Geotechnical Study - VA Administration Building - Mtn View.pdf

Geotechnical Study Proposed New VA Administration Building

Jones Hall Army Reserve Center 1776 Old Middlefield Road

Mountain View, California

Submitted to:

Mr. David Ewell

C/O Steinberg Architects 60 Pierce Avenue

San Jose, California

Geotechnical and Environmental Consulting Engineers

File No. 10540-S February 2011

ADVANCE SOIL TECHNOLOGY, INC.

Engineers, Geologists & Environmental Consultants 343 Baywood Avenue - San Jose, California 95128 Office: (408)-261-1155 ♦ Fax: (408)-261-1588

February 16, 2011

Mr. David Ewell C/O Steinberg Architects 60 Pierce Avenue San Jose, California 95110

Subject: Propose New VA Administration Building Jones Hall Army Reserve Center 1776 Old Middlefield Road Mountain View, California

Geotechnical Study

Dear Mr. Ewell

Pursuant to your request and authorization, Advance Soil Technology, Inc.

conducted geotechnical study for the Proposed New VA Administration Building to be associated with the existing Jones Hall Army Reserve Center located at 1776 Old Middlefield Road in Mountain View, California.

In the proceeding sections of this report, enclosed please find the results of our investigation / study, conclusions, considerations and recommendations that are to be incorporated in the design and during the construction phase of the project.

We are pleased to be of service to you in this matter. If you have any questions or require additional information, please feel free to contact us at your convenience.

Very truly yours, ADVANCE SOIL TECHNOLOGY, INC.

Almirza Alexkassai Al Mirza Alex A. Kassai PE/REA Project Engineer Principal Am/aak/am/cj PE #34882 Cc: File Copies: Enclosed

Geotechnical Study

Jones Hall Army Reserve Center 1776 Old Middlefield Road Mountain View, California

Submitted to:

Mr. David Ewell

C/O Steinberg Architects 60 Pierce Avenue

San Jose, California

February 2011

Inc. Geotechnical / Environmental Consulting Engineers

Jones Hall Army Reserve Center – Mountain View, California AST Project No. 10540-S Page 4

TABLE OF CONTENTS

SOIL INVESTIGATION PAGE

Front Page 1 Transmittal Letter 2 Cover Page 3 Table of Content 4-5

1.0 Introduction / Site Description 6

2.0 Project Description 6

3.0 Scope of Services 6-7

4.0 Site Conditions 7

4.1 Surface Conditions 7

4.2 Field Investigation 7

4.3 Subsurface Soil Conditions 7-8

4.4 Groundwater 8

5.0 Laboratory Testing 8

5.1 Corrosivity Analysis 9-10

6.0 Geologic Setting 10

6.1 Regional Geology 10

6.2 Local Geology 10

7.0 Geological Hazard - Liquefaction 10-11

7.1 Liquefaction Potential 11

7.2 Liquefaction Evaluation & Analysis Criteria 11-12

7.3 Peak Ground Acceleration 12

7.4 Historical Groundwater 12

7.5 Summary of Analysis – Settlement due to Liquefaction 12-13

7.6 Cyclic Densification 13

7.7 Differential Compaction 13

7.8 Lateral Spreading 13

8.0 Geological Hazard - Seismic Hazard Assessment 13

8.1 Seismicity – Ground Shaking 13-14

8.2 Nearest Seismic Source 14

8.3 Maximum Estimated Ground Shaking 14

8.4 Site Characterization / Seismic Criteria 14-15

8.5 Ground Rupture 16

8.7 Ground Lurching 16

8.8 Future Earthquake Probability 16-17

9.0 Conclusions 17-18

10.0 Considerations 18-19

Recommendations -

11.0 Grading Recommendations 19

11.1 Existing Utilities 19

11.2 Earthwork – Demolition, Clearing & Site Preparation 19-20

11.3 Pad Preparation 20

11.4 Lime Treatment 20-21

11.5 Fill Materials 21

11.6 Temporary Slopes, Trench Excavations & Dewatering 21

12.0 Concrete Slab-on-Grade 21

12.1 Interior Concrete Slab-on-Grade 21-22

12.2 Exterior Concrete Slab-on-Grade 22

AST Project No. 10540-S Page 5

SOIL INVESTIGATION PAGE

13.0 Foundation 22

13.1 Structural Rigid Mat Foundation 23-24

13.2 Continuous Perimeter & Interior Isolated Footings w/ Interlocking Grade Beams 24-25

13.3 Anticipated Settlements 25-26

13.3 Lateral Load Resistance 26

14.0 Active & Passive Pressures 26-27

14.1 Drainage behind Walls 27

14.2 Backfill Behind Walls 27

14.3 Foundation for Retaining Walls 27

15.0 On Site Utility Trenching 27-28

16.0 Pavement Design 28

16.1 Subgrade Preparation for Parking Areas, Vertical Curbs, Curb & Gutter Areas 28

16.2 Rigid Concrete Pavement 28-29

16.3 Flexible Pavement 29

16.4 Seepage Control 30

17.0 Site Drainage 30

17.1 Surface Drainage 30

18.0 Additional Services 31

18.1 Plan Review and Construction Observation 31

18.2 Construction Acceptance 31

18.3 Seasonal Limits 31

18.4 Unusual / wet conditions 32

19.0 Limitations & Uniformity of Conditions 32

20.0 References 33-34

Appendix “A”

