CA_FTNP_14(5_ _219(2)_Geotech_Report.pdf

Geotechnical Design and Pavement Report Yosemite National Park South Entrance Wawona Road & Mariposa Grove Road

Mariposa County, California

July 5, 2016

Submitted To:

Jacobs Engineering

707 17th Street Denver, Colorado 80202

By:

Shannon & Wilson, Inc.

1321 Bannock Street, Suite 200 Denver, CO 80204

23-1-01458-030

ALASKA

CALIFORNIA

COLORADO

FLORIDA

MISSOURI

OREGON

WASHINGTON

WASHINGTON DC METRO

WISCONSIN

1321 BANNOCK STREET, SUITE 200

DENVER, COLORADO 80204-4077

303-825-3800 FAX: 303-825-3801

TDD 1-800-833-6388

www.shannonwilson.com 23-1-01458-030

July 5, 2016

Jacobs Engineering 707 17th Street Denver, Colorado 80202

Attn: Mr. Berwyn Wilbrink

RE: GEOTECHNICAL DESIGN AND PAVEMENT REPORT, YOSEMITE

NATIONAL PARK SOUTH ENTRANCE, WAWONA ROAD AND MARIPOSA

GROVE ROAD, MARIPOSA COUNTY, CALIFORNIA

We are pleased to submit our geotechnical design report for the above-referenced project. The enclosed report summarizes subsurface conditions encountered in a subsurface exploration program, laboratory tests, and geotechnical engineering recommendations for the proposed improvements for the South Entrance Wawona Road & Mariposa Grove Road.

We appreciate the opportunity to be of service to you on this project. If you have any questions or require further information, please contact me at 303-825-3800.

Sincerely, SHANNON & WILSON, INC.

Gregory R. Fischer, Ph.D.

Senior Vice President

JCG:GRF

Encl: Geotechnical Report

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TABLE OF CONTENTS

Page

1.0 INTRODUCTION

2.0 PROJECT DESCRIPTION

2.1 Wawona Road Improvements

2.2 Mariposa Grove Road Improvements

3.0 SITE DESCRIPTION

4.0 FIELD EXPLORATIONS AND LABORATORY TEST RESULTS

4.1 Subsurface Explorations

4.2 Laboratory Test Results

5.0 SUBSURFACE CONDITIONS

5.1 Regional Geology

5.2 Subsurface Conditions

5.2.1 Wawona Road/Mariposa Grove Road Rehabilitation Sections

5.2.2 Roundabout/MSE Wall

5.2.3 Four-Mile Access Road

5.2.4 Mariposa Grove Rockery Wall

5.2.5 Snow Chain-up Area

5.3 Groundwater

6.0 GEOLOGIC HAZARDS

6.1 Seismicity

6.2 Faulting

6.3 Liquefaction

7.0 RETAINING WALL DESIGN RECOMMENDATIONS

7.1 Seismic Design

7.1.1 Site Class

7.1.2 Design Parameters

7.2 Mechanically Stabilized Earth (MSE) Walls

7.2.1 Reinforcement

7.2.2 Lateral Earth Pressures

7.2.3 Bearing Resistance and Settlement

7.2.4 Wall Drainage

7.3 Rockery Walls

TABLE OF CONTENTS (cont.)

ii

7.3.1 Global Stability

7.3.2 Lateral Earth Pressures

7.3.3 Bearing Resistance

7.3.4 Sliding Resistance

7.3.5 Wall Drainage

8.0 PAVEMENT DESIGN RECOMMENDATIONS

8.1 Traffic Loading

8.2 Subgrade Conditions

8.3 Pulverized Full Depth Reclamation (FDR)

8.4 Asphalt Pavement Sections

9.0 CORROSION CONSIDERATIONS

10.0 CONSTRUCTION AND MATERIALS SPECIFICATIONS

10.1 Earthwork

10.1.1 Site Preparation

10.1.2 Proof-rolling

10.1.3 Fill Placement and Compaction

10.1.4 Slopes

10.1.5 Benching

10.2 Paving Materials

10.3 Excavation and Shoring

10.4 Dewatering

11.0 PLAN REVIEW AND CONSTRUCTION OBSERVATION

12.0 LIMITATIONS

13.0 REFERENCES

TABLES

1 Recommended Ground Motion Parameters 2 Recommended Parameters for MSE Wall Design 3 Recommended Parameters for Rockery Wall Design 4 Recommended Parameters for Rockery Wall Sliding 5 Proposed Traffic Loading 6 PDDM Flexible Pavement Design Parameters 7 Preliminary Pavement Sections 8 Recommended Materials for Pavements

TABLE OF CONTENTS (cont.)

iii

FIGURES

1 Location and Vicinity Map 2 Site and Exploration Plan 3 Plan and Section at Roundabout Retaining Wall 4 Plan and Section at Rockery Wall 5 Plan and Section at Snow Chain-Up Area 6 Recommended Surcharge Loading For Temporary and Permanent Walls 7 Typical Rockery Detail 8 Rockery Lateral Earth Pressure Loadings

APPENDICES

A Subsurface Explorations B Laboratory Test Results C Exploration Photographs D Pavement Design Calculations E Important Information about Your Geotechnical/Environmental Report

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GEOTECHNICAL AND PAVEMENT DESIGN REPORT

YOSEMITE NATIONAL PARK SOUTH ENTRANCE

WAWONA ROAD AND MARIPOSA GROVE ROAD

MARIPOSA COUNTY, CALIFORNIA

1.0 INTRODUCTION

This geotechnical and pavement design report provides our recommendations for the South Entrance Wawona Road and Mariposa Grove Road Project. The report summarizes our subsurface explorations and laboratory testing, and presents our geotechnical and pavement design recommendations and construction considerations. Our services were completed in general accordance with our Subconsulting Agreement No. WVXY4054-S16-0001 with Jacobs Engineering Group, Inc. (Jacobs) dated February 23, 2016.

