Beaver_Dam_Road_Geotechnical_Report_-_Final.pdf

GEOTECHNICAL REPORT

NV FLAP 200 (1)

Beaver Dam Road Improvements

Lincoln County, Nevada

Yeh Project No.: 217-348

October 5, 2018

Prepared for:

Muller Engineering Company, Inc.

777 S. Wadsworth Boulevard 4-100 Lakewood, Colorado 80226

Attn: Mr. Steven Gabriszeski, 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 200(1)

Beaver Dam Road

Lincoln County, Nevada

Yeh Project No.: 217-348

October 5, 2018

Prepared by:

Judd King, P.E. (CA, NV), G.E. (CA) Wade Hoon Geotechnical Engineer Senior Project Geologist

Independent Reviewer: Independent Reviewer:

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

6-30-2019

Geotechnical Report Yeh Project No. 217-348 Beaver Dam Road October 5, 2018 i

TABLE OF CONTENTS

1. PURPOSE AND SCOPE OF STUDY

2. PROJECT UNDERSTANDING

3. GEOTECHNICAL INVESTIGATION

3.1 GEOLOGIC RECONNAISSANCE

3.2 EXPLORATORY TEST PITS

3.3 THIRTY PERCENT DESIGN SITE VISIT

3.4 EXPLORATORY DRILLING

3.5 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 CONDITIONS

5.2 REINFORCED CONCRETE BOX CULVERTS

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 CUT SLOPE DESIGN

6.2.3 CATCHMENT RESTORATION

6.2.4 RIP-RAP PROTECTION

6.2.5 AGGREGATE SURFACE ROADWAY

ii

6.2.6 HMA PAVEMENT DESIGN – STATION 212+70 TO 219+00

6.3 LOW WATER CROSSING

6.4 CONCRETE BOX CULVERTS

6.5 CORROSION CONSIDERATIONS

7. NOTES TO CONSTRUCTION

8. MATERIAL SOURCES

8.1 PAVEMENT AND AGGREGATE

8.2 GENERAL BORROW

9. LIMITATIONS

10. REFERENCES

List of Figures

FIGURE 1: PROJECT LOCATION MAP

FIGURE 2: GEOLOGIC MAP (EKREN ET. AL 1977)

FIGURE 3: TYPICAL ROADWAY CONDITION

FIGURE 4: STATION 221+50

FIGURE 5: SUBSURFACE PROFILE: RCB STATION 157+87

FIGURE 6: SUBSURFACE PROFILE: RCB STATION 218+11

FIGURE 7: TYPICAL EMBANKMENT CONSTRUCTION

FIGURE 8: CUT SLOPES AT SITE 4

FIGURE 9: SUMMARY OF RCB FOUNDATION PREPARATION AND BACKFILL

FIGURE 10: ACOMA QUARRY

List of Tables

TABLE 1: BEAVER DAM ROAD – PROPOSED IMPROVEMENTS

TABLE 2: SUBGRADE SOIL PROPERTIES TEST SUMMARY

TABLE 3: REINFORCED CONCRETE BOX CULVERTS SOIL PROPERTIES TEST SUMMARY1

TABLE 4: CATCHMENT RESTORATION

TABLE 5: ROADWAY AGGREGATE

TABLE 6: SUMMARY OF REINFORCED BOX CULVERT LOCATIONS

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List of Plates

Field Exploration Plan .......................................................................................................................................1.1 to 1.9

List of Appendices

Page Appendix A – Test Pit and Boring Logs

Boring and Test Pit Record Legend....................................................................................................... A-1 to 2 Test Pit Logs for 18P-01 to 05 ............................................................................................................... A-3 to 7 Boring Logs for 18P-06 to 09 .............................................................................................................. A-8 to 11 Test Pit and Boring Location Photos ................................................................................................. A-12 to 14

Appendix B – Results of Laboratory Testing Summary of Laboratory Results ........................................................................................................... B-1 to 2 Mechanical Sieve Analysis .................................................................................................................... B-3 to 6 Percent Passing No. 200 Sieve..................................................................................................................... B-7 Atterberg Limits ........................................................................................................................................... B-8 Proctor Compaction ........................................................................................................................... B-9 to 10 pH and Resistivity ...................................................................................................................................... B-11 Corrosivity Test Summary (for chloride and sulfate) ................................................................................. B-12 Direct Shear ...................................................................................................................................... B-13 to 14 Unconfined Compressive Strength of Rock ...................................................................................... B-15 to 16 Aggregate Quality Test Summary ..................................................................................................... B-17 to 18

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

Beaver Dam Road in Lincoln

County, Nevada. This project is located on a 2.2-mile segment of

Beaver Dam Road within Beaver

Dam State Park. The project begins just south of Campground B and extends to the southern boundary of the park. 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. A second phase of field exploration was performed in July 2018 at the proposed reinforced concrete box

(RCB) culvert locations. This report provides recommendations for rehabilitation of the existing road and geotechnical considerations for the design of a low water crossing, cut slopes, roadway reconditioning, and RCBs.

