Fossil House Road Geotechnical Report.pdf

GEOTECHNICAL REPORT

NV FLAP 300 (1)

Fossil House Road Improvements

Nye County, Nevada

Yeh Project No.: 217-347

October 30, 2019

Prepared for:

Muller Engineering Company, Inc.

777 S. Wadsworth Boulevard 4-100

Lakewood, Colorado 80226 Attn: Ms. Karen Fuhr, P.E.

Prepared by:

Yeh and Associates, Inc.

391 Front Street, Suite D

Grover Beach, California 93433 Phone: 805-481-9590

GEOTECHNICAL REPORT

NV FLAP 300(1)

Fossil House Road Improvements

Nye County, Nevada

Yeh Project No.: 217-347

October 30, 2019

Prepared by:

Judd King, P.E. (CA, NV), G.E. (CA) Jamie L. Cravens Geotechnical Engineer Staff Engineer

Independent Reviewer: Reviewed By:

Jonathan Blanchard, G.E. (CA) Robert F. LaForce, P.E. (CO) Principal Geotechnical Engineer Senior Materials Manager

6/30/2021

Geotechnical Report Yeh Project No. 217-347 Fossil House Road Improvements October 30, 2019 i

TABLE OF CONTENTS

1. PURPOSE AND SCOPE OF STUDY

2. PROJECT UNDERSTANDING

3. GEOTECHNICAL EXPLORATION AND TESTING

3.1 GEOLOGIC RECONNAISSANCE AND THIRTY PERCENT DESIGN VISIT

3.2 EXPLORATORY DRILLING

3.3 LABORATORY TESTING

4. SITE CONDITIONS

4.1 GEOLOGIC SETTING

4.2 TERRAIN AND VEGETATION

4.3 CLIMATE

4.4 EXISTING ROADWAY

5. SUBSURFACE CONDITIONS

5.1 ROADWAY SUBGRADE AND LOW WATER CROSSING CONDITIONS

5.2 RETAINING WALL CONDITIONS

5.3 GROUNDWATER

6. CONCLUSIONS AND RECOMMENDATIONS

6.1 EARTHWORK - GENERAL

6.1.1 GENERAL GRADING

6.1.2 EROSION AND SLOPE DRAINAGE

6.2 ROADWAY DESIGN

6.2.1 EMBANKMENT DESIGN

6.2.2 RIP-RAP AND REVETMENT MATTRESS PROTECTION

6.2.3 AGGREGATE SURFACE ROADWAY

6.3 LOW WATER CROSSINGS

6.4 GABION WALLS

6.5 UNANCHORED CANTILEVER SOLDIER PILE RETAINING WALL

6.6 CORROSION CONSIDERATIONS

7. NOTES TO CONSTRUCTION

8. MATERIAL SOURCES

8.1 CONCRETE, RIPRAP AND AGGREGATE

ii

8.2 GENERAL BORROW

9. LIMITATIONS

10. REFERENCES

List of Figures

FIGURE 1: PROJECT LOCATION MAP

FIGURE 2: GEOLOGIC MAP (BALINI ET. AL 2014)

FIGURE 3: TYPICAL ROADWAY CONDITION

FIGURE 4: TYPICAL EMBANKMENT CONSTRUCTION

FIGURE 5: LATERAL EARTH PRESSURE DISTRIBUTION

List of Tables

TABLE 1: UNION CANYON ROAD – PROPOSED IMPROVEMENTS

TABLE 2: SUBGRADE SOIL PROPERTIES TEST SUMMARY

TABLE 3: FOSSIL HOUSE ROAD SOIL PROPERTIES TEST SUMMARY

TABLE 4: ROADWAY AGGREGATE

TABLE 5: GEOTECHNICAL PROPERTIES FOR WALL DESIGN

TABLE 6: RESISTANCE AND LOAD FACTORS

List of Plates

Field Exploration Plan

List of Appendices

Page Appendix A –Boring Logs Boring Record Legend ........................................................................................................... A-1 to 2 Boring Logs for 18W-01 to 03 ............................................................................................... A-3 to 7 Boring Logs for 18E-04 to 05 ................................................................................................. A-8 to 9 Drilling Photos ............................................................................................................................. A-10 Appendix B – Results of Laboratory Testing Summary of Laboratory Results .................................................................................................... B-1 Percent Passing No. 200 Sieve ...................................................................................................... B-2 Mechanical Sieve Analyses ................................................................................................... B-3 to 5 Atterberg Limits ............................................................................................................................ B-6 Proctor Compaction .............................................................................................................. B-7 to 8 pH and Resistivity .......................................................................................................................... B-9 Corrosivity Test Summary (for chloride and sulfate) .................................................................. B-10 file://synologygbca/GB_Server/Projects%20-%20Grover/217-347%20Muller%20-%20CFL%20Fossil%20House%20Rd/1.%20Geotechnical%20Report/217-347%20Fossil%20House%20Road%20Geotechnical%20Report.docx#_Toc23315363 file://synologygbca/GB_Server/Projects%20-%20Grover/217-347%20Muller%20-%20CFL%20Fossil%20House%20Rd/1.%20Geotechnical%20Report/217-347%20Fossil%20House%20Road%20Geotechnical%20Report.docx#_Toc23315364 file://synologygbca/GB_Server/Projects%20-%20Grover/217-347%20Muller%20-%20CFL%20Fossil%20House%20Rd/1.%20Geotechnical%20Report/217-347%20Fossil%20House%20Road%20Geotechnical%20Report.docx#_Toc23315365 file://synologygbca/GB_Server/Projects%20-%20Grover/217-347%20Muller%20-%20CFL%20Fossil%20House%20Rd/1.%20Geotechnical%20Report/217-347%20Fossil%20House%20Road%20Geotechnical%20Report.docx#_Toc23315366 file://synologygbca/GB_Server/Projects%20-%20Grover/217-347%20Muller%20-%20CFL%20Fossil%20House%20Rd/1.%20Geotechnical%20Report/217-347%20Fossil%20House%20Road%20Geotechnical%20Report.docx#_Toc23315367 iii

