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Kierstein Residence Retaining Wall <br />Everett Washington Geotechnical Engineering Report <br />Structural Fill <br />All fill placed beneath or behind the SierraScape wall shall be considered structural fill. All <br />references to structural fill in this letter -report refer to subgrade preparation, fill type and <br />placement, and compaction of materials, as discussed in this section. If a percentage of <br />compaction is specified under another section of this letter -report, the value given in that <br />section should be used. <br />Any existing site soils containing organics or debris should be stripped from all areas to receive <br />structural fill. The existing grade should then be compacted to a firm and non -yielding <br />condition. After recompaction or remediation of the exposed ground is approved, structural fill <br />may be placed as required to attain desired grades. Structural fill is defined as non -organic soil, <br />acceptable to the geotechnical engineer, placed in maximum 8-inch loose lifts, with each lift <br />being compacted to at least 95 percent of the modified Proctor maximum density using <br />ASTM D-1557 as the standard. <br />Soils in which the amount of fine-grained material (smaller than the No. 200 sieve) is greater <br />than approximately 5 percent (measured on the minus No. 4 sieve size) should be considered <br />moisture -sensitive. Use of moisture -sensitive soil in structural fills should be limited to <br />favorable dry weather conditions. The fill and pre -Fraser sand contain low to moderate <br />amounts of silt and are considered slightly to moderately moisture -sensitive. Based on the field <br />moisture contents, the near -surface native soils appear to be near optimum moisture content <br />for compaction. If structural fill is to be placed during wet weather and proper compaction <br />cannot be obtained with the on -site soils, a select material consisting of a clean, free -draining <br />gravel and/or sand should be used. Free -draining fill consists of non -organic soil with the <br />amount of fine-grained material limited to 5 percent by weight when measured on the minus <br />No. 4 sieve fraction. <br />A representative from AESI should observe the stripped subgrade and be present during <br />placement of structural fill to observe the work and perform a representative number of <br />in -place density tests. In this way, the adequacy of the earthwork may be evaluated as filling <br />progresses and problem areas may be corrected at that time. Our field technicians and <br />engineers are available to aid the owner in developing a suitable monitoring and testing <br />program, such that quality control is adequately provided. <br />Wall Drainage <br />It is imperative that proper drainage be provided so that hydrostatic pressures do not develop <br />behind the wall. The wall should be provided with a minimum 1-foot-wide blanket drain for <br />within 8 inches of the full wall height and a chimney drain behind the geogrid reinforced zone <br />using imported, washed crushed gravel and a drain pipe consisting of rigid, perforated, <br />polyvinyl chloride (PVC) pipe surrounded by washed crushed gravel. The drains should be <br />July 1, 2022 ASSOCIATED EARTH SCIENCES, INC. <br />SASlih - 20180614EO01-002 Page 7 <br />