CA ERFO SIERRA NF 05S07(1)Norris Creek Bridge Geotech Rpt FINAL March 2022.pdf

NORRIS CREEK BRIDGE

SIERRA NATIONAL FOREST

MADERA COUNTY, CA

CA ERFO 05S07(1)

FINAL Geotechnical Report

Prepared by Federal Highway Administration

Central Federal Lands Highway Division

Geotechnical Services Branch March 2022 ii

SIGNATURE SHEET

Report prepared by: ___________________________________________________________

Devin T. Dixon, P.E., Geotechnical Engineer

Report reviewed by: ____________________________________________________________

Brendan L. McGarity, Geotechnical Engineer

Approved for distribution by: ____________________________________________________

Marilyn D. Dodson, P.E., Lead Geotechnical Engineer

Distribution

Electronic:

N:\CA\erfo05s07(1)\Geotech\7_FinalDocs K:\TechServices\Geotech\1. Geotech Project Reports Project Management Project Development, Lead Designer Bridge

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TABLE OF CONTENTS

SECTION ONE - INTRODUCTION

1.1 BACKGROUND AND LOCATION

1.2 SCOPE AND PURPOSE

SECTION TWO - GEOLOGY AND SEISMICITY

2.1 REGIONAL GEOLOGY

2.2 SITE GEOLOGY

2.3 REGIONAL SEISMICITY

2.4 SEISMIC DESIGN PARAMETERS

2.5 GEOLOGIC HAZARDS

SECTION THREE - SUBSURFACE INVESTIGATION

3.1 SUBSURFACE EXPLORATION PROGRAM

3.2 LABORATORY TESTING PROGRAM

3.3 SUMMARY OF SITE CONDITIONS

3.3.1 General Topography

3.3.2 Surface Reconnaissance

3.3.3 Subsurface Conditions

3.3.4 Groundwater

3.4 ROCK CHARACTERISTICS

3.4.1 Generalized Strength Criterion for Intact Rock

3.4.2 Rock Characterization

SECTION FOUR - ANALYSIS & RECOMMENDATIONS

4.1 FOUNDATIONS

4.1.1 Bridge Foundation Selection

4.1.2 Site Characterization

4.1.3 Drilled Shaft Axial Resistance

4.1.4 Group Effects on Axial Resistance

4.1.5 Lateral Loads on Deep Foundations

4.1.6 Settlement

4.1.7 Field Testing

4.1.8 Scour Potential and Erosion

4.2 ABUTMENT & WINGWALL DESIGN

4.3 PERMANENT EARTHWORKS

4.3.1 Embankment Construction

4.3.2 Shrink/Swell Recommendations

4.4 CONSTRUCTION CONSIDERATIONS

4.5 SPECIFICATIONS

4.6 DISCLAIMER/LIMITATIONS CLAUSE

SECTION FIVE - REFERENCES

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TABLES

TABLE 2.1 Summary of Nearby Seismic Source Faults TABLE 2.2 Summary of Seismic Parameters Corrected for Site Class C TABLE 3.1 Summary of Field Exploration Program TABLE 3.2 Summaries of Laboratory Index Test Results TABLE 3.3 Summaries of Laboratory Corrosivity Results TABLE 3.4 Summary of Uniaxial Compressive Strength Results TABLE 3.5 Strength Parameters Calculated for Rock Based on Hoek Brown Criterion.11 TABLE 4.1 Proposed Bridge Foundation Location TABLE 4.2 Shaft Tip Resistance in Rock TABLE 4.3 LPILE Parameters TABLE 4.4 Lateral Earth Pressures for Bridge Abutments & Wingwalls

PLATES

PLATE 1 Project Vicinity Map PLATE 2 Geology Map PLATE 3 Geology Map Legend PLATE 4 Norris Creek Bridge Geotechnical Boring Locations

APPENDICES

APPENDIX A Field Exploration Program APPENDIX B Laboratory Test Results APPENDIX C Photographs APPENDIX D Excavation Characteristics of Rock & Rippability Charts

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Norris Creek Bridge, CA ERFO 05S07(1) March 2022

SECTION ONE - Introduction

1.1 BACKGROUND AND LOCATION

This report presents the results of the geotechnical engineering study and provides recommendations for the replacement of the Norris Creek Bridge in Madera County, California.

The project proposes to replace the existing Norris Creek Bridge, which is located on Forest Route 05S07 within the Sierra National Forest. A project vicinity map is presented on Plate 1 of this report.

The Norris Creek Bridge was severely damaged by fire during the 2020 season. Existing bridge superstructure and partial substructure components were incinerated.

The former Norris Creek Bridge was constructed as a single lane, two-way traffic, bridge in 1971 and designed to HS20 load-bearing criteria. The superstructure consisted of timber glulam girders, nail laminated deck, and railings. The substructure abutments and wingwalls were timber pile and lagging walls with tiebacks. The bottoms of walls were founded on concrete footings approximately 15 feet below profile grade. Partial bridge plans and an inspection report from August 2019 were available from the Forest Service. Rock bearing of foundations was not noted on the plans.

The Norris Creek Bridge will be replaced to meet HL-93 legal load standards. The proposed replacement structure type is assumed to be a steel prefabricated bridge with rolled girders, structural steel decking, and asphalt fill. The existing timber abutment walls will be removed, and the embankments will be configured with spill-through abutments. The new abutments will be simple cast-in-place concrete caps and wingwalls supported by deep foundations. Deep foundations are proposed due to geometrical constraints caused by the proposed spill-through abutment configuration and because spread footers likely cannot be founded on competent soils or rock at a reasonable cost. The potential for scour also exists at the bridge location and deep foundations bearing on suitable materials below such susceptible soils would provide protection against this problem. Considerations related to the abutments for the Norris Creek Bridge are presented in Section 4 of this report.

1.2 SCOPE AND PURPOSE

The scope of work included a geotechnical investigation, analysis, and recommendations for bridge foundations for use in design and construction. This involved several tasks including field reconnaissance, subsurface sampling, laboratory testing, interpretation and correlation of field measurements, and geotechnical engineering analysis. Specifically, this investigation was conducted to determine the soil profile at the bridge location and develop recommendations

Page | 2 concerning bridge foundations, retaining structures, geologic hazards, and construction considerations.

