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t LOWRY & ASSOCIATES Page 5 `j August 17, 1990 J L & a No. 90-190 ! Vertical geotextile wick drains could be installed to decrease the time of consolidation for the underlying soils. The scope of this preliminary investigation does not include an analysis of wick drains. However, if warranted, an analysis can be provided as the planning proceeds. Material Suitability On-site soils are considered suitable for use in engineered fill construction, as long as these materials are free of significant rubble, rubbish, vegetation or other objectionable substances. Excavated clays may also be used in engineered fill construction provided they are thoroughly blended with on-site silts and sands prior to placement as engineered fill and kept out of the upper 12 inches of fills. RECOMMENDATIONS Site Preparation General site clearing within the proposed building and roadway areas should include removal of vegetation, unwanted trees and their associated root systems and any loose or saturated soils. The resulting excavations should be cleaned to firm soil .and backfilled with engineered fill, placed and compacted in accordance with the following recommendations. Building pad and roadway areas, including overexcavated subgrades designated to receive engineered fill, or which are left at existing grade, should be scarified to a minimum depth of 6 inches, brought to at least the optimum moisture content and recompacted in- place to a minimum of 90 percent of the maximum dry density, per ASTM Specification D1557. Engineered fill used to construct the 20 to 25-foot tall embankment across Tracy Lake should be placed in thin horizontal lifts, moisture conditioned and compacted to a minimum of 95 percent of the maximum dry density, in accordance with ASTM Specification D1557. Engineered fill less than 5 feet in thickness should be placed in thin lifts, moisture conditioned and compacted to a minimum of 90 percent of the maximum dry density. The upper 6 inches of pavement subgrades should be compacted to at least 95 percent of the maximum dry density in accordance with ASTM Specification D1557. Completed slopes for the project should not exceed an inclination of two horizontal to one vertical (2:1).