2. PROJECT UNDERSTANDING

The layout and scope of the improvements are shown on the Muller (2018) plans and described in the Scoping Report (Muller 2015). Beaver Dam Road provides the only access to Beaver

Dam State Park and the surrounding Clover Mountain BLM lands. The existing gravel roadway is typically 12-15 feet wide, with a posted speed limit of 15 miles per hour. The project consists of improvements to approximately 2.2 miles of Beaver Dam Road. The roadway will remain on

Figure 1: Project Location Map essentially the same horizontal and vertical alignment. Project components will include providing a minimum 14-foot road width, installing culverts, performing slope maintenance, and drainage improvements. Catchment ditches for rockfall and debris will be restored along the base of existing cut slopes. The road surface will be reconditioned to improve durability and longevity with a roadway aggregate. Specific project improvements are summarized in Table 1. Site numbers and stationing are referenced to Muller (2018) plans.

Table 1: Beaver Dam Road – Proposed Improvements

Site No. Station Proposed Improvement1

1 135+00 to 140+50, Lt.

140+69, Lt. & Rt. Ditch reconditioning, Replace existing culvert.

2 151+87 to 153+67, Rt. Slope armoring along seasonal creek.

3 157+87, Lt. & Rt.

Replace existing corrugated metal pipe culverts with a new reinforced concrete box culvert with a cross-sectional opening of 12 feet wide and 6 feet tall.

4 162+68 to 164+29, Rt. Lay back existing slope at 1v:0.75h.

5 167+56, Lt. & Rt. Remove and replace existing culvert.

6 171+84, Lt. & Rt. Install new culvert

7 175+98, Lt. & Rt. Installing new culvert ends.

8 177+56 to 179+89, Rt. Lay back existing slope at 1v:1h.

9 181+20 and 182+69, Lt. & Rt.

Remove one of the culverts and replace. Install new culvert ends on the other culvert

10 195+83 to 197+79, Lt.

& Rt.

Remove existing culvert and replace area with low water crossing.

11 218+11, Lt. & Rt.

Replace existing corrugated metal pipe culvert with a new reinforced concrete box culvert with a cross-sectional opening of 8 feet wide and 6 feet tall.

12 221+60, Lt. Repair eroded portion of embankment to match existing embankment slope

13 227+88, Lt. Repair eroded portion embankment to match existing embankment slope

14 242+25, Lt. Grade and widen existing waterfall trail head.

15 244+70, Lt. Grade existing vehicle pullout.

NA 131+45 to 246+36 Recondition subgrade and place 6 inches of new surface aggregate (excluding Stations 212+70 to

219+00)

NA 212+70 to 219+00

Recondition subgrade and slope to drain to downhill side. Construct new structural section consisting of a variable thickness hot-mix asphalt (HMA) leveling course and a 3-inch finish HMA course.

1. Refer to Muller (2018) plans for dimensions and details of improvement.

3. GEOTECHNICAL INVESTIGATION

The geotechnical investigation consisted of a program of geologic reconnaissance, exploratory test pits and sampling, exploratory drilling, laboratory testing, reviewing existing geotechnical data available for the site, and attending the 30-percent design review meeting at the site. The locations of the test pits and borings are shown on Plates 1.1 through 1.9. The logs and photos of equipment set-up of the explorations are presented in Appendix A, laboratory test results are presented in Appendix B.

3.1 GEOLOGIC RECONNAISSANCE

Field reconnaissance was performed on March 15 through 17, 2018. The reconnaissance was performed to visually observe the condition of the roadway, review cut slopes that are proposed to be laid back, and search for potential borrow sources for the project. Yeh also collected bulk samples of soil from proposed cut slope areas for laboratory testing. Conditions and observations relative to the 30 percent design milestone were summarize in the Yeh (2018) memorandum.

3.2 EXPLORATORY TEST PITS

Pearson and Sons Construction of Panaca, Nevada provided backhoe excavation services. A rubber-tired Case 580 model backhoe equipped with an 18-inch wide bucket was used to excavate five test pits at the site on March 16, 2018. The excavations were advanced to depths ranging from approximately 2.5 to 5.5 feet below the ground surface. Yeh staff logged the test pits identifying soil types, bedrock types, and geologic contacts. Bulk samples of soil and rock were collected from excavation spoils. Tube samples were collected from the pits by pushing 3-inch diameter steel tubes into the ground at selected depths and locations using the backhoe’s hydraulics. The sample tubes had a 1/16-inch wall thickness. Samples were classified, labeled and secured for subsequent laboratory testing. After excavation and logging, the test pits were backfilled, tamped with the bucket of the backhoe and wheel rolled. Logs of the test pits are presented in Appendix A.

