2710 14TH ST BLDG A Geotech Report 2023-12-29

techniques and available shoring systems, the design of temporary shoring is most appropriately left up to ' the contractor proposing to complete the installation. Temporary cut slopes and shoring must comply with the provisions of Title 296 Washington Administration Code (WAC), Part N, "Excavation, Trenching and ' Shoring." 4.5.10.1 Temporary Slopes ' For planning purposes, temporary unsupported cuts more than 4 feet high may be inclined at 1.5H:1V maximum steepness in the fill and weathered glacial soils. Steeper slopes, up to 1H:1V, are feasible for cuts made in the very dense glacial till. Flatter slopes may be necessary if seepage is present on the face ' of the cut slopes or if localized sloughing occurs. The above guidelines assume that surface loads such as traffic, construction equipment, stockpiles or ' building supplies will be kept away from the top of the cut slopes a sufficient distance so that the stability of the excavation is not affected. We recommend that this distance be at least 5 feet from the top of the cut for temporary cuts made at 1.51-1:1V or flatter, and no closer than a distance equal to one half the height ' of the slope for cuts made at 1H:1V. Temporary cut slopes should be planned such that they do not encroach on a 1H:1V influence line projected ' down from the edges of nearby or planned foundation elements. New footings planned at or near existing grades and in temporary cut slope areas for the lower level should extend through wall backfill and be embedded in native soils. Water that enters the excavation must be collected and routed away from prepared subgrade areas. We expect that this may be accomplished by installing a system of drainage ditches and sumps along the , toe of the cut slopes. Some sloughing and raveling of the cut slopes should be expected. Temporary covering, such as heavy plastic sheeting with appropriate ballast, should be used to protect these slopes during periods of wet weather. Surface water runoff from above cut slopes should be prevented from flowing over the slope face by using berms, drainage ditches, swales or other appropriate methods. If temporary cut slopes experience excessive sloughing or raveling during construction, it may become ' necessary to modify the cut slopes to maintain safe working conditions. Slopes experiencing problems can be flattened, regraded to add intermediate slope benches, or additional dewatering can be provided if the poor slope performance is related to groundwater seepage. , 4.5.11. Permanent Slopes We recommend that permanent cut or fill slopes be constructed at inclinations of 21-1:1V or flatter. To ' achieve uniform compaction, we recommend that fill slopes be overbuilt at least 2 feet and subsequently cut back to expose properly compacted fill. Permanent slopes constructed at 31-1:1V or flatter provide better I conditions for future maintenance. To reduce erosion, newly constructed slopes should be planted or hydroseeded shortly after completion of ' grading. Until the vegetation is established, some sloughing and raveling of the slopes should be expected. This may require localized repairs and reseeding. Temporary covering, such as clear heavy plastic sheeting, jute fabric, loose straw or erosion control blankets (such as American Excelsior Curlex 1 or North American ' Green SC150) could be used to protect the slopes during periods of rainfall. GEOENGINEERS� Fil October 30, 20 Page 17 ' e No No 21288 002.00