We understand that a hydraulics report has been prepared under separate cover by the CFLHD Hydraulics Engineer. The hydraulics report includes discussion of flood impacts, such as bridge scour and water surface elevations.

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SECTION TWO - Geology and Seismicity

2.1 REGIONAL GEOLOGY

The project is located within the Sierra Nevada Section of the Cascade-Sierra Mountains Province.

This province is part of the Pacific Mountain System physiographic region. The Cascade-Sierra Mountains Province extends from Alaska in the north to the southern tip of South America. This province is divided into two regions: the Cascade Mountains and the Sierra Nevada Mountains (NPS, 2018). Features and landscapes within the Sierra Nevada Section are characterized by rugged and steep mountains, Mesozoic aged granitic rock, and glacier landforms.

Quaternary and Tertiary rocks and deposits that exist within the region include alluvial and glacial deposits, talus, and volcanic rocks such as basalt, andesite, and phonolite. Cretaceous aged units primarily include plutonic rocks such as granite, granodiorite, leucogranite, gabbro, and quartz diorite. Some metavolcanic rocks are also Cretaceous aged including undifferentiated metavolcanic rocks, quartzofeldspathic gneiss, and metarhyolite. Jurassic aged units include metasedimentary rocks such as undifferentiated metasedimentary rocks, tactite, quartz-pebble conglomerate, and marble (Peck, 1980).

2.2 SITE GEOLOGY

Although not mapped, the soil conditions at the site are assumed to be alluvium based on the stream bed deposits. The project site is mapped as underlain by volcanic rock. Glacial deposits are also mapped in the vicinity of the sites. These observations are consistent with the borings as will be discussed in Section 3 of this report. The deposits and landforms are a result of volcanic activity, plate tectonics, and glacial movement and the terrain can be described as mountainous and rugged.

A geology map of the project area and corresponding map legend are presented in Plates 2 & 3.

2.3 REGIONAL SEISMICITY

Seven seismic hazard faults are located within 50 miles of the project. These faults are summarized in Table 2.1 and are located northeast, east, and southeast of the project site. All of these faults have experienced deformation in the last 15,000 years or less. Known slip rates range from less than 0.00787 to 0.19685 inches per year (USGS, 2020a). The site-source distance using the Caltrans ARS Online (v3.0.2) tool was calculated to be approximately 21 miles with a mean magnitude for PGA to be approximately 6 g. Based on the time of most recent deformation and distance to these faults, surface rupture at the bridge site is not anticipated.

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Table 2.1 - Summary of Nearby Seismic Source Faults

FAULT OR

FAULT ZONE

DISTANCE

FROM

CENTER OF

PROJECT

SLIP-RATE

CATEGORY

DIP

DIRECTION

AVERAGE

STRIKE

FAULT

LENGTH

TIME OF MOST

RECENT

DEFORMATION

(miles) (inch/year) (miles) (years) Hartley Springs

Fault Zone, (Class A)

No. 43

17.6 0.00787 to

0.03937 E N5°W 14.3 <15,000

Hilton Creek Fault, (Class A)

No. 44

22.4 0.03937 to

0.19685 E N12°W 18.6 <15,000

Mono Lake Fault, (Class A)

No. 41

29.9 0.03937 to

0.19685 55°-70° E N34°W 14.3 <15,000

Round Valley Fault, (Class A)

No. 45

31.0 0.03937 to

0.19685 45°-89° E N19°W 22.4 <15,000

Robinson Creek Fault Zone, (Class A)

No. 40

43.2 0.00787 to

0.03937 E N15°E 11.8 <15,000

Huntoon Valley Fault System, (Class A) No. 1302

47.4 < 0.00787 Not listed N48°E 24.2 <15,000

Unnamed Faults Near Teels Marsh, (Class A) No. 1303

49.8 < 0.00787 NW; SE N40°E 24.2 <15,000

2.4 SEISMIC DESIGN PARAMETERS

Recommended seismic response parameters for the Norris Creek Bridge project site design are based on the American Association of State Highway and Transportation Officials (AASHTO) LRFD Bridge Design Specifications, 8th Edition, 2017, and represents horizontal peak ground acceleration (PGA) with 7 percent probability of exceedance in 75 years (approximate 1,000-year return period). The 1,000-year return period uniform hazard spectrum for the Norris Creek Bridge project site, located at 37.51140°N latitude and 119.31161°W longitude, was obtained in accordance with the AASHTO ground motion maps.

Based on subsurface conditions encountered during drilling and the USGS Vs30 online map viewer, the onsite soils can be assumed to be reasonably dense. Therefore, the site is classified as Class C according to the site class definitions specified in Table 3.10.3.1-1 of AASHTO. The recommended spectral acceleration coefficient values for probabilistic design are summarized in Table 2.2.

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Table 2.2 - Summary of Seismic Parameters Corrected for Site Class C Horizontal Peak Ground Acceleration, (PGA) 0.298 g

Horizontal Response Spectral Acceleration at Period of 0.2 sec, (Ss) 0.718 g Horizontal Response Spectral Acceleration at Period of 1.0 sec, (S1) 0.226 g

Site Factor at Zero-Period of Acceleration Spectrum, (Fpga) 1.1 Site Factor at Short-Period Range of Acceleration Spectrum, (Fa) 1.1 Site Factor at Long-Period Range of Acceleration Spectrum, (Fv) 1.6

Factored Horizontal Peak Ground Acceleration, (As) 0.328 g Factored Horizontal Response Spectral Acceleration at Period of 0.2 sec, (SDs) 0.799 g Factored Horizontal Response Spectral Acceleration at Period of 1.0 sec, (SD1) 0.356 g

Seismic Zone Zone 3

Based on the long acceleration coefficient SD1 value of 0.356, the project site is assigned to seismic hazard “Zone 3” in accordance with Table 3.10.6-1 of AASHTO. Seismic hazard zones reflect the variation in seismic risk in different regions needing different requirements for design as depicted in Table 4.7.4.3.1-1 of AASHTO.

2.5 GEOLOGIC HAZARDS

Potential geologic hazards at the bridge site include those related to earthquakes, mass movements, and mineral hazards. Earthquakes, as discussed in the previous section, could pose a threat to the Norris Creek Bridge. Central California and the project site are located in an area of moderate to high potential for damaging earthquakes, although it is impossible to accurately predict the timing or location of future earthquakes. Liquefaction potential is also relatively minimal since the site soils are relatively dense and mostly unsaturated. Seismic hazards can be mitigated by appropriate design analysis as specified in AASHTO.

