6624 BROADWAY 2018-01-02 MF Import

Wall Parameters Memorandum Habitat for Humanity Monigan Mohr Project Everett, Washington July 24, 2008 NGA File No. 793408 Page 3 conditions, and the inclination of the backfill. For walls that are free to yield at the top at least one thousandth of the height of the wall (active condition), soil pressures will be less than if movement is . limited by such factors as wall stiffness or bracing (at -rest condition). We recommend that walls supporting horizontal backfill and not subjected to hydrostatic forces, be designed using a triangular earth pressure distribution equivalent to that excited by a fluid with a density of 35 pcf for yielding (active condition) walls, and 50 pcf for non -yielding (at -rest condition) walls. These recommended lateral earth pressures arc for a drained granular backfill and arc based on the assumption of a horizontal ground surface behind the wall for a distance of at least the subsurface height of the wall, and do not account for surcharge loads. Additional lateral earth pressures should be considered for surcharge loads acting adjacent to subsurface walls and within a distance equal to the subsurface height of the wall. This would include the effects of surcharges such as traffic loads, floor slab loads, slopes, or other surface loads. We could consult with you and your structural engineer regarding additional loads oil retaining walls during final design, if needed. This wall will also support traffic surcharges from the driveway along the south edge of the site. We recommend that the wall be designed with an additional uniform load of 50 psf applied on the entire backside of the wall, to account for the traffic surcharges. Permanent drainage systems should be installed for retaining walls. Final site grades should allow for drainage away from the planned structure. We suggest that the finished ground be sloped at a minimum gradient ofthrce percent for a distance of at least 10 feet away from the building and the potential parking garage structure. Surface water should be collected by permanent catch basins and drain lines, and be discharged into an appropriate discharge system. Water should not be allowed to collect in any area where footings, slabs, or pavements are to be constructed. Surface water generated from paved areas and roof drains should be routed into permanent catch basins and then lightlined into appropriate stormwater facilities. We recommend the use of footing drains around the planned structures and behind retaining walls. Footing drains should be installed at least one foot below planned finished floor elevation. The dmins should consist of a minimum four -inch -diameter, rigid, slotted or perforated, PVC pipe surrounded by ftee-draining material, such as washed rock, wrapped in a filter fabric. We recommend that an I8-inch- NELSON GEOTECHNICAL ASSOCIATES, INC.