Encl 6 Geotechnical Report Emergency Service Annex May 17 2013.pdf

GEOLOGICAL AND GEOTECHNICAL INVESTIGATION

EMERGENCY SERVICE ANNEX

VETERANS AFFAIRS MEDICAL CENTER

Menlo Park, California

Polytech Associates Inc.

San Francisco, California

17 May 2013 Project No. 750612401

501 14TH STREET, 3RD FLOOR OAKLAND CALIFORNIA 94612 T 510 874 7000 F 510 874 7001 www.treadwellrollo.com

Project 750612401

Mr. Rich Graziano

235 Pine Street, 17th Floor

San Francisco, California 94104

Subject: Geological and Geotechnical Investigation Emergency Service Annex

Veterans Affairs Medical Center

Dear Mr. Graziano:

We are pleased to present our geological and geotechnical investigation report for the planned Emergency Service Annex to be constructed at the Veterans Affairs Medical Center at 795 Willow Road in

Menlo Park, California (VA Menlo Park). Our work was performed in accordance with our revised proposal dated 16 October 2012. This report presents the recommendations and conclusions regarding the geological and geotechnical aspects of the project.

The Emergency Service Annex is part of VA project 640-382, Design Renovation of Building 349, Homeless Domiciliary. We understand that existing Building 349 will receive architectural improvements but that structural loads are not expected to change; therefore geotechnical recommendations are not needed for this building. The recommendations in this report are limited to the Emergency Service

Annex.

The VA Menlo Park property is bound by Bay Road on the north, Willow Road and Van Buren Road on the east, S. Perimeter Road on the South, and W. Perimeter Road on the west. The Emergency Service

Annex will be located in the southeast portion of the VA Menlo Park property, between Hospital Drive Plaza and the existing chapel. The Emergency Service Annex site is generally level and is occupied by lawns, trees, and sidewalks. We understand that plans are to demolish existing improvements within the planned building footprint and construct the Emergency Service Annex, which will consist of an approximately 5,000-square-foot, one or two-story building. Additional improvements will include new utilities, sidewalks, and landscaping.

Subsurface information from our field investigation indicate the site is generally underlain by layers of medium stiff to hard clay with variable sand content and loose to very dense sand with variable gravel and fines content to the maximum depth explored of 100 feet bgs. Results of Atterberg limits tests performed on the near-surface clay during the investigation indicate it has a moderate expansion potential. Groundwater was measured in the borings and CPTs at depths between about 16 and 25 feet bgs, corresponding to approximate respective Elevations 12 to 4 feet (National Geodetic Vertical Datum of 1929). The groundwater levels observed during the field investigation do not represent stable groundwater table conditions. The groundwater level is expected to vary due to seasonal fluctuations of rainfall.

We conclude that from a geotechnical engineering standpoint, the site can be developed as proposed, provided the recommendations presented in this report are incorporated into the project plans and specifications, and are implemented during construction. The primary geotechnical concerns for the

Geological and Geotechnical Investigation Emergency Service Annex Veterans Affairs Medical Center Menlo Park, California Project 750612401

Emergency Service Annex project are the presence of moderately expansive near-surface soil and the presence of potentially liquefiable soil below the water table.

This report presents our recommendations regarding site preparation, floor slab and foundation design, pavement design, and other geotechnical aspects of the project. The recommendations are based on limited subsurface exploration and laboratory testing programs. Consequently, variations between expected and actual soil conditions may be found in localized areas during construction. Therefore, we should be engaged to observe subgrade preparation, check compaction of fill and backfill, and observe installation of foundations, during which time we may make changes in our recommendations, if deemed necessary.

We appreciate the opportunity provide our services to you on this project. If you have any questions, please call.

Sincerely yours, TREADWELL & ROLLO, A LANGAN COMPANY

Elena M. Ayers, GE Lori A. Simpson, GE

Project Manager Principal

750612401.03 EMA

12/31/13

GEOLOGICAL AND GEOTECHNICAL INVESTIGATION

San Francisco, California

Project No. 750612401

TABLE OF CONTENTS

1.0 INTRODUCTION

2.0 SCOPE OF SERVICES

3.0 FIELD INVESTIGATION

4.0 LABORATORY TESTING

5.0 SUBSURFACE CONDITIONS

6.0 REGIONAL GEOLOGY

7.0 REGIONAL SEISMICITY AND FAULTING

8.0 DISCUSSION AND CONCLUSIONS

8.1 Seismic and Geologic Hazards

8.1.1 Fault Rupture

8.1.2 Soil Liquefaction and Associated Hazards

8.1.3 Lateral Spreading

8.1.4 Cyclic Densification

8.1.5 Landslides, Erosion, and Seepage

8.2 Foundation Support

8.3 Floor Slabs

8.4 Corrosion Potential

9.0 RECOMMENDATIONS

9.1 Earthwork

9.1.1 Site Preparation

9.1.2 Subgrade Preparation

9.1.3 Fill Placement

9.1.4 Utility Trenches

9.2 Foundation Support

9.3 Concrete Floor Slabs

9.4 Concrete Flatwork

9.5 Pavement Design

9.5.1 Asphalt Concrete Pavement

9.5.2 Portland Cement Concrete Pavement

9.6 Drainage

9.7 Irrigation and Landscaping Limitations

9.8 Seismic Design

9.8.1 2012 International Building Code/ASCE 7-10 Mapped Values

9.8.2 Site-Specific Response Spectra

10.0 ADDITIONAL GEOTECHNICAL SERVICES

11.0 LIMITATIONS

REFERENCES

FIGURES

APPENDIX A – Logs of Borings and Cone Penetration Tests

APPENDIX B – Laboratory Test Results APPENDIX C – Site Specific Response Spectra

DISTRIBUTION

LIST OF FIGURES

Figure 1 Site Location Map

Figure 2 Site Plan

Figure 3 Regional Geologic Map

Figure 4 Map of Major Faults and Earthquake Epicenters in the San Francisco Bay Area