Consolidated Undrained Triaxial Test ............................................................................... B-11 to 16 Appendix C – Unanchored Cantilever Soldier Pile Wall Design Calculations Pile Data Table ....................................................................................................................... C-1 to 3 Calculations ..........................................................................................................................C-4 to 12 Appendix D – Slope Stability Analyses Fossil House Road Soldier Pile Wall ...................................................................................... D-1 to 3

1. PURPOSE AND SCOPE OF STUDY

Yeh and Associates was retained by Muller Engineering to provide geotechnical recommendations for the design of roadway improvements as part of the Federal Highway Administration, Central Federal Lands Highway Division (FHWA- CFLHD) project for Fossil House Road in Nye County, Nevada. This project is located on a 0.5-mile segment of Union Canyon Road and Fossil House Road within Berlin Ichthyosaur State Park in the Humboldt Toiyabe National Forest. The project site is on Union Canyon Road approximately 2.6 miles southeast of the junction of Nevada State Route 844 and Berlin Ichthyosaur State Park Road and extends up Union Canyon Road and then to the Ichthyosaur fossil house on Fossil House Road. The location of the site is shown in Figure 1.

The geotechnical evaluation consisted of a program of project coordination, data review, field exploration, laboratory testing, and engineering analyses as a basis for providing the recommendations in this report. This report provides recommendations for the design of five low water crossings, a gabion wall replacement on Union Canyon Road, a cantilever soldier pile retaining wall along Fossil House Road, and roadway reconditioning where planned.

2. PROJECT UNDERSTANDING

The project generally consists of the design of gravel road improvements, low-water crossings and drainage improvements on Union Canyon Road, and a new retaining wall on Fossil House Road. The layout and scope of the improvements to Union Canyon Road and Fossil House Road are shown on the Muller (2019) plans and described in the Muller (2015) Scoping Report. Union Canyon Road is an existing 12-to 22-foot wide gravel road with a posted speed of 15 to 25 miles per hour. Fossil House Road is an existing 10- to 14-foot wide gravel road with limited sight distance, no posted speed limit and terminates at the Fossil House.

Figure 1: Project Location Map

Union Canyon Road. The improvements along Union Canyon Road consist of improvements at four existing low-water crossings and one newly proposed new low water crossing. Grades will be raised or lowered along Union Canyon Road to accommodate grade alterations at the low-water crossings;

however, no widening of the road is planned at this time. Additional sections along Union Canyon Road that are experiencing encroachment from the adjacent stream between approximate Stations 84+78 and 86+51 will be regraded and stabilized with riprap. The road will be reconditioned with new aggregate to help conform to the existing grade where low-water crossings are planned on Union Canyon Road.

Table 1 presents a summary of the low-water crossings locations and proposed improvements. The crossings will help add resiliency to the road during potential seasonal flooding and inundation. The low water crossings at Sites 1 through 5 will be paved with a minor reinforced concrete section underlain by roadway aggregate. Scour barriers will be provided at the upstream and downstream edges of the crossing to protect against scour and underflow. The scour barriers will consist of precast concrete barriers set atop gabion walls. The gabion walls will have heights that range from 3 to 6 feet as summarized in Table 1. Revetment mattresses and/or riprap will be provided beyond the edges of the concrete beyond the scour barriers.

An existing gabion basket gravity wall near Site 5 has been undermined by scour and erosion and will be replaced as part of this project. The existing wall at Site 5 was approximately 3 feet tall and was undercut by approximately 2 feet at the time of our visit to the site.

Table 1: Union Canyon Road – Proposed Improvements

Site No. Station Proposed Improvement1

1 Union Canyon Road 52+61 to 54+59

Proposed low water crossing and channel bank protection using gabion wall to a depth of 3 feet.

2 Union Canyon Road 59+76 to 61+51

Existing low water crossing rehabilitation and gabion wall for scour protection to a depth of 3 feet

3 Union Canyon Road 64+16 to 67+09

Existing low water crossing rehabilitation and gabion wall for scour protection to a depth of 3 feet

4 Union Canyon Road 84+41 to 86+61

Existing low water crossing rehabilitation with a gabion wall to a depth of 3 feet

5 Union Canyon Road 87+49 to 90+74

Existing low water crossing rehabilitation and gabion wall for scour protection to a depth of 6 feet

1. Refer to Muller (2019) plans for site locations, dimensions and details of improvement.

Fossil House Road. The proposed improvements to Fossil House Road include providing a minimum 18-foot road width. Widening of the roadway will include embankments up to 10 feet in height constructed along the downhill side of the road, replacement of an existing gabion wall at the drainage near Union Canyon Road and a new approximately 400-foot long unanchored cantilever soldier pile retaining wall with heights of 3 to 16 feet on the downhill side of the roadway, and providing a catchment ditch along the roadway and placing erosion control on the slope above the road.

3. GEOTECHNICAL EXPLORATION AND TESTING

The geotechnical exploration consisted of a program of geologic reconnaissance, attendance of the 30-percent design review meeting at the site, exploratory drilling, and laboratory testing. The locations of the borings are shown on Plate 1. The boring logs and photos of equipment set-up of the explorations are presented in Appendix A, and laboratory test results are presented in Appendix B.

