSTER MOTORWAY AND

YANKEE FORK ROAD

IMPROVEMENTS

W-24-0477-GS _________________________________________________________________ 2

W-24-0477-GS _________________________________________________________________ 7

SHEAR_REPORT_W-24-0477-GS MP24.0 __________________________________________ 9

Project No.: ID FLAP FS SC MULTI(1) Sample ID: W-24-0477-GS

Materials Laboratory

ISO/IEC 17025:2017 Accredited Date Distributed: 08/15/2024

Material Description: SO-SIM

MilePost:

Offset:

Intended Use:

Remarks:

Source Name:

Source Location:

Sample Location: Other

Submitted By: Eric Lim

Quantity Represented:

Item No.:

Field Sample No.: Grab

Lot No.:

Date Sampled: 5/22/2024

Depth: 0-2' Hole No.: MP24.0

Project Name: CUSTER MOTORWAY AND

YANKEE FORK ROAD

IMPROVEMENTS

Unit of MeasureResult

6"sieve (152.4 mm) % Passing - %

5" sieve (127.0 mm) % Passing - %

4" sieve (101.6 mm) % Passing - %

3.5" sieve (88.9 mm) % Passing - %

3" sieve(76.2 mm) % Passing 100 %

2.5" sieve (63.5 mm) % Passing - %

2" sieve (50.0 mm) % Passing 100 %

1.5" sieve (37.5 mm) % Passing 97 %

1" sieve (25.0 mm) % Passing 93 %

3/4" sieve (19.0 mm) % Passing 86 %

1/2" sieve (12.5 mm) % Passing 76 %

3/8" sieve (9.5 mm) % Passing 69 %

No. 4 sieve (4.75 mm) % Passing 56 %

No. 8 sieve (2.36 mm) % Passing - %

No. 10 sieve (2.0mm) % Passing 43 %

No. 16 sieve (1.18 mm) % Passing - %

No. 20 sieve (0.841 mm) % Passing - %

No. 30 sieve (0.600 mm) % Passing - %

No. 40 sieve (0.425 mm) % Passing 30 %

No. 50 sieve (0.300 mm) % Passing - %

No. 60 sieve (0.250 mm) % Passing - %

No. 80 sieve (0.177 mm) % Passing - %

Methods: AASHTO T 11 & T 27 - Sieve Analysis of Aggregate & Minus No.

200 Wash

Test Date: 7/8/2024

Tested By: Jerrad IschVersion 1

All reported results apply to the sample as received.

Page 2 of 5Sample ID: W-24-0477-GS

Con tro lle d C

No. 100 sieve (0.150 mm) % Passing 22 %

No. 200 sieve (0.075 mm) % Passing 17.3 %

AASHTO T11 (% finer than No. 200 sieve) Good Sieve

D10 Unable to calculate

D30 Unable to calculate

D50 Unable to calculate

D60 Unable to calculate

Comments:

Test Validated By: Jerrad Isch Validated Date: 7/8/2024

Unit of MeasureResult

Classification A-2-7 (0)

Gravel (2.00 mm and larger) 57.0 %

Coarse sand (2.0 to 0.42 mm) 13.0 %

Fine Sand (0.42 to 0.074 mm) 12.7 %

Silt-clay (0.075mm and smaller) 17.3 %

Methods: AASHTO M 145 - Classification (AASHTO M 145 is not an AAP accredited test)

Test Date: 7/8/2024

Tested By: Rob Lange

Comments:

Test Validated By: Rob Lange Validated Date: 7/8/2024

Version 1

Unit of MeasureResult

Liquid Limit From T 89 57

Plastic Limit from T 90 27

Plasticity Index 30

Methods: AASHTO T 89 & T 90 - Atterberg Limits Test Date: 7/3/2024 Tested By: Rob Lange

Comments:

Test Validated By: Rob Lange Validated Date: 7/8/2024

Version 1

Unit of MeasureResult

Classification GM, Silty gravel with sand

Cobbles 0 %

Methods: ASTM D2487 - (Unified Soils Classification System) Test Date: 7/8/2024 Tested By: Rob LangeVersion 1

All reported results apply to the sample as received.