The scope of our services did not include an evaluation regarding the presence or absence of hazardous or toxic materials in the soil, surface water, groundwater, or air, on or below or around this site. If such contamination exists, it would not be possible to document it within this limited scope of work.

2.0 PROJECT DESCRIPTION

The proposed project is shown on preliminary scoping plans, titled, “South Entrance Wawona Road & Mariposa Grove Road,” dated January 15, 2016. Jacobs Engineering electronically provided these plans to Shannon & Wilson on February 22, 2016. The proposed project includes a new roundabout along with resurfacing, restoration, and rehabilitation of Wawona Road and Mariposa Grove Road near the South Entrance of Yosemite National Park in Mariposa County, California (Figure 1). The plans show three project alignments; one for each roadway. The alignments are designated Wawona Road West, Wawona Road South and Mariposa Grove Road.

We reference these alignments and associated stationing throughout this report. The Four-Mile aggregate surfaced access road will also be realigned as part of the project. The locations of the above proposed improvements are shown on Figure 2.

2.1 Wawona Road Improvements

The plans indicate two roadway rehabilitation sections and one realignment section for Wawona Road. The southern Wawona Road rehabilitation section extends for 2,995 feet (Station 212+25 to 242+20, Wawona Road – South) from 800 feet south of the park entrance toll booths to approximately 300 feet south of the intersection of Wawona Road and Mt. Raymond Road. The northern Wawona Road rehabilitation section extends for 1,560 feet (Station 105+00 to 120+60, Wawona Road – West) ending 500 feet west of the tee intersection.

Rehabilitation improvements along the two sections include: rehabilitated roadway, paving existing gravel pullouts and inboard ditches, creating a chain installation area (approximately Station 231+00 to 233+00 Wawona Road South) and installing new drainage and culverts.

The realigned section of Wawona Road extends from Station 120+60 (Wawona Road – West) to Station 300+95 (Mariposa Grove Road) and Station 204+00 (Wawona Road – South). The proposed realignment follows the existing Wawona Road exit lane and has an eighty-foot diameter roundabout forming the new intersection of Wawona Road and Mariposa Grove Road.

The new roundabout/roadway alignment will require widening the road to the south.

A new retaining wall will be required to support the widened roadway section. A Mechanically Stabilized Earth (MSE) wall using welded wire mesh as reinforcement is proposed. The following plan sheets provided by Jacobs Engineering show the preliminary wall layout in plan, profile and station typical section.

CA FTNP YOSE 14(5) 219(2) South Entrance – Sheet S1, dated March 24, 2016

CA FTNP YOSE 14(5) 219(2) South Entrance – Sheet X1, dated March 24, 2016

CA FTNP YOSE 14(5) 219(2) South Entrance – Sheet Y2, dated March 24, 2016

The wall is planned to be 259 feet long and will vary in height from eight to approximately fourteen feet. Plan sheets show the wall layout between retaining wall Station 10+00 (123+83.33, 49.09 feet right – Wawona Road - West) and Station 12+59.74 (125+89.36, 21.52 feet right – Wawona Road - West). The top of wall elevation will be 5,117 and tapers to elevation 5,112.50 from wall Station 11+68.32 to 12+59.74. The base of wall will be stepped and generally follows the existing site topography.

2.2 Mariposa Grove Road Improvements

The proposed improvements along Mariposa Grove Road include a minor realignment and repaving at the intersection with Wawona Road and rehabilitation and partial widening of 9,485 feet of road. The realignment section includes approximately 100 feet of realigned and repaved roadway to integrate into the proposed roundabout improvements. This also includes eliminating the tee intersection with Wawona Road at Station 300+00 (Mariposa Grove Road).

The rehabilitation and repaving improvements extend for 9,485 feet from Station 310+65 to 405+50 (Mariposa Grove Road). Rehabilitation starts approximately 1,000 feet east from the existing tee intersection and extends to the Lower Grove Parking Lot.

In addition to the rehabilitation, minor realignment of the roadway is proposed from Station 398+00 to 403+00 (Mariposa Grove Road) and will require the construction of 400 feet of rockery retaining wall along the inboard side of Mariposa Grove Road. March 24, 2016 plans from Jacobs show the rockery wall height varying from 3 feet to 12 feet with the greatest height from Station 401+00 to 403+00 (Mariposa Grove Road). Temporary cuts will be required to construct these walls. The base of wall is shown at about existing roadway grade.

3.0 SITE DESCRIPTION

The project is located within Yosemite National Park near the State Route 41 (SR 41) southern park entrance. Within the park boundary (approximately 0.7 miles south of the tee intersection), SR 41 becomes Wawona Road and heads northwest. Just past the park entrance, Wawona Road forms a tee intersection with Mariposa Grove Road. Wawona Road serves as the main road from the south entrance of Yosemite National Park to Yosemite Valley from the south and is approximately 28 miles from the entrance to the middle of the valley floor.

Mariposa Grove Road heads east from the tee intersection and provides access to the Lower Grove Parking Lot and the Mariposa Grove of Giant Sequoias. Mariposa Grove Road is approximately two miles in length and is typically closed in the winter.

Mariposa Grove and Wawona Roads are paved two-lane roads with a posted speed limit of 35 miles per hour (mph). The roads have limited gravel backed shoulder widths that are approximately one foot wide or less. The existing pavement condition along the project alignment included areas of significant fatigue cracking, along with longitudinal cracking and rutting.

The Four-Mile access road is an aggregate surfaced road that currently is accessed from the Wawona Road exit lane at approximate Station 123+00. Four-Mile access road is closed to through traffic. The described roadways are at elevations above 5,000 feet. Frost depths are typically 12 inches for this area.