Figure 5 Modified Mercalli Intensity Scale

Figure 6 Regional Seismic Hazard Zones Map

Figure 7 Recommended Horizontal MCER and DE Spectra

APPENDIX A

Figures A-1 Logs of Borings B-1 and B-2 and A-2

Figure A-3 Classification Chart

Figures A-4 Logs of Cone Penetration Tests CPT-1 and CPT-2 and A-5

Figures A-6 Logs of Dissipation Tests for CPT-1 and CPT-2 and A-7

Figure A-8 Log of Shear Wave Velocity Measurements for CPT-2

APPENDIX B

Figure B-1 Plasticity Chart

Figure B-2 Unconsolidated – Undrained Triaxial Compression Test

Figure B-3 Resistance Value Test Data

Figure B-4 Corrosion Test

APPENDIX C

Site-Specific Response Spectra

GEOTECHNICAL AND GEOLOGICAL INVESTIGATION

VETERANS AFFAIRS MEDICAL CENTER

Menlo Park, California

1.0 INTRODUCTION

This report presents the results of the geotechnical and geological investigation performed by

Treadwell & Rollo, A Langan Company, for the planned Emergency Service Annex to be constructed at the Veterans Affairs Medical Center at 795 Willow Road in Menlo Park, California (VA Menlo Park). This investigation was performed in accordance with our revised proposal dated 16 October 2012. This report presents our conclusions and recommendations regarding geotechnical aspects of the project.

The Emergency Service Annex is part of VA project 640-382, Design Renovation of Building 349, Homeless Domiciliary. We understand that existing Building 349 will receive architectural improvements but that structural loads are not expected to change; therefore geotechnical recommendations are not needed for this building. The recommendations in this report are limited to the Emergency Service

Annex.

The VA Menlo Park property is bound by Bay Road on the north, Willow Road and Van Buren Road on the east, S. Perimeter Road on the South, and W. Perimeter Road on the west, as shown on Figure 1. The

Emergency Service Annex will be located in the southeast portion of the VA Menlo Park property, between Hospital Drive Plaza and the existing chapel, as shown on Figure 2. The Emergency Service

Annex site is generally level and is occupied by lawns, trees, and sidewalks. Current ground surface elevations at the site range from approximately 29 to 31 feet.1 We understand that plans are to demolish existing improvements within the planned building footprint and construct the Emergency Service Annex, which will consist of an approximately 5,000-square-foot, one or two-story building. The finished floor of the building will be at Elevation 31 feet. Based on information provided by the project structural engineer, we understand dead plus live loads will be about 90 kips at interior columns and about 25 kips at the columns at the building perimeter. Additional improvements will include new utilities, sidewalks, and landscaping.

Elevations discussed in this report refer to the National Geodetic Vertical Datum of 1929 (NGVD 29) and are based on Sheet C4.1, Grading Plan, prepared by BKF Engineers, dated 3 May 2013.

750612401.03 EMA 17 May 2013

A portion of the VA Menlo Park property, including the Emergency Service Annex, is mapped within a

State of California liquefaction hazard zone as defined by the map entitled State of California Seismic

Hazard Zones, Palo Alto Quadrangle, prepared by the California Geological Survey (CGS)2, dated

18 October 2006. CGS has recommended the content for site investigation reports within seismic hazard zones in Special Publication 117A, Guidelines for Evaluating and Mitigating Seismic Hazards Zones in

California, dated 11 September 2008. These guidelines call for liquefaction potential to be evaluated using rotary-wash borings and/or cone penetration tests (CPTs) extending to a depth of at least 50 feet.

2.0 SCOPE OF SERVICES

The purpose of our investigation was to evaluate subsurface conditions at the site and provide conclusions and recommendations for the geotechnical aspects of the design of the Emergency Service

Annex. We understand that the building is designated a mission critical facility in accordance with the

Department of Veteran Affairs Seismic Design Requirements H-18-8, dated February 2011. Per H-18-8, our geotechnical services for the design of the Emergency Service Annex include preparation of a geologic hazards report and a geotechnical investigation report. As previously discussed with you, our geologic hazards report is presented as part of our geotechnical investigation report. A site-specific response spectrum for characterization of earthquake ground motions has also been included in the geotechnical report per H-18-8.

In accordance with our revised proposal dated 16 October 2012, the scope of our services consisted of exploring the subsurface conditions at the site, and performing engineering analyses to develop conclusions and recommendations regarding:

• soil and groundwater conditions at the site

• site seismicity and seismic hazards, including potential for fault rupture, ground shaking, liquefaction, lateral spreading, and seismically induced settlements

• appropriate foundation type(s)

• design criteria for the recommended foundation type(s), including vertical and lateral capacities

• estimates of foundation settlements, including total and differential settlements

• site preparation and grading, including criteria for fill quality and compaction

2 Formerly the California Division of Mines and Geology.

• flexible (asphalt concrete) and rigid (Portland cement concrete) pavement design

• concrete flatwork

• site grading, including criteria for fill quality and compaction

• subgrade preparation and moisture protection for floor slabs

• corrosion potential of near-surface soil

• seismic design parameters in accordance with the 2012 International Building Code (IBC) and

ASCE 7-10

• site-specific response spectra in accordance with VA Seismic Design Requirements H-18-8, February 2011 edition

• construction considerations.

