Appendix E: Preliminary Foundation Report

County of Calaveras – Dogtown Road over San Domingo Creek Project Initial Study and Mitigated Negative Declaration

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Appendix E: Preliminary Foundation Report

PRELIMINARY FOUNDATION REPORT

Dogtown Road Bridge over San Domingo Creek Calaveras County, California

Prepared by:

Blackburn Consulting 2491 Boatman Avenue

West Sacramento, CA 95691 (916) 375-8706

May 14, 2015

Prepared for:

Mark Thomas & Company, Inc. Sacramento, CA

File No. 2343.6.3.4 May 14, 2015 Mr. Zach Siviglia, P.E. Mark Thomas & Company, Inc. 7300 Folsom Blvd., Suite 203 Sacramento, CA 95826 Subject: PRELIMINARY FOUNDATION REPORT

Dogtown Road Bridge over San Domingo Creek Calaveras County, California

Mr. Siviglia: Blackburn Consulting (BCI) is pleased to submit this Preliminary Foundation Report for the Dogtown Road Bridge over San Domingo Creek Project in Calaveras County, California. BCI prepared this report in accordance with our January 22, 2013 Subconsultant Agreement for the project. Thank you for the opportunity to be part of your design team. Please call if you have questions or require additional information. Sincerely;

BLACKBURN CONSULTING Reviewed by,

David J. Morrell, C.E., G.E. Robert B. Lokteff, C.E., G.E. Senior Project Manager Principal Distribution: PDF to Mark Thomas& Company, Inc.

West Sacramento Office: 2491 Boatman Ave. West Sacramento, CA 95691 (916) 375-8706 Fax (916) 375-8709

Main Auburn Office: (530) 887-1494 Fresno Office: (559) 438-8411

Modesto Office: (209) 522-6273

Geotechnical Geo-Environmental Construction Services Forensics

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PRELIMINARY FOUNDATION REPORT Dogtown Road Bridge over San Domingo Creek

Calaveras County, California

TABLE OF CONTENTS 1 INTRODUCTION ............................................................................................. 1

1.1 Purpose ....................................................................................................................... 1 1.2 Scope of Services ....................................................................................................... 1 1.3 Site Location and Description .................................................................................... 1 1.4 Project Description ..................................................................................................... 1

2 SUBSURFACE CONDITIONS ....................................................................... 1 3 SITE GEOLOGY .............................................................................................. 2

3.1 Regional Geology ...................................................................................................... 2 3.2 Local Geology ............................................................................................................ 2 3.3 Ground Water ............................................................................................................. 2

4 SCOUR EVALUATION ................................................................................... 3 5 CORROSION EVALUATION ........................................................................ 3 6 SEISMIC DATA AND EVALUATION .......................................................... 3

6.1 Ground Motion Study ................................................................................................ 3 6.2 Liquefaction Evaluation ............................................................................................. 4 6.3 Fault Rupture Study ................................................................................................... 5 6.4 Seismic Settlement ..................................................................................................... 5 6.5 Seismic Slope Instability............................................................................................ 5

7 PRELIMINARY FOUNDATION RECOMMENDATIONS ....................... 5 8 CONSTRUCTION CONSIDERATIONS ...................................................... 6 9 LIMITATIONS ................................................................................................. 6 APPENDIX A

Figure 1 Vicinity Map Figure 2 Site Plan Figure 3 Geologic Map Figure 4 Preliminary Design Response Spectrum

PRELIMINARY FOUNDATION REPORT Dogtown Road Bridge over San Domingo Creek BCI Job No. 2343.6.3.4 Calaveras County, California May 14, 2015

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1 INTRODUCTION

1.1 Purpose

Blackburn Consulting (BCI) prepared this Preliminary Foundation Report for the Dogtown Road Bridge over San Domingo Creek Project in Calaveras County, California. BCI prepared this report for preliminary design purposes only. Do not use or rely upon this report for final project design. BCI will provide a Foundation Report for final design.

1.2 Scope of Services

To prepare this report, BCI:

Discussed the project with Mr. Zach Siviglia and Mr. Jason Hickey with Mark Thomas & Company, Inc. (MTCo).

Reviewed published geologic maps and literature pertaining to the site.

Performed a May 3, 2013 field review of existing conditions at the bridge location.

Performed preliminary engineering and seismic analysis.

