2019-12-20 Ice House Road Geotech report - final.pdf

GEOTECHNICAL AND PAVEMENT ENGINEERING REPORT

CA FLAP ED CR147(2)

Ice House Road Improvements

El Dorado County, California

Yeh Project No.: 217-390

December 20, 2019

Prepared for:

JACOBS ENGINEERING GROUP, INC

707 17th Street, Suite 2400

Denver, CO 80202 Attn: Johannah L. Trujillo, P.E.

Prepared by:

Yeh and Associates, Inc.

391 Front Street, Suite D

Grover Beach, California 93433 Phone: 805-781-9590

GEOTECHNICAL AND PAVEMENT ENGINEERING REPORT

CA FLAP ED CR147(2)

Ice House Road

El Dorado County, California

Yeh Project No.: 217-390

December 20, 2019

Prepared by:

Jonathan D. Blanchard, G.E. Wade Hoon Geotechnical Engineer Senior Project Geologist

Pavement Engineering Review: Independent Reviewer:

Robert F. LaForce, P.E. T. Samuel Holder, G.E.

Senior Materials Manager Senior Project Engineer

Geotechnical and Pavement Engineering Report Yeh Project No. 217-390 Ice House Road December 20, 2019 i

Table of Contents

1. PURPOSE AND SCOPE OF STUDY

2. PROJECT UNDERSTANDING

3. GEOTECHNICAL INVESTIGATION

3.1 GEOLOGIC RECONNAISSANCE

3.2 DEFLECTION TESTING

3.3 DRILLING

3.4 LABORATORY TESTING

4. SITE CONDITIONS

4.1 GEOLOGY

4.2 TERRAIN AND VEGETATION

4.3 CLIMATE

4.4 EXISTING PAVEMENT SURFACE CONDITIONS

4.5 SUBSURFACE CONDITIONS

4.5.1 EXISTING PAVEMENT STRUCTURAL SECTION

4.5.2 SUBGRADE CONDITIONS

5. CONCLUSIONS AND RECOMMENDATIONS

5.1 CUT SLOPE DESIGN

5.2 EARTHWORK FACTORS

5.3 SUBGRADE PREPARATION

5.3.1 ROOT INTRUSION AND BOULDERS

5.3.2 DIGOUTS

5.3.3 HARD ROCK

5.3.4 OPEN JOINTS IN ROCK

5.3.5 SOFT OR WET SUBGRADE CONDITIONS

5.4 PAVEMENT DESIGN RECOMMENDATIONS

5.4.1 DESIGN TRAFFIC VOLUME AND SUBGRADE

5.4.2 STRUCTURAL SECTION

5.4.3 BINDER AND MIX RECOMMENDATIONS

5.4.4 PAVEMENT MAINTENANCE

5.5 CORROSION CONSIDERATIONS

5.6 NATURALLY OCCURRING ASBESTOS

ii

6. NOTES TO CONSTRUCTION

7. MATERIAL SOURCES

7.1 PAVEMENT AND AGGREGATE

7.2 GENERAL BORROW

8. LIMITATIONS

9. REFERENCES

List of Figures

FIGURE 1: PROJECT LOCATION MAP

FIGURE 2: SURFACE CONDITION PHOTOS - SEGMENT 1

FIGURE 3: SURFACE CONDITION PHOTOS - SEGMENT 2

FIGURE 4: SURFACE CONDITION PHOTOS: SEGMENT 4

FIGURE 5: SURFACE CONDITIONS PHOTOS - SEGMENT 5

FIGURE 6: CUT SLOPE AT PM 16.07

FIGURE 7: PHOTO OF ROCK CUT T PM18.48

FIGURE 8: PHOTO OF ROCK CUT AT PM18.54

FIGURE 10: TYPICAL BOULDERS IN GLACIAL TILL ALONG SHOULDER

FIGURE 9: TYPICAL DISTRESS FROM ROOT INTRUSION

FIGURE 11: SUMMARY OF STRUCTURAL SECTION RECOMMENDATIONS

List of Tables

TABLE 1: SUMMARY OF AVERAGE BACKCALCULATED LAYER MODULI IN KSI

TABLE 2: SUMMARY OF SURFACE CONDITION OF PAVEMENT BY SEGMENT

TABLE 3: EXISTING PAVEMENT CONDITIONS ENCOUNTERED

TABLE 4: SUMMARY OF SUBGRADE TEST RESULTS

List of Plates

Plate Field Exploration Plan .......................................................................................................................1.1 to 1.44 Regional Geologic Map Field Exploration Plan iii

List of Appendices

Page Appendix A – Boring Logs Boring Record Legend ................................................................................................................... A-1 Legend for Rock Materials ............................................................................................................ A-2 Borings Logs for 17P-01 to 70 ........................................................................................... A-13 to 72 Boring and Drill Rig Setup and Boring .............................................................................. A-73 to 84 Appendix B – Results of Laboratory Testing Summary of Laboratory Results .............................................................................................B-1 to 3 Percent Passing No. 200 Sieve ...............................................................................................B-4 to 5 Mechanical Sieve Analysis .................................................................................................. B-6 to 15 Atterberg Limits .......................................................................................................................... B-16 pH and Resistivity .............................................................................................................. B-17 to 23 Proctor Compaction .................................................................................................................... B-24 R-value Test ....................................................................................................................... B-25 to 33 Asbestos ...................................................................................................................................... B-34 Appendix C – Deflection Test Data Dynatest, FWD Testing Plan ................................................................................................... C-1 to 5 CTL Group, Backcalculated Moduli ......................................................................................C-6 to 14 Appendix D – Pavement Design Calculations Pavement Design Calculations ............................................................................................ D-1 and 2

1. PURPOSE AND SCOPE OF STUDY

Yeh and Associates was retained by Jacobs Engineering Group, Inc. (Jacobs) to provide geotechnical recommendations for the design of roadway improvements and pavement rehabilitation as part of the Federal Highway Administration, Central Federal Lands Highway Division (FHWA-CFLHD) project for Ice House Road in El Dorado County, California. The project location begins at the intersection of Ice House Road and Peavine Ridge Road (Post Mile (PM 6.37) and extends to the northern most intersection of Ice House Road and Wentworth Springs Road (PM 23.94). The location of the site is shown in Figure 1.