Plate 1 Site Location Map Plate 2 Site Location Map – Aerial View Plate 3 Topographic Map Plate 4 Geologic Map Plate 5 Description of Map Units Plate 6 Site Plan Plate 7-9 Soil Classification & Terminology Plate 10-16 Exploratory Log EB-1 to EB-4 Plate 17-18 Plasticity Index Plate 19-23 Unconfined Compression Test Plate 24-25 Particle Size Distribution Plate 26 Results of Corrosivity Analysis

Appendix “B”

Plate 27-28 Site Characterization & Seismic Faults Plate 29-31 IBC 2006 Seismic Hazard Analysis Plate 32 Peak Ground Acceleration Plate 33 Historical Groundwater Plate 34 California Nevada Fault Map Plate 35 Historical Earthquake Map / Epicenters of Earthquakes Plate 36 Magnitude / Intensity Comparison Plate 37 Earthquake Probabilities

AST Project No. 10540-S Page 6

Geotechnical Study Proposed New VA Administration Building Jones Hall Army Reserve Center 1776 Old Middlefield Road Mountain View, California

1.0 Introduction / Site Description

This report provides the results of our geotechnical investigation for the Proposed New VA Administration Building to be associated with the existing development at the Jones Hall Army Reserve Center located at 1776 Old Middlefield Road in Mountain View, California. The purpose of this study was to determine the existing subsurface soil conditions and provide recommendations for the design, based on the laboratory analysis of the materials underlying the site.

In the following sections, this report provides details of the results of this study, conclusions, considerations and recommendations that are to be incorporated in the design and during the construction phase of the project.

The general site description referred to in this report is based on our discussion, site plans and reconnaissance of the site of proposed improvements. Please refer to site plan with approximate boring locations on Plate (6) in Appendix “A” of this report.

2.0 Project Description

Based on the information received and as presently planned, it is our understanding that the project will include construction of a two-story building at the above-mentioned facility. However, the anticipated loads and structural loading conditions are unknown at this time and shall be forwarded to AST for review upon finalizing the proposed design and structural loads. Other associated improvements at the site will include underground utilities, exterior flatwork with other appurtenant improvements associated with them.

3.0 Scope of Services

The scope of our services for this study included the following:

♦ Reconnaissance of the site of proposed improvements, location of the utility lines with respect to the boring locations, prior to drilling.

♦ Review of Existing Available Reports for other improvements.

♦ Exploration of subsurface soil conditions by drilling (4)-exploratory borings for retrieving soil samples for observation and laboratory testing.

♦ Overall assessment of the general surface and subsurface soil conditions.

♦ Laboratory analysis of the soil samples retrieved from the boring locations.

AST Project No. 10540-S Page 7

♦ Seismic evaluation of the site including liquefaction, ground shaking, distance from the earthquake faults, seismic coefficients per the requirements of IBC 2006 and future earthquake probability.

♦ Recommendations for overall grading at the site.

♦ Recommendations for the type of foundation, including design requirements for the retaining walls, slab-on-grade construction, skin friction and modulus of subgrade reaction.

♦ Estimated total and differential settlement between the structures.

♦ Recommendations for pavement design.

♦ Recommendations for surface and subsurface drainage.

4.0 Site Conditions

4.1 Surface Conditions

At the time of this investigation, the site of the proposed improvement was covered with asphalt pavement and was being utilized for parking areas. The site of proposed improvements is located to the south-southwest of Highway (101) bordering to the north and east, Old Middlefield Road to the south, Permanente Creek to the West along other improvements bordering to the north, south and west respectively. Topographic information was not available at the time of this study; however our field observation indicates that the site of proposed improvements is a flat parcel of land and so is the natural topography of the area with surface grade elevation of approximately 22 to 23 feet.

4.2 Field Investigation

The subsurface soil investigation at the site of proposed improvements was conducted on January 12, 2011. The investigation included the drilling of (4)-exploratory borings to a depth of approximately (25)-feet to (50)-feet below the existing ground surface. A truck mounted drill-rig with an eight inch diameter hollow stem auger was utilized for drilling the borings. Undisturbed soil samples were extracted as the borings progressed, by hammering a (3.0) inch O.D split spoon sampler and Terzaghi standard split spoon sampler into the ground. A 140-pound hammer with the free fall of (30)-inches was utilized to drive the sampler into the ground. Undisturbed soil samples were retained within brass liners inside the split spoon sampler and the soils encountered in the borings were continuously logged in the field during the drilling operation. Blow counts for the last one-foot of driving were recorded in the field during the drilling operation.

4.3 Subsurface Soil conditions at the Site

The subsurface soil conditions encountered at the site of proposed improvements included shallow surficial clayey fills ranging between (6.5) to (7.0)-feet below the existing ground surface. Below the above-mentioned depth, the native soils predominantly consisted of stiff to very stiff clayey soils with interbedded layers of

AST Project No. 10540-S Page 8 clayey sands, silty sands and sands with gravels that extended to a depth of the borings, approximately (50)-feet below the existing ground surface. Please note that the above information depicts the existing subsurface soil conditions at the specific boring location as reflected on the site plan. Stratification lines represent the approximate boundaries between the material types. The actual transitions between the materials may be gradual. Subsurface soil and groundwater conditions may vary at other locations from the conditions that were encountered at the boring locations with the passage of time. For information, please refer to the boring logs on Plates (10) thru (25) enclosed in Appendix “A’” of this report.

4.4 Groundwater

Free groundwater was encountered in the borings at a depth of approximately (6.5)-feet below the existing ground surface. However, based on the review of the CGS Seismic Hazard Zone Map Report (060) for the Mountain View Quadrangle, it is our understanding that the historic groundwater elevation in the vicinity of this site is being considered to be at a depth of approximately less than (<±5.0)-feet below the existing ground surface.

