210416_AGI Geotech_MatherB650.pdf

22725 Old Canal Road, Yorba Linda, CA 92887 - (714) 685-3900 - FAX (714) 685-3909 2640 Financial Court, Suite A, San Diego, CA 92117 - (858) 450-4040 - FAX (858) 457-0814 3100 Fite Circle, Suite 103, Sacramento, CA 95827 - (916) 368-2088 - FAX (916) 368-2188

5600 Spring Mountain Road, Suite 201, Las Vegas, NV 89146 - (702) 562-5046 - FAX (702) 562-2457

April 16, 2021 File No. 80977-01

AWEN Solutions Group 4196 Merchant Plaza, Suite 711 Woodbridge, VA 22192

Attention: Mr. Sam Altasaini Senior Project Architect

Subject: GEOTECHNICAL INVESTIGATION Proposed Mather Health Complex Project 10535 Hospital Way Mather, California

Dear Mr. Altasaini:

In accordance with your request, American Geotechnical performed a geotechnical investigation for the proposed improvements at the U.S. Department of Veteran Affairs Northern California Health Care

Systems Mather Campus. The purpose of our investigation was to evaluate the geotechnical conditions at the site in the areas of the proposed construction and to provide geotechnical parameters for design and construction of the proposed improvements. This report is prepared in general conformance with our proposal dated February 15, 2021, and your written authorization.

Based on our investigation, it is our opinion that the proposed Mather Health Complex improvements at the site, consisting of construction of a two-story connector building between Buildings B644, B645, and

B646 and a separate one-story corridor addition adjacent to Building B650, located at 10535 Hospital

Way in Mather, California, are feasible from a geotechnical standpoint, provided that the recommendations contained in this report are incorporated into the project plans and specifications.

The primary geotechnical considerations for the proposed site improvements will be expansive soil influence and long-term soil settlement. This report should be reviewed in detail prior to proceeding further with the planned development. When more detailed plans for the proposed development become available, they should be forwarded to this office for further review and comments.

File No. 80977-01 April 16, 2021

We thank you for choosing American Geotechnical and appreciate the opportunity to be of service.

Should you have any questions regarding the information contained in this report, please do not hesitate to contact our office.

Respectfully submitted, AMERICAN GEOTECHNICAL, INC.

Fei-chiu (Jerry) Huang, Ph.D. Douglas S. Santo Principal Engineer Chief Engineering Geologist G.E. 2601 C.E.G. 1866

Reviewed By:

Gregory W. Axten President/CEO G.E. 103

Enclosures: References Figures 1 – 8 Appendices

Distribution: Addressee (Email: saltasaini@awensolutions.com)

SP/80977-01 Geotechnical Investigation DS JH GWA 4-16-21 DL mailto:saltasaini@awensolutions.com

TABLE OF CONTENTS

1.0 INTRODUCTION

1.1 Purpose

1.2 Scope of Services

1.3 Site Description

1.4 Proposed Development

2.0 INVESTIGATION

2.1 Field Exploration

2.2 Laboratory Testing

3.0 SITE GEOLOGY AND SEISMICITY

3.1 Geologic Setting

3.2 Site Geology

3.3 Groundwater

3.4 100-Year Flood Zone

3.5 Land Subsidence

3.6 Fault Hazard

3.7 Seismic Hazards

3.7.1 Probabilistic Seismic

3.7.2 Historical Earthquakes

3.7.3 Liquefaction

3.7.4 Earthquake-Induced Landslides

3.8 Tsunamis and Seiches

4.0 GEOTECHNICAL CONSIDERATIONS

4.1 Subsurface Soil Conditions

4.2 Expansive Soil

4.3 Settlement

4.4 Foundation Concept

5.0 CONCLUSIONS AND RECOMMENDATIONS

5.1 Basis

5.2 Site Suitability

5.3 Seismic Design Considerations

5.3.1 2019 California Building Code (CBC) Seismic Design Parameters

5.4 Demolition

5.5 Earthwork

5.5.1 General

5.5.2 Site Preparation

5.5.3 Over-Excavation & Remedial Grading

5.5.4 Import Fill Material

5.6 Protection of Adjacent Structures

5.7 Slab-Foundation Design

5.7.1 Foundation Design

5.7.2 Slab-on-Grade

5.8 Exterior Flatwork

5.9 Soil Corrosivity

5.10 Concrete

5.11 Site Drainage

5.12 Utilities

5.13 Plan Review

5.14 Agency Review

5.15 Supplemental Consulting

5.16 Project Safety

6.0 REMARKS

REFERENCES

LIST OF FIGURES AND PLATES

Figure 1 – Site Location Map Figure 2 – Aerial View Map Figure 3 – Boring Locations Map Figure 4 – Regional Geologic Map Figure 5A – Geologic Cross-Section A-A’ Figure 5B – Geologic Cross-Section B-B’ Figure 6 – Fault Activity Map Figure 7 – Probabilistic Seismic Hazard Analysis Figure 8 – Historical Earthquake Map

APPENDICES

Appendix A – Boring Logs Appendix B – Laboratory Testing Data Appendix C – General Guidelines for Grading Projects

1.0 INTRODUCTION

1.1 PURPOSE

The purpose of this geotechnical investigation was to evaluate the existing geotechnical and geologic conditions at the site and to provide design and construction criteria for the proposed improvements at the site.