1.3 Site Location and Description

The site is located on Dogtown Road at San Domingo Creek, approximately 3.4 miles north of Angels Camp in Calaveras County, California. Site coordinates are approximately latitude 38.133303° N and longitude 120.565760° W. We show the site location on Figure 1 (Vicinity Map) in Appendix A. The existing bridge was built in 1940 and consists of an 14-foot wide by 43-foot long steel girder bridge with a timber deck and timber tailing, supported on reinforced concrete abutment walls and pier walls founded on spread footings. At the project location, San Domingo Creek flows to the south on a shallow gradient.

1.4 Project Description

The project will replace the existing bridge with a new two-span structure on a realigned roadway located about 25 feet upstream of the current bridge location. Tentatively, the new bridge will be a two-span cast-in-place concrete slab structure on reinforced concrete abutment walls with cantilever wingwalls. We display the preliminary site plan for the project as Figure 2 in Appendix A.

2 SUBSURFACE CONDITIONS

During our May 3, 2013 field review, BCI observed metasedimentary rock outcrops (predominantly slate) within portions of the streambed beneath and both upstream and downstream of the bridge. Where not exposed in the streambed, the rock is overlain primarily by gravelly sand with cobbles


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and boulders. Within the bank areas, the rock appears to be overlain by a thin layer of soil containing cobble and boulder-size rock fragments. Following bridge type selection, BCI will drill, log and sample one boring at each abutment area to depths of 30 to 40 feet below existing grade to obtain subsurface soil, rock and groundwater data. Soil and rock samples will be retrieved from the borings for laboratory testing. Based on the rock outcrops present at the bridge site, we anticipate drilling through the shallow overlying soil using auger and/or rotary drill methods, followed by rock coring using diamond-core equipment.

3 SITE GEOLOGY

3.1 Regional Geology

The project site is located within the foothills of the Sierra Nevada geomorphic province. This province is a tilted fault block with a length (north-south) of approximately 400 miles. It has a steep eastern face and a gently sloping western slope that is buried beneath sediments of the Great Valley (Sacramento and San Joaquin Valleys). Rock of the Sierra Nevada is primarily igneous and metamorphic units of diverse age and composition, including plutonic, volcanic, metavolcanic, and metasedimentary rocks. Rock structure (faulting, foliation, etc.) has a predominant northwest-southeast trend.

3.2 Local Geology

Published geologic literature1 indicates that the site is underlain metasedimentary rock (chert, argillite, and slate) of the Paleozoic Calaveras Complex. Our field review confirms that the site is underlain by metasedimentary rock consisting predominantly of slate. The rock is slightly to moderately weathered and moderately to intensely fractured. The intensely fractured rock is, in places, friable and breaks down to small fragments of angular rock. We present a geologic map showing the site location as Figure 3 in Appendix A.

3.3 Ground Water

We anticipate that local ground water levels at the site will be at or near the creek water surface elevation throughout the year. At the time of our May 3, 2013 field review, the water depth in the channel was less than a foot.

1Wagner, D.L., et. al., 1981, Geologic map of the Sacramento quadrangle, California, 1:250,000: California Division of Mines and Geology, Regional Geologic Map 1A, scale 1:250,000.


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4 SCOUR EVALUATION

A scour analysis will be completed for this project by others. Our May 3, 2013 field review indicates shallow rock is present at the site given rock outcrops observed in the channel bottom at several locations in the vicinity of the bridge. We anticipate that design scour depths will not exceed more than a few feet below the existing channel bottom elevation at the bridge site, depending on the actual rock surface elevation at the proposed abutments and the rock quality (weathering, hardness, fracturing) determined from the future borings.

5 CORROSION EVALUATION

BCI will perform soil and/or rock corrosivity testing on samples retrieved from the future borings in order to evaluate site corrosivity to foundation elements. Given the site location and geologic setting, we anticipate that the site will not be considered corrosive to foundation elements per current Caltrans corrosion guidelines.

6 SEISMIC DATA AND EVALUATION

6.1 Ground Motion Study

BCI used the Caltrans ARS Online Version 2.2.06 (web-based tool) to evaluate the preliminary minimum design acceleration response spectrum (Design Response Spectrum) for preliminary design of the bridge. Caltrans Seismic Design Criteria Version 1.6 (November 2010) defines the Design Response Spectrum as the maximum design envelope across the period spectrum developed by considering both deterministic and probabilistic spectra. Table 1 provides a summary of our ground motion study results.