Please note that seasonal groundwater studies were beyond the scope of this investigation, it shall be noted that groundwater level and elevation may fluctuate due to variations in rainfall, geological changes, temperature, pumping water from the wells and other factors that were not evident at the time of this investigation.

Localized perched water conditions / seepage may exists and could also be contributing factor for saturated conditions in the upper layers of the soils and the area in general due to excessive irrigation, over-saturated landscape areas, seepage from elevated parcels of land, rainfall or due to use of containment area for storm water disposal, bio-swales and elevated adjacent parcel of land.

5.0 Laboratory Testing

Laboratory testing program performed on the soil samples collected from the site was directed towards a quantitative determination of the physical and engineering properties of the soils underlying the site. In order to determine the consistency of the soil and moisture variation throughout the explored profile, all relatively undisturbed soil samples were tested for moisture content and dry density.

To evaluate the strength characteristics of the soil for the foundation engineering design, unconfined compression tests were performed on relatively undisturbed soil samples collected at various depths along with Atterberg Limits Tests to determine the Liquid Limit and Plasticity Index of the soil samples and particle size distribution. The laboratory analyses were conducted in accordance with the criteria and guidelines set-forth by CGS Special Publication 117 ”Guidelines for Evaluating and Mitigating Seismic Hazards in California, SCEC (1999) – Southern California Earthquake Center Report. The results of laboratory testing are presented on Plates

(10) thru (25) in Appendix "A" of this report.

AST Project No. 10540-S Page 9

5.1 Corrosivity Analysis

The National Association of Corrosion Engineers (NACE) defines corrosion as “deterioration of a substance or its properties because of a reaction with its environment.” For inland construction the “environment is the surrounding soil and the “substances” are reinforced concrete foundation or various types of steel substructures such as piles, pipes, metal fittings etc. that are in contact with the soil.

Henceforth, in order to determine the impact of soil corrosion at the site, soil samples from the exploratory boring locations were collected for chemical analysis.

The samples were collected from varying depths below the existing ground surfaces. The samples were composited and analyzed for chloride and sulfate concentration, pH, saturated resistivity, Redox potential and moisture percentage.

The results of the analysis by Cooper Testing laboratories, Inc. - dated February 02, 2011 were as follows:

Soil Laboratory Analysis

Chemical Analysis Range of Results Corrosion Classification

Chlorides 9 mg/kg Non-corrosive

Sulfates < 5 mg/kg Non-Corrosive pH 7.9 Non-Corrosive

Saturated Resistivity 1216 ohm-cm Highly Corrosive

Redox 197 Corrosive

In general, soil environments that are detrimental to concrete have high concentrations of soluble sulfates and /or pH values of less than 5.5. Based upon the recommendations promulgated by the Portland Cement Association and as adopted by the Building Code, specific guidelines have been established for concrete mix–design when soluble sulfate content of the soil exceeds 0.1 percent by weight or 1000 parts per million (ppm). The minimum concentration of chloride ions in the soil environment that are corrosive to steel, either in the form of reinforcement protected by concrete cover or plain steel substructures such as steel pipes, metal fittings or piles, is 1500 ppm as determined by the test.

Concentrations of chloride ions, above the stated concentration or other characteristics such as soil resistivity or redox potential may warrant special corrosion protection measures.

Please note that the tests above are only an indicator of potential soil corrosivity.

Other soils found on the site may be more or less or of a similar nature. AST Inc.

AST Project No. 10540-S Page 10 does not practice the field of corrosion engineering. A competent corrosion engineer could be retained if needed to provide recommendations and mitigation measures to minimize the impact of soil corrosion on buried concrete, metal pipes, post tensioning strands and anchors etc.

6.0 Geologic Setting

6.1 Regional Geology

Geologically, the site of the proposed improvements is located within the physiographic region known as the San Francisco Bay area, which itself is within the Coast Range geomorphic province of California, which is a series of northwest trending mountains and valleys along the western edge of the North American Continent. This region has undergone a complex geologic history of sedimentation, volcanism, folding, faulting; uplift and erosion. The San Francisco Bay occupies a late Pliocene structural depression bounded by a series of nearly parallel mountain ranges with Diablo Range to the east and Santa Cruz Mountains to the west, which resulted from a down drop block of the Franciscan formation caused by faulting and warping. The northwest trending depression extends from Petaluma Valley on the north to Santa Clara Valley on the south. The bay is bound by the East Bay Hills to the east and the San Francisco-Marin Peninsulas to the west. The sediments in and around the bay are composed of mostly broad alluvial fans, flood plains, deltantic and marine deposits. These deposits vary in composition from alluvial sands, silts and clays to marshy deposits of the San Francisco Bay.

6.2 Local Geology

To identify and characterize the site, geologic maps and CGS Seismic Hazard Zone Open File Report (060) for the Mountain View Quadrangle were reviewed to identify the geological conditions at the site. Review of the above mentioned report and Geologic Map and the quaternary units mapped by Witter and others in 2006 indicates that the site and the surrounding areas in the Mountain View Quadrangle are underlain with Holocene alluvial fan deposits, fine grained facies (Qhff) and Holocene alluvial fan deposits (Qhf) to the west of Highway (101) and mostly artificial fills (af) and artificial levee fills (alf) to the east of Highway (101).