1.2 SCOPE OF SERVICES

The scope of work performed during this investigation included the following:

• Researched and reviewed regional geologic, hydrogeologic and geotechnical maps, documents, and reports available from the County of Sacramento, the California Geological Survey (CGS), and the U.S. Geological Survey (USGS);

• Prepared a Drilling Plan and obtaining approval from your office and the hospital facilities department,

• Coordinated our field activities with hospital personnel;

• Permitted proposed borings with the County of Sacramento;

• Marked proposed boring locations in the field and notified Underground Service Alert (USA) of our intention to drill;

• Conducted subsurface exploration consisting of drilling three (3), track-mounted CME, 4-inch diameter flight auger borings (AGSB-1, AGSB-2, and AGSB-3) to depths of 11.9 feet, 11.8 feet, and 16.8 feet, respectively;

• Performed detailed geotechnical logging of three exploratory borings by a field geologist using both visual and tactile methods in accordance with the Unified Soil Classification System

(USCS);

• Collected both bulk and relatively undisturbed samples considered representative of materials encountered during the subsurface exploration. Samples were collected utilizing both California ring sampler and Standard Penetration Test (SPT) sampler and transported back to our geotechnical laboratory for testing;

• Backfilled and tamped the three borings with the excavated spoils to achieve relatively compacted and unyielding conditions and restored the backfilled borehole locations back to pre-drill conditions to the maximum extent practical;

• Performed laboratory testing of selected representative soil samples collected during our subsurface exploration;

• Conducted engineering and geologic analyses of field and laboratory testing data;

• Preparation of this report summarizing the results of the investigation and our recommendations for the proposed site improvements.

1.3 SITE DESCRIPTION

The project site is about 1.7 miles east of the American River in Mather, California. The site is situated on a slightly elevated and dissected flood plain of the American River near ancestral Morrison Creek.

The site is underlain by non-marine sedimentary deposits of late Pleistocene age. Recent soils include

Holocene sheet flood and over bank deposits of the American River and Morrison Creek.

The Mather Campus is fully built and includes adjacent multi-story hospital buildings identified as

Buildings B644, B645, and B646. The site has paved connector walkways, driveways, parking lots, landscaping, and open space areas. The site is currently in operation. Site elevation is about 90 feet above mean sea level (MSL). The approximate location of the site is shown on Figure 1, Site Location

Map and Figure 2, Aerial View Map.

1.4 PROPOSED DEVELOPMENT

The proposed site improvements are to construct a two-story connector building between Buildings

B644, B645, and B646 and a separate one-story corridor addition adjacent to Building B650. No subterranean levels are planned for the proposed site improvements. During the construction of the proposed site improvements, all existing buildings will remain in operation. No other information is available about the proposed site development at this time.

It is our understanding that data obtained from this investigation will be used in the development of grading and foundation plans. Detailed building plans, including anticipated column loads and other structural details, are not currently available. When grading and construction plans become available, the plans should be forwarded to this office for further review and comment. The recommendations provided herein may be revised upon our review of the grading/construction plan(s) and further site analyses.

80977-01APR 2021AS SHOWN

FIGURE

AMERICAN GEOTECHNICAL, INC.

122725 Old Canal Road, Yorba Linda, CA 92887

(714) 685-3900 (714) 685-3909 www.amgt.com FILE NO.:DATE:SCALE:

SITE LOCATION MAP

MATHER HOSPITAL COMPLEX

N

PROJECT SITE

FIGURE

AMERICAN GEOTECHNICAL, INC.

222725 Old Canal Road, Yorba Linda, CA 92887

(714) 685-3900 (714) 685-3909 www.amgt.com FILE NO.:DATE:SCALE:

AERIAL VIEW MAP

MATHER HOSPITAL COMPLEX

PROJECT SITE

2.0 INVESTIGATION

2.1 FIELD EXPLORATION

A subsurface investigation was conducted at the site on March 6, 2021. Prior to the subsurface investigation, available background documents relevant to the site were reviewed and a detailed on-site review and notification of Dig-Alert service to mark the existing onsite utilities were performed.

Subsurface conditions were explored by drilling of three exploratory borings. The three exploratory borings (AGSB-1, AGSB-2, and AGSB-3) were drilled with a truck-mounted, 4-inch diameter flight auger drill rig. Borings were advanced to depths of 11.9 feet, 11.8 feet, and 16.8 feet below ground surface (bgs), respectively. Drilling refusal was encountered in all three borings at the depths indicated.

Approximate boring locations are shown on Figure 3, Boring Location Map.

The borings were logged by a field geologist using visual and tactile methods in accordance with the

Unified Soil Classification System (USCS). Bulk and relatively undisturbed drive samples, considered representative of subsurface materials, were collected at regular intervals during drilling. Borings were backfilled with excavated spoils, tamped to a relatively compacted and unyielding condition, and restored back to the pre-drill conditions to the maximum extent practical. Soil samples collected at the site were transported to our laboratory for testing.

Drive samples from test borings were obtained with a 2.5-inch inside diameter (3.0-inch outside diameter) split-barrel, thin-wall California ring sampler equipped with brass liner rings and a standard split-spoon sampler with dimensions in accordance with ASTM Standard Test Method D1586. Both samplers were driven with a 140-pound weight falling 30 inches. The blow counts to drive the thin-wall sampler were noted on the logs only as indications of relative driving resistance in the various layers and are not Standard Penetration Test (“N”) values. The Standard Penetration Test (SPT) values (“N” values) were obtained with the standard split-spoon sampler and are also shown on the boring logs.

Logs of test borings are presented in Appendix A.

BORING LOCATIONS MAP

FIGUREAMERICAN GEOTECHNICAL, INC.

322725 OLD CANAL ROAD, YORBA LINDA, CA 92887

(714) 685-3900 (714) 685-3909 www.amgt.com

TITLE:

MATHER HOSPITAL COMPLEX

FILE NO.:DATE:SCALE:

AGSB-1

TD=11.9’

AGSB-2

TD=11.8’

AGSB-3

TD=16.8’

N

646 HOSPITAL WAY,

MATHER, CA 95655

B’ A’A

ARTIFICIAL FILL

OVER ALLUVIUM

B

2.2 LABORATORY TESTING

Samples collected at the site during our field exploration were examined in our laboratory to verify the field classification and to assign laboratory testing. Selected samples were tested for the purpose of estimating material properties for use in subsequent engineering evaluations and analyses. Testing included in-situ moisture and density, maximum dry density and optimum moisture content, grain-size distribution and Atterberg Limits, percentage passing #200 sieve, expansion potential (Expansion

Index), hydro responses (swell/collapse potential), direct shear strength, and soil chemical testing. A brief description of each laboratory test performed, and results of our laboratory testing data are presented in Appendix B.