Existing slopes vary from one vertical to five horizontal (1V:5H) and steeper. Slopes flatter than 1V:5H are generally associated with existing roadways and constructed facilities. Natural drainages are typically shallow channels (two to three feet deep or less) except for the Big Creek crossing on Wawona Road at project Station 236+00, which includes a 7.5-foot diameter corrugated metal pipe culvert (CMP). Typically, 18- to 24-inch diameter CMPs provide drainage beneath the roadways.

A shallow drainage channel is located approximately 95 feet south and downslope of the Wawona Road exit lane. The drainage channel appears approximately 3- to 4-feet deep.

4.0 FIELD EXPLORATIONS AND LABORATORY TEST RESULTS

4.1 Subsurface Explorations

Shannon & Wilson implemented a field exploration program to evaluate subsurface conditions.

The exploration program, conducted from March 8 through March 10, 2016, consisted of drilling 14 geotechnical borings (designated SW-01 through SW-09 for pavement borings and SW-10 through SW-14 for borings at the roundabout and snow chain-up area). In addition, five test pits (designated TP-01, TP-02 A through C, and TP-03) were completed.

The borings were completed using a track-mounted drill rig. The test pits were excavated using a rubber-track backhoe. Figure 2 shows the approximate boring and test pit locations. Appendix A describes the procedures used to complete the drilling and sampling of the borings and excavation of the test pits and also presents individual logs and an explanation of the symbols and terminology used. Appendix C contains photographs of the geotechnical exploration locations.

4.2 Laboratory Test Results

Shannon & Wilson completed geotechnical laboratory testing to determine index and engineering properties of samples retrieved from the borings. Laboratory tests included natural water content, grain size distribution, Atterberg limits, compaction characteristics, R-value, and corrosion testing. Laboratory test results and a discussion of testing procedures are included in Appendix B. In addition, the natural water contents, Atterberg limits, and percent fines are indicated on the individual boring logs and the natural water contents are indicated on the individual test pit logs in Appendix A.

5.0 SUBSURFACE CONDITIONS

5.1 Regional Geology

The project is located within the boundary of the Yosemite National Park, on the western slope of the central Sierra Nevada batholith. The Sierra Nevada is an uplifted tectonic block that has formed between the active Owens Valley Fault zone to the east and the Great Valley on the west.

The Sierra Nevada batholith is primarily composed of intrusive or plutonic rocks with near-surface secondary rock types composed of metamorphic, volcanic, and sedimentary rock roof pendants. Overlying the rock within the Yosemite Valley area and north of the project site are relatively young glacial deposits.

At the project site, published mapping shows that Cretaceous Bass Lake Tonalite and El Capitan Granite underlie both the Wawona and Mariposa Grove Roads across the project limits. The Bass Lake Tonalite Formation is described as consisting of tonalite, granodiorite and quartz diorite that is well-foliated, medium grained, and equigranular; tonalite and calcic granodiorite contain abundant mafic inclusions. The El Capitan Formation is described as a medium-grained, equigranular to weakly porphyritic biotite granite.

Observed rock exposures along the roadway are typically decomposed but appear similar to the descriptions in published mapping.

5.2 Subsurface Conditions

5.2.1 Wawona Road/Mariposa Grove Road Rehabilitation Sections

Borings SW-01 through SW-05 were drilled along Wawona Road and borings SW-06 through SW-09 were drilled along Mariposa Grove Road. The borings were drilled through the existing pavement and encountered 3 to 5-1/2 inches of asphalt underlain by 0 to 7 inches of base course. Photographs of the asphalt pavement cores taken from the borings are shown in Appendix A. Underlying the pavement section, the borings encountered loose to medium dense (occasionally dense), silty sand (silty to clayey sand in boring SW-09). This material was generally classified as decomposed granitoid rock or grus when latent geologic structure was visible in the samples, and extended to the bottom of the borings, except at borings SW-05 and SW-06 where granite bedrock was encountered at depths of 2.5 and 5 feet, respectively.

5.2.2 Roundabout/MSE Wall

Borings SW-10 through SW-13 were drilled at the proposed roundabout wall location.

Boring SW-10 encountered approximately 6 inches of roadway gravel, and boring SW-11 encountered 9 inches of asphalt overlying 9 inches of base course at the ground surface. Boring SW-11 then encountered 2.5 feet of medium dense, silty sand fill below the pavement section.

Borings SW-12 and SW-13 were drilled off-road and encountered about 6 inches of forest duff and topsoil at the ground surface. Below these surficial materials, boring SW-10 encountered loose to medium dense, silty sand (grus). However, borings SW-11, SW-12 and SW-13 did not encounter grus until depths of 17, 12 and 7 feet, respectively. In these borings, layers of very loose to loose, silty sand and clayey sand were encountered above the grus. The grus became very dense at depths of about 35.5 and 37.5 feet in borings SW-12 and SW-13, respectively.

5.2.3 Four-Mile Access Road

Test pit TP-01 was excavated at the proposed Four-Mile Access Road realignment and encountered approximately 6 inches of forest duff and topsoil overlying very loose to loose, clayey sand to the termination depth of the excavation.

5.2.4 Mariposa Grove Rockery Wall

Test pits TP-02 A through C were excavated along the edge of Mariposa Grove Road in the area of the proposed rockery wall and encountered up to 12 inches of forest duff and topsoil underlain by dense, silty sand (grus).

5.2.5 Snow Chain-up Area

Boring SW-14 was drilled at the south end of the proposed snow chain up area. This boring encountered 6 inches of roadway gravel overlying medium dense to dense, silty sand (grus) to the termination depth of the boring. Test pit TP-03 was excavated at the north end of the proposed chain up area and encountered approximately 12 inches of forest duff and topsoil underlain by medium dense to dense, silty sand (grus).

5.3 Groundwater

Groundwater was encountered in borings SW-12, SW-13, and SW-14 at depths of about 14, 13, and 15 feet, respectively. We did not observe seepage within the test pit excavations.