However, the soils layers encountered at the site in general exhibited moderate to high plasticity clays, sandy clays with interbedded layers of clayey silts and sands with some gravel and varying degree of moisture content. These layers were very moist, stiff to very stiff and medium dense to dense.

7.0 Geological Hazard - Liquefaction

Since the site of the proposed improvement is located in a seismically active region, we have evaluated the potential for earthquake induced geological hazards based on the geologic setting, existing soil conditions and the depth of groundwater at the site. The evaluation of the geological hazards that were incorporated as a part of

AST Project No. 10540-S Page 11 this study included liquefaction, ground shaking, ground rupture, ground lurching;

lateral spreading and differential compaction. A brief summary concerning these hazards has been presented in the following section.

7.1 Liquefaction Potential

Liquefaction is a soil behavior phenomenon in which a soil looses a substantial amount of strength due to high excess pore-water pressure generated by strong earthquake ground shaking. Recently-deposited (i.e., within about the past 11,000 years) and relatively unconsolidated soils and artificial fills located below the ground water surface are considered susceptible to liquefaction (Youd and Perkins, 1978).

Typically, the soils that are most susceptible to liquefaction include relatively clean, loose, uniformly graded sand, silty sand, and non-plastic silt deposits (e.g., National Research Council, 1985).

Liquefaction is the transformation of clean, loose saturated sand and silt (cohesionless soil) and some sensitive clayey silt soil from a solid state to a semi-liquid state. This transformation occurs during a seismic event / ground shaking, when soil is subjected to cyclic stresses that cause increase in hydrostatic pressure that induces liquefaction. The resulting upward flow of water will often turn cohesionless soil into a liquefied condition (loss of density). At the ground surface, liquefaction is manifested by the formation of sand boils, ground cracking, and lateral spreading and in some cases development of quicksand like conditions, which results in the settlement or movement of the structures. Cohesive soils are generally not considered susceptible to soil liquefaction. However, the soils that are most susceptible to liquefaction are loose to moderately dense, saturated granular soils. Sensitive clays are vulnerable to significant strength loss under relatively minor strains during seismic event.

The site of proposed improvements is located within the liquefaction zone as outlined by CGS Seismic Hazard Zone report for the Mountain View Quadrangle and could experience vertical settlement during a seismic event.

7.2 Liquefaction Evaluation and Analysis Criteria

This report presents the evaluation of liquefaction potential at the subject property during a seismic event based on the recent publications and standards set-forth by SCEC and CGS Special Publication 117, which is as follows:

A site is not considered to be liquefiable, only if the screening process complies with the following criteria:

Maximum past, current and maximum future groundwater levels are determined to be deeper than (50) feet below the existing ground surface.

If bedrock or similar lithified formational material underlies the site.

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If corrected standard penetration blow counts is greater than 30 in all samples with a sufficient number of tests or if corrected cone penetration test tip resistance is equal or greater than 160.

If clayey soils are encountered during site exploration, then the clayey soil shall comply with the following characteristics (% passing 0.005mm>15, LL>35, and water content <0.9xLL).

The soil is considered to be clayey as defined by Boulanger and Idriss (2004), Bray and Sancio (2006) is now considered as the valid indicator for liquefaction susceptibility. Boulanger and Idriss (2004) suggested that a soil with a PI≥7 can be considered to have clay like behavior. Although clay like soils can undergo cyclic softening, they will not liquefy. Bray and Sancio (2006) suggested defining a soil as being liquefaction susceptible if the PI<12 and the moisture content to liquid limit ratio (Wc/LL)>0.85. Again, no consensus exists within the profession at this time regarding the preferred method; therefore the prudent approach is to check both of the above methods.

7.3 Peak Ground Acceleration

The peak ground acceleration (PGA) for this site has been anticipated to be in the range of 0.55g (1996 data) and 0.47g (2002) with a 10% probability of exceedance in 50 years and 0.71g (1996 data) to 0.59g (2002 data) for a 10% probability of exceedance in 100 years respectively. Based on the CGS Seismic Hazard Zone Report (060) for Mountain View Quadrangle, the peak ground acceleration for the site is anticipated to be 0.59g with 10% probability of exceedance in 50 years.

Please refer to Plate (32) in Appendix “B” of this report.

7.4 Historic Groundwater

Based on review of the CGS Seismic Hazard Report 060 - Liquefaction Map prepared for the Mountain View Quadrangle 7.5-Minute Map Series, it is our understanding that the historic groundwater is considered to be approximately at a depth of (<±5.0)-feet below the existing ground surface. Please refer to Plate (33) in Appendix “B” of this report.

7.5 Summary of Analysis - Settlement due to Liquefaction

In order to determine the settlement due to liquefaction, liquefiable layers (mostly sandy silty layers) were selected for liquefaction analysis (worst condition). The soils encountered in the remaining samples revealed uniform cohesive clayey soil layers with plasticity index (PI) greater than 12 and moisture content to liquid limit (Wc/LL) less than 0.85 (Bray & Sancio 2006), and therefore were not considered to be liquefiable. Our liquefaction hazard evaluation for triggering potential for liquefaction was performed in general accordance with guidelines presented by California Geological Survey (SP117) using the procedures presented by Youd et al.

(2001) and Martin and Lew (1999). We believe that the primary consequence of

AST Project No. 10540-S Page 13 liquefaction at the site will be limited to ground settlement. Vertical settlement was estimated using the procedures developed by Tokimatsu and Seed (1987).

