AgdaPkt 2018-05-21 Joint SA PFA - Laserfiche WebLink

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353 Main Street Apartments Redwood City, California May L, 20L8 lOriginol Report Dated November 78,2076) from 13.5 to 15 feet below the ground surface. Lean to fat clays with variable sand content and consistencies followed thereafter to depths of approximately L8 to 24 feet. Below this layer granular soils consisting of medium dense to dense poorly graded sand with variable silt and gravel were encountered. ln Boring 84, the granular layer extended to approximately 35 feet followed by stiff lean to fat clays to the bottom of the boring at 50 feet. The CPT sounding data generally corroborates the findings in the test boring with the exception of CPT Cl. However, please note that the CPT soil classification is based on soil behavior type which is somewhat different than the USCS Soil Classification. ln general, CPT C2 to CPT C4 show the site underlain by silty clay to clay (assumed to be fill) to approximate depths of 8 to 10 feet. Below the silty clay to clay (fill material), sensitive fine grained (assumed to be Bay Mud) is encountered to depths ranging from L2 to 14 feet. This is followed by intervals of silty clay to clay and clayey silt to silty clay to approximately 2L to 26 feet. A granular horizon consisting of sand,gravellysandtosiltysandwasencounteredtodepthsof32.5to33feet. Belowthegranular horizon, stiffer clay soils were encountered to the end of the soundings at 60 and 70 feet. ln CPT C1, located at the SW edge of the site, the softer sensitive fine-grained soil appears to be absent in the upper L4 feet. lt is unknown whether the Bay Mud was excavated and replaced with fill or not present in this area. Also, a soft lens of soil was encountered from approximately 24to 26 feet which was not encountered in the other soundings. This softer lens appears similar to a soft to medium dense soil sample encountered in Boring 81 at approximately 20 feet. Locations of the soundings and borings are presented in Figure 2. Generalized cross sections of the subsurface profile are presented in Figure 3. Groundwater was generally encountered between L8 and 18.5 feet during drilling. Groundwater was measured roughly at L3 feet below the surface shortly after drilling. This roughly correlates with the depth of the adjacent Redwood Creek. The historic high depth to groundwater level according to the CGS Seismic Hazards Zones Report for the Palo Alto Quadrangle maps is reported to be less than 10 feet below the ground surface. lt should be noted, however, that fluctuations in the level of subsurface water can occur due to variations in rainfall, temperature, tidal fluctuations, and other factors, and groundwater levels should not be considered constant. Laboratory Testing Selected liner samples were tested for moisture content and dry density (ASTM D2276-LO and D 2937-LO) because it is a good indicator of other engineering properties of soil. One sample was 530L842-001 1610-038.SER.REV2 7.B. - Page 63