5117 23RD AVE W 2016-01-01 MF Import

Gcotechi�icnl Engineering Report 51 17 23rd Ave W � January 2, 2U09 RMI Pile No. 50909 Page 8 resis�ance. The soii surface should be horizontal in front of the footing for a distance equal to at least three times the depth of embedment of the footing. The lateral pressure acting on retaining walls is dependent on the nature and density of the soil behind the wall, the :,mount of latern� wall movcment wnich can occur as backfill is plar.ed, wall drainage conditions, and the inclinntion of the backfill. For walls that are frec 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 ia limited by sucu facrors as wall stiffness or bracing (at-rest condition). We recommend that watls supporting horizontal backfill and not subjected to hydrostatic forces be designed using a triangular earth pressure distribution equivalent to that exerted by a fluid with a density of 35 pcf for yielding (active condition) walls, and 60 pcf for non-yielding(at-rest condition) walls. These recommended lateral earth pressures are based on the assumption of a horizontal ground surface adjacent to the wall for a distance of at least the subsurface heigh[ of the wall and do not account for surcharges. Additional lateral earth pressures should be considered for surcharge loads acting adjacent to the subsurface walls and within a distance equal to the subsurface height of the wall. 7'his would include the effects of surcharges such as traffic loads, floor slab londs, slopes, or other surface loads. The lateral pressures on walls may be resisted by friction betwecn the foundation and subgrade soil, and by passive resistance acting on the be.low-grade portion of the foundation. Recommendations for frictional and passivc resistance to lateral loads arc presented above. Pcrmnnent drainage systems should be installed for retaining walls. We recommend that these drainage systems consist of an IS-inch wide zone of cican Qess than 3 percent fines), free-draining granular material placed along thc back of the wall. Pea gravel is an acceptable drain material, or drainage composite may be used instead. We recommend that we be retained to evaluate the proposed wall drain backfill material for its suitability. Sec the scction on Subsurface Drainage for recommendations. All wall back�ll should be well compacted as outlined in the Structurnl Fill subsection of this report. Car� should be taken to prevent thc buildup of cxcess Iateral soil pressures, due to overcompaction of the wnll backfill. "fhis cnn be accomplished by pincing wall backfill in 8-inch thick loose lifts and compacting it with sm�ll hand-operated compactors �vithin a distance behind the wall equal to at lea�t one-half tlic height of the wali. Closurc RMI ASSOCIATEJ LLC �I �