CA ERFO FS ELDOR 2021-02(4) Geotech Report.pdf

SUBMITTED TO:

Jacobs 125 Broadway Avenue Oak Ridge, TN 37830

BY:

Shannon & Wilson, Inc.

1722 3rd Street, Ste 100 Sacramento, CA 95811

916-438-2300 www.shannonwilson.com

GEOTECHNICAL DESIGN REPORT

Alder Creek Bridge

CA ERFO 2021-2(4)

EL DORADO COUNTY, CA

July 14, 2023 Shannon & Wilson No: 109703-002

Alder Creek Bridge

CA ERFO 2021-2(4)

FINAL Geotechnical Design Report

109703-002 July 14, 2023

PAGE INTENTIONALLY LEFT BLANK FOR DOUBLE-SIDED PRINTING

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Submitted To: Jacobs 125 Broadway Avenue Oak Ridge, TN 37830 Attn: Mr. Berwyn Wilbrink

Subject: FINAL GEOTECHNICAL DESIGN REPORT, ALDER CREEK BRIDGE

CA ERFO 2021-2(4), EL DORADO COUNTY, CALIFORNIA

We are pleased to submit this final geotechnical design report for the above referenced project. This report presents our geotechnical design recommendations and was prepared by the undersigned. We previously submitted a draft report on March 8, 2023. This report addresses review comments from FHWA, and it supersedes our draft report.

Our scope of services was specified in Professional Services Task Order Number 148039503, issued under our Professional Services Master Agreement Number 148039369 with Jacobs Engineering Group, Inc. We received and signed the contract on September 30, 2022.

We appreciate the opportunity to be of service to you on this project. If you have questions concerning this report, or we may be of further service, please contact us.

Sincerely, SHANNON & WILSON, INC.

Debanik Chaudhuri, Ph.D., G.E.

Senior Associate

RAL:DXC:TWH:RKT/ral

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CONTENTS

1 Introduction

2 Project And Site Description

3 Subsurface Explorations

3.1 Field Investigation

3.2 Geotechnical Laboratory Testing

4 Regional Geology and Subsurface Conditions

4.1 Regional Geology

4.2 Subsurface Conditions

4.3 Groundwater

5 geologic hazard evaluation

5.1 Seismic Hazards

5.1.1 General

5.1.2 Seismic Ground Motion

5.1.3 Liquefaction

5.1.4 Fault Surface Rupture

5.2 Corrosion

6 GeoTechnical Recommendations

6.1 Seismic Design Ground Motion Parameters

6.2 Abutment Foundations

6.2.1 Axial Resistance

6.2.2 Lateral Resistance

6.3 Abutment Lateral Earth Pressures

7 Construction Considerations

7.1 CIDH Pile Installation

7.1.1 Installation Methods and Equipment

7.1.2 Inspection and Observation

7.1.3 Concrete Placement

7.1.4 Non-Destructive Integrity Tests

7.2 Earthwork and Grading

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7.2.1 Fill Placement and Compaction

8 Closure

9 References

Exhibits Exhibit 6-1: Seismic Design Ground Motion Parameters Exhibit 6-2: CIDH Pile Axial Resistance Design Parameters Exhibit 6-3: Recommended LPILE Parameters Exhibit 6-4: Structural Backfill Lateral Earth Pressure Design Parameters

Figures

Figure 1: Vicinity Map Figure 2: Site and Exploration Plan Figure 3: Subsurface Profile A-A' Figure 4: Recommended Surcharge Loading for Temporary and Permanent Walls

Appendices Appendix A: Subsurface Explorations Appendix B: Geotechnical Laboratory Testing Important Information

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ACRONYMS

AASHTO American Association of State Highway and Transportation Officials Caltrans California Department of Transportation bgs below ground surface CFHLD Central Federal Lands Highway Division CGS California Geological Survey CIDH Cast-in-drilled-hole FHWA Federal Highway Administration psf pounds per square foot pci pounds per cubic inch UCS Unconfined Compressive Strength USGS United States Geological Survey

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1 INTRODUCTION

This report presents the results of our subsurface exploration and laboratory testing and provides geotechnical design recommendations and construction considerations for the proposed Alder Creek Bridge replacement project (Project) in El Dorado County, California.

The Project location is shown in Figure 1. Our services were conducted in general accordance with our Task Order Agreement No. 148039503 with Jacobs Engineering Group, Inc. (Jacobs), dated September 30, 2022. Our conclusions and recommendations in this report are based on:

Our understanding of the Project based on the information provided by Jacobs (Jacobs, 2022)

Subsurface conditions we observed in two borings

Results of laboratory tests performed on selected samples collected from the borings

Limitations of our approved scope, schedule, and budget described in our contract

Discussions with Jacobs, and Central Federal Lands Highway Division (CFLHD)

The replacement bridge will be designed in accordance with the Federal Highway Administration (FHWA) project development and design manual (FHWA, 2008) and American Association of State Highway and Transportation Officials (AASHTO) LRFD Bridge Design Specifications (AASHTO, 2020). Construction should be in accordance with the FHWA Standard Specifications for Construction of Roads and Bridges on Federal Highway Projects (FP-14) (FHWA, 2014).

The objectives of our geotechnical study were to collect subsurface information and provide geotechnical recommendations and construction considerations for the bridge foundation and abutments. The authorized scope of services was based on this objective and this report not specifically indicated in this report, do not assume that it was performed.

2 PROJECT AND SITE DESCRIPTION

The Project is in the Eldorado National Forest approximately 30 miles east of Placerville, California. The Project replaces the existing 16-foot-wide by 50-foot-long bridge the was damaged by fire in 2021. The bridge was constructed of glulam girders with timber abutments. The Project involves replacement of the fire damaged bridge.