3.0 FIELD INVESTIGATION

Subsurface conditions were explored at the Emergency Service Annex site by drilling two borings, designated B-1 and B-2, and advancing two cone penetration tests (CPTs), designated CPT-1 and CPT-2.

The approximate locations of the borings and CPTs are presented on Figure 2. Prior to performing our field investigation, we notified Underground Service Alert and retained a private underground utility locating service to check that locations of exploratory points were clear of existing utilities. Because the borings and CPTs were located on federal property, a drilling permit from San Mateo County

Environmental Health Services Division was not required.

The borings were drilled on 4 February 2013 to depths of about 35 feet below the existing ground surface (bgs) by Exploration Geoservices, Inc. of San Jose, California using a truck-mounted drill rig equipped with hollow-stem augers. During drilling, our field engineer logged the borings and obtained representative samples of the soil encountered for classification. The boring logs are presented in

Appendix A on Figures A-1 and A-2. The soil encountered in the borings was classified in accordance with the soil classification system presented on Figure A-3.

Soil samples were obtained during drilling using Sprague and Henwood (S&H) split-barrel sampler with a

3.0-inch-outside diameter and a 2.5-inch-inside diameter lined with brass or stainless steel tubes with an inside diameter of 2.43 inches. The sampler was driven with a 140-pound, downhole, hydraulic wireline hammer falling 30 inches. The blow counts required to drive the S&H sampler the final 12 inches of an

18-inch drive or to practical refusal were corrected to standard penetration test (SPT) N-values using a correction factor of 0.6 and are shown on the boring logs.

CPT-1 and CPT-2 were advanced to depths of about 51 and 102 feet bgs, respectively, on 4 February

2013 by Middle Earth Geo Testing, Inc. of Fremont, California. The CPTs were performed by hydraulically pushing a 1.4-inch-diameter, cone-tipped probe with a projected area of 10 square centimeters into the ground. The cone-tipped probe measures tip resistance, and the friction sleeve behind the cone tip measures frictional resistance. Electrical strain gauges within the cone continuously measure soil parameters for the entire depth advanced. Soil data, including tip resistance and frictional resistance, were recorded by a computer while the test was conducted. Accumulated data were processed by computer to provide engineering information such as the types and approximate strength characteristics of the soil encountered. Pore pressure dissipation tests were performed in both CPT-1 and CPT-2 to estimate the depth to groundwater. Additionally, shear wave velocity measurements were obtained from

CPT-2 to determine the shear wave velocity profile in the upper 100 feet of the site.

The CPT logs, showing tip resistance and friction ratio by depth, as well as interpreted standard penetration test blow counts and soil classifications, are presented in Appendix A on Figures A-4 and A-5.

The dissipation tests are presented on Figures A-6 and A-7 and the shear wave velocity testing is presented in Figure A-8.

The upper four feet of the borings and CPT-2 were hand augered to check for underground utilities prior to advancing the drilling equipment. Upon completion of the field investigation, the boreholes and CPTs were backfilled with cement grout. Soil cuttings generated from the borings were collected in 55-gallon drums which were transported off-site for disposal.

4.0 LABORATORY TESTING

At the completion of our field investigation, we re-examined the soil samples obtained from our borings in our office to confirm the field classifications and select representative samples for geotechnical laboratory testing. The laboratory testing program was designed to correlate and evaluate engineering properties of the soil at the site. The samples were tested to obtain moisture content, dry density, Atterberg limits, strength, resistance value (R-value), and corrosivity. The laboratory test results are presented in

Appendix B and on the boring logs in Appendix A.

5.0 SUBSURFACE CONDITIONS

Subsurface information from our field investigation indicate the site is generally underlain by layers of medium stiff to hard clay with variable sand content and loose to very dense sand with variable gravel and fines content to the maximum depth explored of 100 feet bgs. Results of Atterberg limits tests performed on the near-surface clay during the investigation indicate it has a moderate expansion potential.3

In boring B-1, a 2½-foot-thick layer of medium stiff silt with variable sand content was encountered at a depth of about 7½ feet bgs (corresponding to approximate Elevation 21.5 feet) and a 5½-foot-thick layer of loose to medium dense clayey sand was encountered at a depth of approximately 14½ feet bgs

(corresponding to approximate Elevation 14.5 feet). Also in boring B-1, a thin layer of layer of medium dense sand (less than one foot thick) was encountered at a depth of approximately 25 feet bgs

(corresponding to approximate Elevation 4 feet). In boring B-2, a thin layer of soft to medium stiff clay, approximately three feet thick, was encountered at a depth of about 7 feet bgs (corresponding to approximate Elevation 22 feet), and a thin layer of loose to medium dense sand (less than one foot thick) was encountered at a depth of about 34 feet bgs (corresponding to approximate Elevation -5 feet).

In the CPTs, the interpreted soil types generally consist of medium stiff to stiff clay and silt. In CPT-1, a

5.5-foot-thick layer of medium dense to very dense sand was encountered at a depth of about 20 feet bgs (corresponding to approximate Elevation 10 feet). In CPT-2, five thin layers of medium dense to very dense sand (ranging from about 1 foot to 4 feet thick) were encountered below a depth of about

20 feet bgs (corresponding to approximate Elevation 8 feet).