Yeh performed dynamic cone penetrometer (DCP) testing at various depths in test pits 18P-01 and 18P-04. Yeh performed the DCP testing using a 15-pound steel mass falling 20 inches to strike an anvil to penetrate a 1.5-inch-diameter, 45-degree cone that was seated in the bottom of the test pit. Yeh recorded the number of blows to achieve 1.75-inch increments of penetration. The DCP penetration resistance was used to qualitatively assess the consistency of the subsurface material.

3.3 THIRTY PERCENT DESIGN SITE VISIT

A second site visit and field reconnaissance trip was performed on May 3, 2018 with representatives from Muller Engineering, Central Federal Lands, ERO, and Nevada State

Parks. The roadway alignment was reviewed with respect to the 30-percent design plans and design decisions were made pertaining to proposed cut slopes, the need for catchment clean-out, culvert locations, roadway reconditioning, and surface materials for the project. Yeh also collected samples of potential roadway aggregate source materials from stockpiles at the

Acoma Quarry, which is located approximately 4 miles northwest of the project. Boring locations for the proposed concrete box culverts were also marked with survey stakes in preparation for the July 2018 exploratory drilling program.

3.4 EXPLORATORY DRILLING

Gulf Shore Exploration Company of Rancho Cordova, California provided exploratory drilling services on July 26, 2018. Gulf Shore drilled two borings at each of the two box culverts for a total of four borings using a truck-mounted CME 75 drill rig equipped with 8-inch hollow-stem augers. The borings were drilled to depths ranging from 15 to 30 feet below the road surface

(approximately 5 to 20 feet below the proposed invert elevation of the culverts). Yeh logged the subgrade conditions encountered, and secured samples for subsequent laboratory testing.

The borings were sampled by collecting bulk samples from the auger flights and with drive samplers. Drive samples were collected using a modified California or standard penetration test

(SPT) split spoon sampler at typical 5-foot intervals. 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, and a description of subsurface conditions encountered are presented on the boring logs in Appendix A.

3.5 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, particle size distribution by sieve analysis, pH and resistivity 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. Unconfined compressive strength tests on rock samples and direct shear tests on soil were performed by Cal Poly Geo-E Lab in San Luis Obispo. Aggregate quality tests including LA rattler, soundness, durability index, fractured faces, and gradation were performed by Earth Systems Pacific 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

The regional geology in the site vicinity as mapped by Ekren et. al. (1977) is shown on Figure 2.

The project is located within the Basin and Range geologic and geomorphic province, which spans from the Sierra Nevada to the Colorado Plateau and from southern Idaho into the state of

Sonora, Mexico. The province is characterized by a series of north-south trending linear mountain ranges paired with low lying intervening valleys.

The topography is a result of extensional tectonics in the east-west direction that caused thinning of the earth’s crust followed by normal faulting that created uplifted mountain ranges and down dropped basins. The project area is within the Caliente Caldera Complex that has filled with pyroclastic volcanic and sedimentary rocks since it was estimated to have erupted 23 to 18 million years ago (DeCourten and Biggar 2017). Volcanic and sedimentary rocks include tuffs and ash flows that are thousands of feet thick (Tschanz and Pampeyan 1961). Surface sediment observed along portions of the project site consisted of colluvium and residual deposits derived from the volcanic materials exposed within the caldera complex. Weide (1982) mapped colluvial and residual deposits up to about 5 meters (16.4 feet) thick within the area.

Volcanic and sedimentary ash-flow tuff was observed below the colluvium in road cuts along the project.

Figure 2: Geologic Map (Ekren et. al 1977)

4.2 TERRAIN AND VEGETATION

The project site is located within Beaver Dam State Park and the Clover Mountains of southeastern Nevada. The park is characterized by steep canyon walls, ephemeral drainages, and rolling hillsides. The existing road surface ranges from approximately elevation (el.) 5,280 feet at the beginning point of the project, to approximately el. 4950 feet at the project terminus.

Beaver Dam Road is constructed along hillsides with cut and fill embankments, sometimes on steep hillsides along the project alignment. The roadway follows and crosses, via culverts, many drainages within the project limits. Pinyon pine and Utah juniper with big basin scrub brush are the predominant vegetation within the project.