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Based on the preliminary plans provided (Jacobs, 2022), the replacement bridge will be 16-foot-wide by 84-foot-long and span the Alder Creek. It will be a single span, prefabricated, modular, steel structure with structural steel decking. The planned forest service road elevation is about 16 feet above Alder Creek. The abutments will be supported by 24-inch-diameter cast-in-drilled-hole (CIDH) shafts.

At the time of our field exploration, we found that the damaged bridge, including the abutments, had been removed and the ground at each abutment location was supported by a temporary concrete block wall.

3 SUBSURFACE EXPLORATIONS AND LABORATORY

TESTING

3.1 Field Investigation

Shannon & Wilson (S&W) conducted a field exploration on October 19 and 20, 2022, to explore subsurface conditions at the proposed bridge location. We drilled and sampled two borings, one near each proposed abutment, designated B-1A/B and B-2. The approximate locations of borings B-1A/B and B-2 are presented on Figure 2.

The borings were advanced using a combination of hollow stem auger and rock core drilling to a maximum depth of about 37 feet below ground surface (bgs). Appendix A presents a discussion of the drilling and sampling procedures used to complete the borings.

Appendix A also presents the boring logs, an explanation of the symbols and terminology used, and photographs of the drilling setup and rock cores.

3.2 Geotechnical Laboratory Testing

Geotechnical laboratory tests were completed on selected samples retrieved from the borings to estimate index and engineering properties. Index tests included natural water content and grain size analysis. Engineering property testing included unconfined compression strength (UCS) and corrosion. Laboratory test results and a discussion of the testing procedures are included in Appendix B. The natural water content and fines content are also shown on the boring logs in Appendix A.

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4 REGIONAL GEOLOGY AND SUBSURFACE

CONDITIONS

4.1 Regional Geology

The Project is located in the Sierra Nevada geomorphic province of California. A review of the Geologic map of the Sacramento quadrangle, California (Wagner and others., 1981) indicates the Project area is mapped as igneous bedrock consisting of Mesozoic granitic rocks.

4.2 Subsurface Conditions

At the north abutment, Boring B-1A/B encountered approximately 6 feet of artificial fill consisting of medium dense sand with silt and gravel, underlain by about 10 feet of creek deposits consisting of dense well-graded sand with silt and gravel with cobbles and boulders. The presence of cobbles and boulders is inferred from drill action and is anticipated to be as shallow as 7 feet bgs. Starting at 16 feet bgs, we encountered very low to moderate strength granodiorite bedrock. Bedrock appears to be variably weathered with few zones of closely space, slightly open joints.

At the south abutment, Boring B-2 encountered approximately 10 feet of artificial fill consisting of medium dense poorly graded sand with silt and gravel, underlain by 7 feet of creek deposits consisting of medium dense to dense well-graded sand with silt to silty sand with cobbles and boulders. The presence of cobbles and boulders is inferred from auger refusal at 11 feet and samples collected in core runs. Starting at 17 feet, we encountered very low to moderate strength granite and granodiorite bedrock. Bedrock appears to be variably weathered with a low average Rock Quality Designation (RQD) and some closely spaced, slightly open to open joints.

We prepared Figure 3, Subsurface Profile A- -1A/B and B-2. Our observations are specific to the location, depth, and time noted on the logs and may not be applicable to all areas of the site. No number of borings or lab testing can precisely predict the characteristics, quality, or distribution of subsurface and site conditions. If conditions different from those described herein are encountered during construction, we should review our description of the subsurface conditions and reconsider our conclusions and recommendations.

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4.3 Groundwater

During drilling, we encountered groundwater in Boring B-2 at 11.5 feet bgs. We did not observe groundwater in Boring B-1A/B prior to switching to rock coring. The surface water in Alder Creek was observed approximately 1 foot above the creek bottom. We anticipate groundwater will be encountered during CIDH shaft drilling and will likely be comparable to elevation of the surface water in Alder Creek during construction. Groundwater fluctuations are likely and will depend on seasonal variations, local precipitation and runoff, creek level, and flood events.

5 GEOLOGIC HAZARD EVALUATION

This section identifies potential geologic hazards at the site, discusses the potential adverse impacts of the geologic hazards, and provides mitigation measures, as necessary.

5.1 Seismic Hazards

5.1.1 General

The Project is located within a seismically active area and is expected to experience the effects of future earthquakes on active faults within the region. Seismic hazards include seismic ground motions, liquefaction (and associated hazards), seismic compression, and surface fault rupture. The following subsections describe our evaluation of the potential seismically induced hazards based on the seismic design criteria.

5.1.2 Seismic Ground Motion

We anticipate the site will experience strong ground shaking during an earthquake along faults in the region. The intensity of earthquake motion and seismic hazards that may impact the Project will depend on the characteristics of the generating fault, distance to the earthquake fault, earthquake magnitude, earthquake duration, and site-specific geologic conditions. Likely sources for strong ground motion are known active faults. Ground motions may be amplified or attenuated at the site depending on the level of ground shaking in the underlying bedrock, underlying soil type, depth to bedrock, and other factors.

To mitigate the potential for future damage from strong seismic events, we recommend the structures be analyzed using seismic design criteria in the governing design code, AASHTO LRFD, as discussed in the Section 6.1.

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5.1.3 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. Loss in shear strength can generate ground settlement, lateral spreading (ground movement on gentle slopes), bearing capacity failure, and/or landslides. Liquefaction potential is greatest where loose granular soil (sand and non-plastic silt) is present below groundwater and is more likely to affect structures when the potentially liquefiable soil is present at depths shallower than 50 feet. Liquefaction potential increases as ground shaking increases and decreases as the fines (clay and silt) content of soil increase.

