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grade, the fill should consist of non~xpansive, granulaz materials. The fill should be uniformly <br />~ placed and compacted in 6 to 8 inch lifts to at least 95% of the maximum standazd Proctor <br />density at or neaz the optimum moisture content, as determined by ASTM D 698. <br />The above precautions and recommendations will not prevent floor slab movement in the event the clays <br />or claystone bedrock materials beneath the floor slabs undergo moisture changes. However, they should <br />reduce the amount of damage if such movement occurs. The only way to eliminate the risk of all floor <br />slab movement is to construct a swcmral floor over swell-vented crawl space. <br />Foundation Walls and Retainin¢ Structures: Foundation walls and retaining structures, which are <br />laterally supported and can be expected to undergo only a moderate amount of deflection, maybe designed <br />for a lateral earth pressure computed on the basis of an equivalent fluid unit weight of 45 pcf for imported, <br />free draining granulaz backfill and 60 pcf for the on-site materials. <br />Cantilevered retaining strucmres on the site can be expected to deflect sufficiently to mobilize the full <br />active earth pressure condition. Therefore, cantilevered stmctures may be designed for a lateral earth <br />pressure computed on the basis of an equivalent fluid unit weight of 35 pcf for imported, free draining <br />granulaz backfill and 50 pcf for the on-site materials. <br />The foundation walls and retaining structures should be designed for appropriate hydrostatic and <br />surcharge pressures such as adjacent buildings, traffic and constmction materials. An upwazd sloping <br />backfill and/or natural slope will also increase the earth pressures on foundation walls and retaining <br />~) swctures. <br />We recommend imported granulaz soils for backfilling foundation walls and retaining structures because <br />their use results in lower lateral earth pressures. The imported granular materials should be placed [o <br />ugthin 2 to 3 feet of the ground surface. Imported granulaz soils should be free draining and have less <br />than 10 percent passing the No. 200 sieve. The upper 2 to 3 feet of fill should be a relatively impervious <br />soil or pavement structure to prevent surface water infiltration into the backfill. <br />The wall bacldill should be carefully placed in uniform lifts and compacted to between 90 and 95 percent <br />of the maximum standard Proctor density, near [he optimum moisture content. Caze should be taken not <br />to overcompact the backfill since this could cause excessive tateral pressure on the walls. Some settlement <br />of deep foundation wall backfill materials will occur even if the material is placed correctly. <br />Surface DraiaaQe-Structures: Proper surface drainage at this site is of paramount importance for <br />minimizing the i~Itration of surface drainage into the wall bacldill and bearing soils, which could result <br />in increased wall pressures, differential foundation and slab movement. The following drainage <br />precautions should be observed during construction and at all times after the building has been completed: <br />1) The ground surface surrounding the building should be sloped (minimum of 1.0 inch per foot) to <br />drain away from the building in all directions to a minimum of IO feet. Ponding must be <br />avoided. If necessary, raising the top of foundation walls to achieve a better surface grade is <br />advisable. <br />lob Number. 03-3838 IVWCC, lnc. Page 6 <br />