3.1 GEOLOGIC RECONNAISSANCE AND THIRTY PERCENT DESIGN VISIT

Field reconnaissance was performed on as a part of the 30 percent design walk on June 20 and 21, 2018 with representatives from Muller Engineering, Central Federal Lands, Nevada State Parks, ERO, the United States Forest Service and the Yomba Shoshone Tribe. The reconnaissance was performed to visually observe the condition of the roadway, low water crossings, proposed retaining wall areas, and search for potential borrow sources for the project. The 30-percent design plans were reviewed during the visit relative to field conditions including: evaluating options for retaining wall types along Fossil House Road, reviewing the scope and mitigation for damage to the existing and proposed low water crossings, construction considerations, and a field review for each low water crossing site. Boring locations were also marked with survey stakes in preparation for the July 2018 exploratory drilling program. Conditions and observations relative to the 30 percent design milestone were summarized in the Yeh (2018) memorandum and the FHWA field trip report (FHWA 2018).

3.2 EXPLORATORY DRILLING

The drilling subcontractor for the project was Gulf Shore Exploration Company of Rancho Cordova, California. Gulf Shore drilled two borings on Union Canyon Road at two of the existing low water crossings that are to be replaced and three borings along the proposed Fossil House Road retaining wall on July 24, 2018. The borings were drilled using a truck-mounted CME-75 drill rig equipped with 8-inch hollow-stem augers. The borings were drilled to depths ranging from 10 to 42 feet below the road surface. Yeh logged the subgrade conditions encountered and secured samples for subsequent laboratory testing.

Sampling within the borings was performed by driving either a modified California or standard penetration test (SPT) split spoon sampler at typical 5-foot intervals and by collecting bulk samples from the auger flights. The SPT sampler has 2-inch outside diameter, 1-3/8-inch inside diameter and is equipped for but was used without liners. The modified California sampler has a 3-inch outside diameter, 2-3/8-inch inside diameter and was used with 1-inch high brass liners. The drive samples were collected using a 140-pound automatic trip hammer in accordance with ASTM D1586, Standard

Penetration Test, procedures. The sampling depth, selected lab test results, recorded blow counts (N-values) for the driven samples, a description of subsurface conditions encountered, and method of backfilling the holes are presented on the boring logs in Appendix A.

3.3 LABORATORY TESTING

The results of laboratory tests are presented in Appendix B. Laboratory tests were performed on selected samples recovered from the field exploration program. Tests for moisture content, unit weight, Atterberg limits, percent passing the 200 sieve, sieve analyses, pH and resistivity, and Proctor compaction were performed at our laboratory in Grover Beach, California.

Tests for soluble sulfates and soluble chlorides were performed by Cooper Testing Labs in Palo Alto, California. Consolidated-undrained triaxial testing was performed by Cal Poly Geo-E Lab in San Luis Obispo, California. Testing was performed in accordance with American Society for Testing and Materials (ASTM) and American Association of State Highway and Transportation Officials (AASHTO) methods as noted on the lab reports. After the completion of the laboratory testing, the field descriptions were confirmed or modified as necessary and boring logs were prepared.

4. SITE CONDITIONS

4.1 GEOLOGIC SETTING

Published geologic information from DeCourten and Biggar (2017) and the Balini et. al (2014) geologic map were used to help characterize the regional geology in the site vicinity. The surface geology in the site vicinity, as mapped by Balini et. al (2014), is shown on Figure 2.

The bedrock in the Berlin-Ichthyosaur State Park is composed of the Luning-Berlin assemblage from the Triassic and early Jurassic Walker Lake terrane. Common in the Luning-Berlin assemblage are shallow marine carbonate rocks, including dolomite and limestone, as well as mudstone, sandstone, and conglomerate. Outcrops of shaley limestone outcroppings of the Triassic Luning Formation bedrock were observed along the canyon walls of Union Canyon Road. The outcrops were primarily composed of shaley limestone and carbonate members of the Luning formation that contains the Ichthyosaur fossils for which the Berlin-Ichthyosaur State Park is named.

4.2 TERRAIN AND VEGETATION

The project site is located within Berlin-Ichthyosaur State Park and the Shoshone Mountains of southwestern Nevada. The park is characterized by rolling hills and steep canyon walls. The existing road surface ranges from approximately elevation (el.) 6,757 feet at the beginning point of the project on Union Canyon Road, to approximately elevation 6,903 feet at the intersection with Fossil House Road, to approximately elevation 6,984 at the parking area at the end of Fossil House Road. Union

Figure 2: Geologic Map (Balini et. al 2014)

Canyon Road and Fossil House Road are primarily constructed on cut and fill through the side hills of the canyon. The hillside that Fossil House Road traverses varies from approximately 15- to 30-degree inclinations. The roadway crosses drainages via low water crossings within the project limits.

Vegetation in the park consists of large sagebrush at lower elevations, with pinyon pine and Utah juniper in the higher elevations.

4.3 CLIMATE

Climate data from (www.usclimatedata.com) for Round Mountain, Nevada (located approximately 35 miles east of Berlin-Ichthyosaur State Park), reports an average annual rainfall of 7 inches and 5 inches of snowfall. The reported monthly average temperature ranges from a low of 41 degrees Fahrenheit for December to a high of 90 degrees Fahrenheit in July. Intense precipitation events have been reported to occur during the summer monsoon season. State park representatives provided a video to the design team that showed a debris flow that ran down Union Canyon Road during an event in 2014.

The estimated frost depth is approximately 1.5 feet according to FHWA documentation.

4.4 EXISTING ROADWAY

Figure 3 presents photographs of typical roadway conditions along Union Canyon Road and Fossil House Road that were taken during Yeh’s June 2018 visit to the site. Union Canyon Road and Fossil House Road are gravel roads less than two lane widths wide that are generally confined by berms at the edge of traveled way. Cut slopes and fill slopes border the edge of the roadway. The road passes through mountainous terrain with relatively sharp turns that have limited sight distance.

Erosion has occurred along the drainage adjacent to Union Canyon Road and at the low water crossings where the main drainage crosses the road. Scour and erosion have undercut the upstream and downstream sections of the crossings to the edge of the roadway. The road was rough where http://www.usclimatedata.com/ maintenance operations had been performed to restore the existing low-water crossings and areas of the road that had been washed out.