Based on our evaluation of the liquefaction potential for soil encountered in our borings, we conclude that the risk of impacts from liquefaction and liquefaction-related hazards, such as lateral spread and ground settlement is low at the Project site during a design-level seismic ground motion.

5.1.4 Fault Surface Rupture

Fault surface rupture hazard classification is based on criteria developed by the California Division of Mines and Geology, now known as the California Geological Survey (CGS), for the Alquist-Priolo (AP) Zone Act program. By definition, an active fault is one that has ruptured within the Holocene epoch (last 11,650 years). Based on the U.S. Quaternary Faults interactive fault map, active faults do not cross the Project site (USGS, 2014). The closest active faults are the West Tahoe Fault and Genoa Fault, approximately 18 and 25 miles east of the Project, respectively (USGS, 2014). Based on the location of the closest known active fault, we consider the potential for surface fault rupture from fault displacement along the Project alignment to be low.

5.2 Corrosion

To assist in estimating the corrosion potential at the site, a sample from Boring B-2 was tested for pH, resistivity, water soluble sulfates, and chlorides. The results are presented in Table B-1 in Appendix B. Appendix B also contains a discussion regarding the corrosion potential based on these laboratory test result which is summarized below:

Resistivity: mildly corrosive

Sulfate concentration: American Concrete Institute (ACI) ACI-318-19 (ACI, 2019) sulfate expose class S0 low sulfates

Chloride concentration: not corrosive to ferrous metal

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The test results and the discussion in Appendix B are provided to assist the designer in selection of project materials, concrete type, or other features with respect to corrosion. As appropriate, the designer should consider protective measures, such as coatings, upsizing for section loss, or using alternative materials to reduce the corrosion potential.

The California Department of Transportation (Caltrans) considers a site to be corrosive to foundation elements if one or more of the following conditions exist: chloride concentration is greater than or equal to 500 parts per million (ppm), sulfate concentration is greater than or equal to 1,500 ppm, or pH is 5.5 or less (Caltrans, 2021). Based on Caltrans criteria, the corrosivity test results suggest that the site soils are generally not corrosive to exposed buried metal or reinforced concrete.

6 GEOTECHNICAL RECOMMENDATIONS

6.1 Seismic Design Ground Motion Parameters

Using AASHTO LRFD criteria (AASHTO, 2020), and based on subsurface conditions encountered in our borings at the proposed bridge, we recommend Site Class B be used for design of the proposed bridge. This designation assumes that similar conditions are present from the bottom of our borings to 100 feet bgs.

We determined the ground motion parameters for the Project site using the USGS AASHTO 2009 Web Service Documentation Web Application (USGS, 2009). Exhibit 6-1 presents recommended seismic design ground motion parameters.

6.2 Abutment Foundations

We understand the bridge abutments will be supported by 24-inch-diameter CIDH piles. In this section we provide recommendations for axial and lateral resistance for the piles. The preliminary plans specify concrete compressive strength of 4,500 pounds per square inch (psi) for the CIDH piles.

6.2.1 Axial Resistance

We recommend that axial resistance of the CIDH piles be based on side friction resistance in the artificial fill, creek deposits, and bedrock present at the site. We recommend the CIDH piles be designed to extend a minimum of 5 feet into bedrock. The structural engineer should confirm adequate embedment length based on design axial and lateral loading.

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Exhibit 6-1: Seismic Design Ground Motion Parameters

Parameter Value

Latitude 38.68892°

Longitude -120.30329

Site Class B

PGA 0.216g

FPGA 1

AS 0.216g

SS 0.524g

Fa 1

SDS 0.524g

S1 0.184g

Fv 1

SD1 0.184g

NOTES:

PGA = peak ground acceleration; FPGA = site coefficient for PGA; AS = design PGA; SS = mapped short-period (0.2-second) spectral acceleration; Fa = site coefficient for SS; SDS = design short-period spectral acceleration; S1 = mapped 1-second spectral acceleration;

Fv = site coefficient for S1; SD1 = design 1-second spectral acceleration

Exhibit 6-2 presents our recommended nominal unit side resistance values with resistance factors for strength and extreme event limits for determining factored axial resistance. If the piles are placed less than three pile diameters on-center a group factor of 0.9 should be applied to axial pile capacity.

Exhibit 6-2: CIDH Pile Axial Resistance Design Parameters

Layer

Approximate

Elevation (ft) Nominal Unit

Side Resistance, qs

(ksf)

Strength Limit

Resistance Factors

Extreme Event

Resistance Factors

Top Bottom Compression Uplift Compression Uplift

Artificial Fill and

Creek Deposits 5,575 5,557 0.25 0.55 0.45 1 0.8

Bedrock 5,557 5,5371 10 0.55 0.4 1 0.8

NOTES:

1 Approximate bottom elevation of deepest boring.

ft = feet; ksf = kips per square feet

For CIDH pile design, a top of bedrock elevation of 5,557 feet may be assumed. However, we recommend that estimates of required rebar cage lengths consider the likely variability in top of bedrock elevations between our borings and each CIDH pile location. A Shannon

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& Wilson engineer or geologist should be on site to confirm actual top of bedrock during construction to ensure adequate embedment in bedrock.

Assuming CIDH piles are constructed using good installation techniques and equipment

Procedures we anticipate that total settlement for a single drilled shaft at the service limit state will be approximately ½ inch or less. This settlement value does not include elastic compression of the shaft under the design load.

6.2.2 Lateral Resistance

Lateral loads acting on the structure from wind, seismic, and other loadings may be resisted by the deep foundation members. The lateral response of the CIDH piles would depend on the soil condition and the degree of fixity of the top of the shaft.