4.3 CLIMATE

Climate data from (www.usclimatedata.com) for Pioche, Nevada (located approximately 40 miles north of Beaver Dam State Park), reports an average annual rainfall of 13 inches and 17 inches of snow. The rainfall occurs throughout the year with snow falling in the winter months and early spring. The reported monthly average temperature ranges from a low of 21 degrees

Fahrenheit for January to a high of 89 degrees Fahrenheit in July.

4.4 EXISTING ROADWAY

Beaver Dam Road is a relatively narrow (less than 2 lanes wide) gravel road that is generally confined by earth windrows and berms along the edge of the roadway. The road profile consists of areas with steep vertical grades and locations with limited sight distance. There are many areas where poor drainage allows storm runoff to travel longitudinally along the roadway resulting in erosion and gullies to form within the road bed and erosion where runoff overtops embankments. A wildfire occurred in the area in 2014, the results of which have had a major impact on the road and drainages. Debris flows triggered by rains in the summer of 2015 overwhelmed many of the drainages and caused damage to the roadway. These events and subsequent storms have and continue to require increased maintenance efforts by Lincoln

County and Nevada State Parks.

http://www.usclimatedata.com/

Maintenance operations have resulted in an entrenched road surface where earth berms border both sides of the roadway for approximately 80 to 90 percent of the roadway alignment. The roadside ditches are filled and rocks periodically fall into the roadway because the catchment zone is filled (see Figure 3, Station. 223+00). Drainage outlets or down-drains are infrequent and erosion of embankments has occurred where water eventually overtops the berms and runs down slopes (see Figure 3, Station. 222+00). Bedrock is exposed at the road surface where the grade of road is estimated at approximately 15 to 19 percent (see Figure 3, Station. 214+00).

There are several locations where over topping has occurred due to plugged and overwhelmed

Figure 3: Typical Roadway Condition Top left: Station 223+00; Top Right: Station 222+00

Bottom left: Station 214+00; Bottom Right: Station 158+00 culverts. At other locations, the drainages are filled with debris flow material, altering their form and geometry with the roadway.

The many curves, combined with short but steep cut slopes, creates sight distance limitations at several locations.

Melting snow and rain had saturated the road surface during Yeh’s field work in March 2018. The wet conditions resulted in softening of the road surface, poor traction and rutting of the existing roadway surface (see Figure 3, Station 158+00). Boulders and rock outcrops protrude up from the roadway surface about 1 to 4 inches in some areas along the road (see Figure 4).

5. SUBSURFACE CONDITIONS

5.1 ROADWAY SUBGRADE CONDITIONS

The subgrade encountered in the roadway was predominantly artificial fill, colluvium and bedrock. The fill and colluvium consisted of medium dense to dense silty sand and well-graded sand with varying amounts of fine to coarse gravel and cobbles and boulders ranging in size from 6 to 18 inches in dimension. The cobbles and boulders were also observed protruding from the roadway throughout the alignment (see Section 4.4). Younger volcanic rock consisting of ash flow tuff and volcanic tuff were encountered in all of the test pits with the exception of

18P-04. The tuff was encountered at the surface of the road to depths of approximately 3 feet.

The tuff was generally massive, moderately hard, and fresh to slightly weathered. Tuff was also observed in outcrops along the roadway surface and had been exposed by recent maintenance activities. Rhyolite igneous rock was observed in the road surface between approximately

Stations 213+00 and 218+00. The grade of the road is approximately 15 to 19 percent in this section and the rock has been cut by maintenance activities. The rhyolite rock was moderately fractured, hard, and fresh.

Figure 4: Station 221+50 Boulder protruding up from subgrade into roadway

Table 2 presents a summary of laboratory test results performed on subgrade samples collected within the upper approximately 5 feet of test pits, borings, and rock samples taken from cut slopes, and the road surface.

Table 2: Subgrade Soil Properties Test Summary1

Location

Locations, Test Pits &

Borings

Dry Unit Wt. (pcf) and Moisture

Particle Size

Analyses (%G, %S, %F)

Atterberg Limits

LL, PI

Proctor γdmax, wopt

Common USCS and AASHTO

Classifications

Project Alignment

Stations 151+00, 164+00, 170+00 18P-01 through 18P-γd: 70-156 wo: 3-31%

8-45 G 46-75 S 3-28 F

33-40 LL

5-13 PI

γdmax: 101 -114 pcf wopt:

10-16%

Well-graded Sand with gravel (SW)

Silty SAND w/ gravel (SM) Clayey SAND with gravel

(SC)

A-1-b, A-2, A-4

Volcanic Tuff and Rhyolite

5.2 REINFORCED CONCRETE BOX CULVERTS

Borings were drilled at each of the proposed reinforced concrete box culverts (Stations 157+87 and 218+11). Subsurface conditions generally consisted of artificial fill overlying igneous rock consisting of volcanic tuff sandstone and/or rhyolite. Table 3 summarizes laboratory test results performed on samples obtained from borings at the proposed reinforced concrete box (RCB) culverts within the expected depths of excavation.