3.0 SITE GEOLOGY AND SEISMICITY

3.1 GEOLOGIC SETTING

The project site is about 1.7 miles east of the American River in Mather, California. The site is situated on a slightly elevated and dissected flood plain of the American River near ancestral Morrison Creek.

The site is underlain by non-marine sedimentary deposits of late Pleistocene age. Recent soils include

Holocene sheet flood and over bank deposits of the American River and Morrison Creek. Site soils include a stratified sequence of clay and silty clay with variable amounts of sand and gravel. Well logs nearby show dense gravel and cobble horizons below the maximum depth of exploration completed as part of this investigation. Regional geologic conditions are shown on Figure 4.

3.2 SITE GEOLOGY

Information obtained from our three test borings indicate that the site is underlain by Artificial Fill to depths of 6 to 7.5 feet below ground surface (bgs) and Alluvium to maximum depth of 16.8 feet at

Boring AGSB-3. Drilling refusal was encountered in each boring. The areal distribution of on-site materials at the project site is shown on Figure 3. Interpreted subsurface conditions are shown on

Figures 5A and 5B, Geologic Cross-Sections A-A’ and B-B’, respectively. Following is a brief discussion of earth materials encountered in the borings.

Artificial Fill Artificial fill was encountered in all three borings to a maximum depth of 6 to 7.5 feet bgs. Fill soils encountered at Boring AGSB-1 consist of Sandy Clayey Silt (ML) with Trace of Gravel. The fill material was slightly moist, reddish brown, and stiff. Gravel is subrounded and becomes more dominant at a depth of 7.5 feet bgs. Sand is fine to medium grained. At Boring AGSB-2, fill soil consists of Sandy

Clayey Silt (ML) with trace of gravel. The fill material was moist in the upper 3 feet and becomes slightly moist at a depth of 3 to 5.5 feet bgs. The fill material is medium stiff in the upper 3 feet and increases in stiffness to a depth of about 5.5 feet bgs. Gravels become more prevalent around depth of

6.5 feet bgs. At Boring AGSB-3, fill material consists of Sandy Clayey Silt (ML) with traces of gravel.

The material is moist in the upper 2.5 feet and becomes slightly moist from depths of 2.5 to 6 feet bgs.

The material is soft in the upper 2.5 feet and becomes medium stiff at a depth of 3.5 feet bgs. Gravels are subrounded and composed of quartz and bedrock material.

FIGUREAMERICAN GEOTECHNICAL, INC.

22725 OLD CANAL ROAD, YORBA LINDA, CA 92887

(714) 685-3900 (714) 685-3909 www.amgt.com

GEOLOGIC MAP

PROPOSED MATHER HEALTH COMPLEX PROJECT

FILE NO.:DATE:SCALE:

10535 HOSPITAL WAY, MATHER, CA

AS SHOWN APRIL 2021 80977-01

References:

Helley, E.J., 1979, Preliminary geologic map of Cenozoic deposits of the Davis, Knights Landing, Lincoln, and Fair Oaks quadrangles, California: U.S. Geological Survey, Open-File Report OF-79-583, scale 1:62,500, portion of Sheet 4.

Miles

Scale 1” = 2,000’

Mather Hospital Complex

Geologic Contact (approx)

A A’

TD=11.8’

TD=16.8’

AGSB-2

PROJ. 12’ W

AF = 0’-7’

GW = NE

AGSB-3

AF = 0’-6’

GW = NE

CL/ML

CL-ML

CL

CL

R 22/10” R 12/10”

R 20/12”

R 62/12”

R 50/5”

S 44/12”

S 50/2”

R 53/12”

R 90/12”

S 74/6”

REFUSAL = 11.6’

REFUSAL = 16.6’

CL/ML

ARTIFICIAL FILL

SECTION B

ALLUVIUM

N

ALLUVIUM SHOWS INCREASE GRAVEL CONTENT COMPARED TO FILL

SCALE: 1” = 20’ H

1” = 5’ V

GEOLOGIC CROSS SECTION A-A’

80977-01APR 2021AS SHOWN

FIGUREAMERICAN GEOTECHNICAL, INC.

5A22725 OLD CANAL ROAD, YORBA LINDA, CA 92887

(714) 685-3900 (714) 685-3909 www.amgt.com

TITLE:

MATHER HOSPITAL COMPLEX

FILE NO.:DATE:SCALE:

EL

EV

AT

IO

N

IN

F

EE

T

EL

EV

AT

IO

N

IN

F

EE

T

B B’

TD=11.9’

AGSB-1

AF = 1’-7.5’

GW = NE

CL-ML

R 40/10”

CONCRETE

EL

EV

AT

IO

N

IN

F

EE

T

EL

EV

AT

IO

N

IN

F

EE

T

GRAVEL BASE

R 29/12”

R 88/10”

S 88/4”

REFUSAL = 11.9’

CL

ARTIFICIAL FILL

SECTION A

ALLUVIUM

N

SCALE: 1” = 20’ H

1” = 5’ V

80977-01APR 2021AS SHOWN

FIGURE

AMERICAN GEOTECHNICAL, INC.

5B22725 Old Canal Road, Yorba Linda, CA 92887

(714) 685-3900 (714) 685-3909 www.amgt.com FILE NO.:DATE:SCALE:

GEOLOGIC CROSS SECTION B-B’

MATHER HOSPITAL COMPLEX

Alluvium Native alluvial soil was encountered beneath fill soils in each boring to the maximum depth of exploration, which was 16.5 feet bgs. Native soils primarily consist of Sandy Clayey Silt (ML) with a trace of gravel. Drilling refusal was encountered at a depth of 16.5 feet at Boring AGSB-3.