To determine the lateral resistance of individual CIDH piles and the deflection, shear, and moment along the foundation, we provide input parameters in Exhibit 6-3 for use with the commercial software LPILE by Ensoft, Inc. (2019). While subsurface conditions vary somewhat between abutment locations, the parameters presented in Exhibit 6-3 are on the conservative side. We understand that lateral response analysis will be performed by the structural engineer using these parameters. LRFD design methods for lateral loading of shafts and piles utilize a resistance factor of 1.0 and are controlled by allowable movement criteria.

Exhibit 6-3: Recommended LPILE Parameters

Layer

Approximate Elevation (ft)

Material Model (pcf) (deg) k

(pci) qu

(psi) mi GSI

Ei

(ksi)Top Bottom

Artificial Fill

5,575 5,564 Sand (Reese) 57.6 32 40 - - - - -

Creek Deposits

5,564 5,557 Sand (Reese) 67.6 37 100 - - - - -

Bedrock 5,557 5,5371 Massive Rock 97.6 - - 4,400 31 0.24 45 2,000

NOTES:

Approximate bottom elevation of Boring B-2.

Ei = intact rock modulus; GSI = Geologic Strength Index;

k = soil modulus parameter; ksi = kips per square inch; mi = Hoek-Brown Material Index; pcf = pounds per cubic foot; pci = pounds per cubic inch; qu = uniaxial compressive strength

Analysis of the horizonal pile foundation movement should consider the pile spacing to account for group effects. The load values should be multiplied by p-multipliers, as provided in AASHTO LRFD Bridge Design Specifications section 10.7.2.4 (AASHTO, 2020).

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For a single row of piles with a center-to-center spacing between three and five times the diameter of the pile, a p-multiplier of 0.8 should be used. For a single row of piles with a spacing greater than five times the diameter, the p-multiplier is 1.0. The center-to-center spacing of the piles should be at least three times the pile diameter.

6.3 Abutment Lateral Earth Pressures

The lateral earth pressures acting on the bridge abutment and wingwalls depend on many factors, including surcharge loads, the soil type, drainage provisions, and whether the top of the wall can yield or deflect laterally/rotate during and after excavation. Where walls are free to deflect, they can be designed for the active condition. Active earth pressures provided in

Exhibit 6-4 assume the walls are backfilled properly with Structural Backfill in accordance with FP-14 Section 704.04 in the active zone.

Exhibit 6-4: Structural Backfill Lateral Earth Pressure Design Parameters

Design Parameter Design Value 1

Total Unit Weight (pcf) 125

Effective Friction Angle (degrees) 34

Cohesion (psf) 0

Static Active Earth Pressure Coefficient, KA 0.25

At-Rest Earth Pressure Coefficient, K0 0.44

Equivalent Fluid Density for Static Active Conditions (pcf) 32

Equivalent Fluid Density for Static At-Rest Conditions (pcf) 55

Dynamic Active Earth Pressure Coefficient, KAE 0.32

Uniformly Distributed Seismic Pressure Increment (psf/ft) 4

NOTES:

Assumes Structural Backfill - FP-14 Section 704.04.

Does not include water pressure, see below.

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

Surcharge loads from motor vehicles and construction equipment will induce additional lateral loads on walls. The pressures provided in

Exhibit 6-4 do not account for surcharge loads. Applicable surcharge loads should be applied based the guidelines provided on Figure 4.

The parameters provided in

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Exhibit 6-4 assume the active zone of the walls is backfilled with Structural Backfill in accordance with FP-14 Section 704.04. It will be important to control surface water and to provide drainage measures that reduce the potential for water to accumulate behind walls.

Surface water behind the wall should not be allowed to discharge directly into the wall backfill materials. In addition, water should not be allowed to discharge or pond around retaining structures. If design flood waters may rise into the backfill zone, additional drainage considerations may be required as described below, or the walls can be designed for additional hydrostatic load.

Drainage behind the wall should consist of a 4-inch diameter perforated pipe placed at the base of the wall or weep holes that extend through the base of the wall. Above the pipe, drainage should consist of gravel or a synthetic drain mat. The gravel layer should be at least 1 foot thick and should consist of ¾-inch crushed rock wrapped in filter fabric or Caltrans Class 2 Permeable Material. The upper 2 feet of wall backfill material should consist of on-site low permeability soil to restrict inflow of surface water and reduce the risk of clogging the drain.

7 CONSTRUCTION CONSIDERATIONS

The applicability of the geotechnical recommendations 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 assume that the Project will be constructed according to FP-14 (FHWA, 2014). The following sections provide additional construction considerations for the Project.

7.1 CIDH Pile Installation

7.1.1 Installation Methods and Equipment

Specifications and installation methods should be in general accordance with our recommendations and Section 565 of FP-14 (FHWA, 2014). The means and methods of CIDH pile installation should be determined by the Contractor. Further, as required by Section 565.04 of FP-14 (FHWA, 2014), the Contractor should provide a construction plan that describes the proposed CIDH pile installation and construction methods. The Contractor should consider site access in their selection of equipment and sequencing of operations.

CIDH piles should obtain their capacity from embedment in the bedrock. Hence, the Contractor should be prepared for drilling into competent bedrock, see Appendix B for

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109703-002 July 14, 2023 unconfined compression test results. The presence of boulders and cobbles is inferred from our geotechnical explorations and are expected to be encountered during CIDH pile construction. Groundwater may be encountered during pile construction. The contractor should be prepared for such conditions.

Temporary casing, drilling slurry, or some combination thereof may be required to prevent raveling or caving in the sandy soils present at the site. Where casing is used, the inside diameter of the casing should be equal to or larger than the specified CIDH pile dimensions.

If slurry methods are used to stabilize the excavation, we recommend the use of polymer or mineral slurry in accordance with Section 565.06 (b) of FP-14 (FHWA, 2014). The Contractor should not be permitted to use natural or uncontrolled slurry methods during construction.