The geotechnical evaluation consisted of a program of project coordination, geologic reconnaissance, pavement deflection testing, drilling, laboratory testing, and analyses as a basis for providing the recommendations in this report. This report provides recommendations for the design of the pavement rehabilitation, maintenance improvements for rock cut slopes. Considerations for an existing retaining wall at PM 19.0 were provided in the Yeh (2017b) memorandum.

2. PROJECT UNDERSTANDING

The layout of the improvements is shown on the Jacobs (2019) plans and described in the Scoping Report (Jacobs 2015). The project consists of a design to rehabilitate approximately

17.6 miles of Ice House Road pavement through the El Dorado National Forest. The existing roadway is typically 24 feet wide with two 11-foot lanes and a typical 1-foot paved shoulder.

The road is paved with asphalt concrete and underlain with various thicknesses of aggregate base. Ice House Road is maintained by El Dorado County and extends through rural, mostly forested, mountainous terrain a total of approximately 30 miles from US Highway 50 to Loon Lake. The road provides access to the Rubicon Trail, Crystal Basin Recreation Area, the

Figure 1: Project Location Map

Desolation Wilderness, and several lakes and campgrounds. The route is intersected by various county roads, forest service roads, campground access roads and driveways. Ice House Road also provides access for to a network of reservoirs and facilities that are part of the Sacramento Municipal Utilities District (SMUD) hydroelectric power system and timber stands harvested by the lumber industry.

The existing road surface profile ranges in elevation from approximately 4,900 feet near Union Valley Reservoir to 5,800 feet near Robbs Peak Road, with three predominant differences in elevation over the length of the project. The road is mostly between elevations 5,000 and 5,500 feet between Peavine Road and Jones Place near Ice House Reservoir, between 4,900 and 5,100 feet within the middle third of the project near Union Valley Reservoir, and between 5,100 and 5,800 feet over the high near Robbs Peak to the north end of the project. The existing pavement shows evidence of distress that is likely associated with weather conditions associated with this high mountain terrain. The roadway will remain on essentially the same horizontal and vertical alignment as the existing facility, with a goal of limiting grade raises to less than 1 inch above the existing pavement surface.

The Scoping Report identified that Ice House Road was burned in the 1992 Cleveland Fire from approximately PM 0.0 to PM15.0, causing surface damage and potentially reducing the life of the pavement. Design plans provided by El Dorado County to FHWA showed that the road was rehabilitated within the project area in 1987 as part of California Forest Highway Project 136‐ 1(2). Those plans showed an existing roadway section of 2‐1/2 to 5 inches of asphalt concrete surfacing over 2 to 10 inches of base course. The 1987 project rehabilitated the road by providing a thickness of 5 inches of cold-in-place-recycled material (CIPR) between PM 6.50 and 10.0, and 4 inches of CIPR between PM 10.0 and 24.0. The entire reach was then overlaid with 2 inches of hot mix asphalt concrete pavement.

3. GEOTECHNICAL INVESTIGATION

The geotechnical investigation consisted of a program of geologic reconnaissance, pavement deflection testing, drilling and sampling, and laboratory testing. The approximate locations of the borings, test locations, and notes on the pavement conditions and existing pavement thicknesses encountered are shown on Plate 1. Logs for each of the borings drilled are presented in Appendix A, laboratory test results are presented in Appendix B, and deflection test data are presented in Appendix C.

3.1 GEOLOGIC RECONNAISSANCE

A geologic reconnaissance was performed during the week of September 25, 2017 to review three existing rock cut slopes located at postmiles 16.07, 18.48, 18.54, and the areas of a retaining wall below the road near postmile 19.0. The general stability, available catchment width and need for scaling of the existing rock cut slopes were reviewed. In addition, the general geology along the route was reviewed and the relationship between geology and roadway conditions was noted. The field investigation plan and preliminary findings were presented in memoranda submitted by Yeh (2018a, 2018b).

3.2 DEFLECTION TESTING

Deflection testing was conducted on September 27 and 28, 2017 in general accordance with the Dynatest testing plan. The testing plan was submitted with the Yeh (2017a) Field Investigation Plan memorandum and is included in Appendix C of this report. The testing was performed by Dynatest of Ventura, California using a Falling Weight Deflectometer (FWD). The FWD was used to measure the load-response characteristics of the pavement layers and subgrade. Tests were performed in the outside wheel path of the northbound and southbound lanes at a typical spacing of approximately 0.1 miles. A total of 347 data points were collected.

The FWD test procedure utilized three load levels acting on a buffered, 12-inch-diameter plate to simulate wheel loading. Geophones and an on-board computer were used to measure the surface deflection of the pavement at various intervals as the FWD strikes the pavement. Nine deflection sensors were set at 6 to 12 inches apart for this project. Sensor No. 1 was located directly under the load and Sensor No. 9 was located 6 feet along the wheel path from the point of the load application. Summary plots and the deflection test data are presented in.