5. SUBSURFACE CONDITIONS

5.1 ROADWAY SUBGRADE AND LOW WATER CROSSING CONDITIONS

Borings 18E-04 and 05 were drilled in Union Canyon Road. The subgrade of Union Canyon Road consisted of artificial fill composed of well-graded sand with silt and gravel and clayey sand. The artificial fill was encountered to depths of approximately 10.7 to 11.5 feet below the road surface. The fill generally consisted of dense to very dense poorly graded gravel with silt and sand, dense silty sand with gravel and medium dense clayey sand with gravel. Table 2 summarizes laboratory testing results on samples collected from the borings.

Figure 3: Typical Roadway Condition

Top left: Union Canyon Road view to east near Station 54+00; Top Right: Union Canyon Road Approx. Station 85+20 Bottom left: Fossil House Road Approx. Station 13+15; Bottom Right: Fossil House Road Approx. Station 14+60

Table 2: Subgrade Soil Properties Test Summary1

Geologic Unit Borings

Dry Unit Wt.

(pcf)

Moisture Content

Particle Size

Analyses (%G, %S, %F)

Atterberg Limits

LL, PI

Corrosion pH, ρ

(Ω-cm) Strength

Parameters Other

Artificial Fill (Af)

18E-04, 18E-05 89 3 - 6

24-25 G 55-60 S 15-20 F

25 LL

10 PI

pH = 7.98 ρ = 1,492 φ’cu = 37° c’cu = 460 psf γMAX. = 136 pcf

WOPT. = 7%

5.2 RETAINING WALL CONDITIONS

Borings 18W-01 through 03 were drilled along Fossil House road near the proposed retaining wall location and encountered units of artificial fill over sedimentary rock shale and sandstone) from the Luning Formation.

Artificial Fill. Artificial fill was encountered from the road surface to a depth of approximately of 8 to 12 feet below the road surface. The fill generally consisted of medium dense to very dense gravel and sand with varying amounts of silt, clay, and gravel, and stiff sandy lean clay with gravel. Luning Formation was encountered below the fill in each of the borings.

Luning Formation. Luning Formation was encountered to the maximum depths explored, approximately 21.5 to 41 feet below the road surface. The formation generally consisted of moderately weathered, soft shale with beds of moderately weathered, moderately soft sandstone.

Table 3 presents the laboratory testing results performed on samples obtained from borings along the length of the proposed retaining wall to depths ranging from 21.5 feet to 41 feet.

1 Geotechnical properties are noted for dry unit weight (γd) and moisture content (wo); particle size as percent gravel (G), sand size (S) and fines content (F); electrical resistivity (ρ) in ohm-centimeters (Ω-cm), soluble sulfates (SO4

2-) and soluble chlorides (Cl-); Atterberg liquid limit (LL) and plasticity index (PI); shear strength (S) in kips per square foot measured by pocket penetrometer (pp), torvane (tv) or unconsolidated undrained (uu) tests; friction angle (φ) or cohesion (c) in kips per square foot measured from direct shear - peak (ds) or consolidated undrained (cu) tests; permeability (k).

Table 3: Fossil House Road Soil Properties Test Summary

Geologic Unit Borings

Dry Unit Wt.

(pcf)

Moisture Content

Particle Size

Analyses (%G, %S, %F)

Atterberg Limits

LL, PI

Corrosion pH, ρ

(Ω-cm) Strength

Parameters Other

Artificial Fill (Af)

18W-01, 18W-02, 18W-03

-123 5 - 9

18-46% G 23-37% S

31 - 55% F

28 - 38 LL

13 - 18 PI

pH = 7.35- 7.69 ρ = 241-φ’cu = 38° c’cu= 100 psf

SO4

2-= 263 - 2,560 mg/kg

Cl- = 98 - 295 mg/kg γMAX. = 129 pcf

WOPT. = 9%

Luning

Formation (Trll, Trls, Trlu)

18W-01, 18W-02, 18W-03

- 115 9 - 14 -- 44 LL

21 PI

pH = 7.59 ρ = 361 φ’cu = 34° c’cu= 100 psf

SO4

2-= 778 mg/kg

Cl- = 177 mg/kg

5.3 GROUNDWATER

Groundwater was not encountered in the borings drilled on Union Canyon or Fossil House Road.

However, a spring was observed near the entrance to the canyon at approximately Station 53+00. Wet soil and seeps are likely to be present during periods of snow melt and spring thawing. Soil moisture and groundwater conditions are likely to vary seasonally and in association with changes in precipitation, runoff, and other factors.

6. CONCLUSIONS AND RECOMMENDATIONS

6.1 EARTHWORK - GENERAL

6.1.1 GENERAL GRADING

The recommendations of this report assume that surface aggregate and fill materials will be placed in general accordance with the Standard Specifications, FP-14. Site grading should conform to the applicable sections of FP-14 and the recommendations of this report. On-site soil encountered within the anticipated depth of excavation should be suitable for reuse as borrow for general embankment fill. The on-site material should not be considered suitable for reuse as select fill, such as structure backfill or aggregate base. Excess fill or cut material should be disposed of offsite, unless an onsite location has been identified for placement of excess fill on the project plans. Temporary excavations should conform to OSHA requirements.

6.1.2 EROSION AND SLOPE DRAINAGE

Erosion can occur where drainage runs uncontrolled along the edge of the roadway, such as between the edge of road and the base of cut slopes. Care should be taken that roadway work does not block or prevent the flow of surface drainage that is provided by existing ditches. Rock lined swales can be provided along the edge of the roadway to help reduce the potential for erosion.

