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• -12- • <br />should have a maximum liquid limit of 30~. Structural fill <br />placed below spread footings should be compacted to at least <br />100a of the standard Proctor density (AST P1 D698) at a <br />moisture content within 2 percentage points of optimum. Care <br />should be taken not to compact the natural soils dry of <br />optimum moisture as this could increase the swell <br />potential. Structural fill sf~ould extend beyond the edge of <br />the footing equal to at least the depth of the fill below the <br />footing. The structural fill should be observed and tested <br />by a representative of the geotechnical engineer on a full- <br />time basis. <br />3) Spread footings should have a minimum width of 20 inches for <br />walls and 36 inches for isolated column pads. <br />4) Footings should be provided with adequate soil cover above <br />their bearing elevaticn for frost protection. Placement of <br />foundations at least 36 inches below the exterior grade is <br />typically used in this area. <br />51 Continuous foundation walls should be reinforced top and <br />bottom to span an unsupported length of at least 15 feet. <br />6) A variation oC the spread footing foundation is a heavily <br />reinforced mat and box type grade beam foundations. These <br />type foundations are more resistant to differential founda- <br />tion movement. than isolated spread footings due to the heavy <br />reinforcement and continuous nature of the foundation. The <br />designer should evaluate the feasibility of these type <br />foundations which may be used overall or in part of the <br />structure. <br />Chen & Associates <br />