Table 3: Reinforced Concrete Box Culverts Soil Properties Test Summary1

Location

Test Pits

Borings

Dry Unit Wt. (pcf) and Moisture

Particle Size

Analyses (%G, %S, %F)

Atterberg Limits

LL, PI

Shear Strength ϕ’, c’

Common USCS and AASHTO

Classifications

RCB Station 157+87

18P-06 and

18P-07 γd: 68-89 wo: 9-31%

14 G 60 S 26 F

-- Φ’: 29° c’: 570 psf

Clayey SAND (SC) Silty SAND (SM)

Well Graded SAND w/ silt (SW-SM)

Well Graded SAND

(SW)

A-1-b, A-2-4

RCB Station 218+11

18P-08 and

18P-09 γd: 70-114 wo: 13-29%

18-29 G 50-65 S 17-21 F

37 LL

12 PI

Φ’: 37° c’: 230 psf

Clayey SAND (SC) Well Graded SAND

(SW)

Clayey SAND w/ gravel

(SC)

Well Graded SAND w/

Clay (SW-SC) Poorly Graded SAND w/

Clay (SP-SC) A-1-b, A-2-6

1 Geotechnical properties are noted for dry unit weight (γd) and moisture content (wo); maximum dry density (γdmax) and optimum moisture content (wopt) particle size as percent gravel (G), sand size (S) and fines content (F); Atterberg liquid limit (LL) and plasticity index (PI); friction angle (φ) or cohesion (c) in kips per square foot measured from direct shear (ds) or consolidated undrained (cu) tests.

Samples of volcanic ash tuff and rhyolite were cut into blocks and tested for unconfined compressive strength. Strengths varied from approximately 400 to 1,500 psi for the tuff to over

7,000 pounds per square inch for the rhyolite. Interpreted subsurface profiles summarizing the subsurface conditions encountered at the proposed reinforced concrete box culvert locations are presented in Figures 5 and 6.

Figure 5: Subsurface Profile: RCB Station 157+87

5.3 GROUNDWATER

Groundwater was encountered in borings 18P-06 and 18P-08 at depths of 10.5 and 23.5 feet, respectively. The groundwater was generally encountered immediately above the bedrock elevation in borings. 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 response to local weather and particularly from runoff from ephemeral drainages.

We understand from Nevada State Parks staff that seasonal springs feed the drainages at the two proposed box culvert locations at Stations 157+87 and 218+11. Water was flowing through existing culverts at both of the proposed reinforced box culvert locations during our field work in

March and May 2018. The drainages were dry at the time of our July 2018 field work.

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 Standard Specification FP-14. Compliance with those specifications is needed for the recommendations in this report to remain applicable. All site

Figure 6: Subsurface Profile: RCB Station 218+11 grading should conform to the applicable sections of FP-14. On-site soil removed from excavations should be suitable for use as borrow for general embankment fill. Excess fill or cut material should be hauled offsite for proper disposal, unless an onsite location has been specifically 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 can run uncontrolled along the edge of the roadway, such as at the base of cut slopes. Care should be taken that roadway reconditioning does not block or prevent the flow of surface drainage that is provided by existing ditches. Lined swales can be provided along the edge of the roadway to help reduce the potential for erosion control.

Graded slopes will be vulnerable to erosion. Topsoil, erosion control matting (if needed) and appropriate vegetation should be placed on graded slopes to reduce the potential for 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 7. The fill should be initiated from a base key excavated at the toe of the new embankment. The base 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.

6.2.2 CUT SLOPE DESIGN

Existing cut slopes between Stations 162+68 to 164+29 (Site 4) and Stations 177+56 to 179+89

(Site 8) will graded to a flatter inclination. Yeh reviewed the existing cut slopes during our site visits in March and May of 2018. Photographs of the two cut slopes are shown in Figure 8.

Figure 7: Typical Embankment Construction

Preliminary recommendations to flatten the slopes and clean the catchment zones were discussed in our preliminary memorandum (2018). The cut slope at Site 4 (Station 162+68 to 164+29) is primarily comprised of volcanic tuff and ash flow tuff. The existing slope varies from approximately 10 to

20 feet in height and is inclined at a slope of approximately 78 degrees. The catchment zone below the slope should be cleared of soil and the new cut slope should be designed to a slope of 1v:0.75h (vertical to horizontal).