TABLE 1: GROUND MOTION STUDY RESULTS Peak Ground Acceleration (PGA) 0.22g

*VS30 (Small Strain Shear Wave Velocity) 500 meters per second

Near Fault Factors

Period = 0.01-0.5 (NFF = 1.00), Period = 0.60 (NFF = 1.04), Period = 0.70 (NFF = 1.08), Period = 0.85 (NFF = 1.14),

Period = 1.0-5.0 (NFF = 1.20) Basin Amplification Factor N/A

Controlling Deterministic Scenario

Minimum Deterministic Spectrum combined with Poorman Gulch Fault (Fault Identification No. 421;

Style: Normal; Maximum Moment Magnitude (Mmax) = 6.3; Site to Fault Rupture Distance (RRUP) = 10.92

km)

DESIGN RESPONSE SPECTRUM

Design Response Spectrum is a combination of the Minimum Deterministic Spectrum, Deterministic

Spectrum (Poorman Gulch Fault), and the Probabilistic Spectrum (probability of exceedance equal to 5% in 50

years, a 975-year return period). *Preliminary estimate for anticipated moderately to intensely fractured rock conditions.


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Figure 4 contains a graphical display of our recommended Preliminary Design Response Spectrum. We include the tabular data used to create the spectrum in Table 2.

TABLE 2: PRELIMINARY DESIGN RESPONSE SPECTRUM DATA

Period SA Period SA Period SA Period SA

0 0.215 0.085 0.388 0.35 0.42 1.4 0.116 0.01 0.215 0.09 0.402 0.36 0.414 1.5 0.109 0.02 0.219 0.095 0.415 0.38 0.402 1.6 0.104

0.022 0.222 0.1 0.428 0.4 0.391 1.7 0.099 0.025 0.226 0.11 0.448 0.42 0.377 1.8 0.094 0.029 0.232 0.12 0.465 0.44 0.363 1.9 0.09 0.03 0.233 0.13 0.481 0.45 0.357 2.0 0.086

0.032 0.238 0.133 0.485 0.46 0.351 2.2 0.077 0.035 0.245 0.14 0.493 0.48 0.339 2.4 0.07 0.036 0.247 0.15 0.505 0.50 0.327 2.5 0.067 0.04 0.256 0.16 0.509 0.55 0.298 2.6 0.064

0.042 0.261 0.17 0.511 0.60 0.273 2.8 0.058 0.044 0.266 0.18 0.513 0.65 0.251 3.0 0.054 0.045 0.269 0.19 0.513 0.667 0.245 3.2 0.05 0.046 0.271 0.20 0.514 0.70 0.233 3.4 0.046 0.048 0.276 0.22 0.502 0.75 0.217 3.5 0.044 0.05 0.281 0.24 0.489 0.80 0.203 3.6 0.043

0.055 0.297 0.25 0.483 0.85 0.19 3.8 0.04 0.06 0.313 0.26 0.477 0.90 0.179 4.0 0.037

0.065 0.329 0.28 0.464 0.95 0.172 4.2 0.036 0.067 0.335 0.29 0.458 1.0 0.165 4.4 0.034 0.07 0.344 0.30 0.451 1.1 0.147 4.6 0.033

0.075 0.359 0.32 0.438 1.2 0.133 4.8 0.032 0.08 0.374 0.34 0.426 1.3 0.123 5.0 0.031

6.2 Liquefaction Evaluation

Liquefaction is a secondary effect associated with seismic loading. It can occur when saturated, loose to medium dense, granular soils (generally within 50 feet of the surface), or specifically defined cohesive soils, are subjected to ground shaking. Based on the shallow rock conditions at the site, we consider the potential for detrimental liquefaction to be very low to nonexistent.


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6.3 Fault Rupture Study

No active faults cross the site based on published mapping and the site is not within or adjacent to an Alquist–Priolo Earthquake Fault Zone for fault rupture hazard. BCI therefore considers the potential for fault rupture (and associated ground displacement) to adversely affect the proposed structure as very low to non-existent.

6.4 Seismic Settlement

During a seismic event, ground shaking can cause densification of granular soil above the water table that can result in settlement of the ground surface. Based on shallow rock conditions at the site, we consider the potential for detrimental seismic settlement to be very low to nonexistent.

