CA ERFO FS SEQUI 2021-02(2) Geotech Design Report.pdf

SUBMITTED TO:

Jacobs Engineering Group 1999 Bryan Street, Suite 1200 Dallas, Texas 75201

BY:

Shannon & Wilson, Inc.

100 North First St., Suite 200 Burbank, California 91502

(818)543-4560 www.shannonwilson.com

GEOTECHNICAL DESIGN REPORT

Powderhorn Bridge

CA ERFO 2021-2(2)

TULARE COUNTY, CALIFORNIA

P

July 2023

Shannon & Wilson No: 109691-002

CA ERFO 2021-2(2)

Geotechnical Design Report

109691-002 July 2023 7/17/2023-CFL_Powderhorn Bridge_Geotech_07-16-2023_sdd.docx i

Submitted To: Jacobs Engineering Group 1999 Bryan Street, Suite 1200 Dallas, Texas 75201 Attn: Mr. Berwyn Wilbrink

Subject: GEOTECHNICAL DESIGN REPORT, POWDERHORN BRIDGE

CA ERFO 2021-2(2), TULARE COUNTY, CALIFORNIA

We are pleased to submit this draft report for the above referenced project. This report presents our geotechnical design recommendations and was prepared by the undersigned.

Our scope of services was specified in Professional Services Task Order Number 148039500, which is associated with Professional Services Master Agreement Number 148039369 with Jacobs Engineering Group, Inc.

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.

Stephen D. Diem, PE, GE, PG, CEG Associate

SKM:RAL:SDD:DXC:RKT/skm

07/17/2023

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CONTENTS

1 Introduction

2 Project and Site Description

3 Subsurface Explorations and Laboratory Testing

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

4.4 Subsurface Variations

5 Geologic Hazard Evaluation

5.1 Seismic Hazards

5.1.1 Seismic Ground Motion

5.1.2 Liquefaction

5.1.3 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

6.2.3 Pile Groups

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

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7.2 Earthwork and Grading

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 for Single CIDH Piles Exhibit 6-4: 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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109691-002 July 2023

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 Powderhorn Bridge replacement project (Project) in Tulare County, California (Figure 1). Our services were conducted in general accordance with our Professional Services Task Order No. 148039500 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 observed in the boring

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

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

Team conference call on October 26, 2022, which included Jacobs, Shannon & Wilson, and Central Federal Lands Highway Division (CFLHD) (October Conference Call)

The replacement bridge will be designed in accordance with the U.S. Department of Transportation 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 provide recommendations and construction considerations, as presented herein, for the Project foundations and abutment walls. The authorized scope of services was based on this objective and this report should not be used for other purposes without Shannon & Wilson’s review. If a service is not specifically indicated in this report, do not assume that it was performed.

2 PROJECT AND SITE DESCRIPTION

The Project is located in the Sequoia National Forest approximately 26 miles east of Porterville, California and consists of replacing the 16-foot wide by 30-foot-long bridge that was damaged by fire in 2021. The bridge was a timber glulam girder bridge on concrete abutments that spanned Bear Creek.

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Based on the preliminary plans provided (Jacobs, 2022), the replacement bridge will be the same width but have a single span of 48 feet. It will be a prefabricated modular steel bridge with structural steel decking. The forest service road elevation is about 13 feet above Bear Creek. The abutments will be supported by 24-inch-diameter cast-in-drilled-hole (CIDH) shafts.

3 SUBSURFACE EXPLORATIONS AND LABORATORY

TESTING

3.1 Field Investigation

We conducted a field exploration program on October 20 and 21, 2022, to explore subsurface conditions and perform reconnaissance mapping at the proposed bridge replacement location over Bear Creek. The subsurface exploration program consisted of drilling and sampling one boring at the proposed eastern abutment, designated B-01-22. Due to adverse access road conditions, the team agreed to forego an attempt to drill a boring at the western abutment (October Conference Call).

Boring B-01-22 consisted of a combination of hollow stem auger and rock core drilling. The location of boring B-01-22 is presented on Figure 2. Appendix A presents a discussion of the drilling and sampling procedures used to complete the boring. Appendix A also presents the exploration log, an explanation of the symbols and terminology used, and photographs of the drilling setup and cores.

3.2 Geotechnical Laboratory Testing

Geotechnical laboratory tests were completed on selected samples retrieved from the boring to estimate index and engineering properties. Index tests included natural water content, grain size analysis, and Atterberg limits. 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, fines content, and Atterberg limits are also shown on the boring log in Appendix A.