Mass movements are also common in California due to major wildfires, heavy rains, and the fines content of the soil. These rock and soil movements include seismically triggered landslides, debris flows, mud flows, and rock falls. The project is located in terrain susceptible to mass movement and these events could impact the bridge site. No specific investigation was conducted to evaluate slope stability in the project area. Mitigation of landslides is outside the scope of this emergency repair project.

Minerals-related hazards, such as asbestos, mercury, and radon, are present in California. Mercury contamination from historic gold mines, however, may be the most likely within Sierra Nevada.

CFLHD does not take responsibility for development, implementation, or enforcement of any sort of management or abatement plan for mineral-related hazards.

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SECTION THREE - Subsurface Investigation

3.1 SUBSURFACE EXPLORATION PROGRAM

A subsurface investigation targeting the bridge site was performed by a Central Federal Lands Highway Division (CFLHD) of the Federal Highway Administration (FHWA) geotechnical engineer on November 2, 2021. The geotechnical subsurface exploration program consisted of drilling a total of one boring to approximately 28 feet deep. The boring was drilled near abutment

2. Hollow-stem augers were used to drill through the overburden soils and rock samples were recovered using NQ diamond core drilling. Standard penetration testing (SPT) and sample collection was performed at 5-foot intervals for each boring when possible. A grab sample of the upper subsurface was also collected. Subsurface conditions were logged, and representative samples were collected and transported to the CFLHD Materials Laboratory in Lakewood, CO, for physical property testing. A log of the exploration and boring location are presented in Appendix A and Plate 4, respectively. Photographs related to this exploration can be found in Appendix C. A summary of the field exploration is provided in Table 3.1. It should be noted that abutment 1 was inaccessible at the time of the investigation due to poor and unsafe road conditions.

Table 3.1 - Summary of Field Exploration Program

EXPLORATION

DESIGNATION LOCATION

APPROXIMATE

GROUND

ELEVATION (ft.)

APPROXIMATE

TERMINATION

DEPTH (ft.)

APPROXIMATE

DEPTH TO

GROUNDWATER

(ft.)

BH21-01 Abutment 2;

STA 103+95, 2 ft. LT 7,044.9 28.0 11.0

Note: The exploration locations were estimated relative to existing features. Ground elevations were acquired from CFL survey data.

3.2 LABORATORY TESTING PROGRAM

Soil samples recovered from the boring by SPT were tested in the laboratory to support the field classifications and to provide an estimate of the engineering characteristics and mechanical properties of the soil. Laboratory tests included moisture content (AASHTO T255), sieve analysis (AASHTO T 11 and T27), classification (AASHTO M145), Atterberg limits (AASHTO T89 and T90), resistivity (AASHTO T 288), and soil pH (AASHTO T 289). When the necessary tests were completed, samples were classified using the Unified Soil Classification System (USCS) and AASHTO soil classification system. Results of the testing are summarized below in Table 3.2 and are presented in Appendix B.

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Table 3.2 - Summaries of Laboratory Index Test Results

BORING

NUMBER

SAMPLE

DEPTH

PERCENT

GRAVEL

PERCENT

SAND

PERCENT

PASSING

#200

LIQUID

LIMIT

PLASTI

C LIMIT

USCS

CLASS.

AASHTO

CLASS.

(feet)

BH21-01 0 - 5 11 65 24 NV NP SM A-2-4(0)

BH21-01 5 - 6.5 11 66 23 NV NP SM A-2-4(0)

BH21-01 10 - 11.5 30 54 16 NV NP SM A-1-b(0)

Soil test results indicated a limited range of material types composed of silty sand classifying as A-1-b to A-2-4 by AASHTO and SM by USCS.

Corrosivity and chemistry testing of select samples were sent to an outside laboratory for testing and are summarized in Table 3.3.

Table 3.3 - Summaries of Laboratory Corrosivity Results

BORING

NUMBER

SAMPLE

DEPTH

RESISTIVITY PH

SULFATE ION

CONTENT

CHLORIDE ION

CONTENT

(feet) (ohm-cm) (ppm) (ppm)

BH21-01 0 - 5 25,194 6.2 - -

- Tests not completed.

Unconfined compressive strength (UCS) of rock material was conducted on intact samples of rock core recovered from the borings. Results of the UCS testing are presented in Table 3.4.

Table 3.4 - Summary of Uniaxial Compressive Strength Results

BORING NUMBER SAMPLE DEPTH RQD1 LENGTH / DIAMETER2 UCS

(feet) (%) (psi)

BH21-01 18.5 41 1.8 18,130

BH 21-01 20.6 41 1.7 11,740

BH21-01 23.8 47 1.5 6,740

BH21-01 25.8 47 2.3 13,090

1Rock Quality Designation for core run from which sample was taken in bedrock surface.

2Values less than 2.0 do not meet the requirements of ASTM D 7012. Not included in analysis.

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3.3 SUMMARY OF SITE CONDITIONS

This section presents the results of the surface reconnaissance and subsurface exploration.

3.3.1 General Topography

The general topography of the project site is characterized by the steep Sierra Nevada Mountains that lie primarily in central and eastern California. Large boulders were observed near the upstream sides of both bridge abutments measuring at least 6 to 7-foot diameter on the ground surface.

Portions of boulders were buried; therefore, the actual sizes may be greater than what was observed. Rock outcroppings were noticeable on the slope southeast of abutment 2, however, rock outcroppings were not noticed within the vicinity of abutment 1. Burnt, dead standing, trees typical of Ponderosa pine intermingled with strands of old growth and scattered lodgepole pine and red fir are abundant at the project site. Signs of revegetation are noticeable in the surrounding grass and shrubs. Norris Creek flows north to south, crosses Forest Route 05S07, and converges with Jackass Creek approximately 1.5 miles downstream of the Norris Creek Bridge project site.

3.3.2 Surface Reconnaissance

Superstructure timber elements were incinerated by the fires and partial remaining elements laid in the creek along with woody debris. Substructure timber abutments and wingwalls of the Norris Creek Bridge, although partially burned and damaged beyond reuse, remain in place. A temporary stream, low-water, crossing was constructed on the south side of abutment 2; however, it was inaccessible at the time of the subsurface investigation.