At Boring AGSB-1, the alluvial material, in general, was reddish brown, very dense to hard, and dry.

Gravel was subrounded and sand was fine to medium grained. Water was added at depths of 9, 11, and 11.9 feet due to drilling difficulty. Grinding at a depth of 11.9 feet was encountered and the drill rig experienced bouncing and boom swaying possibly indicating the presence of nested cobbles. Refusal was encountered at a depth of 11.9 feet. The borehole was backfilled with spoils and sand and tamp compacted with the drill rig. Top hole finish was rapid set concrete. The ring sample at a depth of 7.5 to 8.5 feet was 50 for 4 inches, which is consistent with the very dense to hard and dry soil condition at that depth. The SPT N-value at a depth of 10 to 10.5 feet bgs was 50 for 6 inches (SPT sampling refusal), which is also consistent with the very dense, hard, and dry soil condition at that depth and the increasing difficulty in drilling.

At Boring AGSB-2, the alluvial material was brown, very dense to hard, and dry. Gravels are subrounded and composed of quartz fragments and bedrock material. Due to difficulty in drilling, water was added at depths of 8, 8.5, 10.5, 11, and 11.4 feet, respectively. Grinding occurred at a depth of

11.4’. The drill rig was bouncing up and down and screeching during rotation. The rig was set in 1st gear for 15 minutes and the rig was finally moved west about one foot from the previous boring location and continued to drill down. Refusal was encountered at a depth of 10.9 feet bgs in the second boring.

The borehole was backfilled with spoils and sand and tamp compacted with the drill rig. The ring sample collected at a depth of 7.5 to 8.5 feet bgs was 90 for 6 inches, which is consistent with the very dense to hard and dry soil condition at that depth. The SPT N-value at a depth of 10 to 10.5 feet was

50 for 6 inches, consistent with the very dense to hard and dry soil condition at that depth and the increasing difficulty in drilling.

At AGSB-3, the alluvial material was encountered at a depth of 6 to 16.8 feet bgs. The alluvial material was reddish brown, slightly moist, and stiff. Gravel is subrounded and composed of bedrock material.

Below a depth of 11 feet, the alluvial material was reddish brown, very dense to hard, and dry. Gravel is subrounded. Due to difficulty in drilling, water was added at depths of 13, 13.5, 14, 16.2, and 16.8 feet bgs, respectively. The rig drilled in first gear and grinding occurred on rock for about 18 minutes.

The drill rig boom swayed, and the rig bounced. Refusal was encountered at a depth of 16.8 feet bgs.

This may indicate the presence of nested cobbles at this depth. The borehole was then backfilled with spoils and sand and tamp-compacted with the drill rig. The SPT N-value at a depth of 10 to 11 feet bgs was 44. The ring blow count at a depth of 12.5 to 13 feet bgs was 50 for 5 inches, which is consistent with the very dense to hard soil conditions at that depth during drilling. The SPT N-value at a depth of

15 to 15.2 feet bgs was 50 for 2 inches (SPT sampling refusal), which is also consistent with the very dense to hard soil conditions and the increasing difficulty of drilling at that depth.

Caving Conditions No caving conditions were encountered during our field exploration borings.

3.3 GROUNDWATER

Groundwater was not encountered in the borings. Regional well data indicates depth to groundwater is generally greater than 50 feet bgs. Depth to groundwater can be expected to fluctuate and change due to a variety of factors including seasonal rainfall.

3.4 100-YEAR FLOOD ZONE

Review of data available from the FEMA Flood Map Service Center Website indicates that the site is located on FIRM Map 06067C0208H with an effective date of 08/16/2012. The site is in a FIRM Zone

X which is an area determined to have minimal flood hazard.

3.5 LAND SUBSIDENCE

Review of data available from the California Department of Water Resources SGMA Data Viewer

Website (accessed in April 2021), the site is not in an area experiencing land subsidence resulting from groundwater withdrawal or other causes.

3.6 FAULT HAZARDS

The site is not located in a State of California Earthquake Fault Zone. No known active fault projects into or crosses the subject site. The closest active fault is located about 50 miles to the southwest of the site in the coast ranges. The location of the site with respect to mapped traces of faults is shown on

Figure 6, Fault Activity Map.

3.7 SEISMIC HAZARDS

Seismic design criteria developed in accordance with the 2019 California Building Code (CBC) are provided in a later section of this report. Additionally, we performed a probabilistic seismic hazard analysis assuming an exposure period of 50 years and a 2% probability of exceedance. The return period for this event is 2,475 years.

3.7.1 Probabilistic Seismic Hazard Analysis

A probabilistic seismic hazard analysis (PSHA) was completed to determine ground motion parameters for the Maximum Considered Earthquake (MCE) in accordance with the 2012/15 International Building

Code (IBC) and 2019 California Building Code (CBC). The MCE is defined probabilistically as the ground motion with a 2 percent probability of exceedance in a 50-year exposure period. We used the

U.S. Geological Survey (USGS)/California Geological Survey (CGS) fault model developed as part of the 2008 National Seismic Hazards Mapping Project and modified in 2014 as a basis for the analysis.

We estimated the average shear wave velocity in the upper 30 meters below ground surface at the subject site to be 360 to 490 meters per second partly based on exploratory borings completed for this investigation and partly based on the U. S. Geological Survey’s Vs 30 Models and Data Website and the California Geological Survey’s Data Viewer Website. The average shear wave velocity is consistent with a Site Class C.

We used the USGS Uniform Hazard Tool for the probabilistic analysis. Results were developed from an average of three ground motion prediction equations which also were developed for the 2008

National Seismic Hazards Mapping Project including Boore and Atkinson, 2008, Abrahamson and

Silva, 2008, and Chiou and Youngs, 2008. All results are mean plus one standard deviation. Results indicate the MCE ground motion is equal to 0.27 g. Results are summarized on Figure 7.