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109691-002 July 2023

4 REGIONAL GEOLOGY AND SUBSURFACE

CONDITIONS

4.1 Regional Geology

The Project is in the Sierra Nevada geomorphic province of California. A review of the Reconnaissance Geologic Map of the Southern Sierra Nevada, Kern, Tulare, and Inyo Counties, California (Ross, 1995) indicates that the Project is underlain by igneous bedrock consisting of the Granodiorite of Peppermint Meadow (Kpm) and that the Kern Canyon Fault is located about 6.5 miles east of the Project.

4.2 Subsurface Conditions

Boring B-01-22 encountered approximately 7 feet of fill (af) that consists of medium dense to dense silty sand, underlain by about 3.5 feet of creek deposits (cd) that consists of loose silty sand. Weathered bedrock was encountered from about 10.5 to 14.5 below ground surface (bgs) with unweathered, strong bedrock (fresh bedrock) from about 14.5 feet bgs to the total depth of the boring of 24.5 feet bgs. As discussed below, we recommend embedding the CIDH piles in fresh bedrock, i.e., for vertical and lateral support.

We prepared Figure 3, Subsurface Profile A-A’, based on the findings in boring B-01-22 and by projecting the surrounding surface topography. The purpose of this subsurface profile is to estimate the top of bedrock at the Project site so that structural analyses can be performed, and CIDH rebar cage lengths can be estimated. Our estimation of the elevations at which the top of fresh bedrock will be encountered at each abutment is shown in Figure 2.

We recommend the structural analyses and length of the rebar cages take into consideration the uncertainty in our estimates particularly for the western abutment where we did not drill a boring.

Boring B-01-22 encountered fresh bedrock at an elevation of approximately 5546. As a result, we anticipate a CIDH pile drilled in the center of the eastern abutment will encounter fresh bedrock at approximately 5546. Based on the surrounding topography, we anticipate the CIDH pile on the northern end of the abutment will encounter fresh bedrock at a slightly lower elevation, approximately 5545. Similarly, we anticipate the CIDH pile on the southern end of the abutment will encounter fresh bedrock at approximately the same elevation as the middle of the abutment, approximately 5546.

For the western abutment, we estimated the elevation fresh bedrock will be encountered based on the surrounding surface topography. As shown on Figure 2, we anticipate fresh bedrock will be encountered at an elevation of approximately 5546 on the northern end of

Geotechnical Design Report

109691-002 July 2023 the abutment, approximately 5544 in the middle, and approximately 5541 at the southern end. These estimates are approximate.

4.3 Groundwater

During drilling, we observed subsurface water flowing in the Bear Creek channel and estimated it to be about 1 to 1.5 feet deep; a moist to wet sample of creek deposits was encountered in the sample collected at about 7.5 to 9 feet bgs in B-01-22 during the hollow stem drilling. We anticipate groundwater is transient, migrating along the top of the bedrock in the lower part of the creek deposits; we anticipate it will be encountered during CIDH shaft drilling. Groundwater fluctuations are likely and will depend on seasonal variations, local precipitation and runoff, and flood events.

4.4 Subsurface Variations

Due to access constraints, we performed one subsurface exploration at the Project site to evaluate the subsurface conditions. Our observations are specific to the location, depth, and time noted on the log and may not be applicable to all areas of the site. No amount of explorations or testing can precisely predict the characteristics, quality, or distribution of subsurface and site conditions. Potential variation includes, but is not limited to:

The conditions between the exploration location and adjacent areas may be different.

The passage of time or intervening causes (natural and manmade) may result in changes to site and subsurface conditions.

If conditions differ from those described herein are encountered during construction, we should review our description of the subsurface conditions and reconsider our conclusions and recommendations.

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, where required.

5.1 Seismic Hazards

The Project is located within the seismically active central California 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

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109691-002 July 2023 compression, and surface fault rupture. The following subsections describe our evaluation of the potential seismically induced hazards based on the seismic design criteria.

5.1.1 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, as discussed in the Engineering Recommendations section.

5.1.2 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. The loss in shear strength may 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.

The blow count in the silty sand creek deposit (CD) is low. Assuming the sand is saturated at the time of a significant earthquake, we conclude that the risk of liquefaction is relatively high in those conditions. To reduce the potential for liquefaction to impact the proposed bridge, we recommend reducing the LPILE parameters for the sandy overburden to account for potential strength reduction.

Should the silty sand liquefy, we believe that these design measures will limit deformation of the bridge. The measures will not improve the slopes and ground adjacent to the bridge.