The forested area around the bridge site is severely burned. The significant loss of native vegetation has exposed the soil to erosion and increased water runoff. Regrowth of grass and small bushes has begun to take place; however, many exposed areas remain. Increased sediment transport was observed and is likely to continue until vegetation is well reestablished. Due to the weakened surface conditions and the steepness of the surrounding slopes, sediments, debris, loose rocks and boulders, and tree parts have the potential to slide downslope towards Norris Creek. In general, however, any movements related to the slopes adjacent to the project sites appear to be surficial and slow moving.

The approaches leading to the bridge site consist of an asphalt surface of approximately 100 feet on either side of the bridge. Alluvial soils and sediments encompass the bridge site. Large, flat, and somewhat blocky boulders ranging in size from approximately 6 to 7 feet in diameter were observed on the upstream side of the bridge abutments and embankments. These boulders could have been placed around the previous bridge as scour protection and may have been locally sourced during the original construction. Rock outcroppings, as discussed in the previous section, were observed on the slope southeast of abutment 2.

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3.3.3 Subsurface Conditions

The subsurface conditions at abutment 2 of Norris Creek Bridge were investigated by drilling boring BH21-01. Hollow stem auger drilling was used from approximately 0 to 15 feet below the ground surface and rock coring was used from approximately 15 feet below the ground surface to the termination depth of 28 feet. The ground surface surrounding the boring location consisted of existing asphalt pavement approximately 2.5-inches thick. Beneath the pavement section the boring encountered loose to medium dense silty sand and silty sand with gravel to approximately

12.5 feet. Trace organics and some rock fragments and cobbles were intermixed in this layer.

Basalt bedrock was encountered beneath the silty sand and extended to the termination depth. This rock was grey to dark grey, slightly to moderately weathered, and classified as medium to very strong rock (R3 to R5). Groundwater was encountered at approximately 11 feet.

The subsurface conditions at abutment 1 of Norris Creek Bridge were not investigated by drilling.

Driving routes to abutment 1 were deemed inaccessible at the time of the scheduled subsurface investigation due to poor and unsafe road conditions caused by ice and snow. The low water crossing near abutment 2 also could not be safely traversed with the drill rig.

3.3.4 Groundwater

Groundwater was encountered during drilling in boring BH21-01 at approximately 11 feet below the ground surface. However, fluctuations in the groundwater level due to seasonal and climatic effects are expected and will likely follow water levels in the adjacent creek.

3.4 ROCK CHARACTERISTICS

A natural rock mass is rarely a continuous, isotropic, homogeneous material. It can be highly variable in character. A rock mass is generally composed of intact or weathered blocks of rock separated by discontinuities such as joints or bedding planes. The discontinuity and weathering characteristics help establish the design recommendations for a foundation on rock. These characteristics include, but are not limited to, the rock lithology, strength properties, deformation properties, frequency of discontinuities (RQD), spacing of discontinuities, orientation of discontinuities, aperture, filling, condition, degree of weathering, and the groundwater condition.

This information was observed at the borehole location and laboratory testing of select rock samples. The following sections discuss the rock strength properties and rock characterization based on the field investigation and lab testing results.

3.4.1 Generalized Strength Criterion for Intact Rock

Intact samples of rock core were taken from the Norris Creek Bridge borehole and laboratory testing, uniaxial (unconfined) compression testing, was performed. Table 3.4 summarizes the results of the UCS testing. In the field, most of the rock required more than one firm blow of the

Page | 10 geologic hammer point to fracture and it was estimated that the rock corresponded with the description of “strong rock,” R4, as described in the FHWA Rock Description Guidelines. The range of relative strength for R4 rock as listed in this reference is between 7,250-14,500 psi. The rock also appeared to have slight to moderate weathering.

Based on the aforementioned UCS testing, the rock strength for the Norris Creek Bridge is conservatively assumed to be approximately 13,090 psi for abutments 1 and 2. This value is equal to the single acceptable UCS test result at abutment 2 and is within the range of R4, “strong rock,” as discussed in the previous paragraph. For comparison, the unconfined compressive strength of basalt rock is generally between roughly 14,500 and 43,500 psi (Texas Geosciences, 2021).

3.4.2 Rock Characterization

The Geologic Strength Index (GSI) (Hoek and Marinos, 2000) system was used to characterize the rock. The GSI is a slight modification of the Rock Mass Rating system (RMR) (AASHTO, 2017) which is more appropriate for the bridge foundation evaluation at this site. The GSI is the algebraic sum of ratings assigned for the following rock mass properties:

• Intact rock strength

• Rock Quality Designation (RQD)

• Discontinuities spacing

• Discontinuities condition

• Presence of groundwater

For this project, the GSI was estimated based on collected rock core samples. The rock composition was identified as basalt with slight to moderate weathering and very blocky structure.

The estimated GSI values given these assumptions corresponds to a range of 40 to 50 (Hoek and Marinos, 2000). A GSI value of 45 was then assumed for the rock. Other pertinent rock properties include the Hoek-Brown constant, mi (estimated from Table 10.4.6.4-1 in AASHTO 2017), rock unit weight, γ, and the damage factor, D. These values were assumed to be 25 for basalt, 145 pcf, and 0.5 as an intermediate value for drilled shafts, respectively. For intact rock, the following equations were then used to determine the appropriate curve fitting coefficients:

mb = mi ∗ exp � GSI−100 28−(14∗D)

For GSI > 25: α = 0.5 + 1 ∗ (exp �−GSI

� − exp �− 20 s = exp �

GSI − 100

9 − 3 ∗ D

Page | 11

A summary of the assumed rock properties and the Hoek Brown criteria calculations is presented in Table 3.5 below. These values are directly related to the bearing resistance discussed in Section 4.1.3.

Table 3.5 - Strength Parameters Calculated for Rock Based on Hoek Brown Criterion GSI 𝛔𝛔𝐜𝐜𝐜𝐜 (psi) 𝐬𝐬 𝐦𝐦𝐛𝐛 𝐦𝐦𝐜𝐜 𝛂𝛂

45 13,090 (abutment 2) 0.0007 1.8218 25 0.508

Page | 12

SECTION FOUR - Analysis & Recommendations

This section presents analysis and recommendations for the bridge foundations, abutment wingwalls, permanent earthworks, and construction considerations for the design and construction of the Norris Creek Bridge project. Based on discussions with the project team and the severe damage to all bridge structure components, the bridge will be replaced. Generalized subsurface profiles were developed based on field reconnaissance, surficial visual evaluation, and subsurface investigations.