Based on our analyses, loose and medium dense, saturated silty sands and clayey sands encountered in exploratory borings with low corrected blow counts per foot (N1)60 and fines content will be susceptible to liquefaction during seismic event resulting in about (4.0) to (4.5)-inches of total settlement and a differential settlement of about 1/2 to 2/3 of the total settlement, which is approximately (2.7) to (3.0)-inch between the adjacent columns at the ground surface.

7.6 Cyclic Densification

Seismic densification can occur during strong ground shaking in loose, clean granular deposits above the water table and over the hard / dense material, resulting in ground surface settlement. The soil layers above and below the historic water table are mostly clays and are usually not susceptible to densification. We judge the settlement due to seismic densification to be in the range of one-inch.

7.7 Differential Compaction

If near surface soil varies in composition both vertically and laterally, strong earthquake shaking can cause non-uniform compaction of soil strata, resulting in movement of near surface soils. Based on the clayey nature of the surface soils encountered at the site, we judge the probability of differential compaction at the site to be in the range of ¾-inch to one-inch.

7.8 Lateral Spreading

Lateral spreading typically occurs as a form of horizontal displacement of relatively flat-lying alluvial material toward an open or “free” face such as an open body of water, channel, or excavation. Permanente creek located to the west of the subject property is a concrete lined channel and therefore, it is our professional opinion that the probability of lateral spreading at the site during a seismic event is perceived to be low.

8.0 Geological Hazard - Seismic Hazard Assessment

8.1 Seismicity / Ground Shaking

The site of proposed improvements is located in a highly seismically active region of California. A broad system of inter-related northwest-southeast trending strike slip faults represents a segment boundary between the pacific and North American crustal plates. For 15 million years, the Pacific Plate has been slipping northwest ward with respect to the North American Plate (Atwater, 1970; Graham, 1978). The majority of the movement has been anticipated to be on the San Andreas Fault System, however there are other faults within this broad system that have experienced movement at one time or another. A large number of earthquakes

AST Project No. 10540-S Page 14 have occurred in the past with some of the significant regional earthquakes, which included the 1838 San Francisco / San Mateo Earthquake (M7), 1858 Mission Peak Area Earthquake (M6.1), 1861 San Ramon Valley Earthquake (M5.7), 1868 Hayward Earthquake (M7), 1903 the two San Jose Earthquakes (M5.5), 1906 San Francisco Earthquake (M7.9), 1911 Calaveras Earthquake (M6.6), 1957 Daly City Earthquake and the 1989 Loma Prieta Earthquake (M6.9). During the period of 1910 through October 14, 2009, ANSS catalog contains a record of 4,656 earthquakes between magnitude 3.0 and 3.99, 537 earthquakes between 4.0 and 4.99, 32 earthquakes between 50 and 5.99, 4 earthquakes between 6.0 and 6.99 and only one earthquake of 7.0 or above. Epicenters of some of the significant earthquakes (M>5.0) within the vicinity of the site are shown on Plate (35) enclosed in Appendix “B” of this report.

8.2 Table I - Nearest Seismic Source

Fault Site Distance

(km) Source Type Maximum

Magnitude Slip Rate mm/yr

Monte – Vista Shannon 7.9 B 6.5 0.40

San Andreas (1906) 12.2 A 7.9 24.00

Hayward (SE Extension) 17.7 B 6.5 3.00

Hayward (Total Length) 19.5 A 7.1 9.00

Calaveras (No. of Res) 24.5 B 6.8 6.00

Calaveras (So. of Res) 26.0 B 6.2 15.00

San Gregorio 30.3 A 7.3 5.00

These faults and other faults that are not listed above have the potential for producing a strong ground motion at the site during a seismic event. In general due to the seismic activity of the San Francisco Bay Region, the site will experience strong to severe seismic shaking during the lifetime of the proposed structures from the above and other faults mentioned in the following sections of this report.

8.3 Maximum Estimated Ground Shaking

The peak ground acceleration (PGA) for this site has been anticipated to be in the range of 0.55g (1996 data) and 0.47g (2002) with a 10% probability of exceedance in 50 years and 0.71g (1996 data) to 0.59g (2002 data) for a 10% probability of exceedance in 100 years respectively. Based on the CGS Seismic Hazard Zone Report (060) for Mountain View Quadrangle, the peak ground acceleration for the site is anticipated to be 0.59g with 10% probability of exceedance in 50 years.

8.4 Site Characterization / Seismic Criteria

Table I summarizes the site design criteria from 2001 California Building Code.

AST Project No. 10540-S Page 15

Table I - Site Characterization

Parameter Values CBC Reference

Seismic Zone Factor 0.40 Table 16-I Soil Profile SD Table 16-J Seismic Coefficient, Ca 0.44 Table 16-Q Seismic Coefficient, Cv 0.71 Table 16-R Near Source Factor, Na 1.0 Table 16-S Near Source Factor, Nv 1.1 Table 16-T Seismic Source Type Type A & B (See Table Above) Table 16-U

Seismic Hazard Curves and uniform Hazard Response Spectra, provided by USGS was utilized in computing the 2006 IBC Seismic Design Parameters. Table II summarizes site specific design criteria based on the 2006 International Building Code (IBC), Chapter 16 Structural Design; Section 1613 Earthquake Loads. The short spectral response uses a period of 0.2 second.

