1530 51ST PL SW 2016-01-01 MF Import

Geotechnical [nginecring E•valua��„n I_cner Mosman Basement Evcrc« , Washington NGA Filc No. 886013 December 17, 2013 Page 7 Permanent cut and fill slopes should be no steeper than 2fi:1 V, unless specifically approved by NGA. Also, tlatter inclinations may be required in areas where loose soils arc encountered. Permanent slopes should be vegetated and the vegetative cover maintained until establishul. Foundation Support Thc ncwly pourcd basement foundations appear to consist of conventiooal sprcad Cootings. We do not have prior knoa ledge of the foundation design and construction. The Coundation should be evaluated by thc swcmral engineer and improved, as needed, to meet the requirements of all applicable codes, including the 2009 IBC, and the recommendations found in this letter. Footing widths should be based on actual loads and allowable soil bearing pressurc. The new footings appear to havc been extended through loose surficial soil and founded on thc underlying medium dense or better native soils. We recommend an allowable design bearing pressure of not morc than 2,000 pounds per squarc foot (ps� be used for analyzing the ezisting Coundations. Currcnt IBC guidclines should be used when considering increased allowable bearing pressure for short-term transitory wind or seismic loads. Potential foundation setdement using the recommendcd allowable bearing pressure is estimated to be less than one-inch totai and '/,-inch differential betwecn zdjacent footings or across a distanec of about 30 feet based o0 our experience with similar projects. Lateral loads may bc resisted by fnction on the basc of the footing and passive resistancc agaiost thc subsurfacc portions of the foundation. A coefficicnt of fnction of 035 may 6c used to calculate the base friction and should be applied to thc vertical dead load only. Passive resistance may be calculated as a triangular cquivalcni fluid pressurc distribution. M equivalcnt fluid dcnsiry of 200 pounds per cubic foot (pc� should be used for passive resistance design £or � Ievel ground surface adjacent to the footing. This Icvcl surf•vcc should extcnd a distance cqual to at lcast thrce times the footing depth. l'hese recommcnded ��alucs incorporatc safety factors of ].5 and 2.0. pplicd to the estimated ultimate values for frictional and passive resisiance, respectively. 7'o achicve this value ot passive resistance, compacted slructural fill should be placed against t!�c fcnting afler thc footing dnins havc been installcd. We recommend that the upper one-foot of soil be neglected wheu calculating thc passive resistancc. Retaining Walls The lateral pressure acting on subsurface retaining walls is dependeut on the nawrc and density of the soil behind the waU. [he amount of lateral wall movement which can occur as backfill is placed, wall NELSON GEOTECHNICAL ASSOClATES, INC.