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File No. 20-3445-0- hi ri � �i i)ER March 4 , 1991 stated bearing values are net values, and the weight of concrete in foundations which extend below grade can be neglected in proportioning the foundations. We recommend that all foundation excavations on this project be observed by a representative of our firm prior to placement of reinforcing steel . The purpose of these observations is to confirm that the bearing soils actually encountered in the foundation excavations are the same as those on which our recommendations are based, and to observe for any loose pockets of soil . Lateral Forces Resistance to lateral forces can be provided either by friction between the foundations and the soil, or by passive pressure of the sides of the foundations against the soil . The recommended friction factor is 0. 4 . The recommended passive soil pressure is an equivalent fluid pressure of 350 pounds per square foot per foot of depth. Floor Slabs We recommend that floor slabs be underlain by a minimum of 6 inches of recompacted native soil or Engineered Fill . The recommended minimum degree of compaction is 90 percent of the maximum dry density as obtained from the ASTM D-1557 test procedure at a moisture content near optimum. Due to the sandy nature of the near-surface soils, in our opinion, a capillary moisture break such as provided by a layer of gravel or coarse sand beneath floor slabs can be omitted. However, if cemented silt soils are exposed beneath the floor slabs, a capillary moisture break should be considered. In areas to receive moisture-sensitive floor coverings, we recommend that the subgrade soils be covered by a moistureproofing membrane such as "Moiststop, " or equivalent to act as a vapor barrier. Care should be exercised to avoid tearing, Copyright 1991 Kleinfelder, Inc. 5