7.1.2 Inspection and Observation

In accordance with Section 565.06 (a)(1) of FP-14 (FHWA, 2014), a geologist or engineer familiar with the subsurface conditions at the Project site should observe CIDH pile installation to maintain a boring log of material excavated and to document other pertinent information during construction. The hole should be cleaned in accordance with Section

565.06 (a)(2) of FP-14 (FHWA, 2014) and observed by the geologist or engineer prior to pouring concrete. The drilling and concreting process should be relatively continuous with minimal stoppage of work between the completion of drilling, cleaning the hole, and the placement of concrete after setting the rebar cage. In addition, if concrete needs to be placed under water using a tremie pipe, quality construction techniques and observations by the geologist or engineer will be essential to CIDH pile installation and to confirm they are installed in accordance with Section 565 of FP-14 (FHWA, 2014).

7.1.3 Concrete Placement

Concrete should be specified by the project structural engineer and placed by the contractor in accordance with Section 565.08 of FP-14 (FHWA, 2014). Defects in cased shafts are frequently the result of inadequate head of concrete, particularly when combined with marginal or low slump concrete. If a truck-mounted pump is used to tremie concrete, pull-out of the pipe can occur if a pressure surge causes upward boom movement. Adequate methods should be established to measure and confirm that minimum head requirements are met throughout the concrete placement process.

7.1.4 Non-Destructive Integrity Tests

As recommended in Sections 565.07 and 565.09 of FP-14 (FHWA, 2014), the contractor should perform Crosshole Sonic Logging (CSL) to evaluate the integrity of all production CIDH piles. CSL is a non-destructive testing method that requires steel tubes to be installed

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109703-002 July 14, 2023 in the CIDH pile and tied to the rebar cage. The tubes are attached to the interior of the rebar cage and then the cage is lowered into the hole and the concrete is placed. After the concrete has cured, a sound source and receiver are lowered, maintaining a consistent elevation between source and sensor. A signal generator generates a sonic pulse from the emitter which is recorded by the sensor. Relative energy, waveform, and differential time are recorded and logged. This procedure is repeated at regular intervals throughout the shaft. By comparing the graphs from the various combinations of access tubes, a qualitative idea of the soundness of the concrete throughout the drilled shaft can be interpreted.

7.2 Earthwork and Grading

Earthwork, including site preparation, placement of fill, and subgrade preparation, should conform to the requirements provided in Division 200 of FP-14 (FHWA, 2014).

7.2.1 Fill Placement and Compaction

Wall backfill should consist of Structural Backfill (FP-14 704.04). If a drainage layer at the face of the wall is not used, as discussed in Section 6.3, we recommend the backfill consist of FP-14 704.01 Foundation Fill or 704.07 Select Borrow.

Fill should be placed in uniform, horizontal layers with the loose lift thickness not exceeding 8 inches for heavy, self-propelled compactors, or 4 inches for hand-operated mechanical compact the moisture content and quality of the selected backfill material. Compaction of backfill adjacent to walls can result in higher lateral earth pressures against the walls. Therefore, small equipment that is hand-operated should be required within a line extending upward from the base of the structure at 0.5H:1V, to a maximum horizontal distance of 5 feet from the face of the wall to reduce this potential.

Wall backfill should be moisture conditioned to above optimum moisture content and compacted to at least 95% of the maximum dry density as determined by AASHTO T99 (standard Proctor compaction effort) in accordance with FP-14 Section 208. It should be noted that as the number of fines increases in the wall backfill (portion of soil particles passing a U.S. Standard No. 200 sieve), soil becomes more sensitive to small changes in moisture content, and adequate compaction becomes more difficult to achieve.

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8 CLOSURE

This report has been prepared for the exclusive use of Jacobs and CFLHD for the purpose of providing geotechnical recommendations for the Project. This geotechnical design report should not be used without our approval if any of the following occurs:

Assumptions stated in this report have changed.

Project details change or new information becomes available such that our analysis and recommendations may be affected.

A substantial period of time has passed since the date of this report.

If any of these occur, we should be retained to review the applicability of our analyses and recommendations.

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. We make no other warranty, either express or implied.

Sha

9 REFERENCES

American Concrete Institute (ACI), 2019, Building code requirements for structural concrete (ACI 318-19); commentary on building code requirements for structural concrete (ACI 318R-19): Farmington Hills, Mich., ACI, Code 318-19, 623 p.

AASHTO, 2020, AASHTO LRFD bridge design specifications, Customary U.S. units, 9th edition: Washington, D.C., American Association of State Highway and Transportation Officials.

Brown, D.A., Turner, J.P., Castelli, R.J., and Loehr, J.E., 2018, Drilled Shafts: Construction Procedures and LRFD Design Methods: NHI Course No. 132014, Geotechnical Engineering Circular No. 10, Washington, D.C., Report No. FHWA NHI-18-024.

California Dept. of Transportation (Caltrans), 2021, Corrosion guidelines (ver. 3.2):

Sacramento, California.

Ensoft, Inc., 2019, LPILE 2019, A Program for Analyzing Stress and Deformation of Individual Piles or Drilled Shafts Under Lateral Load, Austin, Texas.

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Jacobs Engineering Group, Inc. (Jacobs), 2022, Alder Creek Bridge, Sequoia National Forest, El Dorado County, California, general notes & estimate: Jacobs, 5 sheets, plotted December 15.

Wagner, D.L, Jennings, C.W., Bedrossian, T.L., and Bortugno, E.J., 1981, California Division of Mines and Geology, Geologic map of the Sacramento quadrangle, California, Regional Geologic Map RGM-1A, 1:250,000

U.S. Department of Transportation (USDOT), Federal Highway Administration (FHWA), 2014, Federal standard specifications for construction of roads and bridges on Federal Highway projects, FP-14 English Units: U.S. Department of Transportation and Federal Highway Administration, available from http://flh.fhwa.dot.gov/resources/pse/specs/.