6.0 GEOLOGIC HAZARDS

6.1 Seismicity

The California Geological Survey (CGS) and United State Geological Survey (USGS) have mapped faults and identified fault activity in the region (Jennings and Bryant, 2010; USGS, 2016). The closest mapped Quaternary faults are the Hartley Springs Fault and Silver Lake Fault, located approximately 35 miles northeast from the South Entrance area. The USGS fault mapping indicates that the Hartley Springs Fault system is Holocene/Latest Pleistocene active with some historic (last 150 years) faulting in the Mammoth Lakes area. The Silver Lake Fault system is indicated by the USGS as Holocene/Latest Pleistocene active. Both faults are believed to be a source of earthquakes with magnitudes greater than six.

6.2 Faulting

The Alquist-Priolo Earthquake Fault Zoning Act produced 1:2000 scale maps of active faults as determined by the State Geologist for the CGS. Based on these maps, the project site is not located within an Alquist-Priolo Earthquake Fault Zone and is not underlain by known active faults (Jennings and Bryant, 2010). Because no recognized active faults are present at the project site, the potential for fault surface rupture at the site is low, in our opinion.

6.3 Liquefaction

Soil liquefaction is a phenomenon in which pore pressure in loose, saturated, granular soil increases during ground shaking to a level near the initial effective stress, resulting in a reduction of shear strength of the soil. As a result of this reduction in shear strength during liquefaction, ground settlement, lateral spreading (ground movement on very gentle slopes), and landslides may occur. Because of the reduced soil strengths, vertical and lateral foundation resistance may also be reduced.

The subsurface explorations reveal that, below the groundwater table, the project area is underlain by moderately dense, residual soils. Therefore, liquefaction potential at the site is considered low.

7.0 RETAINING WALL DESIGN RECOMMENDATIONS

7.1 Seismic Design

7.1.1 Site Class

The AASHTO site class is determined using standard penetration test (SPT) N-values measured in the upper 100 feet of the soil profile. Because our borings did not extend to 100 feet in depth, we extrapolated subsurface conditions beneath the deepest borings for the walls. Using the AASHTO LRFD Bridge Design Specifications (AASHTO, 2014) criteria, the subsurface SPT N-values indicate Site Class D should be used in design.

7.1.2 Design Parameters

Table 1 presents recommended seismic design ground motion parameters for the site.

TABLE 1

RECOMMENDED GROUND MOTION PARAMETERS

Ground Motion Parameters Value

Peak Ground Acceleration1 (PGAB) 0.209 g Site Class D Short-period Spectral Acceleration, Ss 0.502 g Long-period Spectral Acceleration, S1 0.176 g Site Factor, Fpga 1.381 Site Factor, Fa 1.398 Site Factor, Fv 2.096 Peak Design Spectral Acceleration, AS 0.289 g Short-period Design Spectral Acceleration, SDS 0.702 g Long-period Design Spectral Acceleration, SD1 0.369 g T0 0.105 sec.

TS 0.526 sec.

Seismic Zone2 3 Notes:

1. PGAB = peak ground acceleration for a site underlain by Site Class B soil (soft rock).

2. Seismic zone from AASHTO (2014) Table 3.10.6-1.

AASHTO does not require a site-specific ground motion evaluation for Site Class D conditions. Ground motion parameters were determined for the project site using the USGS U.S.

Seismic Design Map Web Application (U.S, Geologic Survey, 2012, accessed on March 15, 2016) and the 2009 AASHTO LRFD Bridge Design Criteria (the design parameters have not changed in the current 2014 manual). The design ground motion used for evaluation is 7 percent probability of exceedance in 75 years.

7.2 Mechanically Stabilized Earth (MSE) Walls

Consistent with AASHTO (2014) requirements, a minimum 4-foot wide horizontal bench should be provided in front of MSE walls bearing on slopes. The horizontal bench may be formed or the slope may be continued above the elevation of the bench. Regardless, the base of the reinforced zone should be embedded a minimum of 2 feet below the bench elevation.

We anticipate the MSE wall reinforced zone will be backfilled with Select Granular Backfill material, as specified in FP-14 Section 704.08 and placed in accordance with the FP-14 Section

255.05 and as described in Section 10.1 of this report.

7.2.1 Reinforcement

We evaluated the global and external stability of the proposed MSE walls in accordance with AASHTO (2014) criteria. To meet global stability requirements (i.e., provide a minimum factor of safety (FS) of 1.3 for static conditions and 1.1 for seismic conditions) and external stability requirements we recommend a minimum MSE wall reinforcement length of 1.0H (where H is the height measured from the bottom of the reinforced fill zone to the top of the wall) or 8 feet, whichever is greater. The reinforcement lengths may need to be increased to meet internal or compound stability requirements. These failure modes should be evaluated by the MSE wall designer/vendor as these failure modes depend on the reinforcement type and spacing.

We recommend extending the top two layers of reinforcement across the entire width of the roadway (to reduce the potential for a crack to develop at the back of the reinforcement).

7.2.2 Lateral Earth Pressures

Our recommended design parameters for design of MSE walls are provided in Table 2. The parameters are based on AASHTO (2014) criteria and assume Select Granular Backfill material as specified in FP-14 Section 704.08 is used in the reinforced zone. We have assumed that on-site soils will be reused within the retained zones (i.e., the 1V:1H zone extending upward from the heel of the reinforced zone).

TABLE 2

RECOMMENDED PARAMETERS FOR MSE WALL DESIGN

Design Parameter Recommended Value3,4

Reinforced Backfill1

Total Unit Weight (pcf) 130 Friction Angle (degrees) 34

Cohesion (psf) 0 Static Active Earth

Pressure Coefficient, KA 0.28

Seismic Active Earth Pressure Coefficient, KAE 0.37

Retained Backfill (recompacted on-site soil)

Total Unit Weight (pcf) 120 Friction Angle (degrees) 32

Cohesion (psf) 0 Static Active Earth

Pressure Coefficient, KA 0.31

Seismic Active Earth Pressure Coefficient, KAE

0.40

Seismic Horizontal Acceleration Coefficient2, kh 0.145g Notes:

1. All load and resistance factors for MSE wall design should be in accordance with AASHTO (2014).

2. The seismic horizontal acceleration coefficient assumes the wall is capable of displacing 1 to 2 inches during the design seismic event, in accordance with AASHTO (2014).