Page 3 of 5Sample ID: W-24-0477-GS

Con tro lle d C

Coarse Gravel 14 %

Fine Gravel 30 %

Coarse Sand 13 %

Medium Sand 13 %

Fine Sand 13 %

Silt 17 %

D50 31.86000 mm

D60 5.87900 mm

Comments: Not able to calculate Cu,Cc based on gradation results. -- 7/8/2024 10:58:04 AM Test Validated By: Rob Lange Validated Date: 7/8/2024

Unit of MeasureResult

See Attached Report Document

Methods: AASHTO T 99/T 180 - Interim Test Date: 7/5/2024 Tested By: Rob Lange

Comments:

Test Validated By: Rob Lange Validated Date: 7/8/2024

Version 1

Unit of MeasureResult

See attached document

Methods: T 236 - AASHTO Test Date: 8/8/2024 Tested By: Jerrad Isch

Comments:

Test Validated By: Jerrad Isch Validated Date: 8/13/2024

Version 1

Unit of MeasureResult

Preparation Method Alternate Method Using No.10 Sieve

Minimum Resistivity Value 1500 Ω-cm

Methods: T 288 - AASHTO Test Date: 7/11/2024 Tested By: Jerrad Isch

Comments:

Test Validated By: Jerrad Isch Validated Date: 7/11/2024

Version 1

Methods: AASHTO T 289 - pH of Soil for Corrosion Testing Test Date: 7/5/2024 Tested By: Rob LangeVersion 1

All reported results apply to the sample as received.

Page 4 of 5Sample ID: W-24-0477-GS

Con tro lle d C pH of Soil 7.0

Comments:

Test Validated By: Rob Lange Validated Date: 7/8/2024

Unit of MeasureResult

Drying Temperature 230 ° F

Moisture Content 17.0 %

Methods: AASHTO T 265 Moisture Content of Soil Test Date: 6/12/2024 Tested By: Jerrad Isch

Comments:

Test Validated By: Jerrad Isch Validated Date: 6/12/2024

Version 1

All reported results apply to the sample as received.

Page 5 of 5Sample ID: W-24-0477-GS

Con tro lle d C

Lab ID:

AASHTO T 99 / T 180 -

Standard Used AASHTO T 99

Method C

Hammer Face Wedge

Maximum Dry Density lb/Cu.Ft 114.0

Optimum Moisture % 13.9

Rock Corrected Dry Density % N/A

Rock Corrected Opt. Moist. % N/A

1.762526

8 10 12 14 15

135.1 130.1 125.5 121.2 117.1

W-24-0477-GS

8.0 10.0 12.0 14.0 16.0 18.0 20.0

D ry

D en si ty lb s/ cu f t)

Moisture Content (%)

AASHTO T 99 / T 180

Sample ID: W-24-0478-GS

Materials Laboratory

ISO/IEC 17025:2017 Accredited Date Distributed: 09/10/2024

Table of Contents

Station:

Material Description: SO-SIM

MilePost:

Offset:

Intended Use:

Remarks:

Source Name:

Source Location:

Sample Location: Other

Submitted By: Eric Lim

Quantity Represented:

Item No.:

Field Sample No.: Grab

Lot No.:

Date Sampled: 5/22/2024

Depth: 0-2' Hole No.: MP25.3

Project Name: CUSTER MOTORWAY AND

YANKEE FORK ROAD

IMPROVEMENTS

W-24-0478-GS _________________________________________________________________ 2

W-24-0478-GS _________________________________________________________________ 7

SHEAR_REPORT_W-24-0478-GS MP25.3 __________________________________________ 9

Project No.: ID FLAP FS SC MULTI(1) Sample ID: W-24-0478-GS

Materials Laboratory

ISO/IEC 17025:2017 Accredited Date Distributed: 09/10/2024

Material Description: SO-SIM

MilePost:

Offset:

Intended Use:

Remarks:

Source Name:

Source Location:

Sample Location: Other

Submitted By: Eric Lim

Quantity Represented:

Item No.:

Field Sample No.: Grab

Lot No.:

Date Sampled: 5/22/2024

Depth: 0-2' Hole No.: MP25.3

Project Name: CUSTER MOTORWAY AND

YANKEE FORK ROAD

IMPROVEMENTS

Unit of MeasureResult

6"sieve (152.4 mm) % Passing - %

5" sieve (127.0 mm) % Passing - %

4" sieve (101.6 mm) % Passing - %

3.5" sieve (88.9 mm) % Passing - %

3" sieve(76.2 mm) % Passing 100 %

2.5" sieve (63.5 mm) % Passing - %

2" sieve (50.0 mm) % Passing 98 %

1.5" sieve (37.5 mm) % Passing 96 %

1" sieve (25.0 mm) % Passing 93 %

3/4" sieve (19.0 mm) % Passing 89 %

1/2" sieve (12.5 mm) % Passing 81 %

3/8" sieve (9.5 mm) % Passing 73 %

No. 4 sieve (4.75 mm) % Passing 53 %

No. 8 sieve (2.36 mm) % Passing - %

No. 10 sieve (2.0mm) % Passing 37 %

No. 16 sieve (1.18 mm) % Passing - %

No. 20 sieve (0.841 mm) % Passing - %

No. 30 sieve (0.600 mm) % Passing - %

No. 40 sieve (0.425 mm) % Passing 23 %

No. 50 sieve (0.300 mm) % Passing - %

No. 60 sieve (0.250 mm) % Passing - %

No. 80 sieve (0.177 mm) % Passing - %

Methods: AASHTO T 11 & T 27 - Sieve Analysis of Aggregate & Minus No.

200 Wash

Test Date: 7/1/2024

Tested By: Chuck MillerVersion 1

All reported results apply to the sample as received.

Page 2 of 5Sample ID: W-24-0478-GS

Con tro lle d C

No. 100 sieve (0.150 mm) % Passing 19 %

No. 200 sieve (0.075 mm) % Passing 15.6 %

AASHTO T11 (% finer than No. 200 sieve) Good Sieve

D10 Unable to calculate

D30 Unable to calculate

D50 Unable to calculate

D60 Unable to calculate

Comments:

Test Validated By: Jerrad Isch Validated Date: 7/3/2024

Unit of MeasureResult

Classification A-2-4 (0)

Gravel (2.00 mm and larger) 63.0 %

Coarse sand (2.0 to 0.42 mm) 14.0 %

Fine Sand (0.42 to 0.074 mm) 7.4 %

Silt-clay (0.075mm and smaller) 15.6 %

Methods: AASHTO M 145 - Classification (AASHTO M 145 is not an AAP accredited test)

Test Date: 7/8/2024

Tested By: Rob Lange

Comments:

Test Validated By: Rob Lange Validated Date: 7/8/2024

Version 1

Unit of MeasureResult

Liquid Limit From T 89 30

Plastic Limit from T 90 22

Plasticity Index 8

Methods: AASHTO T 89 & T 90 - Atterberg Limits Test Date: 7/3/2024 Tested By: Rob Lange

Comments:

Test Validated By: Rob Lange Validated Date: 7/8/2024

Version 1

Unit of MeasureResult

Drying Temperature 230 ° F

Moisture Content 6.7 %

Methods: AASHTO T 265 Moisture Content of Soil Test Date: 6/12/2024 Tested By: Jerrad IschVersion 1

All reported results apply to the sample as received.

Page 3 of 5Sample ID: W-24-0478-GS

Con tro lle d C

Comments:

Test Validated By: Jerrad Isch Validated Date: 6/12/2024

Unit of MeasureResult

See Attached Report Document

Methods: AASHTO T 99/T 180 - Interim Test Date: 7/5/2024 Tested By: Rob Lange

Comments:

Test Validated By: Rob Lange Validated Date: 7/9/2024

Version 1

Unit of MeasureResult

See attached document

Methods: T 236 - AASHTO Test Date: 8/8/2024 Tested By: Jerrad Isch

Comments:

Test Validated By: Jerrad Isch Validated Date: 8/8/2024

Version 1

Unit of MeasureResult

Preparation Method Alternate Method Using No.10 Sieve

Minimum Resistivity Value 4250 Ω-cm

Methods: T 288 - AASHTO Test Date: 7/11/2024 Tested By: Jerrad Isch

Comments:

Test Validated By: Jerrad Isch Validated Date: 7/11/2024

Version 1

Unit of MeasureResult pH of Soil 7.6

Methods: AASHTO T 289 - pH of Soil for Corrosion Testing Test Date: 7/5/2024 Tested By: Rob Lange

Comments:

Test Validated By: Rob Lange Validated Date: 7/8/2024

Version 1

Methods: ASTM D2487 - (Unified Soils Classification System) Test Date: 7/8/2024 Tested By: Rob LangeVersion 1

All reported results apply to the sample as received.