The FWD data was backcalculated by CTL Group, working for Yeh, following the procedures outlined in ASTM D5858 Guide for Calculating In-Situ Equivalent Elastic Moduli of Pavement Materials Using Elastic Layer Theory. The layered elastic model was prepared and analyzed using the computer program FPS-21. The moduli are an indication of the strength of the pavement layers and subgrade. This information provides an indication of the structural capacity of the pavement structure to carry loading. The Percent Average Error per Sensor (PAES) is also calculated to give an indication of the accuracy and reliability of the backcalculated layer moduli. It is desirable to have PAES less than 2 percent. PAES less than 5 percent is acceptable and PAES greater than 5 percent should be used with caution. The average backcalculated moduli in kips per square inch (ksi) for each of the pavement layers and subgrade for Ice House Road (using both directions) are as follows:

Table 1: Summary of Average Backcalculated Layer Moduli in ksi

Segment AC Layer CIPR Layer AB Layer Subgrade

1 708 464 17 31 2 819 636 18 19 3 770 498 14 22 4 834 647 24 42 5 624 310 14 22

There are different performance criteria utilized in pavement design. For flexible pavements, the primary performance criteria are the pavement serviceability (ride quality), fatigue cracking and rutting. The mechanistic model utilized for estimating the performance life due to fatigue cracking was the following Asphalt Institute equation corresponding to 20 percent fatigue cracking.

Nf = 0.0796 (εt)-3.291 (E1)-0.854 where:

Nf = Loads to Failure (ESALs) εt = Tensile Strain (in/in) at the bottom of the AC layer E1 = AC Modulus (psi)

The mechanistic model utilized for estimating the performance lift due to rutting was the following Asphalt Institute equation for an 0.5-inch rutting depth.

Nd = 1.365 X 10-9 (εv)-4.447 where:

Nd = Loads to Failure (ESALs) εv = Vertical Compressive Strain (in/in) at the top of the subgrade

The analysis was conducted utilizing FPS-21 that calculates the critical strains due to a 9,000-pound loading. The estimated remaining life for all existing sections of Ice House Road exceeded 1,000,000 ESALs for fatigue cracking and rutting, far more than the required design life based on the current ADT of 1,409 and design 215,000 ESALs. The pavement design for the project can therefore focus on strategies to rehabilitate the existing pavement with emphasis on reducing the high severity of reflective and transverse cracks that impacts the existing roadway. The use of the performance grade (PG) binder suitable for the climatic conditions should also help to reduce the potential for raveling and thermal cracking that has impacted the existing pavement.

3.3 DRILLING

The drilling was performed during the period of October 9 through 12, 2017. Drilling services were provided by Taber Drilling, Inc. of West Sacramento, California. Statewide Safety Inc, of Sacramento, California provided traffic control and flagging for the drilling. The drilling was performed under an encroachment with El Dorado County who reviewed and approved the traffic control and backfill operations.

Taber drilled 70 borings along the alignment using a truck-mounted CME 55 drilling rig equipped with 6-inch continuous flight augers. The borings were advanced through the asphalt pavement and into the subgrade to a typical depth of 5.5 feet, unless refusal was encountered in bedrock at a shallower depth. A Yeh geologist measured the thicknesses of the existing asphalt pavement and base course materials at the boring locations, 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. Drive samples were typically taken at depths of approximately 2 and 4 feet below the road surface. 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.

3.4 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 U.S Standard No. 200 sieve, particle size distribution by sieve analysis, pH and resistivity were performed at our laboratory in Grover Beach, California. Tests for R-value were performed by the NV5 Labs in Ventura, California.

Samples from 4 borings were sent to EMSL Analytical, Inc. in San Leandro, CA for testing on the presence of asbestos. 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 GEOLOGY

The regional geology in the site vicinity as compiled by Wagner et al. (1981) is shown on Plate 2

- Regional Geologic Map (note that the route on Plate 2 does not match the current road alignment). The project is located within the Sierra Nevada geomorphic province, which extends from the Mojave Desert in southern California to the Cascade Mountains in northern California. The project location is west of the crest of the Sierra Nevada Mountains and about 15 miles southeast of Lake Tahoe. The Sierra Nevada Mountains are derived from the Sierra Nevada Batholith, a collection of granitic plutons that formed during the Triassic/Jurassic Periods. Approximately 25 million years ago tectonic uplift during the Oligocene Epoch caused the Sierra Nevada Mountains to rise. This uplift continues to the present, creating earthquakes in active fault zones throughout the High Sierra Mountains.

Weigers et al (1981) mapped the surface geology along Ice House Road as the following bedrock units:

• PM 6.4-7.8: Mehrten Formation (Tm) comprised of Andesitic conglomerate, sandstone and breccias.

• PM 7.8-19.6 and 21.3-23.9: Mesozoic aged granitic rocks (Mzg, Sierra Granite).

• PM19.6-21.3: undifferentiated units of Paleozoic aged sedimentary and meta-sedimentary rocks (Pzu?).

Locally these units are overlain or interrupted by units of alluvium (Q), glacial deposits (Qg), basalt (Qbs) and road fill.

4.2 TERRAIN AND VEGETATION

Ice House Road crosses mountainous terrain over numerous drainages and high mountain valleys within the project limits. The roadway has relatively flat to moderate grades that rise and descend between approximately elevations 4,900 and 5,800 feet. Vegetation along the roadway is mixed pine and fir forest with associated understory vegetation and grassed meadows.

4.3 CLIMATE

The climate data (www.usclimatedata.com) for South Lake Tahoe, California (located approximately 40 miles east of Ice House Road, reports an average annual rainfall of 52.45 inches and 408 inches of snow. The majority of the rainfall and snow is reported to occur between November and March. The reported monthly average temperature ranges from a low of 23 degrees for February to a high of 75 degrees in August.

http://www.usclimatedata.com/

4.4 EXISTING PAVEMENT SURFACE CONDITIONS

The exposed pavement surface along Ice House Road consists of asphalt concrete. The overall roadway is in poor to fair condition. The pavement surface condition was variable with intermittent occurrences of alligator cracking, transverse cracks, longitudinal cracks, settlement and upheaval from frost, root and boulders. There are five segments of Ice House Road that were differentiated based on the deflection data: PM6.37 to 9.7, PM9.7 to 12.0, PM12.0 to 14.0, PM14.0 to 20.2, and PM20.2 to 24.0. The following table provides a summary of the pavement surface conditions for each segment.

