607 RIVERSIDE RD Geotech Report 2022-10-25 (2)

March 22,2016 Project No.T-7388 For designing foundations to resist lateral loads, a base friction coefficient of 0.35 can be used. Passive earth pressures acting on the sides of the footings can also be considered. We recommend calculating this lateral resistance using an equivalent fluid weight of 300 pounds per cubic foot(pcf). We recommend not including the ' upper 12 inches of soil in this computation because it can be affected by weather or disturbed by future grading activity. This value assumes the foundations will be backfilled with structural fill, as described in Section 5.2 of this report. The values recommended include a safety factor of 1.5. 5.5 Slab-on-Grade Floors Slabs on grade may be supported on subgrade prepared as recommended in Section 5.2 of this report. Long-term floor slab settlement as discussed in the Foundation Section should be expected due to secondary creep compression of the soft organic silt layer. Immediately below the floor slabs, we recommend placing a four-inch thick capillary break layer of clean, free- draining, coarse sand or fine gravel that has less than three percent passing the No. 200 sieve. This material will ' reduce the potential for upward capillary movement of water through the underlying soil and subsequent wetting of the floor slabs. The capillary break layer will not prevent moisture intrusion through the slab caused by water vapor transmission. Where moisture by vapor transmission is undesirable, such as covered floor areas, a common practice is to place a durable plastic membrane on the capillary break layer and then cover the membrane with a layer of clean sand or fine gravel to protect it from damage during construction, and aid in uniform curing of the concrete slab. It should be noted that if the sand or gravel layer overlying the membrane is saturated prior to pouring the slab, it will be ineffective in assisting in uniform curing of the slab, and can actually serve as a water ' supply for moisture transmission through the slab and affecting floor coverings. Therefore, in our opinion, covering the membrane with a layer of sand or gravel should be avoided if floor slab construction occurs during the wet winter months and the layer cannot be effectively drained. We recommend floor designers and ' contractors refer to the 2003 American Concrete Institute(ACI)Manual of Concrete Practice, Part 2, 302.1 R-96, for further information regarding vapor barrier installation below slab-on-grade floors. 5.6 Lateral Earth Pressures The magnitude of earth pressure development on retaining walls constructed in loading dock areas will partly depend on the quality of wall backfill. Where fill is placed behind retaining walls, we recommend placing and compacting it as structural fill. The fill should be compacted to a minimum of 95 percent of its maximum dry unit weight as determined by ASTM Test Designation D-698 (Standard Proctor). To guard against the build-up ' of hydrostatic pressure,wall drainage must also be installed as discussed in the Drainage Section. With granular backfill placed and compacted as recommended and drainage properly installed, we recommend designing restrained (not free to deflect) retaining walls for an at-rest earth pressure equivalent to a fluid weighing 50 pcf. A value of 35 pcf may be used for the case where the wall is unrestrained. These values do not included other surcharge loading such as from fill back-slopes or adjacent footings that may act on the wall. If such conditions will exist, then the imposed loading must be included in wall design. Values of friction at the base of wall foundations and passive earth pressure that are used in design to resists lateral loads are provided in the Foundations Section. 1 Page No. 8 I