(714) 685-3900 (714) 685-3909 www.amgt.com

FAULT ACTIVITY MAP

PROPOSED MATHER HEALTH COMPLEX PROJECT

FILE NO.:DATE:SCALE:

10535 HOSPITAL WAY, MATHER, CA

AS SHOWN APRIL 2021 80977-01

References:

U.S. Geological Survey Interactive Quaternary Faults Database, accessed April 2021, www.usgs,maps.arcgis.com/apps/webappviewer

Mather Hospital Complex

Closest Active Fault

20 Mile Radius

Scale 1” = 10 mi

(714) 685-3900 (714) 685-3909 www.amgt.com

PROPOSED MATHER HEALTH COMPLEX PROJECT

FILE NO.:DATE:SCALE:

10535 HOSPITAL WAY, MATHER, CA

AS SHOWN APRIL 2021 80977-01 7

PROBABILISTIC SEISMIC HAZARD ANALYSISReferences:

U.S. Geological Survey Uniform Hazard Tool, accessed April 2021 www.earthquake.usgs.gov/hazards/interactive

Hazard Curves

Uniform Hazard Response Spectrum

Deaggregation of Hazard

Probabilistic Seismic Hazard Analysis. Exposure Period = 50 years. Risk = 2% Exceedance. Return Period 2,475 Years.

Site Class C

Time Horizon 2475 years

Peak Ground Acceleration

0.10 Second Spectral Acceleration

0.20 Second Spectral Acceleration

0.30 Second Spectral Acceleration

0.50 Second Spectral Acceleration

0.75 Second Spectral Acceleration

1.00 Second Spectral Acceleration

2.00 Second Spectral Acceleration

3.00 Second Spectral Acceleration

4.00 Second Spectral Acceleration

5.00 Second Spectral Acceleration

1e-2 1e-1 1e+0

Ground Motion (g)

1e-14

1e-13

1e-12

1e-11

1e-10

1e-9

1e-8

1e-7

1e-6

1e-5

1e-4

1e-3

1e-2

1e-1

1e+0 A n n u a l F re q u e n c y o f E x c e e d e n c e

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

Spectral Period (s)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

G ro u n d M o ti o n g

Spectral Period (s): PGA

Ground Motion (g): 0.27 ε = (-∞ .. -2.5) ε = [-2.5 .. -2) ε = [-2 .. -1.5) ε = [-1.5 .. -1) ε = [-1 .. -0.5) ε = [-0.5 .. 0) ε = [0 .. 0.5) ε = [0.5 .. 1) ε = [1 .. 1.5) ε = [1.5 .. 2) ε = [2 .. 2.5) ε = [2.5 .. +∞)

9.5

8.5

Magnitu de (M w)

7.5

6.5

5.5

4.5

Closest Distance, rRup (km)

C o n tr ib u ti o n t o H a z a rd

Closest Distance, rRup (km)

9.5

8.5

7.5

6.5 Magnitu

de (M w)

5.5

4.5

Mean contribution to hazard all sources M = 6.5

D = 50 km

Uniform hazard response spectra for MCE horizontal ground motions are also shown on Figure 7.

Probability of exceedance curves were calculated for ten undamped natural periods between 0.1 to 5 seconds for 5% critical damping using the PSHA results. The vertical component of ground motion may be defined by scaling the corresponding horizontal accelerations by a factor of two-thirds.

We deaggregated the PSHA results for MCE peak ground acceleration to determine the magnitude-distance couple that would represent the primary contribution to hazard at the specified exposure period and risk. The primary contribution to hazard is from a moment magnitude Mw 6.5 earthquake at about 50 kilometers. The magnitude-distance couple that contributes the most to hazard may vary at different periods of spectral acceleration.

3.7.2 Historic Earthquakes

We performed a search of historic and recorded earthquakes greater than or equal to M 4.5 using the

U.S. Geological Survey’s Search Earthquake Catalog Website. Between 1855 and 2021 there were 40

M4.5 or larger events located within a 100-mile radius of the site. No event was closer than about 30 miles. Results of this analysis are shown graphically on Figure 8, Historical Earthquake Map.

3.7.3 Liquefaction

The site is not located in a State of California Seismic Hazard Zone for Liquefaction. Liquefaction is a phenomenon in which saturated granular sediments temporarily lose shear strength during periods of earthquake-induced strong ground shaking. The susceptibility of a site to liquefaction is a function of the depth, density, and water content of the sediments and the magnitude of an earthquake. Saturated, unconsolidated silts, sands, silty sands, and gravels within 50 feet of the ground surface are most susceptible to liquefaction. Typical effects of liquefaction include loss of bearing strength, lateral spreading, and settlement.

Alluvial soil encountered in exploratory borings below depths of 6 to 7.5 feet at the three exploration boring locations consisted of sandy clayey silt (ML) with trace of gravel to the maximum depth of 16.5 feet bgs exposed at Boring AGSB-3. These materials are geologically old (Pleistocene), very dense to hard, dry, and caused drilling refusal in each exploratory boring completed for this investigation.

(714) 685-3900 (714) 685-3909 www.amgt.com

HISTORIC EARTHQUAKE MAP

FILE NO.:DATE:SCALE:

80997-01

References:

Toppozada, T., et. al., 2000, Epicenters of and Areas Damaged by M ≥ 5 California Earthquakes,1800 - 1999, CDMG Map Sheet 49.

PROPOSED MATHER HEALTH COMPLEX PROJECT

10535 HOSPITAL WAY, MATHER, CA

AS SHOWN APRIL 2021

Mather Hospital Complex

20 Mile Radius

Alluvium is generally not susceptible to liquefaction. Groundwater is estimated to be 50 feet below ground surface or deeper based on nearby wells. Liquefaction is not anticipated to occur at the site.

3.7.4 Earthquake-Induced Landslides

The site is not located in a State of California Seismic Hazard Zone for Earthquake-Induced Landslides.

Regional geologic maps show no known landslides are located on site or in immediately adjacent areas.

