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

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353 Main Street Apartments Redwood City, California May 1, 20L8 (Original Report Dated November L8,2076) The settlements presented above are mainly resultingfrom long-term settlement of soft Bay Mud layer present at the site beneath the fill material. These settlement estimates are deemed to be excessive for a building structure; therefore, the building loads should be supported on a deep foundation system as described in the following sections of the report. The static settlement analysis is preliminary and based on a number of assumptions (elevations, loadings, foundation size, etc.). Static settlement should be reanalyzed at a later date once foundation type, mitigation measures, loadings, elevations, etc., are known. 5.0 coNclusroNs General The subject site is suitable for the proposed multi-story apartment complex from a geotechnical engineering standpoint, provided the recommendations included in this report are followed. The primary geotechn¡cal concerns at the site are: o Ground Shaking during a future seismic event as the site is located within the seismically active San Francisco Bay Area, o Excessive static post-construction settlement because of relatively high building loads and the presence of soft, compressible, bay mud layer at relatively shallow depths, o Seismic settlement because of the presence of soil layers which could liquefy during a design-level seismic event, o Latera spreading because of the presence of a nearby open face of Redwood Creek, o Presence of corrosive soils at shallow depths, ln order to minimize post-construction distress to the proposed multi-story apartment building, we recommend that the building loads be supported on a deep foundation system capable of transferring the loads to deeper, more-competent soil layers. Based on our experience in the San Francisco Bay Area, it is our opinion that a drilled displacement piles (DDP) type foundation system may be suitable for use at the site. A DDP type foundation system uses a displacement drill to compact soil in the ground, resulting in a higher capacity foundation pile system while generating very low volumes of spoils. A DDP construction produce low noise and no vibrations. It involves drilling to the design depths with a drilling tool capable of laterally displacing and densifying the adjacent soils. Upon reaching the final depth, grout is pumped under pressure through the hollow auger as the drilling tool is extracted out of the hole while rotation continues. The drilling tool is removed and the drilled hole is filled with cement grout, steel reinforcing is inserted in fluid grout column. The DDP would be designed to bypass the compressible soils, and reduce the liquefaction effects to acceptable limits. 301842-001 L2 16r.0-038.SER.REV2 7.B. - Page 70