Reso13 PC 13-09 2859 Initial Study Mitigated Negative Declaration Kensington

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Proposed Senior Assisted Living Facility PSI Project No. 575-308-2 August 3, 2011 Page 12 inches below and 12 inches above the pipe for the full trench width. The bedding material should be mechanically compacted in layers to at least 90 percent of maximum dry density based on ASTM D1557. Flooding should not be permitted. Trench backfill above pipe bedding should consist of approved on-site or import soils placed in lifts no greater than 8 inches loose thickness, moisture conditioned as per our recommendations for fill soils, and compacted to minimum 90 percent of the maximum dry density per ASTM D1557. Some minor settlement of the backfill should be expected and any utilities within the trenches or concrete walks supported on the trench backfill should be designed to accept these differential movements. Except where extending perpendicular under proposed foundations, utility trenches should be constructed outside a 1:1 projection from the base-of-foundations. Trench excavations for utility lines, which extend under structural areas should be properly backfilled and compacted. 5.4 Foundation Support Following site preparation, as recommended in Section 5.1, it is our opinion that conventional continuous strip or isolated footings supported by low expansive Engineered Fill are suitable for the support of the proposed structure. The perimeter footings should have a minimum depth of 18 inches below the lowest adjacent grade, with a minimum width of 18 inches. Column footings should have a minimum depth of 18 inches below the lowest adjacent grade, with a minimum width of 24 inches. Footings with the above recommended minimum dimensions may be designed for an allowable soil bearing pressure of 2,500 psf. The allowable soil bearing pressure can be increased by one-third for short-term wind or seismic load considerations. Based on the estimated liquefaction-induced settlements, we recommend that all strip footings be longitudinally reinforced with at least 4 No. 4 bars (two top and two bottom). This steel reinforcement is not intended to be used in lieu of that needed for structural considerations but is recommended due to site geologic conditions. The actual foundation reinforcement and foundation dimensions should be provided in accordance with the Structural Engineer's design. Lateral loads may be resisted by any rational method, which incorporates sliding friction and/or passive earth pressure. The design may incorporate an allowable passive earth pressure of 250 psf per foot of depth below a depth of 1 foot, provided that the footing concrete is poured tightly against firm native soil or properly compacted fill materials. This value may be increased by 250 psf for each additional foot of depth, to a maximum of 2,000 psf. An allowable friction coefficient of 0.35 may be used at the concrete-soil interface. No reductions are necessary when combining the frictional and passive resistance of the soils to determine the total lateral resistance. We estimate that foundations designed and constructed in accordance with the above recommendations will experience total static settlements of less than 1-inch with differential settlements of '/2-inch over a 40 foot span. While settlement of this magnitude is generally considered tolerable for structures of the type proposed, the design of masonry walls should