Graded slopes will be vulnerable to erosion. Maintenance and repairs to gullied or eroded areas should be performed promptly while vegetation is being established. Concentrated flows of runoff should not be allowed to run over slopes. Overside drains and diversion drainage should be provided to carry water to the base of slopes and reduce the potential for erosion. Energy dissipation devices should be provided at the outlet of pipes and along ditches to reduce the potential for erosion where there are concentrated flows of runoff.

6.2 ROADWAY DESIGN

6.2.1 EMBANKMENT DESIGN

Embankment fill should be keyed and benched into the existing slope where embankment fill will be placed on existing grades steeper than 1v:5h as detailed in Figure 4. This detail supersedes CFL Standard Plan C204-50 that shows 8-foot high precut benches. The fill should be initiated from a base key excavated at the toe of the new embankment. The base key should be at least 2 feet deep and be excavated into firm and stable ground. The new embankment can then be keyed and benched into the existing slope as the fill is placed and such that at least the outer 5 feet of the existing slope is removed. Excavated material removed during keying and benching can be incorporated into the new embankment as the fill is being placed.

Figure 4: Typical Embankment Construction

6.2.2 RIP-RAP AND REVETMENT MATTRESS PROTECTION

Riprap protection is planned at areas where erosion has occurred or where seasonal drainages are encroaching on roadway embankments. The base of the riprap protection should be embedded below the existing stream channel deposits, at least 1-foot below the invert of the drainage.

6.2.3 AGGREGATE SURFACE ROADWAY

The project will include roadway surface reconditioning to provide the design 12- to 22-foot roadway along portions of Union Canyon Road and an 18-foot roadway width for Fossil House Road (Muller 2018b), as well as to provide a more durable road surface. Earthwork for roadway reconditioning should be performed in accordance with Section 303 of FP-14, which includes scarification, moisture conditioning, and compaction.

Roadway Aggregate. A minimum of 6 inches of compacted roadway aggregate should be placed across the prepared roadway surface to finished grade. Roadway aggregate should meet the gradation provided in the project special contract requirements that are summarized in Table 4.

Table 4: Roadway Aggregate

Sieve Size Percent by Mass Passing Designated

Sieve (AASHTO T27 and T 11)1

¾ inch (19 mm) 100

No. 4 (4.75 mm) 41-71

No. 40 (425 µm) 12-28

No. 200 (75 µm) 5-20

1. Plasticity Index (PI) of Roadway Aggregate should be between 4 and 12.

The cross-slope of the aggregate surface roadway should be graded to a typical 4 percent to help minimize erosion and wash boarding. A dust palliative could be applied to help reduce dust and the need for watering for dust control and to help stabilized the graded surface. Regrading and reconditioning of the aggregate surface road should be provided periodically to maintain ride quality, the slope of the road, and proper surface drainage.

Subgrade Stabilization. Subgrade stabilization should be provided in areas where unsuitable materials or soft subgrade conditions are encountered during construction that will not allow for proper compaction of the subgrade or roadway base materials, or where organic or other deleterious materials are encountered at the subgrade elevation that will not provide suitable foundation support for the new roadway. Subgrade stabilization should consist of removing the existing soil to a depth at least 1-foot below the bottom of subgrade elevation. If the subgrade is wet or yielding, subexcavation should be performed using backhoe type equipment such that construction equipment will not operate on the exposed subgrade during excavation.

A geotextile for stabilization should be placed over the undisturbed surface of the excavated subgrade following removal of the unsuitable material in accordance with Section 207 of FP-14. The geotextile should be placed without gaps or wrinkles and conform to Section 714.01, Class 1, Type E Geotextile, of FP-14. Gravel for stabilization should consist of uniformly graded 3/8 to 1.5-inch conforming to Section 703.6, Crushed Aggregate, of FP-14. The aggregate should be fully encased in the geotextile to reduce the potential for the overlying base course or adjacent soil to erode into the gravel.

The subgrade conditions encountered within our explorations were relatively dry. However, the project specifications should include a quantity for stabilizing the subgrade for the roadway, if needed.

Project specifications need to address increasing or decreasing this quantity or deleting the quantity based on the conditions encountered during construction. The geotechnical professional or contracting officer should review the subgrade conditions encountered at the time of construction to evaluate whether stabilization of the subgrade is needed, and to recommend the depth and limits of the subexcavation and stabilization.

6.3 LOW WATER CROSSINGS

Subsurface conditions encountered in two borings drilled in Union Canyon Road at the low water crossings consisted of medium dense to dense artificial fill consisting of sand and gravel soil as discussed in this report. The following is a summary of the recommended grading for support of the new low water crossings:

• Excavate existing material to at least 4 inches below the bottom of the concrete for the crossing.

• Prepare and compact the exposed subgrade in accordance with Section 208.08 (b), and 208.10 of FP-14. Boulders exposed in the excavation (if encountered) should be removed to allow for subsequent placement of the roadway aggregate. Depressions created by the removal of boulders should be backfilled with compacted foundation fill per FP-14 up to the bottom of the structural section.

• Place and compact a minimum of 4 inches of roadway aggregate below the concrete for the low water crossing or a minimum of 6 inches of roadway aggregate for the roadway structural section outside the limits of the concrete. The use of roadway aggregate, a granular material, below the concrete sections will reduce the potential for heave due to frost.

• Construct the low water crossing on the prepared subgrade per the project plans and specifications. The low water crossing should have minimum concrete thicknesses of 8-inches per standard details. The 8-inch concrete section for the low water crossing supported on roadway aggregate is considered sufficient for the intended vehicle use.

6.4 GABION WALLS

The existing gabion wall at Site 5 will be replaced where it has been undermined by the adjacent drainage near Station 89+25 on Union Canyon Road. Gabion walls are also planned at Sites 1-4 where low water crossings will be designed to reduce the impact of scour. The FHWA Eastern Federal Lands Detail E253-012 can be used to estimate the number of courses, widths, and other wall details for the design of the gabions.