Table II - IBC 2006 - Seismic Design Parameters

Parameter Values IBC Reference

Site Class D Table 1613.5.2

Spectral Response - Class B (short), Ss 1.50g Table 1613.5(3)

Spectral Response – Class B (1sec), S1 0.641g Table 1613.5(4)

Site Coefficient, Fa 1.0 Table 1613.5.3(1)

Site Coefficient, Fv 1.5 Table 1613.5.3(2)

Maximum Considered Earthquake Spectral Response Acceleration (short), SMS 1.50g Section 1613.5.3

(Eqn. 16-37) Maximum Considerable Earthquake Spectral Response Acceleration – (1 sec), SM1

0.961g Section 1613.5.3 (Eqn. 16-38)

5% Damped Design Spectral Response Acceleration (short), SDS 1.0g Section 1613.5.3

(Eqn. 16-39) 5% Damped Design Spectral Response Acceleration (1 sec), SD1

0.641g Section 1613.5.4 (eqn. 16-40)

Site specific response spectra are shown in Appendix “B” of this report. Please note that the appropriate design spectrum shall be selected by the Project Structural Engineer for the proposed design.

AST Project No. 10540-S Page 16

8.5 Ground Rupture

Regional fault map illustrating the known active faults by U.S. Geological Survey for the San Francisco Bay Region indicated that the site in question is not located within the state mandated Alquist-Priolo Geologic Hazards Act of 1972 for Special Studies Zones. This special studies zone has been established to evaluate the potential for direct fault offset from a seismic event. The site is located outside of any special study zones defined by the Alquist-Priolo Geologic Hazards Act and no faults have been mapped to be passing through the site, therefore the potential for ground rupture from faulting across the site could be perceived to be low.

8.6 Ground Lurching

Ground Lurching is a lateral movement of portions of the ground normally accompanied by fissuring perpendicular to the direction of lurching, usually occurs along the embankments, such as unconsolidated and unsupported stream banks.

However there are no open channels or banks located in immediate vicinity of the site. Henceforth, it is our professional opinion that the possibility of ground lurching at the site is perceived to be low.

8.7 Future Earthquake Probability

The presence of faults in the San Francisco Bay Area Region and the seismic activity in the recent past has led USGS to constantly upgrade the predictions for the possibility of the next major earthquake in the Bay Area. Per the information received from the review of the documents, it is our understanding that The Working Group on California Earthquake Probabilities (2008) has concluded that the probability of a magnitude 7.0+ earthquake in the San Francisco Bay Area over the next 30 years is 63 percent. This probability is a low estimate since only three active faults in the area; the Hayward Fault, San Andreas Fault and Rodgers Creek Fault were included in the study.

Schwartz (1994) concludes that the probability of occurrence of one or more magnitude 6.7+ earthquakes in the Bay Area is substantially higher than 63 percent, possibly as high as 99.7 percent. It shall be noted that significant earthquakes could occur on an active fault or a potentially active fault for which probabilities might not have been estimated. Even though research on earthquake predictions has increased tremendously in recent years, seismologists still cannot predict when or where an earthquake of that magnitude will occur. Based on the information that is available, it is our understanding that the site will likely be subjected to at least one moderate to severe earthquake within 50 years of the proposed construction. During such an earthquake, the possibility of fault offset could be perceived to be low. However, strong ground shaking will be experienced at the site. The probability of the maximum moment magnitude earthquake occurring on the following segments during the next (30) year period are as follows:

AST Project No. 10540-S Page 17

Fault Segment

(30) –Year Probability (%) Earthquake Magnitude M = 6.7

San Andreas (Peninsula Segment) 21 Hayward (North & South) 31 Calaveras 11

9.0 Conclusions

Based on our field observations and the results of our laboratory analysis, it is our professional opinion that the Proposed New VA Administration Building could be constructed as planned, provided the conclusion and recommendations are incorporated in the design and during the construction phase of the project.

The primary geotechnical concerns for the proposed improvements are as follow:

Presence of Expansive Soils Shallow Groundwater Condition Possibility of Liquefaction and densification Potential for Corrosion

9.1 Presence of Expansive Soils

The near surface soil at the site consists of clayey soils with high expansion and shrinkage potential, when subjected to moisture fluctuations. Due to high expansive nature of the near surface soils, all concrete slab-on-grade construction shall be supported on (18)-inches of non-expansive import material or on (18)-inches of lime treated material. Lime treatment shall include a minimum of 5% lime (HiCal) with a minimum of 120 pcf dry weight of soil. Please refer to the grading section additional recommendations.

9.2 Shallow Groundwater Condition

Based on the review of the CGS Maps for the Mountain View Quadrangle (Seismic Hazard Zone Report 060), historical groundwater elevation at the site was determined to be at a depth of approximately (<±5.0)-feet below the existing ground surface.

9.3 Possibility of Liquefaction and Soil Densification

Settlement due to liquefaction during seismic event / design earthquake will be in the range of about (4.0) to (4.5)-inches of total settlement and a differential settlement of about 1/2 to 2/3 of the total settlement, which is approximately (2.7) to (3.0)-inch between the adjacent columns over a horizontal distance of 40-feet at the ground surface. However, due to the presence of shallow groundwater table and medium stiff to very stiff clays over medium dense to dense sands below the

AST Project No. 10540-S Page 18 subsurface, the soil could be subjected to densification during a seismic event.

Settlement due to the possibility of soil densification during a seismic event could be considered to be in the range of 3/4-inch to one-inch.

9.4 Potential for Corrosion

Based on the results of corrosivity analysis conducted on the soil sample collected from the site, it is our understanding that the potential for corrosion is high for buried steel. Please refer to the results of analysis in the preceding sections of this report.

