Phase 1 of the project consisted of the construction of three multi-story office buildings, two parking structures, and an amenities building.
TRC performed a subsurface investigation of the site which entailed the completion of test borings and a full battery of soil tests to determine the physical and structural properties of the soil. A review of the Seismic Hazard Zone Report had shown that the project site is located in a Liquefaction Hazard Zone as mapped by the California Geological Survey (CGS). Such areas are characterized as “areas where an historic occurrence of liquefaction or local geological, geotechnical or groundwater conditions indicate a potential for permanent ground displacements such that mitigation as defined in Public Resources Code 2693c would be required.” Historic ground water levels in the vicinity of the site had been mapped at depths of about 5 feet.
TRC’s investigation included a combination of hollow-stem auger borings and cone penetration tests (CPT) to depths of up to 120 feet to explore the subsurface conditions. Those exploration methods are consistent with those currently necessary when investigating a site within a mapped liquefaction hazard zone. Our report discussed the potential for liquefaction at the site and concluded that the sands were primarily dense to very dense and not subject to liquefaction. In addition, the buildings were to be supported on pile foundations which would mitigate any minor liquefaction-induced settlement should it occur. Therefore, it was TRC’s opinion that the liquefaction evaluation performed was appropriate for the conditions and adequately addressed the liquefaction potential at the site.
To ensure the proper implementation of our recommendations, TRC staff were utilized to provide geotechnical observation and testing during the sitework construction phase of the project.
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