1815 13TH ST SEATTLE CHILDRENS NORTH CLINIC Geotech Report 2022-10-25

continuously throughout the construction process and to respond to variable soil and groundwater conditions. Therefore, the contractor should have the primary responsibility for deciding whether to use open-cut slopes for much of the excavations rather than some form of temporary excavation support, and for establishing the safe inclination of the cut slope.Acceptable slope inclinations for utilities and ancillary excavations should be determined during construction. Because of the diversity of construction techniques and available shoring systems, the design of temporary cut slopes is most appropriately left to the contractor proposing to complete the installation.Temporary cut slopes and shoring must comply with the provisions of Chapter 296-155 Washington Administrative Code(WAC), Part N, "Excavation,Trenching and Shoring." Temporary unsupported cut slopes more than 4 feet high may be inclined at 1.5H:1V(horizontal to vertical) maximum steepness within the fill soils and no steeper than 1H:1V or 0.5H:1V in the glacially consolidated soils. For open cuts at the site,we recommend that: ▪ no traffic,construction equipment,stockpiles or building supplies be allowed at the top of the cut slopes within a distance of at least 5 feet from the top of the cut; ▪ the 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; ▪ exposed soil along the slope be protected from surface erosion by using waterproof tarps or plastic sheeting; >le construction activities be scheduled so that the length of time the temporary cut is left open is reduced to the extent practicable; • erosion control measures be implemented as appropriate such that runoff from the site is reduced to the extent practicable; • surface water be diverted away from the slope;and ■ the general condition of the slopes be observed periodically by the geotechnical engineer to confirm adequate stability. 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,where necessary.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. Foundations For the current development plan we recommend that the vault foundation bear on glacially consolidated soils. Additionally, we recommend that the light poles be supported on drilled shafts. Recommendations for each of these is provided below. GEOENGINEERS April 22.2016 Page 5 Ana;0r 010