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1 <br /> respond to variable soil and groundwater conditions. Therefore, the contractor should have the primary <br /> responsibility for deciding whether or not to use open cut slopes for much of the excavations rather than <br /> some form of temporary excavation support, and for establishing the safe inclination of the cut slope. <br /> Acceptable slope inclinations for utilities and ancillary excavations should be determined during construction. <br /> Because of the diversity of construction techniques and available shoring systems, the design of temporary <br /> shoring is most appropriately left up to the contractor proposing to complete the installation. Temporary cut <br /> slopes and shoring must comply with the provisions of Title 296 WAC, Part N, "Excavation, Trenching and <br /> IShoring." <br /> Because the contractor has control of the construction operations, the contractor should be made <br /> responsible for the stability of cut slopes,as well as the safety of the excavations. The contractor should take <br /> all necessary steps to ensure the safety of the workers near the slopes. <br /> Temporary Cut Slopes <br /> For planning purpose,temporary unsupported cut slopes more than 4 feet high may be inclined at 1.5H:1V in <br /> the fill soils and 1H:1V in the dense glacial soils encountered at the site. These inclinations may need to be <br /> flattened by the contractor if significant caving/sloughing or groundwater seepage occurs. For open cuts at <br /> the site,we recommend that: <br /> No traffic,construction'equipment,stockpiles,or building supplies be allowed at the top of the cut slopes <br /> within a distance of at least 5 feet from the top of the cut. <br /> The excavation does not encroach on a 1H:1V influence line projected down from the edges of nearby or <br /> planned foundation elements. <br /> Exposed soil along the slope be protected from surface erosion using waterproof tarps or visqueen or <br /> flashcoating with shotcrete. <br /> Construction activities be scheduled so that the length of time the.temporary cut is left open is reduced <br /> to the extent practicable. <br /> tErosion control measures be implemented as appropriate such that runoff from the site is reduced to the <br /> extent practicable. <br /> Surface water be diverted away from the excavation. <br /> AI The general condition of the slopes be observed periodically by GeoEngineers to confirm adequate <br /> 1 stability. <br /> Utility Trenches <br /> Trench excavation, pipe bedding, and trench backfilling should be completed using the general procedures <br /> described in the 2008 WSDOT Standard Specifications or other suitable procedures specified by the project <br /> civil engineer. The glacial till and fill soils encountered at the site are generally of low corrosivity based on our <br /> experience in the Puget Sound area. <br /> Utility trench backfill should consist of structural fill and should be placed in lifts of 8 inches or less (loose <br /> ' thickness)such that adequate compaction can be achieved throughout the lift. Sand backfill,containing less <br /> than 5 percent fines, may be compacted in loose lifts not exceeding 12 inches when placed below five feet of <br /> the finished ground surface. Each lift must be compacted prior to placing the subsequent lift. Prior to <br /> compaction,the backfill should be moisture conditioned to within 3 percent of the optimum moisture content, <br /> Page 10 <br />