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iWN66 <br />•R ENGINEERING <br />Image 3a. HB-01 location - view from east to Image 3b. Index Hall demolition project(2019). <br />west(2021). <br />The following is a generalized description of the soils encountered in the hand borings. <br />Topsoil — A surficial layer of topsoil was encountered at all of our hand borings. The topsoil <br />consisted of loose sandy silt soil with organics and was generally about 6-inches thick. The topsoil <br />was characterized by its dark brown color and a dense mat of roots. This soil layer is not <br />considered suitable for support of foundations, slab -on -grade floors, or pavements. In addition, <br />it is not suitable for use as structural fill, nor should it be mixed with materials to be used as <br />structural fill. <br />FIII —Fill was encountered to a depth up to 4.0 feet below existing grade. The fill was likely placed <br />during/after the demolition of the Index Hall building. The fill consisted of gravelly silty sand, <br />which was characterized by its medium dense condition and the presence of construction debris. <br />Vashon Till Deposits —The native soils underlying the Fill material consisted of medium dense to <br />dense gravelly silty sand. Vashon Till typically possesses high -strength and low -compressibility <br />attributes that are favorable for support of foundations, floor slabs, and paving with proper <br />preparation. Vashon Till is siltyand moisture -sensitive. In the presence of moisture content above <br />the optimum moisture content for compaction purposes, Vashon Till can be easily disturbed by <br />vehicles and earthwork equipment. Careful management of moisture -sensitive soils, as <br />recommended in this report, will be needed to reduce the potential for disturbance of wet <br />Vashon Till soils and costs associated with repairing disturbed soils. Reuse of Vashon Till in <br />structural fill applications will require drying to within 1 to 2 percent of optimum moisture <br />content during wet site and weather conditions. <br />Our geotechnical laboratory tests revealed that the existing native Vashon Till deposits to be currently <br />above their optimum moisture contents and highly sensitive to moisture content variations, due to their <br />MP ENGINEERING, PLLC MPGEOTECH.COM <br />