10.0 Considerations

In order to improve the existing site conditions at the site, we recommend that the following be considered in the design and during the construction phase of the project.

a. Existing pavement section shall be removed completely from the area of the proposed building pad and five feet beyond the building footprint, prior to any grading operation at the site. The contractor shall anticipate soft and unstable surface soil conditions during the grading operation.

b. If desired, the existing pavement section could be ground-up and mixed with the base rock below the asphalt section to be utilized as a part of the non-expansive material and base rock section under flatwork, including walkways, patios and other miscellaneous service pad areas with the exception of building pads, provided the material complies with the gradation requirements, as per CALTRAN Specifications. Non-expansive material and rock section under the building pad areas shall consist of non-recycled material. The contractor shall submit material samples with proper documentation for approval by the Geotechnical Engineer, prior to hauling material to the site.

c. Depressions left by the excavations after the removal of subsurface structures and utility trenches shall be backfilled properly in accordance with the recommendations established in the grading section of this report. If any unexpected variations in soil conditions are encountered during the grading operation, they should be brought to the attention of the Field Engineer.

d. All existing utilities, surface and sub-surface structures that will not be incorporated as part of the proposed improvements shall be removed completely, prior to any grading operation. These objects shall be accurately located on the grading plan to assist the Soil Engineer in establishing proper control over their removal. This is to include, but not limited to any existing abandoned concrete structures, footings, utility lines, underground pipes, stumps, root systems or any other such condition. A representative from AST

AST Project No. 10540-S Page 19 shall be present during the demolition operation to document and provide recommendations as deemed necessary in the field.

e. To achieve a uniform condition at the site, the upper (18)-inches of the subgrade material below the pad area and five-feet beyond the building footprint shall consist of non-expansive import material or lime treated material compacted to 95% relative compaction as per ASTM D1557. Please refer to the grading section for additional information.

f. Provide and maintain positive surface drainage around the proposed structure and to minimize seepage from the adjacent landscape areas. Please note that all the pertinent plans shall be prepared by the Project Civil Engineer including the grading, surface and subsurface drainage, cross sections for the drainage / surrounding areas associated with the project.

g. Advance Soil Technology, Inc. (AST) shall be given the opportunity to review all grading and foundation plans, prior to the final design to assure conformance to the recommendations established in the Project Soils Report and to provide suggestions / recommendations, if necessary.

11.0 Recommendations -

11.1 Existing Utilities

Existing utilities located within the areas of proposed improvements should be removed in their entirety. Utilities within the proposed areas of improvements could be considered for in-place abandonment, provided they do not conflict with new improvements, that the ends and all laterals are located and completely grouted, and the previous fills associated with the utility trenches do not pose a risk to the proposed improvements. Utilities outside the areas of proposed improvements should be removed or abandoned in-place by grouting or plugging ends with concrete. Fills associated with utilities abandoned in place could pose some risk of settlement; utilities that are plugged could also pose some risk of future collapse or erosion should they leak or become damaged. The potential risks are relatively low for smaller diameter pipes abandoned in place and increasingly higher with increase in diameter.

11.2 Earthwork – Demolition, Clearing & Site Preparation

Any areas to be graded should initially be cleared of all obstructions, including the existing buried foundation (if any), existing footings, underground utility pipes, including drain lines, landscape areas, brush, trees not designated to remain, debris, stumps, root balls, existing pavements, rubble and debris should be removed and hauled off from the site. All active or inactive utilities within the construction area should be protected, relocated or abandoned. Any pipes abandoned in place should be filled with sand cement slurry (pressure grout). Holes

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/ excavated areas resulting from the removal of underground obstructions below the proposed finished subgrade levels should be cleared for engineered fill given below.

After the above operation, the holes and excavated areas left from the clearing operation shall be backfilled with native on-site material with moisture content (±2% over optimum) and free of any organic content. The material shall be placed in the above-mentioned holes and excavated areas in (8)-inch lifts (un-compacted thickness) and each lift shall be compacted to a minimum of 95% relative compaction as per the testing procedure ASTM D1557. Additional fill shall be placed in (8.0)-inch lifts, moisture conditioned and compacted to a minimum of 95% relative compaction as per the afore-mentioned procedure.

11.3 Pad Preparation

After the above operation, the areas of proposed improvements / graded areas, including building pad, cut and fill pad areas, walkways, patios and five-feet beyond the footprint shall be scarified to a depth of (12)-inches; moisture conditioned and compacted to a minimum of 95% relative compaction as per ASTM D1557.

Additional fill material, if required to achieve the proposed pad elevation shall then be placed on the compacted bottom in (8.0)-inch lifts and each lift shall be compacted to a minimum of 95% relative compaction. However, the upper (18)-inches of material under all concrete slab-on-grade construction and five-feet beyond the building footprint shall consist of lime treated material or import material with low plasticity index (PI) of 12 and compacted to a minimum of 95% relative compaction all the way up to the required subgrade elevation to achieve a uniform condition.

It shall be noted that the proposed structures, if located in a cut and fill transition areas, would require over-excavation of the upper subgrade areas to a depth of approximately (2.0)-feet to achieve a uniform condition under the proposed foundation and slab areas.

Fro additional information, pertaining to the structural section for all concrete slab-on-grade construction shall be in accordance with the recommendations established under the Concrete Slab-on-Grade and Foundation Sections of this report.