Groundwater was measured during drilling in borings B-1 and B-2 at depths of about 25 and 18½ feet bgs, respectively (corresponding to approximate Elevations 4 to 10.5 feet, respectively). Groundwater was measured in CPT-1 and CPT-2 at depths of 17.7 and 16.1 feet bgs, respectively, corresponding to approximate respective Elevations 12.3 feet and 11.9 feet. The groundwater levels observed during the field investigation do not represent stable groundwater table conditions. The groundwater level is expected to vary due to seasonal fluctuations of rainfall.

Expansive soil undergoes large volume changes with changes in moisture content (i.e. it shrinks when dried and swells when wetted.

6.0 REGIONAL GEOLOGY

The site is located within the Coast Ranges geomorphic province that is characterized by northwest-southeast trending valleys and ridges. These are controlled by folds and faults that resulted from the collision of the Farallon and North American plates, and subsequent strike-slip faulting along the

San Andreas Fault System.

According to the Geologic Map of the Palo Alto and Part of the Redwood Point 7 1/2’ Quadrangles, San Mateo and Santa Clara Counties, California (Pampeyan, 1993), the site is located in an area underlain by Holocene age (approximately 11,000 years old to present) medium-grained alluvium (see Figure 3, Regional Geologic Map). This unit is usually up to about 20 feet thick, and characterized as unconsolidated to moderately consolidated, moderately sorted sand, silt, and clayey silt deposited along the edge of coarse-grained alluvial fans, forming much of the flatland alluvial plain along the bay margin.

The unit interfingers with coarse- and fine-grained alluvium.

The Holocene age alluvium is underlain by older, Pleistocene age (approximately 11,000 to 1.8 million years old) alluvium. The older alluvium generally consists of weathered, unconsolidated to moderately consolidated gravel, sand, and silt, grading coarser to the southwest. A prior borehole shown on Figure 3 drilled along the western side of the campus indicates that the alluvium is underlain at a depth of about

536 feet below ground surface by Franciscan assemblage bedrock.

7.0 REGIONAL SEISMICITY AND FAULTING

The major active faults in the area are the San Andreas, Hayward, and San Gregorio faults. These and other faults of the region are shown on Figure 4. For each of the active faults within 50 kilometers (km) of the site, the distance from the site and estimated maximum Moment magnitude4, Mw, [2007 Working

Group on California Earthquake Probabilities (WGCEP, 2008) and Cao, et al. (2003)] are summarized in

Table 1.

4 Moment magnitude is an energy-based scale and provides a physically meaningful measure of the size of a faulting event. Moment magnitude is directly related to average slip and fault rupture area.

TABLE 1

Regional Faults and Seismicity

Fault Segment

Approximate

Distance from Site (km)

Direction from Site

Mean Characteristic

Moment Magnitude

Monte Vista - Shannon 7.7 Southwest 6.5

N. San Andreas - Peninsula 10.4 Southwest 7.2

N. San Andreas (1906 event) 10.4 Southwest 8.1

Total Hayward 20 Northeast 7.0

Total Hayward - Rodgers Creek 20 Northeast 7.3

San Gregorio Connected 26 West 7.5

Total Calaveras 29 East 7.0

N. San Andreas - Santa Cruz 35 Southeast 7.1

Mount Diablo Thrust 42 Northeast 6.7

Zayante-Vergeles 45 Southeast 7.0

Greenville Connected 50 Northeast 7.0

Figure 4 also shows the earthquake epicenters for events with magnitude greater than 5.0 from

January 1, 1800 through January 1996. Since 1800, four major earthquakes have been recorded on the

San Andreas Fault. In 1836, an earthquake with an estimated maximum intensity of VII on the Modified

Mercalli (MM) scale (Figure 5) occurred east of Monterey Bay on the San Andreas Fault (Toppozada and

Borchardt 1998). The estimated Moment magnitude, Mw, for this earthquake is about 6.25. In 1838, an earthquake occurred with an estimated intensity of about VIII-IX (MM), corresponding to a Mw of about

7.5. The San Francisco Earthquake of 1906 caused the most significant damage in the history of the Bay

Area in terms of loss of lives and property damage. This earthquake created a surface rupture along the

San Andreas Fault from Shelter Cove to San Juan Bautista approximately 470 km in length. It had a maximum intensity of XI (MM), a Mw of about 7.0, and was felt 560 km away in Oregon, Nevada, and

Los Angeles. The most recent earthquake to affect the Bay Area was the Loma Prieta Earthquake of

17 October 1989, in the Santa Cruz Mountains with a Mw of 6.9, approximately 54 km from the site.

In 1868, an earthquake with an estimated maximum intensity of X on the MM scale occurred on the southern segment (between San Leandro and Fremont) of the Hayward Fault. The estimated Mw for the earthquake is 7.0. In 1861, an earthquake of unknown magnitude (probably a Mw of about 6.5) was reported on the Calaveras Fault. The most recent significant earthquake on this fault was the 1984

Morgan Hill earthquake (Mw=6.2).

The site is located about 7.7 kilometers northeast of the Monte Vista fault zone. This fault zone is a portion of the larger Foothills thrust fault system that bounds the southwest margin of the Santa Clara

Valley. The fault zone offsets Quaternary alluvium and Santa Clara Formation materials, and was noted to have experienced slip during the 1989 Loma Prieta Earthquake.