USDOT, FHWA, 2008, Federal Lands Highway project development and design manual:

U.S. Department of Transportation and Federal Highway Administration.

Available from: http://flh.fhwa.dot.gov/resources/manuals/pddm/.

U.S. Geological Survey (USGS), 2009, AASHTO-2009 Web Service Documentation Web Application: Available: https://earthquake.usgs.gov/ws/designmaps/aashto- 2009.html

U.S. Geological Survey (USGS), 2014, Quaternary fault and fold database of the United States: Available: https://www.usgs.gov/programs/earthquake-hazards/faults.

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Appendix A: Subsurface Explorations

Appendix A

Subsurface Explorations

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Appendix A: Subsurface Ex plorations

Appendix A

Subsurface Explorations

CONTENTS

B.1 General

D.1 Field Preparations

D.2 Drilling Procedures

D.3 Backfill Procedures

D.4 Sampling Procedures

D.4.1 Sampling Interval

D.4.2 Standard Penetration Test (SPT)

D.4.3 Rock Coring

D.5 Review and Classification of Samples

D.5.1 Field Observations

D.5.2 Soil Classification System

D.5.3 Geologic Units and Descriptions

D.5.4 Boring Logs

D.6 References

Figures

Figure A-1: Soil Description and Log Key Figure A-2: Rock Classification and Log Key Figure A-3: Log of Boring B-1A/B Figure A-4: Log of Boring B-2 Figure A-5: Site Photographs Figure A-6: Rock Core Photographs

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B.1 GENERAL

The subsurface exploration performed for the project consisted of drilling and sampling two borings, designated B-1A/B and B-2. The approximate boring locations are shown on the Site and Exploration Plan, Figure 2. We estimated the boring locations using existing features and a tape measure and estimated elevations using the plans provided. The boring locations and elevation should be considered accurate to the degree implied by the method used. The methods used to conduct the subsurface exploration are described below.

A representative from Shannon & Wilson was present throughout the field exploration to observe operations, retrieve representative soil samples for laboratory testing, and prepare a descriptive field log of the exploration. Soils were classified in general accordance with the America Society for Testing and Materials (ASTM) International Designation: D 2488, Standard recommended practice for description of soils (visual-manual procedure) (ASTM, 2018a).

Figures A-1 and A-2 present the key to our soil descriptions and rock classifications of the materials encountered.

D.1 FIELD PREPARATIONS

We marked the proposed boring location and notified Underground Service Alert of Northern California (a.k.a. USA North 811) of our planned exploration. Prior to subsurface exploration, we contacted the USFS and confirmed that permits were not required to perform our borings.

D.2 DRILLING PROCEDURES

Drilling was performed on October 19 through 20, 2022, by Cascade Drilling, Inc. of Sacramento, California, under subcontract to Shannon & Wilson. Boring B-1A/B was

-2 near the south abutment. After completing Boring B-1A, the drill crew moved over approximately 5 feet and advanced Boring B-1B to better characterize creek deposits but encountered auger and sampler -1A and B-1B into a single boring log and presented as Log of Boring B-1A/B (Figure A-3).

The drillers used a CME 55 track-mounted drill rig to advance the boring using 8-inch diameter hollow stem augers. Once the driller reached practical refusal, they switched to coring. They advanced the boring to at least 10 feet into bedrock.

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The boring logs are presented in Figure A-3 through A-4. Photographs of the drill rig setup for the borings are shown in Figure A-5. Cores were photographed immediately after retrieval and placement in the core box (Figure A-6, sheets 1 to 2).

D.3 BACKFILL PROCEDURES

After completion of drilling, the drilling contractor backfilled the boring with neat cement grout. The cuttings and drilling fluids were drummed and left onsite, as requested.

D.4 SAMPLING PROCEDURES

D.4.1 Sampling Interval

The drilling contractor performed standard penetration test drive samples at 5-foot intervals in the soil interval. Core runs, with occasionally SPT samples, were collected starting at approximately 9 feet below ground surface (bgs) for Boring B-1A/B and 11 feet bgs for Boring B-2.

D.4.2 Standard Penetration Test (SPT)

Standard Penetration Tests (SPT) were performed in general accordance with ASTM D 1586, Standard Test Method for Standard Penetration Test (SPT) and Split-Barrel Sampling of Soils (ASTM, 2018b). The SPT consists of driving a 2-inch outside diameter split-spoon sampler a distance of 18 inches into the bottom of the borehole with a 140-pound hammer falling 30 inches. An automatic hammer system was used to advance the samplers. During sampling, a Shannon & Wilson field representative recorded the number of blows for each 6-inch increment of penetration. The number of blows required for the last 12 inches of penetration is termed the Standard Penetration Resistance, or N-value. When the resistance exceeded 50 blows for 6 inches or less penetration, the test was terminated, and the number of blows and corresponding penetration were recorded. The N-value is an empirical parameter that provides a means for evaluating the relative density, or compactness, of granular soils and consistency, or stiffness, of cohesive soils. The N-values are plotted on the boring logs.

The split-spoon SPT sampler used during the penetration testing recovered a disturbed sample of the soil. The samples were field classified and recorded on boring logs by a Shannon & Wilson field representative, sealed in jars, and returned to our laboratory for review and testing.

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D.4.3 Rock Coring

We continuously cored the bedrock in general accordance with ASTM D2113-14, Standard Practice for Rock Core Drilling and Sampling of Rock for Site Exploration (ASTM, 2014). The boring was advanced using hollow-stem equipment from the ground surface through soil until bedrock was encountered. The boring was then advanced using HQ rotary core equipment.