Page 4 of 5Sample ID: W-24-0478-GS

Con tro lle d C

Classification GM, Sily gravel with sand

Cobbles 0 %

Coarse Gravel 11 %

Fine Gravel 36 %

Coarse Sand 16 %

Medium Sand 14 %

Fine Sand 7 %

Silt 16 %

D30 0.92200 mm

D50 4.03900 mm

D60 6.05400 mm

Comments: Not able to calculate Cu,Cc based on gradation results. -- 7/8/2024 11:16:45 AM Test Validated By: Rob Lange Validated Date: 7/8/2024

All reported results apply to the sample as received.

Page 5 of 5Sample ID: W-24-0478-GS

Con tro lle d C

Lab ID:

AASHTO T 99 / T 180 -

Standard Used AASHTO T 99

Method C

Hammer Face Circular

Maximum Dry Density lb/Cu.Ft 130.5

Optimum Moisture % 10.6

Rock Corrected Dry Density % N/A

Rock Corrected Opt. Moist. % N/A

1.539976

3 5 6 8 9

152.5 146.9 141.8 137.0 132.5

W-24-0478-GS

4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0

D ry

D en si ty lb s/ cu f t)

Moisture Content (%)

AASHTO T 99 / T 180

APPENDIX C

Slide2 RSS Analysis

1.361.36

W

250.00 lbs/ft2

1.361.36

HuHu Type Water Surface

Phi

Cohesion (psf)

Strength Type Unit Weight (lbs/ ft3) Color

Material Name

1CustomWater Table36100 Mohr‐

Coulomb 120native soil

1CustomWater Table360 Mohr‐

Coulomb 120RSS backfill

1CustomWater Table450 Mohr‐

Coulomb 145Riprap

Allowable Tensile

Strength (lbs/ ft)

Strip Coverage

Anchorage

Force Orientation

Coefficient of

Interaction Input Type

Material Dependent

Force Application

TypeColor Support Name

2000100None Tangent to Slip Surface

0.8 Coefficient

of Interaction

No Active

(Method A) Geosynthetic

Geogrid Type III

-120 -100 -80 -60 -40 -20 0 20 40 60 80 100 120

Scenario CircularGroup MP 25.3 RSS CompanyDrawn By

File Name Custer slide MP25.3.slmdDate 6/14/2024, 6:34:49 PM

Project

Custer Motorway Stabilization Project - ID FLAP FS SC MULTI(1)

SLIDEINTERPRET 9.033

1.751.75

250.00 lbs/ft2

1.751.75

Ru ValueHuHu TypeWater SurfacePhi (°)Cohesion (psf)Strength TypeUnit Weight (lbs/ft3)ColorMaterial Name

1CustomWater Table36100Mohr‐Coulomb120native soil

0None360Mohr‐Coulomb120RSS backfill

Allowable Tensile Strength

(lbs/ft)

Strip Coverage

Anchorage

Force Orientation

Coefficient of

Interaction Input Type

Material Dependent

Force Application

TypeColor Support Name

2000100None Tangent to Slip Surface

0.8 Coefficient

of Interaction

No Active

(Method A) Geosynthetic

Geogrid Type III

-100 -80 -60 -40 -20 0 20 40 60 80

Scenario CircularGroup MP 24 RSS - No rip rap CompanyDrawn By

File Name Custer slide MP24 direct shear.slmdDate 6/14/2024, 6:34:49 PM

Project

Custer Motorway and Yankee Fork Road Improvements - ID FLAP FS SC MULTI(1)

1.481.48

250.00 lbs/ft2

1.481.48

HuHu TypeWater SurfacePhi (°)Cohesion (psf)Strength TypeUnit Weight (lbs/ft3)ColorMaterial Name

1CustomWater Table36100Mohr‐Coulomb120native soil

1CustomWater Table360Mohr‐Coulomb120RSS backfill

1CustomWater Table450Mohr‐Coulomb145Riprap

Allowable Tensile Strength (lbs/ft)

Strip Coverage

Anchorage

Force Orientation

Coefficient of Interaction

Input Type Material Dependent

Force Application

TypeColor Support Name

2000100None Tangent to Slip Surface

0.8 Coefficient

of Interaction No

Active (Method A)

Geosynthetic Geogrid Type III

-80 -60 -40 -20 0 20 40 60 80 100

Scenario CircularGroup MP 24 RSS CompanyDrawn By

File Name Custer slide MP24 direct shear.slmdDate 6/14/2024, 6:34:49 PM

Project

Custer Motorway and Yankee Fork Road Improvements - ID FLAP FS SC MULTI(1)

END MEMO