3. Parameters assume a horizontal backslope.

4. Parameters assume freely drained backfill material (Section 7.2.4).

psf = pounds per square foot pcf = pounds per cubic foot

The MSE vendor/designer may use alternate earth pressure parameters for design based on further testing and characterization of the actual fill materials used for construction. Lateral loads due to various types of surcharges may be calculated using the diagrams included in Figure

6. We recommend a minimum surcharge pressure of 240 psf.

7.2.3 Bearing Resistance and Settlement

To provide uniform subgrade conditions and to reduce the likelihood of loose soils affecting the proposed wall, we recommend over-excavating the soils beneath the entire wall footprint to a depth of at least three feet below the proposed wall base and to five feet horizontally beyond the wall footprint. We recommend that the exposed subgrade be scarified, moisture conditioned to an 8 inch depth below the exposed surface, and compacted with a minimum 10-ton (drum weight) vibratory roller operating at 1,100 to 1,500 vibrations per minute, or equivalent, to 95 percent relative compaction in accordance with FHWA FP-14

Section 204. The intent of the vibratory roller is to provide a deeper compaction influence to the underlying loose soils.

Assuming a minimum reinforcement length of 1.0H, a strength limit state nominal bearing resistance of 4,000 psf is applicable for the wall. In accordance with AASHTO (2014), a resistance factor of 0.65 should be applied to the bearing resistance at the strength limit state.

The service limit state nominal bearing resistance will be controlled by settlement. Based on the proposed wall height, we anticipate up to 2-1/2 inches of total settlement for a service loading of 2,000 psf, with the majority of settlement occurring during construction of the wall.

Further, we anticipate differential settlements of approximately one-half of the total settlement occurring over a distance of 50 feet. These settlement values should be accounted for in the design of the wall facing.

7.2.4 Wall Drainage

We assume the design incorporates a drainage system behind the wall and water will not accumulate behind the wall. As such, we recommend that MSE walls include the drainage measures shown in the FHWA CFL Detail C257-50 Contractor Designed Mechanically Stabilized Earth (MSE) Wall, which includes the use of geocomposite sheet drains installed on the cut surface behind the retained zone and a heel drain at the back of the reinforced zone.

Providing adequate drainage to reduce hydrostatic forces against the back of the wall and accumulation of water in the reinforced zone will be critical to the long-term stability and performance of the wall.

The toe of the wall may encroach on a small drainage channel near the base of the wall.

If the wall base encroaches into the channel and conditions are expected to be wet, the channel should be graded and surface water drainage directed away from the toe of the wall. Erosion control measures such as riprap or similar placed at the toe of the wall could be considered to help prevent potential undermining of the wall toe by surface water drainage.

7.3 Rockery Walls

One rockery wall is proposed at the west end of Mariposa Grove Road, at approximate Station 398+00 to 403+00, with a maximum wall height of approximately 12 feet. Based on test pits TP-02 A through C and boring SW-09, we anticipate that the walls will be excavated into and founded on medium dense to dense, silty sand (grus). The second rockery wall is proposed at the snow chain-up area and is expected to be founded on similar materials.

This section provides geotechnical parameters for the design of the rockery walls. The parameters were developed in accordance with the Rockery Design and Construction Guidelines, Publication No. FHWA-CFL/TD-06-006, November 2006 (Rockery Guidelines) and AASHTO LRFD Bridge Design Specifications Seventh Edition, 2014 (AASHTO). We evaluated the global and external stability of the proposed rockery walls, considering a proposed critical section of the wall based on the foreslope and backslope, wall height, and subsurface conditions.

We understand the rockery walls will be designed by others.

7.3.1 Global Stability

The global stability of the proposed rockery walls considers the depth of the silty sand (grus), steepness of the slope, and height of the fill wall. The existing ground at the proposed wall locations is at a slope of approximately 1V:1H. The 1V:1H slope was likely cut as part of the original roadway construction. Above the 1V:1H roadway cut the existing the ground surface slopes at about 20 degrees (approximately 1V:3H). The maximum proposed wall height will be approximately 12 feet. The static and seismic factor of safety of this section are 1.3 and 1.1, respectively. These safety factors meet the recommended Rockery Guidelines for allowable stress design (ASD). Our analyses indicate a minimum base rock width of 4 feet is needed for wall heights less than 10 feet, and 6 feet for wall heights between 10 and 12 feet.

7.3.2 Lateral Earth Pressures

Static and seismic earth pressures coefficients for the rockery walls are provided in Table

3. The earth pressures are for sloping backfill conditions and do not include hydrostatic pressure related to accumulation of water in the backfill.

Seismic earth pressures were calculated in accordance with AASHTO Section 11.6.5.2.2, where the horizontal coefficient (kh) is equal to 0.145, which is one-half of the site-adjusted peak ground acceleration (As). This method assumes the rockery walls can tolerate displacements of 1 to 2 inches or more during a seismic event. The Rockery Guidelines indicate the resulting permanent displacement is typically taken as 5 percent of the base width (Mack and others, 2006). We anticipate base widths on the order of 4 to 6 feet, corresponding to approximately 2.5 to 3.5 inches of displacement.