Table 2: Summary of Surface Condition of Pavement by Segment

Segment Post Miles

Segment Stations Existing Pavement Conditions

6.37-9.7 2000+00 to 2170+00

• Fair

• Existing pavement is typically about 7 inches of asphalt pavement over an average of about 12 inches of aggregate base course (ABC)

• Moderate to severe transverse cracks common ~50’ spacing. Severe secondary cracking and subsidence in some areas.

• Localized low to moderate longitudinal cracks in wheel paths

• Moderate to severe localized edge cracking. Possibly relating to limits of previous CIPR near existing edge of traveled way near PM7.0.

9.7-12.0 2170+00 to 2300+00

• Fair to Poor

• Existing pavement is typically about 5 inches of asphalt pavement over an average of about 10 inches ABC

• low to severe transverse cracks common ~50’ spacing. Severe secondary cracking and subsidence in some areas.

• Localized severe fatigue cracking, raveling and rutting in wheel paths

12.0-14.0 2300+00 to 2410+00

• Fair

• Existing pavement is typically about 6 inches of asphalt pavement over an average of about 12 inches ABC

• Low to severe transverse cracks common ~50’ spacing. Severe secondary cracking and subsidence in some areas.

• Localized severe fatigue cracking and rutting in wheel paths

• Localized low to moderate longitudinal cracks in wheel paths suggesting strengthening overlay is needed

14.0-20.2 2410+00 to 2730+00

• Fair

• Existing pavement is typically about 6 inches of asphalt pavement over an average of about 8 inches ABC

• Localized areas of severe frost and root heaving

• Localized low longitudinal cracking

• Localized areas low to moderate transverse cracks

20.2-24.0 2730+00 to 2950+00

• Poor

• Existing pavement is typically about 6 inches of asphalt pavement over an average of about 8 inches ABC that varies from 0 to 18 inches

• Common areas of moderate to severe fatigue cracking in roadbed and rutting and potholing in wheel paths

• Areas of poor drainage, phreatophyte plants and willows on cut slopes adjacent to road or within a narrow ditch beside the road. Springs pop out through the pavement in some areas.

• Localized moderate to severe frost heaves and root heaves.

• ABC thickness is variable or was not encountered

Photos of selected pavement conditions observed in each of the five segments are shown on Figures 2 through 5.

Figure 2: Surface Condition Photos - Segment 1

Left: Sta. 2013+50 NB; Right: 2060+00 NB

Figure 3: Surface Condition Photos - Segment 2

Left: Sta. 2180+75; Right Sta. 2832+25

Figure 4: Surface Condition Photos: Segment 4

Left: Sta. 2514+00 SB; Right Sta. 2659+25 NB:

Figure 5: Surface Conditions Photos - Segment 5

Left: Sta. 2749+25 SB; Right: Sta. 2885+75 SB

4.5 SUBSURFACE CONDITIONS

4.5.1 EXISTING PAVEMENT STRUCTURAL SECTION

The pavement structural section encountered in the drill holes (17P-1 through 17P-70) consisted of approximately 5 to 8 inches of asphalt over approximately 5 to 18 inches of aggregate base course (ABC). The approximate locations of the borings are shown on Plate 1 and noted on the logs in Appendix A. A description of the conditions encountered is summarized in Table 3 below.

Table 3: Existing Pavement Conditions Encountered

Boring No. Station

Asphalt Thickness (inches)

Base Thickness (inches)

Subgrade soil and

AASHTO1

17P-01 2021+43 7 11 Silty SAND (SM) A-2

17P-02 2034+38 7 11 Silty SAND (SM)

17P-03 2048+28 8 12 Clayey SAND (SC) A-2

17P-04 2061+13 5 18 Silty Sand (SM) A-2

17P-05 2073+88 6 12 Well graded SAND with silt (SW-SM) A-1-b

17P-06 2086+80 6 12 Poorly graded SAND with clay (SP-SC) A-2

17P-07 2100+12 5 12 Poorly graded SAND with clay and gravel

(SP-SC)

A-2

17P-08 2114+29 5 9 Silty SAND (SM) A-2-5

17P-09 2126+37 6 12 Silty SAND (SM) A-2

1 AASHTO symbol may be based on manual classification of soil.

Boring No. Station

Asphalt Thickness (inches)

Base Thickness (inches)

Subgrade soil and

AASHTO1

17P-10 2142+45 6 10 Silty SAND with gravel (SM)

17P-11 2152+31 6 12 Well graded SAND with gravel (SW) A-1

17P-12 2166+24 6 10 Silty SAND (SM) A-2

17P-13 2178+51 7 18 Silty SAND (SM) A-2

17P-14 2192+65 8 16 Well Graded SAND (SW) A-1

17P-15 2205+12 5 5 Poorly graded SAND with silt (SP-SM) A-1/A-2

17P-16 2218+38 5 11 Poorly graded SAND with silt and gravel (SP-SM) A-1/A-2

17P-17 2231+07 5 5 Silty SAND (SM) A-2

17P-18 2246+75 6 9 Well Graded SAND with silt (SW-SM) A-1/A-2

17P-19 2258+48 5 12 Well Graded SAND with silt and gravel (SW-SM) A-1/A-2

17P-20 2270+67 5 13 Silty SAND with gravel (SM) A-2

17P-21 2281+41 6 5 Silty SAND (SM) A-2

17P-22 2297+70 5 18 Well graded SAND (SW) A-1

17P-23 2309+48 2.5 14 Poorly graded SAND with silt (SP-SM) A-2

17P-24 2323+93 6 12 Silty SAND with gravel (SM) A-2

17P-25 2326+50 6 18 Clayey SAND with gravel (SC) A-2

17P-26 2349+23 7 12 Well Graded SAND with silt and gravel (SW-SM) A-1-b/A-2

17P-27 2362+75 6 18 Poorly graded SAND with silt (SP-SM) A-2

17P-28 2377+88 7 17 Silty SAND with gravel (SM) A-2

17P-29 2388+18 7 4 Silty SAND (SM) A-2

17P-30 2402+34 6 3 Silty, Clayey SAND (SM-SC) A-2-4

17P-31 2414+88 7 12 Silty SAND (SM) A-2

17P-32 2428+40 6 18 Silty SAND with gravel (SM)