4.1 FOUNDATIONS

The existing single span bridge will be replaced with a modular steel bridge with steel girders and structural steel decking with asphalt pavement fill. The remaining existing bridge elements will be removed. Based on the 95 percent design plans, the proposed abutment centerline station and cap elevation are shown in Table 4.1.

Table 4.1 - Proposed Bridge Foundation Location

FOUNDATION APPROXIMATE STATION TOP OF SHAFT ELEVATION*

Abutment 1 103+21.00 7,038.35 FT Abutment 2 103+91.00 7,039.05 FT

*As presented on the 95% design plans.

4.1.1 Bridge Foundation Selection

A drilled shaft foundation system is proposed for the new abutments due to the relatively high axial and lateral loads. Spread footers and GRS-IBS were considered but determined impractical due to additional materials to extend the bridge span beyond lateral scour potential, time, and cost that would be required for construction. These shallow foundation systems would also prove to be disruptive to the proposed spill-through abutment configurations and geometry. A driven pile foundation was also considered but determined impractical due to the relatively short distance, in terms of pile construction, to bedrock potentially not meeting minimum length requirements, as well as the limited space available and accessibility to the site being difficult for standard pile driving equipment.

A drilled shaft foundation is feasible from a geotechnical perspective. Drilled shafts are able to provide a small footprint, support large foundation loads, and provide lateral resistance at a shallower elevation than driven piles. Based solely on hydraulic recommendations and assumptions stated in the Final Hydraulics Report (December 2021), scour potential as measured from the thalweg was determined to be present at the bridge abutments. Based on available data, Page | 13 it was determined by the combined team of Bridge, Hydraulics, and Geotechnical Engineers that drilled shafts would provide the best foundation system for this bridge.

The following final bridge load factored for the strength limit state was provided by the CFL bridge engineer in January 2022:

Both abutments = 255 kips (per shaft; ×3-24 inch shafts per abutment)

4.1.2 Site Characterization

The subsurface profile was assumed to be sand underlain by basalt bedrock (strong, R4, bedrock) for analysis purposes. Although gravel, silt, cobbles, and rock fragments were encountered in the designated borehole, the subsurface materials, in general, were of a sand-like nature and composition. Groundwater was also assumed to be at the channel thalweg elevation of 7,034.3 feet.

4.1.3 Drilled Shaft Axial Resistance

Drilled shafts for the Norris Creek Bridge will be socketed into basalt bedrock. The side resistance provided by overburden soils and the rock socket are neglected for the shaft capacity analysis when shafts are socketed into competent bedrock. Side resistance is neglected due to potential strain-softening behavior of the sidewall, degradation of material in the borehole wall, and uncertainty of roughness in the socket sidewall. The competent bedrock is considered non-scourable;

therefore, depth of scour was only considered in effects on vertical stress.

The UCS values of the competent bedrock were somewhat variable due to the fact that three of the four samples did not meet the required specimen length to diameter ratio, between 2.0:1 and 2.5:1, required by ASTM D 7012 (Table 3.4). Since these specimens were in non-conformance, the individual accepted value of 13,090 psi for abutment 2, was used for UCS to evaluate the axial capacities of the drilled shafts. This value was also applied to abutment 1 where drilling could not be performed.

The shaft tip axial bearing resistance was calculated in accordance with the provisions of Article 10.8.3.5.4c. Based on the assumption of basaltic or otherwise very blocky and fractured bedrock, the tip resistance was calculated using Equations 10.8.3.5.4c-2 and 10.8.3.5.4c-3.

𝑞𝑞𝑝𝑝 = 𝐴𝐴 + 𝑞𝑞𝑢𝑢 �𝑚𝑚𝑏𝑏

𝐴𝐴

𝑞𝑞𝑢𝑢

+ 𝑠𝑠� 𝑎𝑎

𝐴𝐴 = 𝜎𝜎′𝑣𝑣𝑏𝑏 + 𝑞𝑞𝑢𝑢 �𝑚𝑚𝑏𝑏

𝜎𝜎′𝑣𝑣𝑏𝑏 𝑞𝑞𝑢𝑢

+ 𝑠𝑠� 𝑎𝑎

Page | 14

In these equations, mb, s, and a are Hoek-Brown strength parameters for fractured rock masses and qu is the unconfined compressive strength of intact rock. σ'vb is the vertical stress at the tip elevation. A minimum estimated tip elevation for each foundation element has been used to calculate the nominal and factored tip resistance for various socket geometries at the strength limit state for each foundation element. This minimum tip elevation assumes a rock socket length equal to at least 150 percent of the diameter of the shaft (36 inches for a 24-inch diameter shaft). The factored resistance for the strength limit state was calculated by applying a 0.50 resistance factor for tip resistance. Based on the aforementioned calculations and the selected drilled shaft diameter of 24 inches, a minimum rocket socket length of 3 feet (36 inches) is required to meet axial resistance. The rock socket length shown in the plans has been rounded up to 4 feet per guidance from the bridge engineer and due to the limited geotechnical investigation. Assumed tip elevations and resistances are summarized on Table 4.2. The surface elevations referenced on this table are located at approximately the bottom of the new abutment caps, or the top of drilled shafts, as discussed with the Bridge Engineer and noted in Table 4.1. Overburden and bedrock depths were only confirmed at abutment 2 in boring BH21-01 and assumed to be similar at abutment 1. The geotechnical engineer should be notified if actual subsurface conditions do not meet anticipated conditions.

Table 4.2 - Shaft Tip Resistance in Rock

STRUCTURE

ELEMENT

TOP OF SHAFT

ELEV.

(feet)

ESTIMATED

SHAFT

LENGTH

(feet)

ESTIMATED

TIP ELEV.

(feet)

NOMINAL

TIP

RESISTANCE

(kip)

FACTORED

TIP

RESISTANCE

(kip) Abutment 1

(west) 7,038.35 10.35 7,028.0 1,573.0 786.7

Abutment 2 (east) 7,039.05 11.05 7,028.0 1,573.0 786.7

*Estimated bedrock elevation assumed to be at approximately 7,032 feet per boring BH21-01.