The triple-tube core barrel used in the rotary core drilling method consists of inner and outer barrels and a split inner core tube. The outer barrel rotates while the inner barrel and the inner split tube remain stationary. This system helps protect the core from the drilling fluid (mixture of soil/rock cuttings and water) and reduces the torsional forces transmitted to the core. In addition, the split inner tube allows for detailed visual analysis of the relatively undisturbed core.

Fresh water was circulated through the hole as drilling progressed to cool the drill bit and flush cuttings. The soil and rock cuttings were collected in a tank at the ground surface.

Our field representative observed the coring process, logged the core, and noted the

Quality Designation (RQD), which is defined as the sum of the length of core pieces in a given core run that are greater than 4 inches in length divided by the total core run length.

The percent recovery and RQD are represented on the boring log.

D.5 REVIEW AND CLASSIFICATION OF SAMPLES

D.5.1 Field Observations

A Shannon & Wilson field representative was onsite throughout the subsurface exploration to collect, classify, store, and transport soil samples, and to record blow count values. In addition, the field representative also noted drill action, problems during drilling (i.e., heave, hole collapse, etc.), and other issues if applicable.

D.5.2 Soil Classification System

Soil classification for this project was based on ASTM D 2487, Standard Practice for Classification of Soils for Engineering Purposes (Unified Soils Classification System) (ASTM, 2020) and ASTM D 2488, Standard Practice for Description and Identification of Soils (Visual-Manual Procedures) (ASTM, 2018c). The system is called the Unified Soils Classification System (USCS) and is summarized in our Soil Description and Log Key, Figure A-1.

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Rock classification for this project was in general accordance with the International Society of Rock Mechanics (ISRM) classification method. According to this system, rocks are classified based on the stratigraphic structure, rock strength, degree of weathering, and other properties. The rock classification system is summarized in our Rock Classification and Log Key, Figure A-2.

D.5.3 Geologic Units and Descriptions

The geologic units as described in the report are used to maintain consistency when defining geologic units encountered in the borings throughout the project area. These geologic units are interpretive and are based on our review of existing geologic literature for the project area. The geologic unit designation for each soil layer is shown in the boring log descriptions.

D.5.4 Boring Logs

A boring log is a written record of the subsurface conditions encountered in the exploration.

It shows the soil and rock encountered in the exploration and USCS symbol of each layer.

Other information shown in the boring logs includes groundwater level measurements, horizontal coordinates, surface elevation, and types and depths of each sample.

We reviewed the completed boring logs following our Quality Assurance/Quality Control (QA/QC) process. This program includes review of the samples by an experienced geologist after initial field observations are made, cross-checks with laboratory test results, and further cross-checks with developed geologic profiles. This detailed procedure is followed to assure consistency of the data presentation and to provide adequate QC for each exploration.

D.6 REFERENCES

ASTM International, 2014, Standard practice for rock core drilling and sampling of rock for site exploration, D2113-14: West Conshohocken, PA, ASTM International, Annual book of standards, v. 04.08, soil and rock (I): D420-D5876, 20 p., available:

www.astm.org.

ASTM International, 2018a, Standard practice for description and identification of soils (visual-manual procedures), D2488-17e1: West Conshohocken, PA, ASTM International, Annual book of standards, v. 04.08, soil and rock (I): D420-D5876, 13 p., available: www.astm.org.

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ASTM International, 2018b, Standard test method for Standard Penetration Test (STP) and split-barrel sampling of soils, D1586-18: West Conshohocken, PA, ASTM International, Annual book of standards, v. 04.08, soil and rock (I): D420-D5876, 26 p., available: www.astm.org.

ASTM International, 2020, Standard practice for classification of soils for engineering purposes (Unified Soil Classification System), D2487-17: West Conshohocken, PA, ASTM International, Annual book of standards, v. 04.08, soil and rock (I): D420- D5876, 10 p., available: www.astm.org.

ROCK STRENGTH

DESCRIPTION FIELD IDENTIFICATION

APPROXIMATE

UNCONFINED

COMPRESSIVE

STRENGTH (MPa)

APPROXIMATE

UNCONFINED

COMPRESSIVE

STRENGTH (psi)

Very Low Strength Crumbles under firm blows with point of geological hammer, can be peeled by a pocket knife

<5.0 <700

Low Strength Can be peeled by a pocket knife with difficulty, shallow indentations made by firm blow with point of geological hammer

5.0 to 25 700 to 4,000

Moderate Strength Cannot be scraped or peeled by a pocket knife, specimen can be fractured with a single blow of geological hammer

25 to 50 4,000 to 7,000

Medium High Strength Specimen requires more than one blow of geological hammer to fracture it

50 to 100 7,000 to 15,000

High Strength Specimen requires many blows of geological hammer to fracture it

100 to 250 15,000 to 36,000

Specimen can only be chipped with geological hammer

Very High Strength >250 >36,000

WEATHERING

DESCRIPTIONTERM

Fresh No visible signs of rock material weathering: perhaps slight discoloration on major discontinuity surfaces.

Slight penetration of discoloration away from fracture. Fractures may contain thin filling.Slightly Weathered

Moderately Weathered Partial to complete discoloration away from fracture. Rock not friable except for poorly cemented rock. Fractures may contain thick filling.

Highly Weathered All rock is discolored. Rock is friable except for poorly cemented rock. Corestones may be present.