The slopes adjacent to the bridge will not be constrained and deformation or yielding of these slopes could occur from soil liquefaction. Similarly, liquefaction of the creek deposits may result in an additional lateral load on the piles due to the overlying artificial fill, which

Geotechnical Design Report

109691-002 July 2023 is not anticipated to liquefy. We anticipate that some maintenance will be required to the areas adjacent to the bridge and abutments should liquefaction occur.

5.1.3 Fault Surface Rupture

Surface fault 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 site (U.S. Geological Survey [USGS] , 2014). The closest active fault is the Kern County Fault, approximately 6.5 miles east of the site (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, two samples were 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. Based on the test results, the corrosion potential of the subsurface soils is:

Resistivity: mildly to essentially non-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 pH: not considered damaging to concrete

The test results and the discussion in Appendix B are provided to assist the designer in the 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.

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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 total depth of our boring 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.

Exhibit 6-1: Seismic Design Ground Motion Parameters

Parameter Value1 Latitude 35.952811⁰

Longitude -118.577697⁰

Site Class B

PGA 0.311

FPGA 1.0

AS 0.311

SS 0.736

Fa 1.0

SDS 0.736

S1 0.231

Fv 1.0

SD1 0.231

NOTES:

Based on AASHTO 2020 Guide Specifications.

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

6.2 Abutment Foundations

We understand the bridge abutments will be supported by 24-inch-diameter CIDH piles.

The plans provided specify 4,500 pounds per square inch concrete for the CIDH piles (Jacobs, 2022).

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6.2.1 Axial Resistance

We recommend that axial resistance of the CIDH piles be derived from side friction resistance in the fresh bedrock, i.e., ignore side friction in the surficial soils and weathered bedrock and end bearing. The CIDH piles should extend at least 5 feet into fresh bedrock.

Exhibit 6-2 presents our recommended nominal unit side resistance values with strength and extreme resistance factors for determining factored axial resistance.

Exhibit 6-2: CIDH Pile Axial Resistance Design Parameters

Layer

Nominal Unit Side Resistance

(ksf)

Strength Limit Resistance Factors

Extreme Event Resistance Factors

Compression Uplift Compression Uplift

Fresh Bedrock 37 0.5 0.4 1 0.8

NOTES:

ksf = kips per square feet

Assuming CIDH piles are constructed using good installation techniques and equipment based on criteria described in the 2018 FHWA Manual “Drilled Shafts: Construction Procedures and LRFD Methods” (Brown and others, 2018), 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 behavior of the CIDH piles is highly dependent on 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 have provided input parameters for the commercial software LPILE by Ensoft, Inc. (2019) in Exhibit 6-3. 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.

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Exhibit 6-3: Recommended LPILE Parameters for Single CIDH Piles

Layer1 Model

Material

Total Unit Weight, γ

(pcf)

Friction Angle, φ

(deg)

Soil

Modulus, k4

(pci)

Uniaxial Compressive

Strength (psi)

Hoek- Brown

Material Index, mi

Poisson’s Ratio, ν

Geological Strength

Index, GSI

Intact Rock

Modulus, Ei

(ksi)

Artificial Fill Sand (Reese) 120 36 145 (85) - - - - -

Creek Deposits2,3

Sand (Reese) 120 28 15 (10) - - - - -

Weathered Bedrock

Sand (Reese) 135 44 215

(120) - - - - -

Fresh Bedrock

Massive Rock 150 - - 9,400 29 0.24 90 3,000

NOTES:

Refer to Figure 3 for layer depths.

When considering residual strength due to liquefaction, change material model to Liquefied Sand (Rollins).

When considering residual strength due to liquefaction, use buoyant unit weight for the liquefiable layers.

Parameter values for when modeling material above (below) groundwater.

deg = degrees; ksi = kips per square inch; pcf = pounds per cubic foot; pci = pounds per cubic inch; psi = pounds per square inch

6.2.3 Pile Groups

The center-to-center pile spacing should be at least 3 times the pile diameter. The axial capacity should be reduced by a factor of 0.9 for spacings between 2 and 3 times the diameter. Pile spacings less than 2 times the diameter should be avoided.

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).

For a single row of piles with a spacing greater than 5 times the diameter, the p-multiplier is

1.0. For a single row of piles with a center-to-center spacing between 3 and 5 times the diameter of the pile, a p-multiplier of 0.8 should be used. The center-to-center spacing of the piles should be at least 3 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, 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. For walls that are restrained at the top we recommend that they be designed for the at-rest condition. Active and at-rest earth pressures provided in Exhibit 6-4 assume the active zone of the walls are backfilled with Structural Backfill in accordance with FP-14 Section 704.04.