TABLE 3

RECOMMENDED PARAMETERS FOR ROCKERY WALL DESIGN

Design Parameter Recommended Value

Retained Material Total Unit Weight (pcf) 125 Friction Angle (degrees) 34 Cohesion (psf) 0

Seismic Horizontal Acceleration Coefficient1, kh 0.145g Note:

1. The seismic horizontal acceleration coefficient assumes the wall is capable of displacing 1 to 2 inches during the design seismic event, in accordance with AASHTO (2014). See text.

psf = pounds per square foot pcf = pounds per cubic foot

7.3.3 Bearing Resistance

The rockery walls will generally be founded on medium dense silty sand (grus).

However, there is potential for this material to be loose in areas at the proposed bearing elevation. To provide adequate subgrade support and to reduce potential settlement and differential settlement associated with such soils, we recommend over-excavating any areas that are identified as being loose, soft, or yielding to expose a firm and unyielding subgrade. The excavation limits should extend laterally to include a 1V:1H projection from the base rock to the depth of the over-excavation. We then recommend that the exposed subgrade be scarified, moisture conditioned, and compacted to 95 percent relative compaction in accordance with FHWA FP-14 Section 204.11.

Assuming minimum base rock widths of 4 and 6 feet, an ultimate bearing capacity of 11,000 psf and 14,500 psf, respectively, is applicable for the rockery walls, assuming support on medium dense or dense grus. In accordance with the Rockery Guidelines an ASD factor of safety of 2 to 3 is appropriate for bearing resistance.

Based on the proposed wall height, we anticipate up to 1/2 inch of total settlement for a service loading of 2,000 psf, with the majority of settlement occurring during construction of the wall. Further, we anticipate differential settlements of approximately one-half of the total settlement occurring over a distance of 20 feet.

We recommend a minimum embedment depth of 2 feet for design.

In addition, to provide uniform support for the rockery walls, we recommend placing a minimum of 12 inches of Foundation Fill (FP-14 704.01) on the subgrade beneath the wall before placing the base rock layer. This layer should extend laterally 12 inches in each direction perpendicular to the wall length and be compacted to 95 percent relative compaction.

7.3.4 Sliding Resistance

The resistance of the rockery walls to sliding is provided by friction along the base of the wall. The coefficient of friction between the base of the wall and the underlying Foundation Fill is provided in Table 4. We recommend ignoring passive resistance.

TABLE 4

RECOMMENDED PARAMETERS FOR ROCKERY WALL SLIDING

Parameter Value

Unit weight of rockery, γrock 150 (pcf)1

Soil friction angle, φ 35° Coefficient of friction for rock-Structural Fill, μr-SF

0.7 Sliding Resistance Factor 0.61

Note:

1. From Rockery Design and Construction Guidelines, Publication No. FHWA-CFL/TD-06-006.

7.3.5 Wall Drainage

Based on conditions encountered in the subsurface explorations, we do not anticipate the presence of groundwater near the base of the proposed rockery walls. Nevertheless, surface water can make its way into the backfill, regardless of the permeability of the material.

Therefore, we recommend providing drainage measures that reduce the potential for water to accumulate in the backfill and for hydrostatic pressures to act on the wall. A minimum of 12 inches of Granular Rock Backdrain material (FP-14 703.03c) should be provided behind the wall to reduce the potential for the buildup of pore water pressure. The final drainage measures should collect water from the base of the wall and not allow water to collect in a bathtub-type situation.

8.0 PAVEMENT DESIGN RECOMMENDATIONS

The performance of a pavement system depends on the type of paving materials and thicknesses, design life, traffic loads and repetitions, and subgrade strength and subgrade drainage characteristics. The following sections discuss each of these aspects as they relate to the Wawona Road and Mariposa Grove Road pavements.

Our pavement designs are based on the design procedures presented in the 1993 AASHTO Guide for the Design of Pavement Structures (AGDPS) with guidance from the U.S. Department of Transportation and Federal Highway Administration (FHWA) Federal Lands Highway Project Development and Design Manual (PDDM), dated March 2008.

8.1 Traffic Loading

To estimate an 18-kip Equivalent Single-Axle Loading (ESAL) value for the roadways, assumptions were made regarding traffic distributions. Traffic loading for Wawona Road and Mariposa Grove were determined based on discussion with Jacobs. Table 5 presents the average daily traffic (ADT) for the paving year (2017) and at the end of the 3R project design life (20 years - 2037), along with the assumed traffic distribution.

TABLE 5

PROPOSED TRAFFIC LOADING

Roadway Segment ADT 2017 ADT 2037 Traffic Distribution Wawona Road

(STA 105+00 to 120+60 and STA 212+25 to 242+20)

3,209 4,171 - 96 % Passenger Cars

- 4 % Trucks

Mariposa Grove Road (STA 242+20 to 310+65) 372 372 - 62 % Passenger Cars

- 38 % Buses

Assuming the completion of paving in 2017, our estimated ESAL calculations are provided in Appendix D. The flexible pavement equivalency factors used in the calculation are in accordance with the ranges provided in the PDDM and result in an ESAL value of approximately 842,000 for each traffic lane of Wawona Road, and 775,000 for Mariposa Grove Road.

8.2 Subgrade Conditions

As discussed in Section 5.2, the subsurface explorations completed along the roadways generally consisted of silty sand. To estimate the strength of the subgrade materials, we collected bulk samples from the borings and four Hveem Stabilometer (R-value) tests were completed.

Laboratory index testing indicated the bulk samples consisted of AASHTO classification A-2-4, A-4 and A-5. R-value test results ranged from 34 to 49 at an exudation pressure of 300 pounds per square inch (psi), with an average value of about 44. Based on criteria established by the PDDM, the average R-value was used for the design subgrade strength in our design calculations, resulting in a resilient modulus value of 16,800 pounds per square inch (psi).

8.3 Pulverized Full Depth Reclamation (FDR)

We understand that a pulverized full depth reclamation (FDR) may be considered for rehabilitation of the existing roadway pavement sections. The process involves pulverizing and mixing the existing hot asphalt concrete pavement (HACP) with the underlying layers to create a uniformly blended, homogeneous material that will be incorporated into the proposed pavement section as a base course. The benefit of the FDR process is that it allows the existing material to be recycled in place and eliminates the expense to export the material offsite. The requirements in the PDDM indicate a minimum R-value of 70 percent for the pulverized FDR.