6.5 UNANCHORED CANTILEVER SOLDIER PILE RETAINING WALL

An unanchored cantilever soldier pile and lagging retaining wall is planned along the downhill side of Fossil House Road to accommodate the proposed roadway widening. The proposed wall will have a design (lagged) height (H) ranging from 3 to 16 feet and a length of 396 feet (Muller 2019). Yeh has performed design calculations for this wall that are summarized in the following sections.

Methodology and Basis for Design. The unanchored cantilever solider pile wall was designed based on the AASHTO LRFD Bridge Design Specifications, 8th edition (2017). The spreadsheet calculations used for the analysis and pile data tables are provided in Appendix C. The wall height (H) is the lagged height of the wall. The bottom of the lagging should extend to at least 2 feet below finished grade in front of

2 https://flh.fhwa.dot.gov/resources/standard/efl/pdf/E253-01.pdf

Figure 5: Lateral Earth Pressure Distribution https://flh.fhwa.dot.gov/resources/standard/efl/pdf/E253-01.pdf the wall. A 4-foot wide bench sloped at 5 percent away from the wall face should be provided in front of the wall.

Geotechnical Properties. Geotechnical properties were assigned to foundation and retained materials based on the site conditions and topography, subsurface exploration, and laboratory testing.

Geotechnical and geometric properties were assigned to the wall location for use in estimating the simplified earth pressure distributions presented in the AASHTO LRFD Bridge Design Specifications. The lateral pressure distribution for granular soil was used to estimate the lateral earth pressures on the wall, the pile embedment and spacing needed to retain the soil and is shown in Figure 5.

The traffic surcharge from Fossil House Road was considered as an equivalent uniform pressure (qs) of 240 psf applied vertically over the traveled way behind the wall. The retaining wall design parameters were estimated assuming drained backfill conditions. The retained portion of the wall was characterized as granular soil as the wall will be constructed to retain existing granular soil and be backfilled with Structural Backfill. The embedded portion of the wall was characterized as granular soil to account for the weathered nature of the bedrock encountered in the borings. The wall design parameters used in our calculations from Figure 5 are shown in Table 5.

Table 5: Geotechnical Properties for Wall Design

Element Property

Wall

Wall Height (H) 3 to 16 ft.

Center to Center Pile Spacing (l) 6 ft.

Pile Diameter (b) 2.5 ft.

Backslope (β) 0°

Bench width at base of wall (not shown on Fig. 5) 4 ft.

Grade below wall (β′) 26° (1v:2h)

Structural Backfill

Soil Unit Weight (γs1) 120 pcf

Friction Angle (φ′f1) 34°

Active Coefficient (ka1) 0.28

Foundation Material

Soil Unit Weight (γs2) 123 pcf

Friction Angle (φ′f2) 34°

Active Coefficient (ka2) 0.28

Passive Coefficient (kp2) 3.5

Element Property

Passive Slope Correction for β′ 0.92(1)

Arching factor at pile 3b

1. Slope correction was estimated graphically assuming a 45-degree wedge would develop within the upper five pile diameters of the embedment zone that could be intersected by the slope in front of the wall and beyond the 4-foot bench width.

Load and Resistance Factors. Load and resistance factors provided in AASHTO LRFD Bridge Design Specifications were applied during the analyses and are summarized in Table 6.

Table 6: Resistance and Load Factors

Factor Type Value ϕPASSIVE Passive Resistance Factor for Vertical

Elements 0.75 ϕ fy Resistance Factor for Flexural Capacity of

Vertical Wall Elements 0.9 γ p,EH Active Horizontal Earth Pressure Load Factor, Strength Limit State I 1.5 γ p,EQ Active Horizontal Earth Pressure Load Factor, Extreme Limit State I 1.0 γ LS Live Load Surcharge Load Factor, Strength

Limit State I 1.75 γ LS, EQ Live Load Surcharge Load Factor, Extreme Limit State I 0.5 γ EH,SER Active Horizontal Earth Pressure Load Factor, Service Limit State I 1.0 γ LS,SER Live Load Surcharge Load Factor, Service Limit State I 1.0

Extreme Limit State. The retaining wall should be designed to resist lateral pressures from the design the earthquake. Earthquake loads were estimated using the General Limit Equilibrium (GLE) method presented in FHWA (2011) and referenced in the AASHTO (2018) Bridge Design Specifications. The design peak ground acceleration and earthquake magnitude used for the GLE analysis were estimated using the USGS Unified Hazard Tool (accessed May 10, 2019) corresponding to a 5 percent in 50-year (or 975 year) return period. The site coordinates were estimated as 38.8741 degrees latitude and -

117.5912 degrees longitude. An average shear wave velocity of 350 meters per second was used for the analysis, corresponding to a borderline Site Class D, stiff soil, or Site Class C, very dense soil or soft rock, site. A design peak ground acceleration of 0.28g was estimated by the probabilistic hazard analysis for an earthquake with a mean magnitude of 6.4 likely occurring on the Ione Valley and Reese River Valley faults.

Subsequently, the computer program SLIDE 2018 (Rocscience 2019) was used to perform a Generalized Limit Equilibrium model for the wall to estimate the seismic increment of active earth pressure for the wall design for an average wall height of approximately 12 feet. A horizontal pseudostatic coefficient of

0.13 was estimated for the design earthquake using simplified procedures presented in the California Geologic Survey (CGS 2008) Special Publication 117a, and similar to those described in FHWA (2011), that consider the design earthquake, duration, and displacement. The active earth pressure was estimated by applying a triangular shaped surcharge against the vertical face of the slope to represent a retaining wall supporting the static load, and then a uniformly applied pressure that was varied to estimate the dynamic load at a corresponding resistance factor of 1.0. The estimated dynamic earth pressure of 3.5H was added to the static earth pressure (Pa1 on Figure 5), and the deformation and stresses in the wall checked to see if the deflections were in tolerable limits for the wall structural elements. The governing design limit state for this wall is the strength limit state base on the calculations. The output of this analyses is included in Appendix D.