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Exhibit 6-4: 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, KO 0.44

Equivalent Fluid Density for Static Active Condition (pcf) 32

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

Dynamic Active Earth Pressure Coefficient, KAE 0.36

Uniformly Distributed Seismic Pressure Increment (psf/ft) 7

NOTES:

ft = foot; 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. Surcharge loads should be applied as recommended on Figure 4.

The parameters provided in Exhibit 6-4 assume a free draining backfill condition. 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 saturated backfill conditions.

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. 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

Geotechnical Design Report

109691-002 July 2023 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.

Access constraints at the abutments may restrict the size of drill rigs and construction equipment that can access the drilled shaft locations. The Contractor should consider site access in their selection of equipment and sequencing of operations.

CIDH piles should obtain their capacity from rock sockets in the fresh bedrock. Hence, the Contractor should be prepared for drilling into competent bedrock, see Appendix B for unconfined compression test results. Boulders and cobbles were observed during our geologic reconnaissance. As a result, boulder and cobble sized material may be encountered during CIDH pile construction, and 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 overburden 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

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109691-002 July 2023 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 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.

As an alternative, gamma-gamma testing in accordance with the California Department of Transportation test method (CT 233) may be used to evaluate the integrity of the production CIDH piles.

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, Section 704.04 of FP-14 (FHWA, 2014). If a drainage layer at the face of the wall is not used, as discussed in the Abutment Lateral Earth

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Pressures Section, we recommend the backfill consist of Foundation Fill or Select Borrow, Sections 704.01 and 704.07 of FP-14, respectively (FHWA, 2014).

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 compactors. The appropriate lift thickness will depend on the Contractor’s equipment and 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 the 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 amount 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.

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.

Shannon & Wilson, Inc. has prepared “Important Information about Your Geotechnical Report,” to assist you and others in understanding the use and limitations of our reports.

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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.

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

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

Ross, D.C., 1995, U.S. Geological Survey (USGS), Reconnaissance Geologic Map of Southern Sierra Nevada, Kern, Tulare and Inyo Counties, California, USGS Miscellaneous Investigations Series Map I-2295

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/.

U.S. Department of Transportation (USDOT), Federal Highway Administration (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, USGS seismic design web services, 2009 AASHTO guide specifications (AASHTO-2009): 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.

http://flh.fhwa.dot.gov/resources/pse/specs/ https://earthquake.usgs.gov/ws/designmaps/aashto-2009.html https://www.usgs.gov/programs/earthquake-hazards/faults

0.36569°

Sacramento

CALIFORNIA

Project Location

Los Angeles

San Francisco

VICINITY MAP

PROJECT

LOCATION

Aerial imagery downloaded from Google Earth Pro on 2-13-23.

Fi le na m e:

E

:\J

LA

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\1

1-

Fi g

- V ic in ity

M ap

.d w g

D at e:

2-

-2

L og in : S

AC

Fo re st R te

0 5 10

Scale in Miles

FIG. 1

July 2023 109691-002

Powderhorn Bridge

CA ERFO 2021-2(2)

Tulare County, California

INSET

1" = 1000 Ft.

PROJECT

LOCATION

Fresno

SPRINGVILLE

PONDEROSA

TULE RIVER

RESERVATION

WORTH

PORTERVILLE

TERRA

BELLA

DUCOR

WOODY

CALIFORNIA

HOT SPRINGS

23S16

Be ar

C re ek

23S02

Be ar

C re ek

Forest R te

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A

Map adapted from map titled "Powderhorn Bridge Over Bear Creek, dated 12-15-2022.

NOTE

SCALE: 1" = 20'

0 20 4010

B-01-22

Boring Designation and Approximate Location

Top of Fresh Bedrock Elevation at Abutment Based on Exploratory Boring

Top of Fresh Bedrock Elevation at Abutment Based on Interpretation

Subsurface Profile (See Figure 2)

LEGEND

B-01-22

SITE AND EXPLORATION PLAN

July 2023

FIG. 2

109691-002

Powderhorn Bridge

CA ERFO 2021-2(2)

Tulare County, California

A'

