13110068Geotechnical Investigation 27 March 2018
Vallco Town Center 770633101
Cupertino, California Page 4
During drilling, our field engineer logged the borings and obtained representative samples of
soil encountered for visual classification and laboratory testing.
Logs of the borings are presented in Appendix B on Figures B-1 through B-5. The soil
encountered in the borings was classified in accordance with the Classification Chart,
presented on Figure B-6.
Samples were obtained using the following split -barrel sampler types.
• Sprague & Henwood (S&H) sampler with a 3.0 -inch outside diameter and 2.5 -inch inside
diameter, lined with steel or brass tubes with an inside diameter of 2.43 inches
• Standard Penetration Test (SPT) sampler with a 2.0 -inch outside diameter and 1.5 -inch
inside diameter, without liners.
The sampler types were chosen on the basis of soil type and desired sample quality for
laboratory testing. In general, the S&H sampler was used to obtain samples in medium stiff to
very stiff cohesive soils. The SPT sampler was used to evaluate the relative density of granular
soils.
For the rotary wash borings (Borings B-1 and B-2), the SPT and S&H samplers were driven with
a 140 -pound, above -ground, automatic safety hammer falling 30 inches. The blow counts
required to drive the S&H and SPT samplers were converted to approximate SPT N -values
using factors of 0.7 and 1.1, respectively, to account for sample type and hammer energy and
are shown on the boring logs.
For the hollow stem auger borings (Borings B-3 to B-5), the SPT and S&H samplers were driven
with a 140 -pound, downhole, wireline safety hammer falling 30 inches. The blow counts
required to drive the S&H and SPT samples were converted to approximate SPT N -values using
factors of 0.6 and 1.0, respectively, to account for sample type and hammer energy and are
shown on the boring logs. Boring B-4 was drilled with two different drilling rigs due to
equipment issues. The conversion factors to account for sample type and hammer energy
were similar between the both drilling rigs and hammers.
The SPT and S&H samplers were driven up to 18 inches and the hammer blows required to
drive the samplers every six inches of penetration were recorded and are presented on the
boring logs. A "blow count" is defined as the number of hammer blows per six inches of
penetration or less if the blow count approached 50 blows. The driving of sampler was
discontinued if the observed (recorded) blow count was 50 for six inches or less of penetration.
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Geotechnical Investigation 27 March 2018
Vallco Town Center 770633101
Cupertino, California Page 5
The blow counts used for this conversion were: 1) the last two blow counts if the sampler was
driven more than 12 inches, 2) the last one blow count if the sampler was driven more than
six inches but less than 12 inches, and 3) the only blow count if the sampler was driven
six inches or less.
NorCal Geophysical was retained to perform in-situ downhole suspension logging to measure
the shear wave velocity of the subsurface materials within boring B-1. The details of the
suspension logging methodology, procedures, and the results are presented in Appendix C.
Upon completion of drilling or suspension logging, the borings were backfilled with grout
consisting of cement, bentonite, and water in accordance with the requirements of SCVWD.
The borings were completed at the ground surface with cold patch asphalt. The soil cuttings
and drilling fluid were placed in 55 -gallon drums stored temporarily at the site, tested, and have
been transported off-site for proper disposal.
3.3 Laboratory Testing
The soil samples recovered from the field exploration program were re-examined in the office
for soil classification, and representative samples were selected for laboratory testing.
The laboratory testing program was designed to evaluate engineering properties of the soil at
the site. Samples were tested to measure moisture content, dry density, plasticity (Atterberg
Limits), gradation, shear strength, and compressibility, where appropriate. Results of the
laboratory testing are included on the boring logs and in Appendix D on Figures D-1
through D-15.
3.4 Cone Penetration Test
To supplement the soil boring data, five CPTs, designated as CPT -1 through CPT -5, were
performed on 29 and 30 September 2016 by Gregg Drilling and Testing (Gregg) at the
approximate locations shown on Figures 2 and 3. The CPTs were advanced to depths of
approximately 75 feet bgs.
The CPTs were performed by hydraulically pushing a 1.4 -inch -diameter, cone -tipped probe, with
a projected area of 15 square centimeters, into the ground. The cone tip measures tip
resistance, and the friction sleeve behind the cone tip measures frictional resistance. Electrical
strain gauges or load cells within the cone continuously measured the cone tip resistance and
frictional resistance during the entire depth of each probing. Accumulated data was processed
by computer to provide engineering information, such as the types and approximate strength
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Geotechnical Investigation 27 March 2018
Vallco Town Center 770633101
Cupertino, California Page 6
characteristics of the soil encountered. The CPT logs, showing tip resistance and friction ratio
by depth, as well as interpreted SPT N -Values, friction angle, soil strength parameters, and
interpreted soil classification, are presented in Appendix E on Figures E-1 through E-5. Soil
types were estimated using the classification chart shown on Figure E-6.
After completion, the CPTs were backfilled with cement -bentonite grout in accordance SCVWD
requirements. The CPTs were completed at the ground surface with cold patch asphalt.
3.5 Soil Corrosivity Testing
To evaluate the corrosivity of the soil near the foundation subgrade, we performed corrosivity
tests on samples obtained at depths of 18'/2 feet, 26 feet and 63'/2 feet. The corrosivity of the
soil samples was evaluated by CERCO Analytical using the following ASTM Test Methods:
• Redox — ASTM D1498
• pH — ASTM D4972
• Resistivity (100% Saturation) — ASTM G57
• Sulfide —ASTM D4658M
• Chloride — ASTM D4327
• Sulfate — ASTM D4327
The laboratory corrosion test results and a brief corrosivity evaluation by JDH Corrosion are
presented in Appendix F.
4.0 SITE AND SUBSURFACE CONDITIONS
The existing site and subsurface conditions observed and encountered at the site,
respectively, are discussed in this section.
4.1 Site Conditions
The existing shopping center includes a two-level shopping center located on the east and west
sides of N. Wolfe Road, multi-level parking structures, surface parking lots, a pedestrian bridge
spanning N. Wolfe Road, a vehicular tunnel crossing below N. Wolfe Road, and several
stand-alone buildings. Based on a topographic survey of the project site (Sandis, 2011), the
range of existing ground surface elevations is:
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