6307 36TH AVE W Geotech Report 2025-07-29

August 13,2008 Project No.T-6241 ' 5.4 Foundations Spread Footings The buildings may be supported on conventional spread foundations bearing on properly prepared subgrades of ' competent native soil or structural fills placed above competent native soils. Foundation subgrades should be prepared as recommended in Section 5.2 of this report. Perimeter foundations exposed to the weather should be a minimum depth of 18 inches below final exterior grades. Interior foundations can be constructed at any Iconvenient depth below the floor slab. We recommend designing foundations supported by competent medium dense to dense native soils or properly placed and compacted structural fill for a net allowable bearing capacity of 3,000 pounds per square foot (psf). For short-term loads,such as wind and seismic,a one-third increase in this allowable capacity can be used. For designing foundations to resist lateral loads, a base friction coefficient of 0.35 can be used. Passive earth pressure acting on the sides of the footings may 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 they can be affected by weather or disturbed by future grading activity. This value assumes the foundations will be constructed neat against competent native soil or the excavations are backfilled with structural fill, as described in Section 5.2 of this report. The recommended passive and friction values include a safety factor of 1.5. 5.5 Slab-on-Grade Floors ' Slab-on-grade floors may be supported on subgrade prepared as recommended in Section 5.2 of this report. Immediately below the floor slab, we recommend placing a four-inch thick capillary break layer composed of clean, 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 slab. 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 uniform curing of the slab, and can actually serve as a water supply for moisture seeping through the slab with potential for adverse impacts to 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 2.302.1R- 96, for further information regarding vapor barrier installation below slab-on-grade floors. ' Other methods are available for preventing or reducing water vapor transmission through the slab. We recommend consulting a building envelope specialist or contractor for additional assistance regarding this issue. I ' Page No.9