Aeromagnetic surveys performed in the area revealed several linear, positive magnetic anomalies that have been interpreted as steeply dipping, planar serpentinite bodies at depth within the Franciscan assemblage bedrock, formed in zones of crustal weakness (Brabb and Hanna, 1981). A subsequent gravity survey revealed a broad, negative isostatic residual anomaly in the same area, which was interpreted to represent a serpentine body at depth, beneath greywacke sandstone (Carle and

Langenhein, 1990). The serpentinite bodies have been interpreted to be occurring in a wide zone of faulting, designated the Redwood City Fault Zone, which has been deemed inactive during Holocene time as they have not been found to offset sediments within the overlying alluvium.

The 2007 WGCEP at the U.S. Geologic Survey (USGS) predicted a 30-year probability of a magnitude 6.7 or greater earthquake occurring in the San Francisco Bay Area to be about 63 percent. More specific estimates of the probabilities for different faults in the Bay Area are presented in Table 2.

TABLE 2

WGCEP (2008) Estimates of 30-Year Probability of a Magnitude 6.7 or Greater Earthquake

Fault

Probability

(percent)

Hayward – Rodgers Creek 31

North San Andreas 21

Calaveras 7

San Gregorio Connected 6

Mount Diablo Thrust 1

8.0 DISCUSSION AND CONCLUSIONS

We conclude that from a geotechnical engineering standpoint, the site can be developed as proposed, provided the recommendations presented in this report are incorporated into the project plans and specifications, and are implemented during construction. The primary geotechnical concerns for the

Emergency Service Annex project are the presence of moderately expansive near-surface soil and the presence of potentially liquefiable soil below the water table. Our conclusions regarding seismic hazards, the most appropriate foundation type(s), settlement, and other geotechnical issues are presented in this section.

8.1 Seismic and Geologic Hazards

During a major earthquake on one of the nearby faults, strong to very strong shaking is expected to occur at the site. Strong shaking during an earthquake can result in ground failure such as that associated with soil liquefaction,5 lateral spreading,6 and cyclic densification.7 We used the results of the borings and CPTs to evaluate the potential for these phenomena to occur at the site. The results of our evaluation are presented below.

8.1.1 Fault Rupture

Historically, ground surface displacements closely follow the trace of geologically young faults. The site is not within an Earthquake Fault Zone, as defined by the Alquist-Priolo Earthquake Fault Zoning Act, and no active or potentially active faults exist on the site. In a seismically active area, the remote possibility exists for future faulting in areas where no active faults previously existed; however, we conclude the risk of surface faulting and consequent secondary ground failure from previously unknown faults is low.

Liquefaction is a transformation of soil from a solid to a liquefied state during which saturated soil temporarily loses strength resulting from the buildup of excess pore water pressure, especially during earthquake-induced cyclic loading. Soil susceptible to liquefaction includes loose to medium dense sand and gravel, low-plasticity silt, and some low-plasticity clay deposits.

Lateral spreading is a phenomenon in which surficial soil displaces along a shear zone that has formed within an underlying liquefied layer. Upon reaching mobilization, the surficial blocks are transported downslope or in the direction of a free face by earthquake and gravitational forces.

Cyclic densification is a phenomenon in which non-saturated, cohesionless soil is compacted by earthquake vibrations, causing differential settlement.

8.1.2 Soil Liquefaction and Associated Hazards

Liquefaction is a phenomenon in which saturated soil temporarily loses strength from the build-up of excess pore water pressure, especially during earthquake-induced cyclic loading. Flow failure, lateral spreading, differential settlement, loss of bearing strength, ground fissures, and sand boils are evidence of excess pore pressure generation and liquefaction. We evaluated liquefaction potential at the site in accordance with Special Publication 117A, Guidelines for Evaluating and Mitigating Seismic Hazards Zones in California, dated 11 September 2008. The California Geological Survey (CGS) has prepared a map titled State of California Seismic Hazard Zones, Palo Alto Quadrangle, dated 18 October 2006. This map was prepared in accordance with the Seismic Hazards Mapping Act of 1990. Based on this map, the site is within a liquefaction hazard zone, as shown on Figure 6.

A peak ground acceleration (PGA) of 0.48g was used for the project; this PGA was calculated based on the spectral response accelerations Ss and S1 from the Department of Veterans Affairs Manual H-18-8, Seismic Design Requirements, dated February 2011 for the VA Menlo Park campus. We assumed an earthquake magnitude of 8.1, which is the maximum Moment magnitude for the San Andreas Fault, located 10.4 kilometers from the site.

The liquefaction analyses were performed in accordance with the methodology presented in the publication titled Proceedings of the NCEER Workshop on Evaluation of Liquefaction Resistance of Soils, prepared by the National Center for Earthquake Engineering Research (NCEER), dated 31 December

1997. The susceptibility of sand to liquefaction under seismic loading was evaluated in general accordance with the procedure presented by Seed and Idriss (1982). Our liquefaction analysis using the boring and CPT data indicates that thin, isolated, and discontinuous layers of loose to medium dense granular soil below the groundwater table are susceptible to liquefaction (FSliq<1.3) following a major earthquake on a nearby fault.

We estimated liquefaction-induced settlement using the procedure outlined in the NCEER report. The strain potential of any potentially liquefiable layers was estimated in accordance with the method developed by Tokimatsu and Seed (1984), which relates (N1)60,CS values to strain potential. The estimated liquefaction-induced settlement is summarized below in Table 3.

TABLE 3

Estimated Liquefaction-Induced Settlement

Location

Approximate Total Thickness of

Potentially Liquefiable Soil Layers

(feet)

Estimated Settlement

(inches)

B-1 5 1/3

B-2 0.5 1/8

CPT-1 3 1/4

CPT-2 10 1¼

Based on our liquefaction analyses, we conclude that up to about 1¼ inches of liquefaction-induced total settlement may occur in the vicinity of the Emergency Service Annex after a major earthquake on a nearby fault. We estimate that differential settlements on the order of about 1 inch may occur between columns.