A

SDD

Engineer Eastern Abutment

SDD

Engineer Western Abutment

Ap pr ox im at e

El ev at io n in

F ee t

West A

200+00

PROPOSED BRIDGE

5540 5540

PR

O

PO

SE

D

BR

ID

G

E

AB

U

TM

EN

T

ST

A

9+

PR

O

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D

BR

ID

G

E

AB

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EN

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ST

A

0+

200+30199+60

? af cd af cd

Kpm (weathered)

Kpm (fresh)

GRAB

50/0"

CORE

CORE

CORE

B-01-22

10-20-22

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SUBSURFACE PROFILE A-A'

July 2023

1. Ground surface derived from map titled "Powderhorn Bridge Over Bear Creek, dated 12-15-2022.

2. This subsurface profile is generalized from materials observed in the soil boring. Variations will exist between profile and actual conditions.

NOTES

Vertical = Horizontal

74/10"

B-01-22

10-20-22

(Proj. 0') Designation of Boring Projected Distance and Direction

LEGEND

Bottom of Boring Date of Completion

0 10 20

Scale in Feet af cd

Kpm

GEOLOGIC UNITS

FIG. 3

Approximate Geologic Contact

USCS Symbol

? ?Approximate Rock Contact

0 50 100

East A'

109691-002

Powderhorn Bridge

CA ERFO 2021-2(2)

Tulare County, California

GRAB Grab Sample Sample and Penetration Resistance in Blows/Foot or Blows per Inches Driven

Rock Core Sample

Rock Coring Recovery (%) Rock Quality Designation (%)

Stationing Along Centerline Bridge Between Stations 199+60 and 200+25

Approximate Existing Ground Surface

Approximate Existing Abutment (Typical)

Artificial Fill

Creek Deposits

Granodiorite of Peppermint Meadow (Bedrock)

SDD

Engineer Eastern Abutment

SDD

Engineer Western Abutment

SDD

Line

RECOMMENDED SURCHARGE

LOADING FOR TEMPORARY AND

PERMANENT WALLS

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FIG. 4

For m ≤ 0.4: sH = 0.28 (psf) (see Note 3)

W al l

PLAN VIEW

2.0 q

1.5

D ep th F ac to r, Z/

B

1.0

0.0

0.5

W al l

Z

Wall Line

UNIFORM SURCHARGE

a d

EARTH BERM

(see Note 4)

Note:

H z=nH

Bottom of Excavation x = mH

Point Load in Pounds sH (psf) sH (psf)

ELEVATION VIEW

x = mH

H

Bottom of Excavation

W al l z=nH Line Load in Pounds/Foot

B) LATERAL PRESSURE DUE TO LINE LOAD

i.e. NARROW CONTINUOUS FOOTING

PARALLEL TO WALL

C) LATERAL PRESSURE DUE TO STRIP LOAD

R ig id W al l

W al l

W al l

A) LATERAL PRESSURE DUE TO POINT LOAD

i.e. SMALL ISOLATED FOOTING OR WHEEL LOAD y

D) LATERAL PRESSURE DUE TO EARTH BERM

OR UNIFORM SURCHARGE

Bottom of Excavation

Bottom of Excavation

E) LATERAL PRESSURE DUE

TO ADJACENT FOOTING

(see Notes 5 and 6)

0 0.5 1.0

L

B

NOTES

1. Figures are not drawn to scale.

2. Applicable surcharge pressures should be added to appropriate permanent wall lateral earth and water pressure.

3. If point or line loads are close to the back of the wall such that m £ 0.4, it may be more appropriate to model the actual load distribution (i.e., Detail E) or use more rigorous analysis methods.

4. See text for recommended K values.

5. The stress is estimated on the back of the wall at the center of the length, L, of loading.

6. The estimated stress is based on a Poisson's ratio of 0.5.

W al l

Bearing Pressure q (psf)

Ip, Influence Factor sH = 2(Ip) qs

Lateral Footing Pressure on Wall

(derived from NAVFAC DM 7.02, 1986; and Sandhu, Earth Pressure on Walls Due to Surcharge, 1974)

(derived from Poulos and Davis, Elastic Solutions for Soil and Rock Mechanics, 1974; and Terzaghi and

Peck, Soil Mechanics in Engineering Practice, 1967)

(NAVFAC DM 7.02, 1986)

(AASHTO LRFD Bridge Design Specifications, 2020)

(NAVFAC DM 7.02, 1986)