3.8 TSUNAMIS AND SEICHES

Tsunamis are tidal waves generated by fault displacement or major ground movement on the floor of the ocean. The geographic location of the site precludes the possibility of damage due to tsunamis.

Seiches are large waves generated in enclosed bodies of water in response to ground shaking. The waves can top dams or reservoirs and flood down-gradient areas. Local topographic conditions preclude the possibility of damage due to seiches.

4.0 GEOTECHNICAL CONSIDERATIONS

4.1 SUBSURFACE SOIL CONDITIONS

As discussed earlier in this report, subsurface material at the site includes a maximum of about 7.5 feet of artificial fill overlying alluvium. Fill soil consisted of sandy clayey silt (ML) with trace of gravel, slight moist, reddish brown, and stiff. Alluvium thickness is at least to depth of 16.8 feet below ground surface to the maximum exposed depth at AGSB-3 location. Alluvial soil consisted of sandy clayey silt

(ML) with traces of gravel, similar to the fill soil above, slightly moist, brown, very dense to hard and dry.

Alluvial soil is very difficult to drill through as grinding and refusals were encountered at all three exploratory boring locations suggesting that the very dense to hard alluvial material encountered at the three borings is most likely extended all over the project site.

The primary geotechnical considerations at the site are expansive soil influence and long-term soil settlement. The following paragraphs provide a general discussion about these geotechnical influences.

4.2 EXPANSIVE SOIL

Soil with a significant clay fraction tends to possess expansive characteristics. Expansive soil heaves when water is introduced and shrinks as it dries. Pressures produced by heaving soil can be large enough to lift most buildings. Slabs over expansive soil are often said to "walk" as a result of expansive soil movement. This process generally tends to increase separation of slab joints and/or cause exterior improvements such as patios, originally abutting structures, to separate. Expansive soil can also cause cracking of slabs and foundations. Relatively light slab and foundation systems on expansive soil will tend to curl up at the building perimeter; a process sometimes referred to as edge lift or dishing. Over the long term, as moisture migrates further under the building and in response to drying along the building perimeter, the process reverses and central doming sometimes referred to as a heave pattern results.

This doming process is also alternatively described as edge drop and can be further aggravated near descending slopes by ordinary slope creep by long-term clay desiccation of the slope areas. Relatively stiff foundations are needed to resist the adverse influence of expansive soil.

Expansive soil tends to be active near the ground surface. The actual depth varies with specific material type and environmental differences. To reduce the effect of expansive soil on surface structures, foundation systems are usually deepened. Slabs and foundations are usually reinforced to increase their resistance to differential movement. It is usually suggested in planning site improvements and a landscape theme that maintaining uniform moisture conditions, as much as practical, around isolated individual structures is desirable. Preferably, soil should be kept on the moist side without allowing ponding. Since water tends to migrate under slab areas, saturation of the slab subgrade for conventional construction is usually recommended prior to placement of slab concrete. This process, presaturation, activates the soil expansion prior to slab placement and thereby limits both the tendency toward edge lift and long-term heave. Deepened exterior footings and/or membrane barriers for a conventional foundation system also serve to limit the degree to which drying can occur and thereby limit edge drop as well. While adopting these practices plus generally good drainage can modulate moisture changes to some degree, preventing moisture changes is generally thought of as impossible. Placing small and moderate sized trees within about 10 to 20 feet (respectively) of the structures’ conventional foundations is not desirable because they tend to extract water and contribute to edge drop. Large trees should be kept at even greater distance unless designed tree-root barriers are provided. Unless a conservative approach to design is taken, actual tree/soil/structure interaction should consider actual tree species.

Where mat or conventional foundations are constructed with relatively deep cut-offs, which also serve as root barriers, no special planting prohibitions are necessary but landscape can influence appurtenant improvements, such as flatwork.

Our laboratory Expansion Index (EI) testing result (EI = 30) revealed that the onsite near-surface soil possesses at least “Low” expansion potential (i.e., EI 21 to 50). At EI = 30, ground surface elevation change potential is estimated at about 2.5 inches over a depth of about 7 feet. Expansive soil influence is anticipated to affect the future performance of the proposed two-story connector building between

Buildings B644, B645, and B646 and a separate one-story corridor addition adjacent to Building B650, as such, special foundation design to accommodate expansive soil influence at the site should be considered. At the time when development plans become more refined, detailed criteria for design on expansive soil can be provided.

4.3 SETTLEMENT

To some degree, all materials are compressible. Settlement occurs as a result of the stresses imposed and most significant stresses usually result from the weight of the structure, as well as the weight of the earth materials. Settlement can, in some cases, be aggravated by the introduction of water to the subsoils. Fill material and natural soil tend to be more compressible than bedrock materials (e.g., many

"cut" areas). Accordingly, settlement potential usually increases with increases in the depth of fill and natural soils. Where the depth of fill and natural soil vary, the potential for differential settlement increases. The amount of differential settlement is of most concern since differential movements can result in distress.

At this site, although the boring logs revealed generally dense or stiff conditions, laboratory testing indicated that relative compaction estimates for fill soil material were mostly greater than 90 percent relative compaction as is typically called for as a minimum. The fill soil at a depth of 2.5 to 3 feet at boring AGSB-1 was estimated to have 63 percent relative compaction. It is our opinion that such a low relative compaction is most likely as result of sample disturbance during sample collection. Relative compaction ranging from 79 to 84 percent were estimated for fill soil at AGSB-3 location which is below the minimum required 90 percent relative compaction. There are many reasons why post-construction relative compaction estimates may vary. Expansive soil characteristics may be the most cited influence contributing to post-construction compaction loss. What is most important is the long-term performance potential at any site. At this site, hydro-response (swell/collapse potential) test data indicates that the onsite fill and alluvial soils at Boring AGSB-3 location is not a concern. The soil sample at a depth of

12.5 to 13 feet at the Boring AGSB-3 location has a minus 4.6% of collapse potential under 1500 pounds per square foot (psf) of loading condition. Closer examination of this soil sample and review of

AGSB-3 boring log revealed that this sample is most likely disturbed during sample collection as result of rig boom swaying and bouncing.