4.1.4 Group Effects on Axial Resistance

The resistance of a shaft group to the applied axial loads is not necessarily the sum of the axial resistance of individual shafts within the group. The zone of influence from an individual shaft in a shaft group may intersect with other shafts, depending on the shaft spacing. Historically, the efficiency of groups of drilled shafts has not been a concern as long as the center-to-center spacing between shafts is greater than three times the shaft diameter (3D) to avoid interference between adjacent shafts, assuming a single row shaft group configuration. An efficiency factor (η) should be applied for spacing less than 3D as shown in Table 10.8.3.6.3-1.

Besides the effect of overlapping zones of influence, effects of construction on ground conditions in and around the group can be significant. Excavated deep foundation elements in cohesionless soils tend to decrease the effective stress of the surrounding soils. Poorly controlled shaft

Page | 15 construction methods can result in soil loosening during drilling and adversely reduce the lateral stress around other shafts within the group. Casing driven in advance of excavation may increase the relative density and effective stress of the surrounding soil and prevents caving of overburden material.

4.1.5 Lateral Loads on Deep Foundations

Lateral load analysis was performed by the bridge engineer using the software program LPILE developed by Ensoft, Inc. This program analyzes a single pile or shaft considering deflection as a function of design loads, foundation construction, and subsurface conditions. Table 4.3 provides LPILE input parameters for the foundation soils based on available subsurface information and presumptive engineering correlations. We recommend that lateral support above the scour elevation defined in the CFLHD Hydraulics Report be neglected due to potential loss of material during the design flood event. It is also recommended that lateral support within five feet of the final road grade be neglected due to the potential loss of support from frost penetration or other shallow ground disturbance.

Table 4.3 - LPILE Parameters

APPROXIMATE

ELEVATION

(ft)

DEPTH BELOW

TOP OF SHAFT

(ft)

LPILE P-Y

MODEL

EFFECTIVE

UNIT WEIGHT,

ɣ’ (pcf)

FRICTION

ANGLE, Փ

(deg)

HORIZONTAL

SUBGRADE

MODULUS, Ks

(pci) MODEL No. 1 (SAND AND STRONG ROCK)

7,038.35 to 7,034.30 (Abutment 1)

7,039.05 to 7,034.30 (Abutment 2)

0 to 4.1 (Abutment 1)

0 to 4.8 (Abutment 2)

Sand (Reese) 127 38 90

7,034.30 to 7,032.40 (Abutments 1 & 2)

4.1 to 6.0 (Abutment 1)

4.8 to 6.7 (Abutment 2)

Sand (Reese) 64.6 38 60

TRANSITION TO ROCK PROPERTIES

LPILE P-Y

MODEL

EFFECTIVE

UNIT WEIGHT

(PCF)

UNIAXIAL

COMPRESSIVE

STRENGTH (PSI)

7,032.40 to 7,010.35 (Abutment 1)

7,032.40 to 7,011.05

6.0 to 28.0 (Abutment 1)

6.7 to 28.0 (Abutment 2)

Strong Rock

(Vuggy Limestone)

145 13,090

Material properties provided are for single shafts and do not account for the reduced lateral resistance of shafts in a group. P-multipliers are a function of the number of rows of shafts and center-to-center shaft spacing in the direction of loading. P-multipliers are required even for a single row of shafts if the center-to-center spacing is less than 5 shaft diameters. P-multipliers are

Page | 16 specified in Table 10.7.2.4-1 in AASHTO. When this analysis method is used, the resistances at the strength limit state as represented by the P-y curves should not be factored since they already represent the nominal conditions.

4.1.6 Settlement

A resistance factor of 1.0 for the service limit state is recommended to assess the ability of the foundation to meet the specified deflection criteria. Elastic settlements will occur immediately and be essentially complete at the end of construction and are estimated to be less than one inch at all locations based on the loads provided. Differential settlements are not anticipated. Shaft group settlement is not anticipated.

4.1.7 Field Testing

Steel crosshole sonic logging tubes (1.5-inch diameter steel tubes) should be installed in all drilled shafts prior to concrete placement for integrity testing. The recommended number of access tubes and tube spacing are dependent on the selected shaft diameter, typically one access tube per 12-inches of shaft diameter, with a minimum of three access tubes per shaft. The crosshole sonic logging tests should be conducted in accordance with ASTM D-6760 and FP-14 for quality assurance/quality control of the drilled shafts.

4.1.8 Scour Potential and Erosion

Contraction scour and local abutment scour depths were estimated by the hydraulics engineer.

Section 4.4.3 in the Final Hydraulic Report details the scour depth estimates.

Provision of scour countermeasures can be used to mitigate scour effects and reduce maintenance.

For additional scour and countermeasure information please refer to the previously mentioned Final Hydraulic Report dated December 2021.

4.2 ABUTMENT & WINGWALL DESIGN

Abutments and wingwalls should be designed to resist lateral earth pressures and other applicable lateral loads in accordance with AASHTO. Lateral earth pressure is influenced by the strength of the abutment backfill, the presence or absence of water, and the ability of the abutment or wall to move in response to lateral loads. Other loads, such as live loads, construction loads, and soil compaction loads should also be considered in the design.

Unbalanced water behind an abutment or wall adds significant lateral pressure and should be avoided by using free draining gravity outlets for water. Abutment and wingwall backfill should consist of structural backfill as specified in Section 704.04 of FP-14.

The coefficient of at-rest earth pressure should be used for design if the abutment is so restrained that it cannot be expected to rotate (deflect at the top) 0.002 times the wall height. Where deflection

Page | 17 of the abutment can be expected, a coefficient of active earth pressure should be used for wall design. Active and at-rest lateral earth pressures of native materials and properly placed and compacted structural backfill above the water table are presented in Table 4.4. The values are unfactored loads and assume that the surface of the soil slope behind the wall is horizontal.

Table 4.4 - Lateral Earth Pressures for Bridge Abutments & Wingwalls

BACKFILL TYPE

ASSUMED

BACKFILL

PROPERTIES

CASE

UNFACTORED

EQUIVALENT

FLUID DENSITY

(PCF)

NOMINAL

FRICTION

FACTOR

Structural Backfill c = 0 psf φ = 34 deg.

γ = 125 pcf

Active 35 0.67

At-Rest 55 0.67

Native Soil c = 0 psf φ = 38 deg γ = 127 pcf

Active 30 0.78

At-Rest 49 0.78

4.3 PERMANENT EARTHWORKS

4.3.1 Embankment Construction

Embankment construction will be necessary with regards to the concrete wingwalls. Construct permanent long-term embankments with a maximum slope ratio of 1V:2H to maintain slope stability and promote slope vegetation.

