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CASCADE TESTING LABORATORY, INC. <br />TESTING d INSP[CTION/ENGIN[ERS/GEOLOGISTS <br />December 16, 1981 <br />Cert. No. 8112-13G <br />Paper Warehouse Corporation <br />Page S <br />the proposed base of the slab elevation. With heavy compaction <br />equipment, no vibrati��:, proofroll the slab area and note any spots <br />that compact under load and rebound when unloaded (subgrade pump- <br />ing). These areas should be removed and replaced with compacted <br />structural fill to achieve a dense non-yielding condition. Then <br />backfill the subslab area with structural fill as outlined in the <br />section on Structural Fill. The subslab area should include a mini- <br />mum four (4) inch thickness of pea gravel or building sand placed <br />directly under the•slab. Subsurface water encountered within most <br />of the test pits is an indication that wet subslab soil should be <br />anticipated. Proper control and drainage should be expected. <br />Structural Fill <br />' The suitability of soils for use as compacted structural fill is a <br />function of many variables, such as gradation and moisture content. <br />- As the amount of fines (minus �k200 sieve) increase, the soi.l becomes <br />increasi�igly sensitive to smail cha�ges in moisture content and <br />adequate compaction becomes more difficult. �Soil containing more <br />than five (5) pe�cent fines are difficult to consistently compact <br />,z. <br />into a dense non-yielding condition and.achieve a suitable struc- <br />tural mat when the moisture content is signif;cantly (+2 percent) <br />� greater than or less than optimum. Optimum moisture is that percent <br />of the soils dry weight that is svater, at which the maximum density <br />can be achieved for that particular soil. <br />� With the above information at hand, there is a wide range of soils <br />� that would fulfill the requirements for structural fill. We arc noar <br />in the rainy season. A soil that drains well should be of high con- <br />� sideration. We recommend that all structural backfill conform to <br />Section 9-03.12(1)A, Gravel Backfill for Foundations as contained in <br />� the Washington State Standard Specifications or asr.approved by the <br />.' 4� <br />