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353 Main Street Apartments <br />Redwood City, California <br />May 1, 2018 <br />(Originol Report Dated November 78,2016) <br />ln general, the design of the DDP type foundation system is performed by design-build <br />foundation contractors because of their patented foundation design technologies. The piles <br />should be designed to provide sufficient vertical and lateral load bearing capacity to mitigate loss <br />of strength due to liquefaction during a design-level seismic event. Earth Systems will review the <br />design analysis performed by these firms and collect and analyze data during a load test <br />performed on indicator piles installed using the same technology as the production piles. The <br />load test data will be analyzed to confirm the actual load bearing capacity of the piles. <br />Since the building is goingto extend over most of the site, we recommend a minimum of three <br />load test locations to estimate load bearing capacities of piles in the eastern, middle, and western <br />portions of the site. <br />Mitigation of Site Soils <br />Generally, the site is underlain by undocumented fill up to 6.5 to L0 feet thick (implied from test <br />borings and CPT data) and Bay Mud to approximately 13 to L5 feet below the site. This is then <br />followed by a variably thick layer of medium stiff to stiff clay over a zone of potentially liquefiable <br />sands in the depth range of 18 to 33 feet, subsequently followed by stiff to very stiff clay to the <br />bottom of our explored depths. Our preliminary static settlements analysis indicates excessive <br />settlement if the building is supported on conventional spread/strip footings. Therefore, it will <br />be necessary to support the building on a deep foundation system to minimize post-construction <br />settlement as recommended in the previous section of the report. Additionally, liquefaction <br />related settlement at the site is estimated to be on the order of 0.4 to 2.1 inches with a possibility <br />of surface manifestation. We calculated lateral spreading in the range of 5 to 48 inches. <br />The goal of the chosen liquefaction mitigation system would be to reduce seismically-induced <br />settlement to less than one inch and minimize lateral spreading. The success of the mitigation <br />system will depend on the contractor's design and the quality of their installation. <br />CPT soundings will need to be performed post-improvement of the ground to assess the quality <br />of the ground improvement and calculate the possible post-installation seismically induced <br />settlements. <br />Soil Conditions at Foundation Grade <br />Final pad elevations were not available when this report was prepared, but they are assumed to <br />be roughly the same as the existing grade. The near surface soils soil samples collected during <br />subsurface exploration from the borings had moisture contents on the order of L3 to 23 percent <br />and pocket penetrometer readings as low as 1.5 tsf, and may be unstable under construction <br />301842-00L 13 1610-038.SER.REV2 <br />7.B. - Page 71