17P-33 2441+27 6 3 Silty SAND (SM) A-2-4

17P-34 2455+67 7 12 Clayey SAND with gravel (SC)

Boring No. Station

Asphalt Thickness (inches)

Base Thickness (inches)

Subgrade soil and

AASHTO1

17P-35 2467+78 7 7 IGNEOUS ROCK (GRANITE);

17P-36 2480+68 5.5 4 Poorly Graded SAND with silt (SP-SM) A-2

17P-37 2493+73 6 18 Well Graded SAND with silt and gravel

(SW-SM)

A-1/A-2

17P-38 2507+19 6 8 Well-graded SAND with silt and gravel (SW-SM);

17P-39 2520+08 6 10 Clayey SAND (SC) A-2

17P-40 2533+74 7 3 Well graded SAND (SW) A-1

17P-41 2549+19 6 3 Clayey SAND (SC) A-2

17P-42 2558+53 6 No ABC IGNEOUS ROCK (GRANITE)-

17P-43 2572+66 7 13 Poorly Graded SAND with silt (SP-SM) A-2

17P-44 2586+08 6 15 Clayey SAND (SC) A-2

17P-45 2600+58 7 5 Silty SAND (SM) A-2

17P-46 2612+25 8 6 Well graded SAND with clay (SW-SC) A-1/A-2

17P-47 2623+86 6.5 4 Well graded SAND with clay (SW-SC) A-1/A-2

17P-48 2639+23 7 6 IGNEOUS ROCK (GRANITE); decomposed to “Silty SAND

(SM)”

A-2

17P-49 2651+68 6 6 Poorly graded GRAVEL with sand (GP)

17P-50 2664+37 7 12 Poorly graded GRAVEL with sand (GP) A-1

17P-51 2667+03 7 10 Silty SAND (SM) A-2

17P-52 2690+18 6 No ABC Well graded SAND with clay and gravel (SW-SC) A-2

17P-53 2703+47 7 No ABC Poorly graded GRAVEL with silt and sand (GP-GM) A-2

17P-54 2716+01 6 5 Poorly graded SAND with silt (SP-SM) A-2-4

17P-55 2730+39 7 10 Poorly graded GRAVEL with sand (GP) A-1

17P-56 2744+86 7 8 Clayey SAND with gravel (SC) A-2

17P-57 2760+13 7 6 Silty SAND with gravel (SM) A-2

17P-58 2768+97 9 18 Poorly graded SAND with clay (SP-SC) A-2

17P-59 2781+93 7 8 Clayey SAND (SC)

Boring No. Station

Asphalt Thickness (inches)

Base Thickness (inches)

Subgrade soil and

AASHTO1

17P-60 2799+70 3 14 Poorly graded SAND with clay (SP-SC) A-2

17P-61 2809+98 7 8 Poorly graded SAND with clay (SP-SC);

17P-62 2819+12 6 6 Poorly graded SAND with clay and gravel (SP-SC)

17P-63 2834+54 6 8 Poorly graded SAND with clay (SP-SC) A-2

17P-64 2846+84 6 4 Poorly graded SAND with gravel (SP) A-1

17P-65 2862+11 10 8 Poorly graded SAND with silt and gravel

(SP-SM) A-2

17P-66 2873+71 4 12 Poorly graded SAND with clay (SP-SC) A-2

17P-67 2886+42 8 8 IGNEOUS ROCK (GRANITE); decomposed to “Poorly graded

SAND with clay (SP-SC)” A-2

17P-68 2897+77 7 No ABC IGNEOUS ROCK (GRANITE); decomposed to “Well graded

SAND (SW)”

A-1

17P-69 2913+65 5 12 Poorly graded SAND with silt (SP-SM) A-2

17P-70 2930+22 6 12 Silty SAND (SM) A-2

4.5.2 SUBGRADE CONDITIONS

The subgrade soil encountered in the borings was generally consistent with the surface geology. The subgrade was predominately composed of medium dense granitic sands with varying amounts of silt, clay and gravel and areas of decomposed or hard igneous rock (granite). The sandy subgrade generally consisted of embankment fill placed within the existing roadway, weathered or eroded granitic sand, and glacial deposits. There are areas of very loose and very dense soil that were encountered in the borings as noted on the logs in Appendix A.

Cobbles, boulders and rock outcrops are commonly exposed alongside of Ice House Road and were encountered in selected borings. There is evidence that frost heave has caused boulders to penetrate the structural section and caused distress to the existing pavement surface. Roots have also intruded below the roadway and have also distressed the pavement surface in various locations. Springs and wet subgrade conditions area common within Segment 5. Table 4 presents a summary of selected laboratory test results performed on subgrade samples generally taken within the upper 4 feet of the borings.

Table 4: Summary of Subgrade Test Results2

Segment

Borings Dry Unit Wt. (pcf) and moisture

Particle Size

Analyses

(%G, %S, %F)

Atterberg Limits

LL, PI

Proctor γdmax, wopt

R-value

Median, Mr.