The PDDM also indicates that pulverized FDR can be utilized in roadway widening projects.

The FDR process can accommodate approximately up to 2 feet of roadway widening with the pulverization process. Areas where the roadway is anticipated to be widened greater than 2 feet will require import fill or stockpiling and placing excess pulverized base course from other areas of the project. Based on the existing pavement sections we expect FDR depths of up to 6 inches.

8.4 Asphalt Pavement Sections

Using the PDDM design procedures, the following table summarizes design parameters used in the flexible pavement analysis.

TABLE 6

PDDM FLEXIBLE PAVEMENT DESIGN PARAMETERS

Design Parameter Design Value

Wawona Road

Mariposa Grove Road

Pavement Design Life (3R Project) 20 years Subgrade Resilient Modulus, MR 16,800 psi Resilient Modulus of Pulverized FDR 30,000 psi Reliability, R 85% 75% Standard Normal Deviate, ZR -1.036 -0.674 Serviceability Loss, ∆PSI 2.2 1.7 Overall Deviation, So 0.49 Structural Layer Coefficient for Hot Asphalt Concrete Pavement (HACP) 0.44 Structural Layer Coefficient for Untreated Aggregate Base Course (UTBC) 0.11 Structural Layer Coefficient for FDR 0.11 Drainage Coefficient of UTBC 1.0

Using the above parameters, the recommended pavement sections are summarized in the below table.

TABLE 7

PAVEMENT SECTIONS

Location 18 kip ESAL Pavement Section

Wawona Road (STA 105+00 to 120+60 and STA 212+25 to 242+20)

842,000 4.5” HACP over 4” UTBC

4.5” HACP over 6” Pulverized FDR

Mariposa Grove Road (STA 242+20 to 310+65) 775,000

4.0” HACP over 4” UTBC

4.0” HACP over 6” Pulverized FDR

9.0 CORROSION CONSIDERATIONS

Corrosivity testing of the site soils consisted of pH, sulfate content, chlorides, and electrical resistivity. The results are presented in Table B-1 in Appendix B.

Laboratory testing indicated that the saturated resistivity of the samples was between 13,500 and 39,000 ohm-cm. Based on Roberge (2000) the soil resistivity encountered at the site indicates a mildly corrosive to essentially noncorrosive environment for metal in contact with soil at the site.

The concentration of water soluble sulfates measured in the samples from the site was less than

0.05 percent by weight. Based on classifications as defined by ACI-318-14 (ACI, 2014), this test result suggests a negligible degree of sulfate attack on concrete exposed to site soils (exposure class S0).

Lab testing for pH indicated results varying between 5.1 and 5.9, which falls at the low end of the recommended limits for steel reinforcement based on the Mechanically Stabilized Earth Walls and Reinforced Soil Slopes Design & Construction Guidelines (FHWA-NHI-00-043, 2001). Chloride test results ranged from 0.006 to 0.013 percent by weight, and aggressive subsurface conditions exist when the chloride content exceeds 0.01 percent by weight according the Mechanically Stabilized Earth Walls and Reinforced Soil Slopes Design & Construction Guidelines (FHWA-NHI-10-024, 2009).

The construction materials and methods should be reviewed by a specialist in corrosion-resistance design based on the test results included in Table B-1 and their experience.

10.0 CONSTRUCTION AND MATERIALS SPECIFICATIONS

The applicability of the design parameters is contingent on good construction practice. Poor construction techniques may alter conditions from those upon which our recommendations are based, and therefore result in poor performance. Our analyses assumed that this project is constructed according to FP-14 U.S. Customary Units (FHWA, 2014) construction standards.

The following sections provide additional construction considerations for this project.

10.1 Earthwork

Site grading and earthwork should be performed in accordance with Section 200, 250, 300, 400 and 700 of the Federal Highway Administration Standard Specification for Construction of Roads and Bridges on Federal Highway projects (FP-14) and the Project Development and Design Manual.

10.1.1 Site Preparation

Prior to site grading, surface vegetation and surficial topsoil containing organics should be removed. The depth of this removal is expected to be approximately 3 to 12 inches. Trees or shrubs to be removed should include the entire rootball and all roots larger than ½-inch-diameter.

This may require laborers handpicking the roots from the subsurface soils prior to compaction.

Deleterious materials and vegetation should be disposed offsite. Test pit locations will have loose, un-compacted backfill soil within the excavations. Materials within the test pits should be removed and replaced with compacted Foundation Fill if structure support or wall backfill is required in the vicinity of test pits.

In addition, construction areas should be cleared to a depth necessary to remove all surface and subsurface structures associated with current development of the site, including underground utilities and any other deleterious materials. Topsoil and organic rich soils can be re-used to cover embankment side slopes once the embankments are constructed with imported granular materials.

10.1.2 Proof-rolling

Proper subgrade preparation is required for adequate pavement performance and structural support for walls. After excavation to the required depth, the subgrade should be probed with a steel rod for rockery walls or proof-rolled using a fully-loaded, tandem-axle dump truck or equivalent. Any areas that are delineated to be loose or yielding during proof-rolling should be removed until dense and unyielding subgrade is exposed. The subgrade should then be scarified to a depth of 8 inches, and then moisture conditioned and compacted to the relative compaction indicated in Section 7.2.3. It should be noted that the native soils contained 21 to 44 percent fines (material passing the U.S. No. 200 sieve). These materials are moisture sensitive and can deteriorate quickly when exposed to water and can be easily disturbed by construction activity, resulting in pumping and yielding conditions.

In pavement areas, if dense and unyielding conditions are not encountered after removal of the upper 24 inches, we recommend installing a stabilization geogrid, in accordance with FP- 14 Section 714.03.