6.5 Seismic Slope Instability

We consider the potential for seismic slope instability of the existing creek banks to be very low, limited to some potential for minor bank distortion.

7 PRELIMINARY FOUNDATION RECOMMENDATIONS

Based on the shallow rock conditions at the site, spread footings appear to be the most feasible foundation alternative for the new bridge. Cast-in-Drilled Hole (CIDH) pile “rock sockets” could also be used to support the bridge abutments, but would likely require rock coring and dewatering for installation. For spread footings, site foundation characteristics and/or constraints that affect the details of support level and bearing include:

Depth to rock and variation of rock surface along/across individual support lines,

Hard rock excavation to bearing levels,

Rock discontinuities (fractures/joints), and

Potential semi-detached blocks of rock within footing excavations. BCI recommends a preliminary presumptive allowable gross bearing capacity of 15 ksf for spread footings established below design scour depths and at least 2 feet into the underlying rock unit. Rock dowels/anchors are feasible if required to develop additional foundation lateral/uplift resistance. Driven piling is not considered feasible since these piles would not achieve sufficient penetration to resist lateral load demands.


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8 CONSTRUCTION CONSIDERATIONS

Excavation within the rock unit will be locally difficult, but should be generally achievable by use of air tools without blasting. Rock blasting may disrupt/degrade integrity of the surrounding rock and is discouraged. If necessary, perform blasting with light charges and under the direction of a licensed blasting contractor. BCI will further evaluate rock excavatability based on rock conditions encountered in the future borings. Excavations extending below the surface water level in the creek will likely encounter seepage. In addition, perched water above the underlying rock unit could seep into excavations during and shortly following the rainy season. We expect the seepage can be controlled with sump pumps/surface diversion methods.

9 LIMITATIONS

This Preliminary Foundation Report is not intended for final design. Once the foundation type and loading conditions are defined/confirmed, BCI will complete subsurface exploration, laboratory tests, and perform additional engineering evaluation/analysis to provide a design level Foundation Report. Do not use or rely on this report for different locations or improvements without the written consent of BCI.

Geotechnical Geo-Environmental Construction Services Forensics

APPENDIX A

Figure 1 – Vicinity Map

Figure 2 – Site Plan

Figure 3 – Geologic Map

Figure 4 – Preliminary Design Response Spectrum

11521 Blocker Drive, Suite 110

Auburn, CA 95603

Phone: (530) 887-1494

Fax: (530) 887-1495

www.blackburnconsulting.com

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Figure 1

May 2015

File No. 2343.6.3.4

SCALE: 1:48,000

VICINITY MAP

Hwy 49

SOURCE: USGS Calveritas Quadrangle, 7.5 Minute Series

topographic, dated 1962. Terrain Navigator Pro, Ver. 9.21.

NO SCALE

SITESacramento

SITE

Figure 2

11521 Blocker Drive, Ste 110

Auburn, CA 95603

Phone: (530) 887-1494

Fax: (530) 887-1495


Source: Figure 3, Area of Potential Effects by Mark Thomas & Company, Inc., dated July 2, 2014.

5/1

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Dogtown Road Bridge

at San Domingo Creek

Calaveras County, California

SITE PLAN

May 2015

File No. 2343.6.3.4


Auburn, CA 95603

Phone: (530) 887-1494

Fax: (530) 887-1495


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Figure 3

May 2015

File No. 2343.6.3.4

NO SCALE

GEOLOGIC MAP

SOURCE: Wagner, D.L., et. al., 1981, Geologic Map of the

Sacramento Quadrangle, 1:250,000: California Division of Mines

and Geology, Regional Geologic Map 1A, scale 1:250,000.

SITE

L E G E N D

Tm

Tg

Pzcc

Pzcv

Mehrten Formation (Andesitic conglomerate, sandstone, and breccia)

"Auriferous" Gravels

Calaveras Complex (Metasedimentary rock)

Calaveras Complex (Metavolcanic rock)


Auburn, CA 95603

Phone: (530) 887-1494

Fax: (530) 887-1495


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Figure 4

May 2015

File No. 2343.6.3.4

SOURCE: Caltrans ARS Online V2.206.

Appendix E: Preliminary Foundation Report

Documents

Transcript of Appendix E: Preliminary Foundation Report