The potential for liquefaction-induced ground rupture and sand boils to occur at the site depends on the thickness of the liquefiable soil layer relative to the thickness of the overlying non-liquefiable material.

Ishihara (1985) presented an empirical relationship that provides criteria that can be used to evaluate whether liquefaction-induced surface ruptures and sand boils would be expected to occur under a given level of shaking for a liquefiable layer overlain by a non-liquefiable surficial layer. The potentially liquefiable soil layers encountered in the borings and CPTs are between 1 and 5 feet thick, and are located below a depth of 15 feet bgs. We conclude that the potential for manifestations of liquefaction to occur at the ground surface is low.

8.1.3 Lateral Spreading

Lateral spreading occurs when a continuous layer of soil liquefies at depth and the soil layers above move toward an unsupported face, such as an open slope cut, or in the direction of a regional slope or gradient. The potential for lateral spreading to occur at a site is typically evaluated using an empirical relationship developed by Youd et al. (2002). This relationship incorporates the thickness of the liquefiable layer, the fines content and mean grain-size diameter of the liquefiable soil, the relative density of the liquefiable soil, the magnitude and distance of the earthquake from the site, the slope of the ground surface, and boundary conditions (such as a free face or edge of shoreline), to estimate the horizontal ground movement. The potentially-liquefiable soil layers encountered at the site are thin, isolated, and discontinuous. In addition, the ground surface at the site is relatively level. Therefore, we conclude the potential for lateral spreading at the site is low.

8.1.4 Cyclic Densification

Cyclic densification of non-saturated sand (sand above the groundwater table) caused by earthquake vibrations may result in settlement. Several feet of loose to medium dense clayey sand was encountered above the design groundwater level in boring B-1. We compute that shallow foundations and surface improvements bearing within these non-saturated granular layers may settle up to approximately

1/4 inch due to strong shaking from a large earthquake, with a possibility of abrupt differential settlements of up to 1/4 inch.

8.1.5 Landslides, Erosion, and Seepage

The site is relatively level and groundwater is anticipated to be below about 15 feet bgs. We conclude the potential for geologic hazards such as landsliding, erosion, and seepage to occur at the site is very low.

8.2 Foundation Support

Based on our field investigation, we anticipate the soil exposed at the foundation level of the Emergency

Service Annex will be medium stiff to stiff clay or loose clayey sand. The soil at the foundation level has moderate strength and relatively low compressibility.

The site is underlain by moderately expansive near-surface soil. Expansive soil is subject to high volume changes during seasonal fluctuations in moisture content, which can cause cracking of foundations and floor slabs. The detrimental effects of near-surface expansive soil can be mitigated by moisture conditioning the expansive soil below slabs, placing non-expansive fill below slabs, supporting foundations below the zone of severe moisture change, and/or designing foundations to resist the movements associated with the volume changes. Because expansive soil is present, we conclude the

Emergency Service Annex foundations should be deepened to reduce the potential for movement due to moisture change. We conclude the Emergency Service Annex can be supported on deepened isolated spread footings at interior column locations and continuous, deepened perimeter footings bearing on native soil.

We estimate the total static settlement of properly constructed spread footings due to static loading, designed using the recommendations presented in Section 9.2, will be less than 1/2 inch, with up to

1/4 inch of differential settlement across a horizontal distance of 25 feet. In addition to the static settlements, seismically-induced settlement may occur during a major earthquake, as discussed in

Section 8.1.

8.3 Floor Slabs

The near-surface soil is generally medium stiff to stiff, and we conclude the floor slab may be supported on grade, provided the settlement predicted due to a major earthquake is acceptable. The slab-on-grade floor may experience cracking and differential settlement resulting from seismically-induced liquefaction and cyclic densification. If moisture on the floor slab is undesirable, a capillary moisture break and water vapor retarder (recommended in Section 9.3) can be installed beneath the slabs to reduce water vapor transmission through the slabs.

To mitigate the potential for movement of the slab where expansive soil is present, the floor slab and capillary break/vapor retarder should be underlain by at least 12 inches of non-expansive soil. The following two alternatives may be used to provide a 12-inch-thick layer of non-expansive soil beneath the slabs-on-grade:

Alternative No. 1: The building pad should be overexcavated to allow for the placement of 12 inches of select (nonexpansive) fill beneath the floor slab and capillary break/vapor retarder. The soil subgrade at the base of the excavation should be properly moisture-conditioned prior to placement of the select fill.

Alternative No. 2: As an alternative to importing select fill, the upper 12 inches of soil beneath the floor slab and moisture barrier may be lime-treated. The purpose of the lime treatment is to reduce the expansion potential of the surface soil and provide a firm surface for construction of the floor slab.

8.4 Corrosion Potential

We performed corrosivity tests on soil samples collected from borings B-1 and B-2 at 8.5 feet bgs and

2.0 feet bgs, respectively. The soil samples were tested in accordance with Caltrans and ASTM protocols by Environmental Technical Services (ETS) of Petaluma, California. The corrosivity test results are presented in Appendix B on Figure B-4.

9.0 RECOMMENDATIONS

Our recommendations regarding earthwork, foundation design, floor slabs, pavement design, and other geotechnical aspects of this project are presented in this section.

