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GEOTECHNICAL ENGINEERING STUDY <br /> - 1920 Grand <br /> c/o Stuchell Enterprises E-9466 <br /> December 21, 2000 Page 9 <br /> .. Retaining and Foundation Watls <br /> f Retaining walis and foundation walls that act as retaining walfs should be designed to <br /> resist lateral earth pressures imposed by the re;ained soils. VValis that are designed to <br /> yield can be designed to resist the lateral earth pressures imposed by an equivalent fluid <br /> with a unit weight of thirty five (35) pc`. If walis are to be restrained at the top from free <br /> movement, the equivalent fluid weight shoulC be increased to fifty (50) pcf. These <br /> values are based on horizcntal backfill and tha: surcharges due to backfill slopes, <br /> hydrostatic pressures, traffic, structural loads, or o:he- surcharge loads wili not act on the <br /> wall. !f such surcharges are to apply, they should be added to the above design lateral <br /> pressure. For calculating the base resistance to sliding, the passive pressure and friction <br /> coefficient provided in the Foundations section of this report should be used. <br /> In order to reduce the potential for hydrostatic forces buiiding up behind the walls, <br /> retaining walls should be backfilled with a suitable free-draining material extending at <br /> least eighteen (18) inches behind the wall. The remainder of the backfill should consist of <br /> structural fiil. The free-draining backfill should conform to the WSDOT specification for <br /> � gravel backfill for walls (WSDOT 9-03.12(2)1. A perforated drainpipe should be placed at <br /> the base of the wall and should be surrounded by a minimum of one cubic foot per lineal <br /> foot with three-eighths inch pea gravel. <br /> Slab-on-Grade Floors <br /> � Slab-on-grade floors may be supported on competent native soil subgrade or on structural <br /> • fill. Disturbed subgrade soil must either be recompacted or replaced with suuctural fill. <br /> Concrete slabs resting on soil ultimately cause the moisture content of the underlying <br /> ( soiis to rise. This results from continued capillary rise and the ending of normal <br /> L evapotranspiration. As concrete is permeable, moisture will eventually peneuate the siab <br /> resulting in a condition commonly known as a "wet slab" and poor aahesion of floor <br /> [' coverings. <br /> �c <br /> f <br /> �. <br /> L <br /> IErM Conwlnnn. Inc. /i j� <br /> � \� <br /> L <br />