9512 EVERGREEN WAY 2022-08-29 - Laserfiche WebLink

May 4, 2017 HWA Project No. 2017-036-21 • No soil should be left uncompacted so it can absorb water. The ground surface within the construction area should be sealed by a smooth drum vibratory roller. Soils which become too wet for compaction should be removed and replaced with clean granular materials; • Excavation and placement of fill should be observed by the geotechnical engineer to verify that all unsuitable materials are removed and suitable compaction and site drainage is achieved; and • Bales of straw and/or geotextile silt fences and other Best Management Practices (BMP's) should be employed to control erosion in accordance with City of Seattle regulations. 4.7 TEMPORARY EXCAVATIONS We anticipate that the on -site soils can be excavated using conventional excavating equipment such as backhoes and trackhoes. However, the on -site material may contain debris, cobbles, and boulders. As such, the contract documents should contain provisions that address the potential presence, handling, and disposal of oversize materials/obstructions. All temporary cuts more than 4 feet in height should be sloped in accordance with Part N of Washington Administrative Code (WAC) 296-155, or shored. The fill and outwash materials at the site classify as Type C soil. Unsupported excavations in Type C soils must be inclined no steeper than 1 %2H: IV (horizontal to vertical). Flatter slopes may be required where ground water seepage occurs. The existing non -weathered glacial till classifies as a Type A soil; temporary unsupported excavations in Type A soils may be sloped as steep as 3/4H: IV. The recommended maximum inclinations for temporary slopes assumes that the ground surface behind the slope is level and surface loads from equipment and materials are kept a sufficient distance away from the top of the slope. The recommended maximum allowable temporary cut slope inclinations are also applicable to temporary excavations above the water table only. Flatter slopes may be required where ground water seepage is present. With time and the presence of seepage and/or precipitation, the stability of temporary unsupported cut slopes can be significantly reduced. Therefore, all temporary slopes should be protected from erosion by installing a surface water diversion ditch or berm at the top of the slope and by covering the cut face with well -anchored plastic sheeting. In addition, the contractor should monitor the stability of the temporary cut slopes and adjust the construction schedule and slope inclination accordingly. Exposure of personnel beneath temporary cut slopes should be kept to a minimum. Construction should proceed as rapidly as feasible, to limit the time temporary excavations are open. In addition, heavy construction equipment, building materials, excavated soil, and vehicular traffic Final Geologic Assessment 10 HWA GeoSciences Inc.