The cut slope at Site 8 (Station

177+56 to 179+89) is about 8 feet in height and inclined at about 80 degrees. The cut is primarily comprised of cemented silty sand with clay and gravel.

The slope is unstable at the current inclination and has experienced surficial slope instability and sloughing. This cut slope should be graded back at a slope of 1v:1h (vertical to horizontal) and the existing catchment zone cleaned of material.

6.2.3 CATCHMENT RESTORATION

Existing windrows along both sides of the road should be removed as a part of roadway restoration to reduce the entrenched condition of the roadway. The existing windrows are approximately 2 feet wide and 1 foot tall. Catchment areas along zones summarized in Table 4

Figure 8: Cut Slopes at Site 4 Station 162+68 to 164+29 (top) and Site 8: Station 177+56 to 179+89

(bottom), looking north should be cleared of material in addition to removal of the windrows. Removal of material within catchment zones should extend from the edge of the road to the undisturbed surface of the adjacent cut slope.

Table 4: Catchment Restoration

Stations Catchment

Width Catchment

Height Notes

162+00 to 164+95, Rt 6 feet 4 feet

Remove material from catchment zone back to undisturbed face1 of cut slope

172+70 to 174+40, Rt 6 feet 4 feet

Remove material from catchment zone back to undisturbed face of cut slope

177+75 to 179+30, Rt 7 feet 4 feet

Remove material from catchment zone back to undisturbed face of cut slope

1. Undisturbed face is defined as intact igneous rock or colluvium.

The contractor should not undermine the ascending slope when performing roadway or ditch reconditioning between Stations 224+75 and 226+80, Rt. The ascending slope could be prone to instability if the toe of the slope is removed.

6.2.4 RIP-RAP PROTECTION

Riprap protection is planned at areas where erosion has occurred or seasonal drainages are encroaching on roadway embankments. The base of the riprap protection should be embedded below stream channel deposits and at least 2 feet below the invert of the drainage.

6.2.5 AGGREGATE SURFACE ROADWAY

The project will include roadway surface reconditioning to provide the design 14- to 16-foot roadway width, a more durable road surface, and to remove berms, clear the existing ditches, and add/re-establish catchment below cut slopes along the roadway. Earthwork for roadway reconditioning should be performed in accordance with Section 303 of the FP-14 which includes scarification, moisture conditioning, and compaction. Boulders that protrude into the existing roadway by more than 4 inches should be removed or cut down to allow placement of roadway aggregate or the boulder could remain at the discretion of the Contracting Officer if it does not protrude up through the roadway aggregate surface.

Roadway Aggregate. A minimum of 6 inches of compacted roadway aggregate should then 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 5.

Table 5: 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 used to help reduce dust and the need for watering for dust control. 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.

6.2.6 HMA PAVEMENT DESIGN – STATION 212+70 TO 219+00

The section of roadway between Stations 213+00 and 218+00 is sloped at approximately 15 to

19 percent and the surface is hard rhyolite bedrock that has been eroded along fractures.

Surface drainage has washed gravel and loose soil across the roadway surface reducing traction. Rerouting the roadway along this section is not an option due to cultural resource constraints and the topography of the area. Options considered for improving this section of roadway included cutting the bedrock to grade and performing maintenance, placing a concrete roadway, and surfacing the section with hot-mix asphalt (HMA). Hot-mix asphalt (HMA) concrete pavement is the selected surface material for the design of the roadway between Stations 212

+70 to 219+00. This decision was made by the design team and CFL during a meeting on May

10, 2018. The following recommendations are provided for the paving of the roadway in this area:

• The surface of the roadway should be cleaned of loose gravel and material to expose bedrock or existing subgrade.

• Eroded channels and rock fractures should be backfilled with a leveling course of roadway aggregate and compacted to 95 percent relative compaction in accordance with

FP-14.

• The roadway should be surfaced with a layer of HMA. A full-depth HMA section has less of a potential for constructability issues with traction than placing HMA over a roadway aggregate surface. The HMA should be placed in two lifts with the first lift used as a leveling course with a variable thickness to establish the roadway cross-slope and fill any voids within the subgrade. The final lift should be a minimum of 3 inches thick and be placed to finished grade for the roadway.

• New HMA should be placed in an uphill direction.

• Using a Material Transfer Vehicle (MTV) to transfer HMA into the paver could be problematic on the steep slope. Use of a MTV is therefore not recommended for this project.

• The new edge of pavement (NEP) should be shouldered up with roadway aggregate to reduce the potential for erosion and cracking along the edge of pavement. Shoulder backing should be placed to match the finished surface of the pavement at the NEP and be tapered out away from the roadway for a width of 1 to 3 feet or as directed by the

Contracting Officer while still providing the design roadway width along the HMA section.

