5700 23RD DR W 2018-06-28 - Laserfiche WebLink

November 29,2016 Project No.T-5922-6 A base friction coefficient of 0.35 can be used for designing foundations to resist lateral loads. 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 above include a safety factor of 1.5. 5.5__ Floor Slab-on-Grade Support The floor slab may be supported on the 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 of clean free- draining sand or 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. Installation of a capillary break layer will not be necessary where the floor subgrade is composed of the clean native outwash or structural fill comprised of the clean outwash. A representative of Terra Associates should observe the subgrade at the time of construction to verify this condition and determine if an imported capillary break layer is required. 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 transmission 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 current American Concrete Institute (ACI) Manual of Concrete Practice for further information regarding vapor barrier installation below slab-on-grade floors. 5.6 Lateral Earth Pressures for Below-Grade Walls and CIP Concrete Retaining Walls The magnitude of earth pressures developing on the below-grade basement walls or cast-in-place (CIP) concrete retaining walls will depend on the quality and compaction of the wall backfill. We recommend placing and compacting wall backfill as structural fill, as described in Section 5.2 of this report. To prevent overstressing the walls during backfilling, heavy construction machinery should not be operated within five feet of the wall. Wall backfill in this zone should be compacted with hand-operated equipment. To prevent hydrostatic pressure development,wall drainage must also be installed. A typical wall drainage detail is shown on Figure 3. Page No. 8