Due to expansive soil characteristics of the onsite near-surface soils, we do not anticipate any significant settlement from foundation loads. We estimate that maximum total settlement is anticipated to be less than 1-inch and a total maximum differential settlement is anticipated to be one-half of total settlement over a 40-foot span (i.e., ½-inch). Analyses of specific foundations with respect to settlement could be conducted on request. Each proposed foundation configurations depth and loading conditions would be needed from the structural engineer.

4.4 FOUNDATION CONCEPT

Based on the results of our geotechnical investigation, we recommend that a conventional slab-on-grade foundation with proper steel reinforcement and subgrade preparation founded on a uniform, properly compacted fill blanket could be utilized to support the proposed two-story connector building between Buildings B644, B645, and B646 and a separate one-story corridor addition adjacent to

Building B650.

5.0 CONCLUSIONS AND RECOMMENDATIONS

5.1 BASIS

Conclusions and recommendations contained in this report section are based upon information provided, information gathered, laboratory testing, engineering, geologic, and seismic hazards evaluations, experience and professional judgment. Recommendations contained herein should be considered minimums consistent with industry practice. More rigorous criteria could be adopted if lower risk of future problems is desired.

5.2 SITE SUITABILITY

The site is within an area including completed health complex developments similar to that anticipated for these proposed site improvements. Geotechnical exploration, analyses, experience, and professional judgment result in the conclusion that the site is feasible for the proposed development provided that the recommendations presented in this report are followed and incorporated into the design and construction of the project.

It is our opinion that the site can be developed without significant geologic or geotechnical hazards, and development can occur without similar adverse impact on adjoining properties. Realizing this expectation will require adherence to good construction practice, agency and code requirements, the recommendations in this report, and possibly addendum recommendations made after plan review and at the time of construction.

5.3 SEISMIC DESIGN CONSIDERATIONS

5.3.1 2019 California Building Code (CBC) Design Parameters The following site seismic design parameters were determined in accordance with the 2019 California

Building Code (CBC). Seismic design parameters based on the 2019 California Building Code (CBC) are summarized below:

Site Latitude 42.8686684 Site Longitude -112.4172199

1. Site Class: C – Very Dense soil and Soft Rock

2. Mapped Spectral Accelerations

a. MCER ground motion. (for 0.2 second period), Ss = 0.459 g

b. MCER ground motion. (for 1.0 second period), S1 = 0.225 g

3. Site Adjusted Spectral Accelerations

a. Site-modified spectral acceleration value (for 0.2 second period), SMS = 0.597 g

b. Site-modified spectral acceleration value (for 1.0 second period), SM1 = 0.335 g

4. Design Spectral Acceleration

a. Numeric seismic design value at 0.2 second period SA, SDS = 0.398 g

b. Numeric seismic design value at 1.0 second period SA, SD1 = 0.225 g

5. Site Coefficients:

Site design category, SDC = D Site amplification factor at 0.2 second, Fa = 1.3 Site amplification factor at 1.0 second, Fv = 1.5 MCEG peak ground acceleration, PGA = 0.194 g Site amplification factor at PGA, FPGA = 1.206 Site modified peak ground acceleration, PGAM = 0.234 g

The seismic design parameters presented herein are considered “minimum design values” as dictated in the Code. It should be realized that the purpose of the seismic design utilizing the above parameters is to safeguard against major structural failures and loss of life but not to prevent damage altogether.

Even if the structural engineer provides designs in accordance with the applicable codes for seismic design, the possibility of damage cannot be ruled out if moderate to strong shaking occurs as a result of a large earthquake. This is the case for essentially all structures in northern California.

5.4 DEMOLITION

Prior to the start of earthwork, the existing improvements at the site will require demolition and removal, and any other miscellaneous improvements. The presence and location of all existing utilities on the property should be clearly identified and marked by the project civil engineer and contractor prior to the start of earthwork. Special care should be taken to remove, relocate, or protect all existing utilities as appropriate.

5.5 EARTHWORK

5.5.1 General

It is anticipated that the proposed construction will require grading at the site. When grading is conducted, it should be done in accordance with good construction practices, minimum code and governing agencies requirements, and the recommendations to follow. General guidelines for grading projects are also provided in Appendix C.

5.5.2 Site Preparation

Prior to the start of excavation, utility lines within the project area should be located and marked in the field so they can be rerouted or protected during site development. All debris and perishable material should be removed from the site.

5.5.3 Over-Excavation and Remedial Grading

Footings for the proposed site improvements can be supported by a uniform, properly compacted new fill blanket derived from the onsite fill material. A minimum 4-foot deep excavation of the existing onsite fill soil should be removed and recompacted to minimum 90 percent relative compaction within the building envelope area plus 10 feet in accordance with the ASTM Standard Test Method D-1557 in order to provide uniform fill thickness blanket for supporting the proposed building foundations. The footings should be founded entirely within the new compacted fill.

Excavation of onsite fill and native soil material is not expected to pose difficulty by utilizing conventional excavation equipment. It is anticipated that the depth of removal will be minimum 4 feet within the proposed site improvements area. Actual removal depth may be locally increased based on the observation of the soil conditions encountered during grading. Temporary construction slopes should not steeper than 1:1 (horizontal:vertical).

As discussed earlier, no groundwater was encountered during our subsurface field exploration. It should be noted that groundwater table can fluctuate as results of climate and season changes, prolonged precipitation, drought, irrigation practice, and other environmental and non-environmental factors. If local perched groundwater conditions are encountered during excavation, the contractor should deal with these conditions by either using pumping or other appropriate measures. A groundwater control system may be appropriately designed, if needed, to lower the potential of heaving/piping. Filter material for groundwater control system should be designed to reduce the probability of heaving/piping. Grain-size distribution of representative subsurface soil is presented in the laboratory testing data in Appendix B of this report and may be used for this purpose.