Point Load in Pounds g = Unit Weight of Earth Berm

Bearing Pressure

Earth Berm sH = Lateral Pressure in radians

ELEVATION VIEW

(see Note 3) (see Note 3) qs

L 2B

Qp

H2 n2

(0.16 + n2)3

For m > 0.4: sH = 1.77 (psf) Qp

H2 m2n2

(m2 + n2)3

Qp sH s'H = sH cos2 (1.1q) (psf) s'H sH

For m ≤ 0.4: sH = 0.20 (psf) (see Note 3) Ql

H n

(0.16 + n2)2

For m > 0.4: sH = 1.28 (psf) Ql

H m2n

(m2 + n2)2

QlQp y ≤ 33° Hs ≤ 15 Feet

(K)(g)(Hs) sH

Hs sH = (K)qs (see Note 4) qs (psf) sH = [d - sin d cos (d + 2a)] (psf)2q p

L

= 0.25 = 0.5

= 1 sH

L 2B

L 2B

L 2B

July 2023 109691-002

Powderhorn Bridge

Tulare County, California

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Appendix A: Subsurface Ex plorations

Appendix A

Subsurface Explorations

CONTENTS

A.1 General .................................................................................................................................... A-1

A.2 Field Preparations ................................................................................................................. A-1

A.2.1 Underground Utility Locates ................................................................................. A-1

A.2.2 U.S. Forest Service Coordination ........................................................................... A-1

A.3 Drilling Procedures ............................................................................................................... A-1

A.4 Backfill Procedures ............................................................................................................... A-2

A.5 Sampling Procedures ............................................................................................................ A-2

A.5.1 Sampling Interval ..................................................................................................... A-2

A.5.2 Standard Penetration Test (SPT) ............................................................................ A-2

A.5.3 Rock Coring .............................................................................................................. A-3

A.6 Review and Classification of Samples ................................................................................ A-3

A.6.1 Field Observations ................................................................................................... A-3

A.6.2 Soil Classification System........................................................................................ A-3

A.6.3 Geologic Units and Descriptions ........................................................................... A-4

A.6.4 Boring Logs ............................................................................................................... A-4

A.7 References .............................................................................................................................. A-4

Figures

Figure A-1: Soil Description and Log Key Figure A-2: Rock Classification and Log Key Figure A-3: Log of Boring B-01-22 Figure A-4: Site Photographs Figure A-5: Rock Core Photographs

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A.1 GENERAL

The subsurface exploration performed for the project consisted of drilling and sampling boring B-01-22. The approximate exploration location is shown on the Site and Exploration Plan, Figure 2. We estimated the exploration location by using the existing features and a tape measure and estimated elevations using the plans provided. The exploration location 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.

A.2 FIELD PREPARATIONS

A.2.1 Underground Utility Locates

We marked the proposed boring location and notified Underground Service Alert of Northern California of our planned exploration.

A.2.2 U.S. Forest Service Coordination

Prior to subsurface exploration, we contacted the U.S. Forest Service (USFS) and confirmed that permits were not required to perform our boring. A permit was required to use the access roads and was obtained. The boring was performed on an access road behind a locked gate and traffic control was not needed. A representative of the USFS opened and closed the locked gate and was present during drilling of the boring.

A.3 DRILLING PROCEDURES

Drilling was performed on October 20, 2022, by Cascade Drilling, Inc. of Sacramento, California, under subcontract to Shannon & Wilson.

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The boring was hand-augered to 2.5 feet bgs prior to drilling. The drillers used a CME truck-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 fresh bedrock.

The boring log is presented in Figure A-3. Photographs of the drill rig setup for the boring and western abutment area are shown in Figure A-4. Cores were photographed immediately after retrieval and placed in a core box (Figure A-5).

A.4 BACKFILL PROCEDURES

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

Quickcrete cement was used to patch the upper 12-inches of the bore hole that was drilled through the roadway’s existing asphalt pavement.

A.5 SAMPLING PROCEDURES

A.5.1 Sampling Interval

The drilling contractor performed standard penetration test drive samples at 2.5-foot intervals in the soil. Bedrock was encountered at approximately 10.5 feet below the existing ground surface (bgs).

A.5.2 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.

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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 the boring log by a Shannon & Wilson field representative, sealed in jars, and returned to our laboratory for review and testing.

A.5.3 Rock Coring

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. 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 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 bedding, fractures, and rock “quality”. Rock quality is typically conveyed in terms of Rock 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.

A.6 REVIEW AND CLASSIFICATION OF SAMPLES

A.6.1 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 (e.g., heave, hole collapse), and other issues if applicable.

A.6.2 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)

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S 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.

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.

A.6.3 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.

A.6.4 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…