Subgrade USCS and AASHTO Classifications

Sta. 2000+00 to 2170+00

17P-01 to 17P-12 γd: 79-104 wo:6 -28%

2-12 G

72-82 S

11-21 F

48 LL

10 PI

(26 ksi)

Silty, clayey, well graded and poorly graded SAND with varying amounts of gravel, clay, cobble and boulders (SM, SC, SW, SW-SM, SP-SC) and

IGNEOUS ROCK (GRANITE)

A-1, A-1-b, A-2, A-2-5

Sta. 2170+00 to 2300+00

17P-13 to 17P-22 γd: 78-111 wo: 4-17%

0-16 G

72-88 S

13-27 F

(17 ksi)

Silty, poorly graded, well graded SAND (SM, SW-SM, SP-SM) with areas with gravel and cobbles and IGNEOUS ROCK (GRANITE)

A-1, A-2

Sta. 2300+00 to 2410+00

17P-23 to 17P-29 γd: 80-97 wo: 8-34%

0-24 G

69-89 S

10-13 F

114.5

16.5%

(19 ksi)

Silty, clayey, poorly graded, well graded SAND (SM, SC, SP-SM SW-

SM)

and IGNEOUS ROCK (GRANITE)

A-1-b, A-2

Sta. 2410+00 to 2730+00

17P-30 to 17P-54 γd: 92-116 wo: 3-15%

0-24 G

62-90 S

7-26 F

26-27 LL

3-5 PI

50-69

(36 ksi)

Silty, clayey, well graded, poorly graded SAND with varying amount of clay and gravel (SM, SC, SC-SM, SP-

SM, SW, SW-SM, SW-SC), poorly graded gravel (GP, GP-GM) with varying amount of silt and IGNEOUS

ROCK (GRANITE)

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

Sta. 2730+00 to 2950+00

17P-55 to 17P-70 γd: 75-118-wo: 1-31%

0-16 G

70-89 S

9-20 F

(16 ksi)

Silty, clayey, poorly graded, well graded SAND (SM, SC, SP-SC, SP- SM, SW-SM) with varying amounts of gravel and clay, and poorly graded GRAVEL (GP, GP-GC) with varying amounts of clay and IGNEOUS ROCK

(GRANITE)

A-1, A-2

2 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); 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 (ds) or consolidated undrained (cu) tests.

5. CONCLUSIONS AND RECOMMENDATIONS

5.1 CUT SLOPE DESIGN

Yeh personnel reviewed the cut slopes within the project limits on September 27, 2017. Most of the cut slopes are minor, vary from soil to rock, and are low in height with adequate catchment. These minor slopes are generally performing well and aside from ditch cleaning do not appear to need mitigation. Scaling, cleaning of the roadside ditch/catchment area of rock and debris is recommended for the following three slopes, and as general maintenance improvement for the cuts along the project. It is estimated that a typical 3 person scaling crew with traffic control with roadway clearing ability could effectively hand scale the predominant rock slopes in three 8-hour days, with subsequent crew to remove debris and rock from ditches.

A more detailed assessment was performed for the following three cut slopes that would benefit from scaling and maintenance as part of the planned construction.

Post Mile 16.07. This cut slope is located on the northbound side of Ice House Road and extends for approximately 530 feet north from the referenced Post Mile. The slope is cut into glacial deposits, consisting of granitic cobbles and boulders in a matrix of silty sand and gravels.

The cut varies in height from 6 feet to approximately 20 feet, with an overall slope angle of approximately 40 degrees. The catchment width, as measured from the toe of slope to the edge of travel way (ETW) is approximately 5 feet unpaved and 3 feet paved, for a total of 8 feet.

The slope is vegetated with immature conifers and weak topsoil development.

Figure 6: Cut Slope at PM 16.07

Rockfalls are occurring at this location, the majority of which are being contained in the catchment area, however there is evidence that some rocks are reaching the travelled way.

The rocks in the ditch ranged in size from 3 inches to 1 foot in diameter; however, one boulder measuring approximately 2.5 feet in diameter was contained in the unpaved catchment area.

Sloughing and erosion of the cut slope matrix material has created an outward sloping condition in the unpaved catchment area toward the travel way and enabling rockfall further from the base of the slope. Resloping the unpaved catchment area to create an inward backslope of 4H:1V to the base of the cut slope is recommended to help contain rockfall at this location.

Post Mile 18.48. This cut slope is located on the northbound side of Ice House Road and extends for approximately 150 feet north from the referenced Post Mile. The slope is comprised of fresh, slightly to very slightly fractured granite. The slope is approximately 20 feet in height, and has a typical angle of approximately 60 degrees, with relatively short areas where the cut is vertical. Because of the intersecting nature of rock discontinuities (joints, fractures, foliations), the cut slope face is irregular with vertical faces and others that dip favorably into the slope at 20 degrees below horizontal. The catchment width is 8 feet as measured from the toe of the slope to the edge of the traveled way. Cleaning of the catchment is recommended for this slope.

Figure 7: Photo of Rock Cut t PM18.48

Figure 8: Photo of Rock Cut at PM18.54

Post Mile 18.54. This cut slope was located on the northbound side of Ice House Road immediately north of the bridge at Post Mile 18.51. The slope was comprised of fresh, moderately to slightly fractured granite. The slope height varied from approximately 20 to 25 feet with an overall slope angle of approximately 45 degrees. The cut slope face is irregular because of the intersecting nature of the discontinuities, with vertical faces and others at 20 degrees from horizontal. Catchment width varied from 3 to 6 feet, as measured from the toe of slope to the ETW. Several prominent discontinuities intersected throughout the cut slope face creating a potential for toppling and wedge failures, with block dimensions of up to approximately 2 feet high x 3 feet wide x 1.5 feet deep.

5.2 EARTHWORK FACTORS

The subgrade generally consisted of loose to medium dense clayey sand and medium stiff clay.

The drive samples that were tested had dry unit weights ranging from approximately 78 to 118 pounds per cubic foot, with average unit weight of 92 pounds per cubic foot. It is recognized that disturbance to drive samples occurs due to compaction of samples during driving, loosening of the soil when recovering the sampler from the drill hole, and disturbance during trimming in the laboratory. A Proctor test performed on a sample of silty sand with gravel had an estimated maximum dry unit weight of approximately 114 pounds per cubic foot.