9.1 Earthwork

9.1.1 Site Preparation

Site preparation should include removal of all existing structures, foundations, slabs, pavements, and underground utilities within the footprint of the planned development. Existing foundations should be removed to expose native soil. All areas to receive improvements should be stripped of vegetation and organic topsoil. Stripped materials should be removed from the site or stockpiled for later use in landscaped areas, if approved by the landscape architect. Any existing fill encountered should be removed and recompacted. Underground utilities should be removed to the service connections and properly capped or plugged with concrete. Where existing utility lines will not interfere with the planned construction, they may be abandoned in-place, provided the lines are filled with lean concrete or cement grout to the limits of the project. Voids resulting from demolition activities should be properly backfilled with engineered fill as described in Section 9.1.3.

From a geotechnical standpoint, concrete and asphalt generated by demolition may be crushed and reused providing it is free of organic material and rocks or lumps greater than three inches in greatest dimension. The acceptability of using crushed asphalt at the site should be verified by the VA and architect. Where crushed asphalt pavement materials are used, particles between 1-1/2 and 3 inches in greatest dimension should comprise no more than 30 percent of the fill by weight.

9.1.2 Subgrade Preparation

The floor slab and underlying capillary break/vapor retarder (recommended in Section 9.3) should be underlain by at least 12 inches of non-expansive soil consisting of either select fill or lime-treated native soil, as described in the following sections. The soil subgrade should be kept moist until it is covered by fill or improvements.

Slabs-on-Grade

Placement of Select Fill (Alternative No. 1)

If Alternative No. 1 is selected, we recommend the building pad be overexcavated to allow placement of at least 12 inches of select fill beneath the slab-on-grade floor and underlying capillary moisture break.

The limit of overexcavation for select fill placement should extend at least five feet beyond the building footprint. If the building pad will be raised at least 12 inches above the existing ground surface following demolition, overexcavation will not be necessary. However, the fill used to raise the grade should be non-expansive. The native expansive soil at the base of the overexcavation or at current grade prior to raising grades should be scarified to a depth of at least 12 inches, moisture-conditioned to at least three percent above optimum moisture content, and compacted to between 88 and 92 percent relative compaction.8 If non-expansive soil is exposed at the base of the overexcavation, it should be scarified to a depth of at least 6 inches, moisture-conditioned to at least two percent above optimum moisture content, and compacted to at least 90 percent relative compaction.

Lime Treatment (Alternative No. 2)

If Alternative No. 2 is selected, the upper 12 inches of the building pad (measured below the capillary moisture break) should be treated in place with between four to eight percent (to be determined by the contractor) dolomitic quicklime by dry weight of soil. The limit of lime treatment should extend at least five feet beyond the building footprint. A specialty subcontractor typically performs lime treatment, and we recommend this work be performed only by an experienced contractor. The contractor should determine the percent lime to be used. Prior to lime treatment, we recommend the site be graded to a level pad elevation in accordance with our previous recommendations and all below-grade obstructions be removed. The soil treated with lime should be mixed and compacted in one lift. The lime should be

8 Relative compaction refers to the in-place dry density of soil expressed as a percentage of the maximum dry density of the same material, as determined by the ASTM D1557-09 laboratory compaction procedure.

thoroughly blended with the soil and allowed to cure for 24 hours prior to compaction. The lime-treated soil should be moisture-conditioned to above optimum moisture content and compacted to at least

90 percent relative compaction. Lime-treated soil should be removed from landscaping areas as it will inhibit growth of vegetation. It should be noted that disposal of lime-treated soil is typically expensive because of the high pH of the treated soil.

Pavement Areas

In asphalt and concrete pavement areas, where on-site engineered or select fill is exposed at soil subgrade, the upper six inches should be moisture-conditioned to above optimum moisture content and compacted to at least 95 percent relative compaction to provide a smooth non-yielding surface. Where expansive soil is present, concrete pavement sections should be underlain by at least six inches of select fill. Additionally, the upper 12 inches of expansive clay should be moisture-conditioned to at least two percent over optimum moisture content and compacted to at least 90 percent relative compaction.

Concrete Flatwork Areas

As a minimum preparation for exterior concrete flatwork, including patio slabs and sidewalks, the upper

12 inches of expansive native soil at subgrade should be moisture-conditioned to at least three percent above optimum moisture content and compacted to between 88 and 92 percent relative compaction.

If it is desirable to reduce the potential for differential movement and cracking, exterior concrete flatwork should be underlain by at least 12 inches of select fill, lime-treated soil, or Caltrans Class 2 aggregate base (AB), as recommended in Section 9.4. Select fill at subgrade in concrete flatwork areas should be moisture-conditioned to above optimum moisture content and compacted to at least 95 percent relative compaction.

9.1.3 Fill Placement

We anticipate fill placement at the site will consist primarily of minor grading for the building pad and backfill for utility trenches. Because the on-site soil is moderately expansive, on-grade floor slabs should be underlain by at least 12 inches of select fill or lime-treated soil, and concrete flatwork should be underlain by at least 12 inches of select fill, lime-treated soil, or Caltrans Class 2 AB, as recommended in

Section 9.1.2. Prior to placement of fill, the subgrade soil should be scarified, moisture-conditioned, and recompacted as recommended in Section 9.1.2.

If native expansive clay is to be used as general site fill, it should be moisture-conditioned to at least three percent above optimum moisture content, placed in horizontal lifts not exceeding eight inches in loose thickness, and compacted to between 88 and 92 percent relative compaction.

Select fill should consist of imported or on-site soil that is free of organic matter and hazardous material, contain no rocks or lumps larger than three inches in greatest dimension, have a liquid limit less than 40 and plasticity index less than 12, and be approved by the geotechnical engineer. In addition, select fill placed outside the building footprint should contain at least 20 percent fines (particles passing the No.

