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-~~- <br />tions for a spread footing foundation to support the dewatering <br />structure are presented below. <br />Spread Footiny.s: Spread footing foundations should be placed on <br />compacted structural fill. This will require removal of the <br />natural soils below ttie structure and replacement with approved <br />material. We recommend at least 5 feet depth of fill be placed <br />below footing bearing level. Recommended fill material type and <br />compaction are presented below in this section. We expect that <br />the fill material can be derived on-site. Surface drainage will <br />be important to prevent ponding of water near the structure. <br />Recommendations for surface drainage are presented in "Site <br />Grading" below. The following design and construction criteria <br />should be observed for a spread footing foundation system. <br />1) Spread footings placed on compacted structural fill should be <br />designed for a maximum allowable soil bearing pressure of <br />4000 psf. Initial foundation settlement is expected to be <br />about 1/2 to 1 inch. If wetting of the bearing soils were to <br />occur, additional foundation movement of about similar <br />magnitude should be expected. The foundation movement poten- <br />tial should be considered as general and additional analysis <br />with specific load information is needed for a better <br />estimate. <br />2) The till material should consist of a relatively impervious <br />granular soil to achieve moderate bearing capacity and to <br />reduce surface water infiltration. The on-site soils may be <br />used and should be mixed to achieve a maximum silt and clay <br />content (-200 sieve) of 50% and a minimum of 25`6. The soil <br />Chen & Associates <br />