Differences in soil density likely occur in areas where the existing pavement subgrade and embankment fill materials were compacted, topsoil or softer soil is present near the subgrade elevation, and inherent differences in soil type and consistency. The estimated earthwork factors3 do not account for losses for removal of vegetation or unsuitable material. An average earthwork factor of 1 can be used considering the pulverization and compaction of the existing structural section. An average earthwork factor of 0.9 can be used for areas where the subgrade will be compacted outside the limits of the existing structural section, or in areas where subexcavation or digouts are recommended. The earthwork factors are approximate and should be checked and adjusted as the grading work progresses.

5.3 SUBGRADE PREPARATION

The existing road has areas of distress that are manifested by settlement and cracking along in the wheel tracks, through curves, and as a result of root and frost heave. Subexcavation can be used to improve the subgrade support for the new pavement. The typical types of distress that

3 The earthwork factor represents the ratio of the existing in-situ unit weight of the soil before construction to the unit weight of the same soil after compaction. For example, an earthwork factor of 0.95 represents a 5 percent loss in the volume of soil following compaction. An earthwork factor of 1.05 represents a 5 percent gain in volume of the soil or pavement following compaction due to bulking of a relatively dense material.

were noted during the field work are noted on Plate 1. “Digouts” noted on Plate 1 are areas where the existing material should be removed and replaced with compacted fill, or to remove roots or boulders as discussed in the following sections. “Stabilization” refers to areas where the subgrade may be relatively wet and where the existing subgrade should be removed and replaced with suitable material as recommended in the following section. The recommended subgrade preparation should be performed before performing pulverization for full depth reclamation.

5.3.1 ROOT INTRUSION AND BOULDERS

The approximate areas where digouts are recommended to remove roots, boulders or address pavement distress are noted on Plate 1. Roots have intruded below the existing roadway that has resulted in heaving and cracking along sinusoidal ridges above the roots.

Boulders have been moved upward by frost heaves resulting in dome shaped cracks and mounds in the pavement. Where roots or boulders have resulted in heaving and damage to the existing pavement, they should be removed prior to pulverization.

Remove all portions of the root that are more than ½-inch in diameter to at least 1 foot beyond the finished edge of pavement. If the removal extends below the anticipated depth of pulverization, a trench at least 12 inches wide should be provided in association with the removal to allow for backfill and compaction following removal of the root. Where the excavation to remove roots or boulders extends below the recommended depth of pulverization (about 7 inches), the excavation

Figure 10: Typical Distress from Root Intrusion

Figure 10: Typical Boulders in Glacial Till along shoulder

Geotechnical and Pavement Engineering Report Yeh Project No. 217‐390 Ice House Road March 10, 2020 should be backfilled to adjacent grade according to FP‐14, Section 209.09 and compacted per

209.10. Excavated on‐site soil should be suitable for reuse as compacted fill (Section 704.03a).

5.3.2 DIGOUTS

Digouts are noted on Plate 1 for areas of pavement distress relating to severe fatigue or longitudinal cracks in the pavement. The digout areas would need to be removed and replaced with compacted fill if Ice House Road were to be rehabilitated with an overlay or seal coat. The digouts relating only to pavement distress do not apply if full‐depth reclamation is used for the entire route as currently planned, although digouts relating to root intrusion would still apply.

5.3.3 HARD ROCK

Portions of the alignment are adjacent to existing rock slopes. Hard rock within the subgrade can interfere with or damage pulverization equipment. The contractor should review the borings information and perform potholing along the existing cuts to check that outcrops of the hard rock will not interfere with pulverization equipment.

As discussed in the previous section, glacial till was encountered and is exposed in cuts along the alignments. Where boulders are present along the road or exposed in existing road cuts, the contractor should take care to avoid damaging equipment. Ripping the ground in these area prior to pulverization should help flush out and preexcavate boulders. Ripping and excavating boulders that are noticeably heaved and distressing the existing pavement should help reduce the potential for encountering rocks or boulders during pulverization. The existing

5.3.4 OPEN JOINTS IN ROCK

The scoping report, and discussions with the El Dorado County Public Works Department.

identified a potential for voids and sinkholes to develop in the subgrade due to a loss of overburden soil into joints and fractures within the underlying bedrock. These areas had been patched at the time of our October 2017 field exploration program. The design team subsequently agreed that no special mitigation will be addressed in the design.

5.3.5 SOFT OR WET SUBGRADE CONDITIONS

Stabilization should be provided where the subgrade is wet, soft or yielding. The approximate areas where stabilization of the subgrade may be needed are noted on Plate 1. The areas shown for stabilization are generally where closely spaced fatigue cracking of the pavement was noted that could be associated with loose or wet subgrade conditions. Areas of distress within Segment 5 (Station 2730+00 to end of project) contain zones of poor drainage, springs, and potentially wet subgrade conditions. Subgrade stabilization should be provided in those areas that are noted on Plate 1, or where unsuitable materials or soft subgrade conditions are

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encountered during construction that will not allow for proper compaction of the subgrade or FDR materials. Subgrade stabilization should consist of removing the existing soil to a depth at least 1 foot below the bottom of the structural section or to the bottom of the unsuitable material, whichever is deeper. 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 and placement of the geotextile and backfill.

A geotextile for stabilization should be placed over the undisturbed subgrade in accordance with Section 207 of FP-14. The geotextile should be placed without gaps or wrinkles and conform to Section 714.01a, Class 1, Type E Geotextile, of FP-14. If the subgrade is relatively dry, firm and unyielding the excavated onsite soil should be suitable for use as backfill. The backfill should otherwise consist of Soil Backfill material per Section 704.03a of FP-14. If the subgrade is relatively wet, the backfill should consist of uniformly graded 3/8 to 1.5-inch Gravel Backfill conforming to Section 703.6, Crushed Aggregate, of FP-14. Gravel Backfill 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 drained to a suitable outlet if springs or standing water are present in the exposed subgrade.