4.3.2 Shrink/Swell Recommendations

On-site soils expected to be encountered within the project limits generally consist of silty and clayey sands with varying amounts of gravel. It is estimated that these soils will have a 10 percent shrink percentage, corresponding to a shrink/swell factor of 0.90. The recommended shrink/swell factor is based on a combination of standard tabled values for common materials in the FLH Technical Guidance Manual (2006) and experience with other CFLHD projects in similar materials.

4.4 CONSTRUCTION CONSIDERATIONS

Roadway Excavation: Excavate using equipment capable of removing the material while preventing material from escaping outside the construction limits.

Based on the subsurface investigation and surface geologic mapping, the rock encountered, primarily basalt, is expected to be rippable in the areas surrounding the abutments of the Norris Creek Bridge; however, final determination of rock rippability is the responsibility of the contractor. Shear wave velocity of the geologic layers was not evaluated by geophysical methods.

Page | 18

However, based on Table D.1 in Appendix D, the rock encountered can be presumed to be within the extremely hard rock description. Additional information regarding the excavation characteristics of rock and rippability charts can also be found in Appendix D.

Evidence of definitive in-place bedrock was encountered from the subsurface investigation detailed in this report. Appropriate construction equipment should be mobilized to the site based on the rock information detailed above. The handling of boulders of at least 6 feet in diameter will be required for excavations in the project area. The contractor is responsible for the safety of excavations and shoring design.

Drilled Shafts: The contractor will be required to submit a drilled shaft construction plan as required in Section 565.04 of the FP-14 which includes the outlining of proposed methods to maintain borehole stability, manage the excavation of boulders, concrete placement, and dewatering.

Basaltic rock was encountered at the exploration borehole. Bedrock elevation may be variable based on the subsurface geology and the limited subsurface investigation and, therefore, the contractor should be prepared to extend the drilled shafts by 20 percent, if necessary, according to Section 565.06(a). Be prepared for cobbles and boulders ranging in size from approximately 12 to 72 inches and larger. Loose subsurface materials were also encountered at shallow depths, which may warrant the use of temporary casing.

It is anticipated that groundwater will be encountered at the foundation excavations. The likelihood of flowing sands could also present a challenge for the driller as the mixture of fine sand and water could infiltrate the drilling equipment. The contractor should be prepared to maintain the excavation through flowing sand conditions.

Dewatering: Dewatering may be needed due to water infiltration from the river. Perform dewatering according to Section 208.07 of the FP-14.

Slope Instability: Slopes could become unstable during construction operations due to precipitation, flooding events, or heavy loading on soft subgrade soils. Precautions should be taken if movement or cracking is observed. Seepage is a contributor to slope instability and similar dewatering and stabilization methods could be used to suspend slope movement. The contractor is responsible for temporary working platforms including those needed for cranes and shaft drilling rigs.

Hard Layers: Hard layers, such as rock, were encountered during the geotechnical investigation.

The Contractor should be prepared with appropriate equipment based on the local geology as discussed in Sections 2.1 and 2.2, and Appendix D (Rippability).

Page | 19

4.5 SPECIFICATIONS

Special provisions were provided prior to the 95% design milestone to be consistent with geotechnical recommendations stated above and were incorporated into the special contract requirements (SCR) to amend the FHWA Standard Specification for Construction of Roads and Bridges on Federal Highway Projects; known as FP-14.

4.6 DISCLAIMER/LIMITATIONS CLAUSE

The recommendations in this report are based on the data obtained from exploratory borings, field review, and laboratory test results. The results of these explorations and tests represent conditions at the specific locations indicated. Subsurface variations across the site are likely and may not become evident until excavation is performed. The Analysis and Recommendations sections in this report include interpretations and recommendations developed by the Government in the process of preparing the design. These interpretations are not intended as a substitute for the personal investigation, independent interpretation, and judgment of the Contractor.

Page | 20

SECTION FIVE - References

American Association of State Highway and Transportation Officials (AASHTO), 2017, LFRD Bridge Design Specifications, 8th Edition.

Brown, Dan A., Turner, John P., and Castelli, Raymond J., 2010, “Drilled Shafts: Construction Procedures and LRFD Design Methods,” NHI Course No. 132014, Geotechnical Engineering Circular No. 10, Report No. FHWA NHI-10-016, dated May.

Federal Highway Administration (FHWA), 2007, Geotechnical Technical Guidance Manual, dated May.

Federal Highway Administration (FHWA), 2008, Federal Lands Highway Project Development and Design Manual (PDDM), dated March.

Federal Highway Administration (FHWA), 2014, Standard Specifications for Construction of Roads and Bridges on Federal Highway Projects FP-14.

Federal Highway Administration (FHWA), 2017, Soil Description and Identification Guidelines, dated December.

Federal Highway Administration (FHWA), 2017, Rock Characterization Guidelines, dated December.

Federal Highway Administration (FHWA), 2021, “CA ERFO 05S07(1) Norris Creek Bridge Final Hydraulics Report,” dated December.

Hawthorne Cat, 2018, “Caterpillar Performance Handbook,” Edition 48, dated June.

Hoek E. & Marinos, P., 2000. “GSI: A Geological Friendly Tool for Rock Mass Strength

Estimation.”

Huber, N.K., 1968, “Geologic Map of the Shuteye Peak Quadrangle, Sierra Nevada, California”:

U.S. Geologic Survey, Geologic Quadrangle Map GQ-728, scale 1:62,500.

Isenhower, William M., Wang, Shin-Tower, and Vasquez, Gonzalo L., 2016, “Technical Manual for LPile 2016 (Using Data Format Version 9),” Ensoft, Inc., dated January.

National Park Service (NPS), 2018, “Series: Physiographic Provinces, Cascade-Sierra Mountains

Province,” updated April 30, <https://www.nps.gov/articles/cascadesierra.htm>.

Peck, D.L., 1964, “Preliminary Geologic Map of the Merced Peak Quadrangle, California”: U.S.

Geologic Survey, Mineral Investigations Field Studies Map MF-281, scale 1:48,000.