11.4 Lime Treatment

Due to the presence of high expansion potential in the soil at the site, the subgrade soils and areas with excessive moisture could be lime (HiCal Lime) treated to lower the moisture content and expansion potential. The lime treatment shall penetrate the proposed subgrade / the bottom of the excavation to a minimum depth of (18)-inches, below the exposed ground surface. Lime treatment shall be conducted with appropriate equipment, such that a uniform mix is achieved over the entire area. A

AST Project No. 10540-S Page 21 minimum of 5% lime (HiCal) by weight of the soil, approximately (120.0)-pounds per cubic feet shall be utilized in determining the amount of lime required for the building pad area. Upon achieving the uniform mix, the lime treated material shall then be compacted to a minimum of 95% relative compaction, minimum of (36)-hours after the completion of the mixing operation. The lime treatment contractor shall discuss the process with the Soil Engineer for recommendations and for the type of equipment usage.

11.5 Fill Materials

All fill materials under all at grade concrete slab-on-construction and behind the walls shall be primarily granular material with low plasticity and expansion potential and shall comply with the following:

Resistance R-Value Not less than 25 Plasticity Index 12 or less Liquid Limit 30% or less Expansion Index 20% or less % Passing Sieve #200 between 10 and 20% Maximum rock size (3)-inches

All imported soil / fill materials shall be submitted to the Geotechnical Engineer for approval, prior to hauling the material to the site. The submittal shall include material sample (approximately five-gallon bucket) and proper documentation from the material source.

11.6 Temporary Slopes, Trench Excavations and Dewatering

The contractor should be responsible for all temporary excavations, slopes and trenches excavated at the site and the design of any required shoring system.

Shoring, bracing and benching shall be performed by the contractor in accordance with the strict governing safety standards. Temporary shoring is usually considered as a construction issue (means and methods) and has to be addressed by the contractor. Shoring and bracing should be provided in accordance with all applicable local, state and federal safety regulations, including but not limited to the current OSHA excavation and trench safety standards.

12.0 Concrete Slab on Grade Construction

12.1 Interior Concrete Slab-On-Grade Construction

All above grade interior structural concrete slabs on grade shall be a minimum of five (5) inches thick, reinforced with a minimum of #4 rebar spaced (18)-inches on center both ways for shrinkage control to minimize the impact of expansion and shall be designed as per the latest edition of ACI. In addition to the above grading recommendations, all structural concrete slab-on-grade construction shall be supported as follows:

(2) Inches of clean washed sand Vapor membrane for capillary-break, minimum 15 mil-Visquine or Stego wrap.

AST Project No. 10540-S Page 22

Four (4) inches of ¾-inch clean crushed rock compacted properly to achieve locking action (No recycled rock shall be used on the building pads).

(18)-inches of non-expansive import material (Please note that (4.0)-inches of rock and (2.0)-inches of sand shall not be considered as a part of the non-expansive material).

The slab reinforcing mentioned above could exceed the minimum requirement depending on the anticipated usage and loading conditions. However, the Project Structural Engineer shall determine the final thickness and reinforcing based on a modulus of subgrade reaction equal to 15 pounds per cubic inch. Post-construction cracking of concrete slabs is inherent on any project especially where soil has high expansion potential. To minimize the cracks in the slabs, we recommended that proper spacing of expansion and contraction joints.

The vapor membrane should be covered with two-inches of sand to protect it during installation of rebar and to aid in the curing of concrete. Water should not be allowed to accumulate in the capillary break or in the sand, prior to casting the slab. The areas where moisture infiltration through the slab is not desired, we recommend the installation of a water proofing membrane. The waterproofing membrane should consist of a pre-applied, self-adhering high-density polyethylene (HDPE) or high quality bentonite product. The Project Architect and the Structural Engineer shall incorporate moisture protection considerations as needed in the design to enhance the performance of the slabs.

12.2 Exterior Concrete Slab-on-Grade

The recommendations of this section are limited to patios, sidewalks and walkways.

Due to expansive nature of the soil, all exterior concrete slabs on grade shall be a minimum of (5)-inch thick concrete reinforced with #4 rebar spaced (18)-inches on center both ways supported over (8)-inches of Class II base rock and compacted subgrade. The subgrade and base rock shall be compacted to a minimum of 90 and 95% relative compaction respectively. The slab reinforcing mentioned above could exceed the minimum requirement depending on the anticipated usage and loading conditions. To minimize the cracks in the slabs, it is recommended that proper expansion and contraction joints be provided in the slab every (5)-foot on center both ways.

13.0 Foundation

The proposed structure may be supported on a structural rigid mat foundation or on continuous perimeter and isolated interior footings with interlocking grade beams.

Recommendations for these types of foundation has been outlined and discussed in the following sections of this report.

AST Project No. 10540-S Page 23

13.1 Structural Rigid Mat Foundation

The proposed structure could be supported on a shallow structural rigid mat foundation. The mat foundation shall be a minimum of (18)-inches thick and shall be designed for an allowable surface bearing value of 1000 pounds per square foot for dead plus live loads and the bearing value could be increased by one-third for short term wind and seismic forces, provided the load bearing surfaces are prepared in accordance with the “Subgrade Preparation” requirement established in the preceding sections of this report. The allowable bearing pressures are net values; the weight of the mat can be neglected for design purposes.

As discussed above, for the mat design, a uniform subgrade modulus of “k” of 15 pounds per square inch per inch may be used for dead plus live loads. We recommend that a more detailed analysis (Discrete Area Method) be performed using SAFE iterations in conjunction with variable “k”. Using a lower “k” in the center of the mat and a higher “k” towards the edges and corners will allow for a more accurate prediction of shears and moments. The mat should be reinforced with top and bottom steel, as appropriate to provide structural continuity and help span local irregularities. It is essential that we observe the subgrade of the mat foundation.