It should be noted that lowering groundwater table through pumping will increase the effective stress in the soil. This would result in consolidation of the soil, thereby inducing settlement of the structure in the affected zone. If any dewatering is needed, the effects of groundwater control should be taken into consideration in design.

Where new fill is to be placed, placement of fill at about 2 to 3 percent over optimum moisture content is also advised along with a minimum of 90 percent relative compaction.1 If localized areas of relatively loose soil prevent proper compaction, over-excavation, and re-compaction will be necessary.

The on-site soil is generally suitable for use as compacted fill and backfill. Backfill around the footings and in utility trenches within the building and paved areas should conform to the same material and compaction requirements as for the new fill.

All grading should be conducted in accordance with the applicable codes, agency requirements, the aforementioned recommendations, and the grading guidelines which accompany this report as mentioned above.

5.5.4 Import Fill Material

If practical, import fill material should meet the following criteria:

1. No particles larger than 6 inches in largest dimension.

2. Free of perishable material.

1 Relative compaction refers to the ratio of the in-place dry density of soil to the maximum dry density of the same material as obtained by the "modified proctor" (ASTM D1557-12e) test procedure.

3. Plasticity Index of 20 or less and Liquid Limit of 40 or less.

4. Expansion Index of 20 or less.

If no such material is readily available, our office should evaluate any proposed import source.

Less desirable material could be used, but more rigorous foundation and slab criteria may be required.

5.6 PROTECTION OF ADJACENT STRUCTURES

Appropriate measures should be taken during construction to prevent potential damage to the existing, nearby structures.

5.7 SLAB-FOUNDATION DESIGN

The minimum criteria for the design of foundation and slab applicable to the project are provided below. The criteria should not be considered as substitutes for actual design by the structural engineer. The structural engineer should analyze the actual soil-structure interaction and consider, as needed, bearing, expansive soil influence, strength, stiffness, and deflections in the various slab, foundation, and other elements of the structure, in order to develop appropriate, design-specific details. As conditions dictate, it is possible that other influences will also have to be considered.

The structural engineer should consider all applicable codes and authoritative sources where needed. If analyses by the structural engineer result in less critical details than are provided herein as minimums, the minimums presented herein should be adopted. It is considered likely that some, more restrictive details will be required. If the structural engineer has any questions or requires further assistance, please do not hesitate to call or otherwise transmit the engineer's requests.

5.7.1 Foundation Design

Foundation support for the proposed two-story connector building between Buildings B644, B645, and

B646 and a separate one-story corridor addition adjacent to Building B650 could be derived by utilizing conventional, well reinforced, shallow foundation system embedded directly within minimum 3 feet deep, uniform, properly compacted new fill compacted to minimum 90 percent relative compaction.

Allowable design parameters for foundation embedded in the newly-placed compacted fill are provided below. It should be noted that the following design parameters are provided assuming that the near-surface soil has ‘Low’ expansive soil potential (i.e., EI = 31 to 50). These design parameters may be revised once additional testing is performed during rough grading of the project.

Minimum depth for interior and exterior footing (measured from lowest adjacent grade) ....................................................... 24 inches

Minimum width ............................................................................... 16 inches (1-story)

................................................................................ 18 inches (2-story) ............................................................ 24 inches (isolated pad footing)

Bearing pressure

a. Sustained loads (pounds per square foot) ..................................... 2,400 psf

b. Total loads (including wind or seismic) .......................................... 3,200 psf

Resistance to lateral loads

a. Passive soil resistance (pounds per cubic foot)........ 300 pcf (compacted fill)

b. Coefficient of sliding friction (allowable) .................................................. 0.4

The above-recommended allowable bearing pressure can be increased by 500 psf for each additional foot of the foundation embedment, but not to exceed 4,000 psf.

The allowable bearing pressures are for dead plus long-term live loads and include a factor-of-safety of at least 3.0.

Soil-Structure Interaction Designs Criterion

Edge-lift moisture variation distance ................................................................ 10 feet

Edge-lift unconfined heave potential ............................................................ 1.5 inches

Center-lift moisture variation distance .............................................................. 10 feet

Center-lift unconfined differential heave-shrink potential ............................. 1.5 inches

Footings can be designed to resist lateral loads by using a combination of sliding friction and passive resistance. The coefficient of friction should be applied to dead load forces only. The upper 1 foot of passive resistance should be neglected where the soil is not confined by slabs or pavements.

Excavations for footings should be carefully prepared to achieve a neat and undisturbed condition and all exposed footing subgrades should be evaluated thoroughly to ensure firm and unyielding conditions prior to placement of footing concrete.

Total static settlements resulting from compression of subgrade soils for conventional footings designed and constructed in accordance with the forgoing criteria are expected to experience less than 1 inch.

Differential fill settlement of approximately half of the total static settlement (i.e., 0.5 inches) within a 40-foot span is expected.

5.7.2 Slab-on-Grade

The slab-on-grade in the interior of the proposed two-story connector building between Buildings B644, B645, and B646 and a separate one-story corridor addition adjacent to Building B650 should be a minimum 6.0 inches thick and reinforced with at least No. 4 bars at 12 inches on center, both ways.

Slab steel should continue into all exterior footings by separate 36x24 inch #4 bar dowels at 12 inches on center. Slabs should have at least two #4 bars within 6 inches of all perimeters and at least two 48-inch long #4 bars placed diagonally across all re-entrant corners within 6 inches of the corner. The slab should be underlain by one layer of 20-mil Stego plastic moisture membrane. The membrane should be sealed at all perimeter locations, splices, and protrusions (e.g., plumbing, see ASTM E1643). Every effort should be made to provide a continuous barrier and care should be taken not to puncture the membrane. A continuous layer of Mirafi 140N atop the membrane will add limited protection against puncture from the crushed aggregate in the concrete.