Slope Stability. The retaining wall is designed to retain earth pressures within the active wedge that extends to approximately H/2 behind the wall. The new wall will be located on the shoulder of the widened Fossil House Road. The foundation support material below the wall location is the Luning Formation. Existing or previous instability of the slope below road has not been observed. The potential for a slope failure to develop below the wall is expected to be less than for the existing slope conditions, therefore design of the new wall to support the lateral earth pressures shown in Figure 6 is considered appropriate for design.

Pile Embedment Calculation (D). The pile embedment is the embedment needed to resist lateral forces and bending stresses for the lateral earth pressures shown in Figure 6. Resistance and load factors were applied to the lateral earth pressures values in our analyses. The embedment depth, Do, represents the pile embedment where the moments from the net passive resistance and the lateral earth pressures acting on the wall sum to zero providing moment equilibrium. The passive resistance is applied using the solider pile for the embedded portion of the pile cast into a drilled hole of diameter (b). The passive pressure acting on the pile is assumed to active over 3 pile diameters (3b) to account for arching for a pile embedded in granular soil. The final embedment of the pile was increased by 10 percent to the design embedment depth, D = 1.1Do. The H-pile was then sized to resist bending moments and stresses for the earth pressures.

Lagging. The lagging for the wall should be consist of 6-inch thick, preservative treated per AWPA U1 Use Category UC4B, Douglas Fir Treated Timber Lagging per Section 716.03 of the Standard Specifications. A 1/2-inch gap should be provided between members. Shims should be used to provide the gap. The lagging thickness was checked based on the lateral earth pressures and traffic surcharge.

Calculations for the estimated lagging pressure is provided Appendix C based on AASTHO LRFD Bridge Design Specifications commentary provides equation C11.8.5.2-2 for estimating the maximum moment on simple span lagging with soil arching.

Drainage. Drainage should be provided behind the wall to maintain drained backfill conditions. A Class 1, Type E nonwoven geotextile conforming to Section 714.01 should be provided behind the lagging to reduce the potential for soil to pipe or erode through the lagging. Drainage should be provided using ½ inch gaps between the lagging boards and installing 2-inch diameter weep holes located 4 inches above finish grade centered between the piles.

6.6 CORROSION CONSIDERATIONS

FHWA foundation design manuals define potentially aggressive conditions of fill, natural soil, and groundwater as the following:

• The soil pH is less than 4.5.

• The soil or water resistivity is less than 2000-ohm-cm.

• The sulfate ion content exceeds 200 parts-per-million (ppm) or the chloride content exceeds

100 ppm.

• Soils with resistivity greater than 5000 ohm-cm are considered non-aggressive towards concrete and steel.

• A corrosion rate of 0.0015 inch/year is used for steel piles buried in fill or disturbed natural soil

(Caltrans 2018).

Tests for pH, electrical resistivity, as well as water soluble chlorides and sulfates were performed on selected samples. The test results are presented in Appendix B. The pH for the samples tested ranged from 7.35 to 7.98 and the soil resistivity ranged from 241 to 1,492 ohm-centimeters. Samples with soil resistivities of 1,000 ohm-centimeters or less were tested for water-soluble chloride and sulfate contents. The water-soluble chloride content for the samples tested were 98 to 295 ppm. The water-soluble sulfate content for the samples tested was 263 to 2,560 ppm. The samples tested are considered aggressive towards concrete. Three samples tested for water soluble chlorides and four samples tested for water soluble sulfates exceed FHWA limits. We recommend that the concrete structures and cement types are selected that are compatible with the potentially corrosive environment. Type V cement is recommended for structures based on the corrosion potential of soil tested. The recommended pile sections for the unanchored cantilevered soldier pile wall on Fossil

House Road accounted for the estimated steel degradation over the 75-year life of the wall. Culverts for the project should be selected to account for the corrosive soil environment. HDPE is a good material for resisting soil and water corrosivity but could be prone to melting during a fire. Metal pipes are not suggested given the potential for corrosion; however, if they are used increasing the thickness of sidewalls should be considered. The corrosion rate of 0.0015 inch per year should be used when considering increased pipe thicknesses.

7. NOTES TO CONSTRUCTION

1. The contractor should not undermine the cut slopes when performing roadway or ditch reconditioning. Slopes above the road could be prone to instability if the toe of the slope is removed.

2. Temporary slopes should be braced or sloped according to the requirements of OSHA. We expect the soil within temporary excavations will generally consist of existing fill and dense to very dense sandy alluvium, which can be classified as Type C soil. Type C soil can be sloped to 1.5:1 for slope heights up to 20 feet. The design of temporary slopes or shoring systems needed for construction is the responsibility of the contractor. The solder pile and lagging retaining wall on Fossil House can be constructed from top down and act as shoring as the wall is constructed below existing grade.

The slope inclination used for the construction of temporary slopes will be determined by the contractor’s competent person per OSHA guidelines and the subsurface conditions encountered at the time of construction. Slopes or shoring systems exceeding 20 feet in height are not addressed by OSHA and should be designed by a qualified registered professional. If needed, the contractor should submit an excavation and shoring plan for slopes more than 20 feet in height for review by the geotechnical professional prior to beginning the excavation.

3. Groundwater was not encountered in any of the borings drilled. However, groundwater and surface could enter or be encountered within excavations for the low-water crossings depending on the time of year and precipitation. The Contractor should be prepared to control surface water during construction and to maintain a dry and stable excavation through the duration of construction. Sumps, well screens, and dewatering pits should be properly filtered such that fines and the surrounding soils are not removed or disturbed by dewatering.