Peck, D.L., 1980, “Geologic Map of the Merced Peak Quadrangle, Central Sierra Nevada, California”: U.S. Geologic Survey, Geologic Quadrangle Map GQ-1531, scale 1:62,500.

State of California (CA.gov), 2019, “Geologic Hazards,”

< https://www.conservation.ca.gov/cgs/geohazards>, Accessed March 3, 2021.

State of California (CA.gov), 2020, Caltrans ARS Online (v3.0.2), <https://arsonline.dot.ca.gov/index.php?>, Accessed September 16, 2021.

Page | 21

The University of Texas at Austin Jackson School of Geosciences (Texas Geosciences), 2021, “Some Useful Numbers on the Engineering Properties of Materials (Geologic and Otherwise),” GEOL 615, <https://www.jsg.utexas.edu/tyzhu/files/Some-Useful- Numbers.pdf>, Accessed February 18.

U.S. Department of Agriculture (USDA), 2012, “National Engineering Handbook (NEH), Part 631 Geology,” Chapter 4: Engineering Classification of Rock Materials, dated January.

U.S. Geological Survey (USGS), 2020(a), “Quaternary Fault and Fold Database of the United States,” Interactive fault map & database search, USGS Earthquake Hazards Program, <https://www.usgs.gov/natural-hazards/earthquake-hazards/faults?qt-science_support_page_related_con=4#qt-science_support_page_related_con>.

U.S. Geological Survey (USGS), 2020(b), “Vs30 Map Viewer,” online map, USGS Earthquake Hazards Program, <https://earthquake.usgs.gov/data/vs30/>.

U.S. Geologic Survey (USGS), 2020(c), “U.S. Seismic Design Maps,” USGS Earthquake Hazards Program, <http://earthquake.usgs.gov/designmaps/us/application.php> & <https://earthquake.usgs.gov/ws/designmaps/aashto-2009.json?latitude=34&longitude=- 118&siteClass=C&title=Example>.

Weaver, J.M., (1975), “Geologic Factors Significant in the Assessment of Rippability,” The Civil Engineer in South Africa (Die siviele ilngenieur in Suid-Afrika), Volume 17, Issue 12, pgs. 313-316.

PLATES

PROJECT VICINITY MAP,

GEOLOGY MAP & LEGEND, AND

GEOTECHNICAL BORING LOCATIONS MAP

STATE PROJECT

CENTRAL FEDERAL LANDS HIGHWAY DIVISION

FEDERAL HIGHWAY ADMINISTRATION

U.S. DEPARTMENT OF TRANSPORTATION

NOT TO SCALE

PLATE

PROJECT VICINITY MAP

CA

NORRIS CREEK BRIDGE

CA ERFO SIERRA NF 05S07(1)

July 29, 2021.

Google Maps, 2021. Norris Creek Bridge. Google Maps [online].

Eureka

SAN

FRANCISCO

LOS

ANGELES

San

Diego

Sacramento

OREGON

N

EV

A D

A

ARIZONA

MEXICO

Redding

KEY MAP OF CALIFORNIA

INTERSTATE

INTERSTATE

INTERSTATE

INTERSTATE

INTERSTATE

INTERSTATE

INTERSTATE

Project Location

(37.511399°, -119.311606°)

Project Location

U.S. DEPARTMENT OF TRANSPORTATION

NOT TO SCALE

PLATE

CA

NORRIS CREEK BRIDGE

CA ERFO SIERRA NF 05S07(1)

GEOLOGY MAP

U.S. Geologic Survey, Geologic Quadrangle Map GQ-728, 1:62,500.

Huber, N.k., 1968, Geologic map of the Shuteye Peak quadrangle, Sierra Nevada, California, U.S. Geological Survey, Geologic Quadrangle Map GQ-1531, 1:62,500.

Peck, D.L, 1980,Geologic map of the Merced Peak quadrangle, central Sierra Nevada, California, (37.511399°, -119.311606°) Project Location

GQ-1531

GQ-728

U.S. DEPARTMENT OF TRANSPORTATION

PLATE

CA

NORRIS CREEK BRIDGE

CA ERFO SIERRA NF 05S07(1)

LEGENDS

GEOLOGY MAP

U.S. Geological Survey, Geologic Quadrangle Map GQ-1531, 1:62,500.

Peck, D.L, 1980,Geologic map of the Merced Peak quadrangle, central Sierra Nevada, California, Map Legend GQ-1531 Map Legend GQ-728

U.S. Geologic Survey, Geologic Quadrangle Map GQ-728, 1:62,500.

Huber, N.k., 1968, Geologic map of the Shuteye Peak quadrangle, Sierra Nevada, California, U.S. DEPARTMENT OF TRANSPORTATION

NOT TO SCALE

PLATE

CA

NORRIS CREEK BRIDGE

CA ERFO SIERRA NF 05S07(1)

July 29, 2021

Google Maps, 2021. Norris Creek Bridge. Googla Maps [online].

LOCATIONS

GEOTECHNICAL BORING

Latitude Longitude Elevation

BH21-01

Location

Boring Locations

Boring

CFL survey data.

Boring locations are approximate. Surface elevations acquired from

BH21-01

37.511361° -119.309444°East Abutment 7,044.9 ft

APPENDIX A

FIELD EXPLORATION PROGRAM

APPENDIX A

FIELD EXPLORATION PROGRAM

A.1 INTRODUCTION

The Central Federal Lands Highway Division (CFLHD) Geotechnical Section completed a field exploration program for CA ERFO SIERRA NF 05S07(1), Norris Creek Bridge, on November 2nd, 2021. The scope of work for the field exploration program included drilling a total of one boring to a depth of approximately 28 feet. The boring was drilled near the east bridge abutment.

The field exploration program was coordinated and observed by a Geotechnical Engineer from CFLHD. The field exploration location is illustrated on the “Geotechnical Boring Locations” sheet in Plate 4. The individual boring log is attached. This log represents a compilation of field and laboratory data and description of the soil samples by CFLHD Geotechnical personnel. The methods used to conduct the field exploration program are described below. Photos of drilling equipment and field exploration activities are included in Appendix C. All soil and rock samples collected during the field exploration program were transported to the CFLHD Materials Laboratory in Lakewood, Colorado for testing. A summary of the laboratory testing program is provided in Appendix B.

A.2 EXPLORATIONS

Borings

Taber Drilling of West Sacramento, California provided the drilling services for the soil and rock boring.