Binder and Mix Recommendations. The recommended binder for this area is PG 64-34CC for elevations greater than 5,000 feet based on 2011 specifications from Clark County, Nevada.

This project is in a relatively remote location and we understand the location of existing commercial asphalt plants may result in relatively long-haul distance to the construction site.

Loss of temperature and segregation of the hot asphalt mix can occur during transport. We recommend that the project specifications require the loads be tarped and that the ambient temperature along the haul route and at the site be such that the heat of the HMA can be maintained per project specifications during transport. Paving in the summer months would help to maintain the temperature of the HMA during transport.

Pavement Maintenance. The pavement condition should be periodically evaluated to help plan and scope the need for maintenance and rehabilitation following the initial construction of the pavement. Local ranchers periodically traverse the roadway with heavy equipment such as excavators and bulldozers. The tracks of such equipment will damage the HMA surface and reduce its service life. Traversing the HMA surface with such equipment should be avoided or pavement appropriate tracks should be used. Maintenance of the asphalt concrete pavement should also include clearing the surface of potentially erosive soil and debris, and periodic fog, chip or slurry seals to reduce the potential for weathering of the road surface. Overlaying the pavement with additional HMA when needed would help to strengthen and further the life of the pavement.

6.3 LOW WATER CROSSING

The low water crossing between Stations 195+83 to 197+79 will replace an existing culvert and address potential flooding and inundation from seasonal drainage. The existing grade of the roadway will be lowered by approximately 3 to 3.5 feet at the crossing. The surface of the crossing will consist of 8-inches of reinforced concrete pavement underlain by 4 inches of roadway aggregate. The upstream and downstream edges of the concrete pavement will be constrained by precast concrete cutoff barriers (k-rails or jersey barriers) that will extend to approximately 2.7 feet below the roadway surface. The edges beyond the concrete will be bordered with revetment mattresses to reduce the potential for scour and erosion of the streambed adjacent to the new crossing.

Excavation for the low water crossing could be relatively difficult as a result of encountering layers of boulders and cobbles. Subsurface conditions encountered at the crossing consisted of artificial fill overlying colluvium comprised of dense silty sand with gravel and cobbles and boulders. Boulders and cobbles ranging in size from approximately 6 to 18 inches in size. The following recommendations are provided for construction of the low water crossing.

• Excavate existing material to 4 inches below the bottom of the concrete for the crossing and prepare and compact the surface in accordance with Section 208.08 (b), and

208.10 of FP-14. Boulders should be removed such that a minimum of 4-inches of roadway aggregate can be placed below the concrete. Depressions created by the removal of boulders should be backfilled with foundation fill per FP-14 up to the bottom of the roadway aggregate grade.

• Place and compact a minimum of 4 inches of roadway aggregate below the concrete.

• Construct the low water crossing per the project plans and specifications.

6.4 CONCRETE BOX CULVERTS

Table 6 summarizes the locations and details for the two reinforced concrete box culverts.

Figure 9 presents a detail that shows the recommended preparation of the subgrade below the new culverts for a wet and dry case. The culverts will be precast units and designed according to Nevada Department of Transportation Standard Plans. The approximate bottom, maximum cover thickness estimated from the Muller (2018) plans are also shown in 6 with a generalized description of the foundation soil encountered at each location.

Table 6: Summary of Reinforced Box Culvert Locations

Location Structure

Bottom (below existing grade)

Maximum Cover

Case per

Figure 9

Yeh Boring

No.

Generalized Foundation Soil

Encountered

157+87

Single Barrel RCB at 10o Skew2

12 ft. span x 6 ft. high x 34 ft. length

8 ft. 2 ft. Wet 18P-06 & 07

Loose to medium dense sand with potential for saturated conditions depending on time of year

218+11

Single Barrel RCB at 36o Skew

8 ft. span x 6 ft. high x 53 ft. length

4 ft. 4 ft. Wet 18P-08 & 09

Loose to medium dense sand with potential for saturated conditions depending on time of year

The recommended foundation preparation shown in Figure 9 should be provided below both the

RCB and the headwalls at the inlet and outlet of the culverts. The quality of the foundation support for the RCBs will depend on the flow of water within the drainages. Project specifications should

2 Skew measured perpendicular to centerline of roadway.

Figure 9: Summary of RCB Foundation Preparation and Backfill provide quantities for the additional subgrade stabilization associated with wet conditions if need depending on the conditions at the time of construction.