200 sieve) to reduce the potential for surface water to infiltrate beneath slabs. Select fill should be placed in lifts not exceeding eight inches in loose thickness, moisture-conditioned to above optimum moisture content, and compacted to at least 90 percent relative compaction for fill thickness equal to or less than five feet and 95 percent relative compaction for fill thickness greater than five feet.

We should approve all sources of engineered fill at least three days before use at the site. The grading subcontractor should provide analytical test results or other suitable environmental documentation indicating the imported fill is free of hazardous materials at least three days before use at the site. If this data is not available, up to two weeks should be allowed to perform analytical testing on the proposed import material.

9.1.4 Utility Trenches

Excavations for utility trenches can be made with a backhoe. All trenches should conform to the current

CAL-OSHA requirements for slopes, shoring, and other safety concerns. Site Condition C (swelling soils) should be used for utility boxes designed using Section 33 63 00, Appendix II, of the VA Specifications.

To provide uniform support, pipes or conduits should be bedded on a minimum of four inches of sand or fine gravel. After the pipes and conduits are tested, inspected (if required), and approved, they should be covered to a depth of six inches with sand or fine gravel, which should be mechanically tamped. If groundwater is encountered during trench excavation, the gravel used as bedding and cover should be replaced with Caltrans Class 2 permeable material below the water level, or the open-graded gravel used as bedding and cover should be wrapped in filter fabric (Mirafi 140N or equivalent) to reduce the potential for infiltration of fines.

Backfill for utility trenches and other excavations is also considered fill and should be placed and compacted according to the recommendations previously presented. If imported clean sand or gravel

(defined as soil with less than 10 percent fines) is used as backfill, it should be compacted to at least

95 percent relative compaction. Jetting of trench backfill should not be permitted. Special care should be taken when backfilling utility trenches in pavement areas. Poor compaction may cause excessive settlements, resulting in damage to the pavement section.

Where utility trenches backfilled with sand or gravel enter the building pads, an impermeable plug consisting of native clay or lean concrete, at least five feet in length, should be installed at the building line. Further, where sand- or gravel-backfilled trenches cross planter areas and pass below asphalt or concrete pavements, a similar plug should be placed at the edge of the pavement. The plug should extend from the bottom of the trench to the subgrade elevation. The purpose of these recommendations is to reduce the potential for water to become trapped in trenches beneath the building or pavements.

This trapped water can cause heaving of soils beneath slabs and softening of subgrade soil beneath pavements.

9.2 Foundation Support

Based on our field investigation, we anticipate the soil exposed at the foundation level of the Emergency

Service Annex will be medium stiff to stiff clay and loose clayey sand. The soil at the foundation level has moderate strength and relatively low compressibility. Considering the building loads are relatively light, we conclude the Emergency Service Annex can be supported on a combination of isolated interior spread footings and deepened continuous perimeter footings bearing on native soil. Because of the presence of near-surface expansive soil, foundations should be deepened below the zone of severe moisture change, as discussed in Section 8.2.

Continuous footings should be at least 18 inches wide and isolated spread footings should be at least

24 inches wide. To reduce the potential for movement of the footings due to shrink and swell of the expansive clay, we recommend the perimeter footings be bottomed at least 24 inches below the lowest adjacent exterior soil subgrade or the top of the select fill or lime-treated layer (recommended in

Section 9.1.2), whichever is deeper. Interior footings should extend at least 24 inches below the lowest adjacent soil subgrade (measured from the top of the select fill or lime-treated soil). Footings located adjacent to utility trenches should bear below an imaginary 1.5:1 (horizontal to vertical) plane projected upward from the bottom edge of the adjacent trench.

Footings should be designed using allowable bearing pressures for dead plus live loads of 3,300 pounds per square foot (psf). The allowable bearing pressure may be increased by one-third for total loads, including wind or seismic forces, and includes factors of safety of at least 2.0 and 1.5 for dead plus live loads and total loads, respectively. To design footings using the modulus of subgrade reaction method, we recommend a modulus of subgrade reaction of 70 kips per cubic foot; this modulus is representative of the anticipated settlement under the building loads provided.

Lateral loads can be resisted by a combination of passive pressure acting on the vertical faces of the footings and friction along the base of the footings. We recommend passive resistance be calculated using the following values:

• an equivalent fluid weight (triangular distribution) of 350 pounds per cubic foot (pcf) in select fill

• a uniform pressure of 2,000 psf in lime-treated soil

• a uniform pressure of 1,500 psf for onsite soil.

The upper foot of soil should be ignored unless it is confined by slabs or pavement. Frictional resistance at the base of the footings should be computed using a friction coefficient of 0.25. These values include a factor of safety of about 1.5. Uplift loads may be resisted by the weight of the footing and any overlying soil.

The footing excavations should be free of standing water, debris, and disturbed materials prior to placing concrete. If non-engineered fill is encountered in a footing excavation, the fill should be overexcavated to expose native soil. The excavated material should be replaced with either structural concrete or sand-cement slurry with a 28-day compressive strength of at least 50 pounds per square inch (psi). The bottoms and sides of excavations should be wetted following excavation and maintained in a moist condition until concrete is placed. If the foundation soil dries during construction, the foundation will eventually heave, which may result in cracking and distress. We should check foundation excavations prior to placement of reinforcing steel to confirm suitable bearing material is present. We should recheck the condition of the excavations just prior to concrete placement to confirm the excavations are sufficiently moist.

9.3 Concrete Floor…