4. Sand with varying amounts of silt, clay, gravel, and cobbles as well as boulders were exposed on where widening of the cut slope is planned to be laid back. Luning Formation that consisted of shale and sandstone were encountered in the borings drilled along Fossil House Road at a depth of approximately 8 to 17 feet below the road surface and may be encountered during drilling of the soldier pile foundations. These materials are anticipated to be excavatable with heavy earthmoving equipment such as excavators and bulldozers and single shank rippers. Rock teeth and core barrels may be needed to drill into the Luning Formation.

5. Cobbles and boulders ranging in size from approximately 6 to 18 inches in dimension were observed along Union Canyon Road and Fossil House Road. Similar material was observed in upstream and downstream of the drainage crossings along the roadway. The drainage crossings are generally constructed across drainages that are subject to periodic debris flows that transport cobbles, boulders, trees, and other materials that may be encountered during construction

8. MATERIAL SOURCES

8.1 CONCRETE, RIPRAP AND AGGREGATE

The main material requirements for this project are likely to include concrete, riprap and aggregates that are available from commercial suppliers in the vicinity of Fallon in Churchill County, Nevada. Haul times to the site from commercially available supplier yards will exceed 2 hours. Yeh contacted material suppliers for riprap and aggregate. A&K Earthmovers, INC3 (A&K) was the closest company that responded to our inquiries for material sources. A&K has the ability to provide concrete, riprap, aggregate for the project from their yard in Fallon, Nevada (approximately 150 miles northwest of the site). A&K can also provide on-site crushing services to meet material requirements for aggregate and they have a portable concrete batch plant. A&K have also worked at the site in the past and most recently assisted with an emergency reopening of Union Canyon Road when it was inundated in 2014.

This report is not a statement that this potential supplier or proposed borrow sources are pre-approved nor implies that the plants will meet quality control and material compliance for the project or materials to be placed at the site.

8.2 GENERAL BORROW

Excavated onsite soil and excess material from the project area should be suitable for reuse as general borrow. Excavated onsite soil and rock may contain large particles that will need to be broken down or segregated from the fill to make the material suitable for compaction. Control of moisture content, compaction layer thickness and selecting suitable equipment will be necessary to achieve the relative compaction for compacted fill.

A Nye County borrow pit is located approximately 3 miles west along State Route 344. Mr. Stretch Baker of Nye County4 is the representative for contacting about use of the borrow pit. The location of the pit is at 38.8734 north and 117.6596 west. The County has used this pit in the past for roadway materials.

9. LIMITATIONS

This study has been conducted in general accordance with currently accepted geotechnical practices in this area for use by the client for design purposes. The conclusions and recommendations submitted in this report are based upon the data obtained from field reconnaissance, exploratory test pits, drilling and sampling, and our understanding of the proposed project and type of construction described in this report. If there are any changes in the project or site conditions, Yeh should review those changes and provide additional recommendations, if needed. Any modifications to the recommendations of

3 A&K Earthmovers, Inc., 515 Windmill Drive, Fallon, NV 89406 (775)-423-6085 4 Nye County, Stretch Baker, (775) 482-4119 this report or approval of changes made to the project should not be considered valid unless they are made in writing. The report and drawings contained in this report are intended for design-input; and are not intended to act as construction drawings or specifications.

Site conditions will vary between points of observation or sampling, seasonally, and with time. The nature and extent of subsurface variations across the site may not become evident until excavation is performed. If during construction, fill, soil, or water conditions appear to be different from those described herein, Yeh should be advised and provided the opportunity to evaluate those conditions and provide additional recommendations, if necessary. The geotechnical professional should observe portions of the construction and site conditions, such as excavations, exposed subgrades and earthwork, to evaluate whether or not the conditions encountered are consistent with those assumed for design, and to provide additional recommendations during construction, if needed.

10. REFERENCES

American Association of State Highway and Transportation Officials (AASHTO 2017), LRFD Bridge

Design Specifications, Eighth Edition, September 2017.

Balini et. al (2014). The Carnian/Nornian boundary succession at Berlin-Ichthyosaur State Park (Upper Triassic, central NV, USA), Plaontologische Gesellschaft (Palentological Society – Germany)

California Geological Survey (CGS 2008). Special Publication 117A, Guidelines for Evaluating and Mitigating Seismic Hazards in California, September 11, 2008.

California Department of Transportation (Caltrans 2011), Trenching and Shoring Manual, August 2011

California Department of Transportation (Caltrans 2018), Corrosion Manual, March 2018

DeCourten, F., and Biggar, N. (2017). Roadside geology of Nevada. Mountain Press Publishing Company, Missoula, MT

Federal Highway Administration (FHWA 2011), LRFD Seismic Analysis and Design of Transportation Geotechnical Features and Structural Foundations Reference Manual, Geotechnical Engineering Circular No. 2, NHI Course No. 130094, Publication NO. FHWA-NHI-11-032

Federal Highway Administration (FHWA 2018), Fossil House Road, 30 percent Field Review, NV FLAP 300(1), August 21, 2018

Muller Engineering Company, Inc. (Muller 2015), Scoping Report, US Forest Service – Humbolt Toiyabe National Forest, Nye County, Nevada, NVFLAP NV 300 (1), Fossil House Road, prepared for the FHWA Central Federal Lands Division, October 2, 2015.

Muller Engineering Company (Muller 2019), Inc., 95% Plans, Fossil House Road, Nye County, Nevada, NVFLAP NV 300 (1), prepared for the FHWA Central Federal Lands Division, print date August 2019.

Muller Engineering Company (Muller 2018a), 30 Percent Design Project Technical Memorandum, Fossil House Road, Nye County, Nevada, NVFLAP NV 300 (1), prepared for the FHWA…