All rock is decomposed and/or disintegrated to soil. The original mass is still largely intact.Completely Weathered

STRATIGRAPHIC

Very Thick

Thick

Medium

Thin

Very Thin

Laminated: Thickly

Laminated: Thinly

STRUCTURE SPACING TERMS

SPACING

>6 ft. (2 m)

2 to 6 Ft. (0.6 to 2 m)

8 to 24 in. (0.2 to 0.6 m)

2-1/2 to 8 in. (60 to 200 mm)

3/4 to 2-1/2 in. (20 to 60 mm)

1/4 to 3/4 in. (6 to 20 mm)

<1/4 in. (<6 mm)

DISCONTINUITY *

Very Wide

Wide

Medium

Close

Very Close

Extremely Close

Extremely Close

BASED ON INTERNATIONAL SOCIETY FOR ROCK MECHANICS (ISRM) ROCK CLASSIFICATION METHODS

SHANNON & WILSON, INC.

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STRATIGRAPHIC

STRUCTURE TERMS

MASSIVE - Rock without significant structure

BEDDED - Regular layering from sedimentation

FISSILE - Tendency to break along laminations

FOLIATED - Parallel arrangement or distribution of minerals for metamorphic rocks:

SCHISTOSE - Parallel arrangement of tabular minerals giving a planar fissility

GNEISSOSE - Segregation of minerals into bands

CLEAVAGE - Tendency to split along secondary, planar textures or structures

Slightly Vesicular

Moderately Vesicular

Highly Vesicular

Scoriaceous

VESICULARITY

1 to 10%

10 to 30%

30 to 50%

>50%

SMALL SCALE

JOINT ROUGHNESS

INTERMEDIATE SCALE

Rough

Smooth

Slickensided

Stepped

Undulating

Planar

* Refers to apparent spacing along core axis unless measured orthogonal to discontinuity; should then report for each set

FRACTURE - Collective term for any natural break excluding shears, shear zones, and faults

JOINT (JT) - Planar break with little or no displacement

FOLIATION JOINT (FJ) or BEDDING JOINT (BJ) - Joint along foliation or bedding

INCIPIENT JOINT (IJ) or INCIPIENT FRACTURE (IF) - Joint or fracture not evident until wetted and dried; breaks along existing surface

RANDOM FRACTURE (RF) - Natural, very irregular fracture that does not belong to a set

BEDDING PLANE SEPARATION or PARTING - A separation along bedding after extraction from stress relief or slaking

FRACTURE ZONE (FZ) - Planar zone of broken rock without gouge

MECHANICAL BREAK (MB) - Breaks due to drilling or handling; drilling break (DB), hammer break (HB)

SHEAR (SH) - Surface of differential movement evident by presence of slickensides, striations, or polishing

SHEAR ZONE (SZ) - Zone of gouge and rock fragments bounded by planar shear surfaces

FAULT (FT) - Shear zone of significant extent; differentiation from shear zone may be site-specific

DISCONTINUITY TERMS

L=

0.5 ft.

L=

0.4 ft.

L= 0.9 ft.L= 1.2 ft.

L=0 (Core Loss)

Core Recovery = 4.2 ft. = 84% Core Run Total Length = 5.0 ft.

Mechanical Break RQD = x 100% RQD = x 100% RQD = 60%

1.2 + 0.5 + 0.4 + 0.9 5.0

Length of Core Pieces > 4 in.

Total Core Run Length

STRUCTURAL GEOLOGY

ROCK CLASSIFICATION

FIG. A-2

Inclined Bedding - Showing Strike and Dip

Horizontal Bedding

Vertical Joint - Showing Strike

Vertical Bedding - Showing Strike

Inclined Joint - Showing Strike and Dip

Inclined Fault - Showing Strike and Dip

Inclined Shear - Showing Strike and Dip

NOTE: North Orientation Up

FIG. A-5

CA ERFO 2021-2(4)

El DOrado County, California

DRILLING SITE PHOTOGRAPHS

2023 109703-002

SHANNON & WILSON, INC.

Geotechnical and Environmental Consultants Sheet 1 of 2

Photograph 1: Boring B-1A/B (during drilling)

Photograph 2: Boring B-1A/B (finished)

El DOrado County, California

DRILLING SITE PHOTOGRAPHS

2023 109703-002

FIG. A-5SHANNON & WILSON, INC.

Geotechnical and Environmental Consultants Sheet 2 of 2

Photograph 1: Boring B-2 (setup)

Photograph 2: Boring B-2 (finished)

109703-002 Fig. A-6 Core Photos.xlsm 3/3/2023

FIG. A-6

Alder Creek Bridge

CA ERFO 2021-2(4)

El Dorado County, California

ROCK CORE PHOTOGRAPHS

2023 109703-002

SHANNON & WILSON, INC.

Geotechnical and Environmental Consultants Sheet 1 of 2

Photograph 1: Boring B-1A/B Core Box 1

Photograph 2: Boring B-1A/B Core Box 2

109703-002 Fig. A-6 Core Photos.xlsm 3/3/2023

FIG. A-6

Alder Creek Bridge

CA ERFO 2021-2(4)

El Dorado County, California

ROCK CORE PHOTOGRAPHS

2023 109703-002

SHANNON & WILSON, INC.

Geotechnical and Environmental Consultants Sheet 2 of 2

Photograph 1: Boring B-2 Core Box 1

Photograph 2: Boring B-2 Core Box 2

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Appendix B: Geotechnical Laboratory Testing

Appendix B

Geotechnical Laboratory Testing

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Appendix B: Geot echnical Laboratory Testin g

Appendix B

Geotechnical Laboratory Testing

CONTENTS

B.1 General

B.2 Samples

B.3 Laboratory Testing Procedures

B.3.1 Water Content

B.3.2 Grain Size Analysis

B.3.3 Unconfined Compression Test

B.3.4 Corrosivity Evaluation

B.4 References

Exhibits

Exhibit B-1: Corrosivity Ratings Based on Soil Resistivity Exhibit B-2: Sulfate Exposure

Tables

Table B-1: Summary of Laboratory Test Results

Attachments

Grain Size Distribution Test Results Unconfined Compression Strength of Intact Rock Core…