Wet Condition. Dewatering and diversion of the stream flow should be provided, if needed, to provide a dry working area for construction and fill placement. Foundation preparation for the wet case should include subexcavation to at 2 feet below bottom of proposed RCB. The subgrade below the RCB should be excavated using an excavator or backhoe type equipment to avoid the need for construction traffic to operate on the subgrade. A layer of geotextile conforming to Section 714.01, Class I, Type E should then be placed over the subgrade in accordance with FP-14. Gravel for stabilization should be placed over the geogrid and should consist of uniformly graded 3/8 to 1-inch conforming to Section 703.06, 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 gravel should be placed in two lifts up to within 4 inches of the bottom of the RCB and should be consolidated with a minimum of 4 passes using a vibroplate or small vibratory roller for each lift.

Dry Condition. If the foundation area below the RCB is dry, the foundation preparation for the remaining RCB should conform to the dry case in Figure 9. The subgrade below the culvert excavations should be scarified to a depth of 9 inches, conditioned to a moisture content suitable for compaction, and compacted in-place to at least 95 percent relative compaction. Compacted foundation fill consisting of the excavated material or borrow conforming to Section 704.01 of FP-

14 should then be placed over the prepared subgrade and to fill any voids or low spots left from the foundation preparation.

A 4-inch layer of aggregate base course material conforming to Section 703.05b, Class C, D or E

Base, should then be placed over the prepared subgrade (for either case) to the bottom of the box culvert elevation to provide a working mat for the RCB construction. The aggregate base should be compacted to at least 95 percent relative compaction in accordance with FP-14.

The design of the RCB’s should consider the potential for at least 1-inch of total settlement and for approximately ¾ inches in 30 feet of differential settlement. The foundation settlement should generally occur relatively rapidly, near to the rate of construction.

6.5 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.

• A corrosion rate of 0.003 inch/year is used for steel piles buried in fill or disturbed natural soil.

Tests for pH, electrical resistivity, 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 6.5 to 8.0 and the soil resistivity ranged from 429 to 3,533 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 was 4 to 81 ppm. The water-soluble sulfate content for the samples tested was 93 to 304 ppm. The samples tested are considered aggressive towards concrete. One of the water-soluble sulfate content of samples tested exceeds FHWA limits. We recommend that concrete structures and cement types should be selected that are compatible with the potentially corrosive environment.

7. NOTES TO CONSTRUCTION

1. Hard rock or boulders within the subgrade could damage equipment or obstruct equipment from roadway reconditioning. Boulders were measured protruding 1 to 4 inches out of the existing subgrade. Boulders should either be removed or cut down where they extend 4 inches or more into the design roadway aggregate section or the boulders may be left at the discretion of the Contracting Officer. Where boulders are removed, the resulting excavation should be replaced with backfill or unclassified borrow per FP-14.

2. Material within catchment zones along cut slopes and within berms may be used as general backfill or unclassified borrow. The material does not meet the specifications for roadway aggregate per FP-14 based on laboratory tests on collected samples.

3. The contractor should not undermine the ascending slope when performing roadway or ditch reconditioning between Stations 224+75 and 226+80, Rt. The ascending slope could be prone to instability if the toe of the slope is removed.

4. Volcanic tuff and cemented silty sand with gravel are exposed in the cut slopes planned to be laid back. These materials are anticipated to be excavatable with heavy earthmoving equipment such as excavators and bulldozers. Rock teeth may be needed to cut the volcanic tuff. Blasting is not anticipated to be necessary.

5. Cobbles and boulders ranging in size from 6 to 18 inches in dimension were encountered at a depth of 2.5 feet in test pit 18P-03 where the low water crossing is proposed. Similar material was observed in upstream and downstream of other 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. Boulders up to approximately 3 feet in dimension were observed upstream of the proposed low water crossing and where the concrete box culvert is proposed at Station 218+11. Provisions for removing and disposing of oversize materials (greater than 24 inches) and deleterious materials should be provided in the contract documents.

6. Volcanic tuff and rhyolite bedrock were encountered in borings drilled at both of the proposed RCB locations. We do not expect that these materials will be encountered during excavation for the RCB structures unless a shoring system is installed that extends 2 feet or deeper below the bottom of the RCB.

7. Hot-mix asphalt pavement will be placed along slopes estimated to range from 15 to 19 percent. Placing HMA on steep slopes requires special attention to spreading, compacting, and consolidation. Placement of HMA should be per FP-14.

8. MATERIAL SOURCES

8.1 PAVEMENT AND AGGREGATE

The main material requirements for this project are likely to include hot mix asphalt and aggregates that are available from commercial suppliers in the vicinity of Lincoln County, Nevada or Cedar City, Utah. Haul times to the site could exceed 1 hour and special hauling measures may be required where Beaver Dam Road crosses the Union Pacific Railroad Tracks.

Yeh attempted to contact material…