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� January� 23, Z00� <br /> Project No. T-�6�9 <br /> i <br /> For desiening foundations to resist latcral loads, a basc friction coefficicnt of 0.35 can be used. Passive eanh <br /> j pressures acting on the sides of t;: f�,otings can also Ue considered. We recommend calculating this lateral <br /> � resist�nce using an ecuivalent fluid wcigUt of 300 pounds ner cubic foet (pc�. We recommend not includine thc <br /> upper 12 inches of soil in this computation because it can be afCected by wcather or disturbed by future grading <br /> Iactivity. This value assumes the foundation �vill be constructed neat against competent soil or backfilled aith <br /> structural fill, as dcscribed in Section 4.2 of this repurt. The values recommended include a safety fac'or of 1.�. <br /> I4.5 Slab-nn-Gradc Ploors <br /> I S1aU-on-grade floors may be supported on suherades prepared :+s recommended in Scetion 4.2 0£ this repoR. <br /> immediately below the floor slahs, we recommend placing a four-inc; thick capillary break layer of clean, free- <br /> draining, coarse sand or fine gravel that has less than thrce percent Uy �veiglu of material passing die No. 200 <br /> Isicve. This material will reduce the potential for upward capillary movement of water through the underlying soil <br /> and subsequent wetting of tl�e Floor slabs. <br /> IThe capillary break layer will not prevent moiswre i�urusion through the slab caused by�vater vapor transmission. <br /> Nhere moisture by vapor transmission is undesirable, such as covered floor areas,a cocnmon pcactice is to place a <br /> � durable p!astic membrane on the capillary break layer and then cover the membrane with a layer of clean sand or <br /> fine gravel to protect it Gom damagc during construction, and aid in unifonn curing of the concrete slab. It <br /> should be noted Hiat iC the sand or gra�cl laycr overlying the membrane is saturated prior to pouring the slab, it <br /> j will be ineffective in assisting in uniform curing of the slab, and can actually serve as a water supply for moisture <br /> � transmission through the slab and affecting floor coverings. TUerefore, in our opinion, covering the membranc <br /> � with a layer of sand or gravel should be avoided if floor slaU construction occurs during the ���et winter months <br /> and tha laycr cannot be effectively drained. <br /> , Other methods are available for prevcnting or reducing water vapor transmission through the slab. �Ve <br /> f recommend consulting with a buifding envclope specialist or contractm' for additional assistance regarding this <br /> issue. <br /> � �or thickness design of tt�c slab subjected to point loading from storage racks, forklift, and ott�er vehicle traffic, <br /> �ve reoommend using a subgrade modulus(k,) oC 200 pounus square inch per inch(pci) of deflection. <br /> 4.( Rctaining 1�'alls <br /> , �i The magnitude of earth pmssure devclopmznt on below-grade �valls will partly depend on the quality of the �vall <br /> Uackfill. Ne recommend placing and compacting ���all backfill as stn�ctural fill. Below improved areas, such as <br /> pavements or floor s!aUs, the backfill should be compacted to a minimum of 9� percent of its maximum dry unit <br /> �i ��cight, as detenniced by ASTM Test Designation D-693 (Standard Proctor). In unimproved areas, the relativc <br /> compaction can be r.duced to 90 pereent. <br /> I <br /> ' l'o guard against h��drostatic pressure dc��elopment, �vall drainage must also he installed. A typical wall drainage <br /> dctail is sho��n on Picurc 3. <br /> � <br /> Page No. 6 <br /> �� <br />