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LOWRY & ASSOCIATES <br /> Page 7 <br /> August 17, 1990 <br /> L & a No. 90-190 <br /> Embankment Construction <br /> It is recommended that the proposed embankment be constructed as early as possible <br /> with a three horizontal to one vertical (3:1) slope on the upstream face and a two <br /> horizontal to one vertical (2:1) slope on the downstream face. All fills should be <br /> compacted to at least 95 percent of the maximum dry density, as recommended earlier <br /> within this report. <br /> Erosion protection should be provided to guard against wave and surface run-off erosion. <br /> Suitable erosion protection may consist of vegetative cover or rip rap. <br /> Retaining Falls <br /> Retaining walls, or other earth retaining structures capable of deflection at least 0.1 <br /> percent of the wall height should be designed to resist active lateral soil pressures <br /> equivalent to a fluid weighing 40 pounds per cubic foot. Rigid retaining walls should be <br /> designed to resist at-rest lateral soil pressures of 60 pounds per cubic foot. Where <br /> retaining walls cannot be adequately drained and hydrostatic pressures will build up <br /> behind the retaining walls, then the walls should be designed to resist a combination of <br /> at-rest soil and hydrostatic lateral pressures equivalent to a fluid weighing 95 pounds per <br /> 1 cubic foot. <br /> Backfill adjacent to retaining walls should be placed in lifts not exceeding 12 inches in <br /> ' thickness and compacted to at least 90 percent of the maximum dry density in <br /> accordance with ASTM Specification D1557. <br /> t <br /> ! Ground Floor Support <br /> Concrete slab-on-grade floors should be underlain by a 4-inch thick blanket of free <br /> draining granular material intended to serve as a capillary moisture barrier. Gradation of <br /> this material should be such that 100 percent will pass a 1-inch sieve and none will pass a <br /> No. 4 sieve. <br /> If additional mitigation of slab moisture penetration is desired, a moisture vapor barrier <br /> ' membrane should be placed above the gravel blanket. A 1 or 2-inch thick layer of damp <br /> clean sand placed above the membrane is suggested to promote uniform curing of slab <br /> concrete and to provide some degree of membrane puncture protection during the <br /> construction process. <br /> j <br /> 1 <br />