1400 W MARINE VIEW DR WATERFRONT PLACE APARTMENTS Geotech Report 2022-10-25

Slab-On-Grade Support Design Parameters The exposed slab subgrade for the building will be supported on improved ground.We recommend that the slab-on-grade for the building be supported on a minimum 4-inch layer of capillary break material over improved ground/structural fill placed above improved ground. Capillary break material should consist of material meeting the requirements of Mineral Aggregate Type 22 (3/4-inch crushed gravel), City of Seattle Standard Specification 9-03.16. Vapor Barrier A vapor barrier should be used below slab-on-grade floors located in occupied portions of the buildings. Specification of the vapor barrier requires consideration of the performance expectations of the occupied space,the type of flooring planned and other factors, including the potential presence of methane gas,and is typically completed by other members of the project team. Below-Grade Walls Conventional cast-in-place walls may be necessary for small retaining structures located on-site.The lateral soil pressures acting on conventional cast-in-place subsurface walls will depend on the nature, density and configuration of the soil behind the wall and the amount of lateral wall movement that can occur as backfill is placed. For walls that are free to yield at the top at least 0.1 percent of the height of the wall,soil pressures will be less than if movement is limited by such factors as wall stiffness or bracing. Assuming that the walls are backfilled and drainage is provided as outlined in the following paragraphs, we recommend that yielding walls supporting horizontal backfill be designed using an equivalent fluid density of 35 pcf (triangular distribution), while non-yielding walls supporting horizontal backfill be designed using an equivalent fluid density of 55 pcf(triangular distribution). For seismic loading conditions,a rectangular earth pressure equal to 7H psf(where H is the height of the wall in feet)should be added to the active/at-rest pressures. If cast- in-place walls will be subjected to the influence of surcharge loading from traffic or nearby retaining walls within a horizontal distance equal to the height of the retaining wall, the walls should be designed for the additional horizontal pressure using an appropriate design method. A common practice is to assume a surcharge loading equivalent to 2 feet of additional fill to simulate traffic loading;we consider this method appropriate for typical situations. Other surcharge loading should be applied as appropriate. Lateral resistance for conventional cast-in-place walls can be provided by frictional resistance along the base of the wall and passive resistance in front of the wall. For walls founded on native soils,the allowable frictional resistance may be computed using a coefficient of friction of 0.35 applied to vertical dead-load forces. The allowable passive resistance may be computed using an equivalent fluid density of 300 pcf (triangular distribution). The above coefficient of friction and passive equivalent fluid density values incorporate a factor of safety of about 1.5. The above soil pressures assume that wall drains will be installed to prevent the buildup of hydrostatic pressure behind the walls,as discussed below. GEOENGINEERS_O May 31,2017 Page 10 File No.22360-003-00