The project specifications should include a quantity for stabilizing the subgrade for the roadway based on the limits noted on Plate 1, and for increasing, decreasing for deleting the quantity based on the conditions encountered during construction. The subgrade conditions should be reviewed at the time of construction to evaluate the final limits and need for stabilization.

5.4 PAVEMENT DESIGN RECOMMENDATIONS

The new structural section for design of the Ice House Road improvements is recommended based on Chapter 11 of the CFLHD Project Development and Design Manual (PDDM) and the AASHTO (1993) Guide for the Design of Pavement Structures. Preliminary pavement structural sections were evaluated and presented in the Yeh (2018) Preliminary Pavement Recommendations memorandum. The concept to use full depth reclamation (FDR) and a hot mix asphalt pavement overlay was selected during a conference call between the design team and FHWA as being the appropriate alternative for all segments of this project. The spreadsheet calculations for our recommended traffic loading and thickness recommendations are presented in Appendix D.

5.4.1 DESIGN TRAFFIC VOLUME AND SUBGRADE

Traffic Data. The design traffic volume was estimated using traffic count data provided by El Dorado County and procedures in the Federal Lands Highway Project Development and Design

Manual (FHWA 2008). The design traffic volume is a current average daily traffic (ADT) of 1,409 vehicles per day with 1 percent trucks and a 2 percent growth factor. These data were used to estimate the number of 18-kip equivalent single axle loads (ESALs) considering a design life of 20 years. The design ESAL value was 210,000.

Subgrade. The subgrade encountered along Ice House Road was predominantly classified as sand and silty sand with varying amounts of clay and gravel (A-1, A-2) and is considered relatively good support for the roadway. R value tests performed on subgrade samples had results ranging from approximately 50 to 69. The recommended structural section thicknesses were estimated considering a resilient modulus (Mr) of 13,168 psi corresponding to a minimum R-value of 50.

5.4.2 STRUCTURAL SECTION

The recommended structural section for the Ice House Road improvements is 3 inches of HMA over 6 inches of FDR material for all segments. The Yeh (2018) Preliminary Pavement Recommendations memo identified five segments of Ice House Road that were differentiated based on the deflection data: PM6.37 to 9.7, PM9.7 to 12.0, PM12.0 to 14.0, PM14.0 to 20.2, and PM20.2 to 24.0. The existing pavement typically consist of 2 inches of hot mix asphalt placed over 5 or 6 inches of cold-in-place recycled material. The pulverization should extend through the existing CIPR material and at least 1 inch into the subgrade. The depth of pulverization, reuse or hauling off pulverized material should be considered and adjusted where the finished grade of the new pavement will match the existing grade or is limited to 1 inch above existing grade.

Figure 11: Summary of Structural Section Recommendations

Imported roadway aggregate (Type C) may be added to supplement the FDR depending on the final quantity of base course material needed for design. It should be anticipated that the FDR and any supplemental base course material will need to be compacted in a maximum 6-inch lift to achieve compaction. The FDR material should be moisture conditioned and compacted to at least 95 percent relative compaction in accordance with FP-14 Standard Specifications. A summary of the structural section recommendations is shown in Figure 11.

The new edge of pavement (NEP) should be shouldered up with FDR or roadway aggregate to reduce the potential for edge cracking. Shoulder backing should consist Class D base conforming to Section 7.03.05 of FP-14 and placed as Roadway Aggregate, Method 2. Shoulder backing should be placed to match the finished surface of the pavement at the NEP and be tapered out away from the roadway.

5.4.3 BINDER AND MIX RECOMMENDATIONS

The State of California (Caltrans 2012) has adopted a program of Asphalt Binder Grade Selection that classifies this project area as the High Mountain Region. The recommended binder for this area based on Caltrans data is PG 64-28M.

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 use of a material transfer device at the point of placement to provide more uniform temperatures and prevent segregation of the mix during placement.

5.4.4 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.

Maintenance of asphalt concrete pavements should typically include periodic fog, chip or slurry seals to reduce the potential for weathering and overlaying with additional HMA when needed to strengthen and further the life of the pavement. Pavement condition index and deflection surveys can be performed to evaluate the structural capacity of pavements and the need for future overlays and maintenance.

5.5 CORROSION CONSIDERATIONS

FHWA foundation design manuals define 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 5.2 to 6.6 and the soil resistivity ranged from 2,739 to 53,210 ohm-centimeters.

The soil samples that were tested are not considered aggressive towards concrete. Corrosion and corrosion test data should be considered in the design of reinforced concrete or steel structures.

5.6 NATURALLY OCCURRING ASBESTOS

Naturally occurring asbestos (NOA) is distributed through the Sierra Nevada, Coast Ranges and Klamath Mountains and is most commonly associated with ultramafic rocks and serpentinite.

Dust generated from excavating through rocks that contain NOA is a recognized health concern.

Four subgrade samples of soil and rock were submitted to EMSL Analytical of San Leandro, California to test for asbestos. The samples tested had no reported fibrous material and no asbestos was detected. Ultramafic rocks are mapped by Wagner et al. (1981) along a series of north-south trending faults in the Sierra Foothills just west of Placerville and not within the project limits.

6. NOTES TO CONSTRUCTION

• Excavation and subgrade preparation to address heaving of the existing pavement due roots, boulders, voids or stabilization should be performed in advance of the FDR.

Attention should be paid to ensure that the contractor is compacting backfill placed below the planned depth of FDR.

• Hard rock, boulders or roots within the subgrade could damage equipment or prevent pulverization of the subgrade.