10.1.3 Fill Placement and Compaction

All fill and backfill should be compacted to a dense/firm and unyielding condition as specified in accordance with FP-14 Section 209.09. Fill and backfill should be moisture treated within 2 percent of the optimum moisture content and compacted to at least 95 percent of the Modified Proctor maximum dry density within the wall backfill and pavement areas.

The on-site soils can be reused as retained fill behind MSE walls provided the material contains less than 50 percent fines (based on the minus ¾ inch fraction). Based on our laboratory testing, we anticipate the site soils will meet this criteria. However, if any soils are encountered with greater than 50 percent fines are encountered, such soils should only be used in landscaping or drainage areas of the site. Fill and backfill should be placed in maximum 6-inch-thick lifts when using heavy compaction equipment. The lift thickness should be reduced to 4 inches when using small compaction equipment for backfilling against retaining walls.

If import fill is required for the project, it should consist of Backfill Material (FP 704.03).

Materials with less fines will be easier to place and compact.

10.1.4 Slopes

We understand that slopes less than 5-feet high will be constructed as part of the project.

We recommend 1V:2H or flatter slopes to satisfy global stability requirements. We recommend that fill slopes be seeded and/or planted with relatively fast-growing vegetation to reduce the potential for surface sloughing and erosion.

10.1.5 Benching

We recommend benching new fill is to be placed onto existing fill slopes or natural slopes exceeding 1V:3H in accordance with FP-14 Section 204.

10.2 Paving Materials

The following table summarizes our recommendations for pavement material selection. All specification sections reference the FP-14 U.S. Customary Units (FHWA, 2014).

TABLE 8

RECOMMENDED MATERIALS FOR PAVEMENTS

Material Specification Additional Requirements/Comments

UTBC Section 301 • Use Gradation C, D, or E

Pulverized FDR Section 303 • Minimum R-value of 70

• Compact according to Section 204.11

HACP Section 403 • Aggregate must meet requirements for ESAL values more than 300,000

Regarding the asphalt binder for HACP, the PDDM requires SuperPave performance grade (PG) binders. The PG binders are chosen based on local weather and anticipated traffic level conditions. Using the PDDM guidelines, 95-percent reliability is required in terms of binder performance. Using a binder within an appropriate temperature and traffic loading range allows for a higher strength and better durability, and improved cohesion will translate into improved long term performance.

Using the LTPP Bind Program, the minimum required binder for the site is a PG 64-16 (a binder that performs in a temperature range of 64 degrees Celsius to negative 16 degrees Celsius).

However, based on CalTrans, the PG binders typically used in the high mountain climatic region is PG 64-28. As such, the PG binder should be chosen based on the PDDM guidance and local experience.

10.3 Excavation and Shoring

We expect that excavation to the indicated foundation depths can be achieved using typical heavy-duty construction equipment.

We anticipate temporary excavations will be required to construct the project. The type of excavation support system selected for construction will depend on proposed depth of the excavation, proximity to existing structures, anticipated surcharge loads, and materials exposed during construction.

Temporary, unbraced excavations should be sloped, as needed, to provide a safe, stable slope.

Consistent with conventional construction practice, the Contractor should be responsible for temporary excavation slopes. The Contractor is continually at the site, is able to observe the nature and conditions of the subsurface materials encountered, and is responsible for the methods, sequence, and schedule of construction.

For planning purposes, we recommend using the excavation criteria in OSHA 29 CFR, Part 1926, Subpart P, Excavations (1989).

If required, temporary, unbraced excavations should be sloped, as needed, to provide a safe, stable slope. Consistent with conventional construction practice, the Contractor should be responsible for temporary excavation slopes. The Contractor is continually at the site, is able to observe the nature and conditions of the subsurface materials encountered, and is responsible for the methods, sequence, and schedule of construction.

10.4 Dewatering

Soils below groundwater may be capable of transmitting seepage to open excavations. However, construction dewatering for retaining wall excavations is not expected. If shallow groundwater is encountered during construction, it is expected that it can be controlled by the use of sump pumps, as necessary.

11.0 PLAN REVIEW AND CONSTRUCTION OBSERVATION

We recommend that we be retained to review the geotechnical aspects of the plans and specifications before construction begins to determine that they are in accordance with our recommendations.

Unanticipated soil conditions are commonly encountered and cannot be fully determined by a limited exploration and testing program. Such unexpected conditions frequently require that additional expenditures be made to attain a properly constructed project. Therefore, some contingency fund is recommended to accommodate such potential extra costs.

Geotechnical design recommendations are developed from a limited number of explorations and tests. Therefore, recommendations may need to be adjusted in the field. To this end, we recommend that a construction observation and monitoring program be implemented for the project and that Shannon & Wilson be retained to monitor the geotechnical aspects of construction. This monitoring would allow us to confirm that conditions encountered are consistent with those used in our analyses. At the same time, it will allow us to provide expedient recommendations should conditions be revealed during construction that are different from those anticipated.

12.0 LIMITATIONS

This report has been prepared for the exclusive use of Jacobs and CFLHD for the purpose of providing geotechnical recommendations for the referenced project. It should be made available to prospective contractors for the purpose of providing information on factual data only, and not as a warranty of subsurface conditions, such as those interpreted from the logs and discussions of subsurface conditions in this report.

The analyses, conclusions, and recommendations contained in this report are based on site conditions as they existed at the time of our explorations. If there is a substantial lapse of time between the submission of this report and the start of construction at the site, or if conditions change due to natural causes or construction operations at or adjacent to the site or appear different from those described in our report, we recommend that we be retained to review our report to determine the applicability of the conclusions and recommendations considering the changed conditions and time lapse.

Within the limitations of scope, schedule and budget, the analyses, conclusions and recommendations presented in this report were prepared in accordance with generally accepted professional geotechnical and geological principles and practice in this area at the time this report was prepared.