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Harmon 3 Associatzs W-4545 , <br />15 April 1985 Page 6 <br />fill. the surfaces to receive fill should be prepared as previously recommended. <br />Structural fill should be placed in loose lifts not exceeding 8 inches in <br />thickness� and compacted such that a density of at least 90 percent of the <br />modified Proctor dry �ensity (ASTM:D 1557) is achieved. We recommend that a <br />representative from our firm be present during placement of structural fill to <br />observe the work and perform a representative number of in-place density tests. <br />In this way, the adequacy of the earthwork may be evaluated as grading <br />progresses. " ' <br />The suitability of soils for use as structural fill depends primarily on the <br />yradation and moisture cantent of the soil when it is placed. As the amount of <br />fines (that portion passing the U.S. No. 200 sieve) increases, the soil becomes <br />increasingly sensiL•ive to smali changes in moisture content and adequate <br />compaction becomes more difficutt to achieve. Soils containing more than about• <br />5 percent fines by weight cannot be consistently compacted to a firm, non- <br />yielding; condition wfien the moistu�e content is more than a few percent from <br />optimum. <br />The onsite soils may be difficult or impossible'to use as structural fill except <br />during the �ummer months when drying is possible. Even then� delays in grading <br />can be common due to inclement weather. If rain occurs while the subgrade is <br />exposed, or during placement of the onsite material (cr any soil with over <br />5 percent fines) the material should be allowed to dry prior to additional <br />filling. It may be necessar,y to scarify the upPer layer, allow it to dry and <br />recompact prior td additional filiing. Overexcavation or removal of wet soils .� <br />may be necessary if it is not possible to dry and compact them. � <br />5.3 Shallow Foundations <br />If the southwest building is constructed without relocation, foundation elements <br />should extend to bear on dense native materials or at a higher elevation above <br />densely compacted structural fill beariny on suitable native deposits at depth. <br />The laterai limits of the struct�ral fill below footings should extend from the <br />edge of the footing a distance at least equal to the cat height. If the <br />