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Gcotcchni�:al Lne�nccrin_Rrpuii <br /> Singlc-Pamily IZc>idcncc <br /> Gverctt,Washington <br /> Deccmber 9, 200� <br /> CG File No. ?0 U <br /> P'�ec G <br /> Site speci�ic cucl(icients :in�l aJj!iste�3 iva�cimurr. considered c�rihcuake spectral respunse acceleration <br /> parametcrs apply as sho��m in Scction 1G15.1 of thc II3C. <br /> � Additional seismic considerations irclude liquefaction potcrti;,l and amplific:uion of ground motions by <br /> solt soil deposits. 7'hc liquefaction potential is highest for loosc sand�vith a high ground water table. Thc <br /> � underlying medium dense to dcn:c sandy soil is cor�sidercd to h��e a low potential for liqucfaction and <br /> amplification of ground motion. <br /> � <br /> CONCLUSIONS AND RGCO�inIGNDA'I'IONS <br /> � General <br /> It is our opinion Qiat thc sitc is comp�tiblc �cith thc planncd dc�clopmcnt. The undcrlying mcdium dcnsc <br /> 1 to dense, native soils arc capaUlc of supporting the planned structures and pa��ements. We recommend <br /> ;� <br /> that the foundations for the structures extcnd Qvough nny topsoil, fill, loose, or disturbcd soils, and hear <br /> ,,j on the underlying medium dense to dense.native soils, or on stnicmnl fill estending to thcse soils. <br /> �, <br /> � Effective Structure S^ bad: <br /> Unccrtainties rclatcd to Uuilding alone thc top ol ,tccp slopcs arc typicaliy addresscd by thc usc oC <br /> building scthacks. The purpose of thc sctUack is to establish a "bufCer zone" bch��ecn the strucmre and <br /> Ithe top of the s�ope, so that amplc room is allowcd for normal slope recession during a rcasonable liie <br /> span of the swemre (usually takcn to be 100 ycers). In a general sensc, a grcater�etback will r�_duce thc <br /> Irisk. From a geological standpoint, thc sctUack dimension is based on the slope's physical characteristics, <br /> such as slope height, surface nngle, material compo;ition and hydrology. Other facrors such as historical <br /> slope acti�'ity, rate of rc,�ression. and thc [�'pe .md dcsired lifr span o� t;ic stiuctures �rc important <br /> considerations as«cll. <br /> We recommend the building iiiutin�s ii:���c adcyu:�te sctback an�i cmbcdment to bc stable. "Chis can bc <br /> achieved by establishing ai� "cffecuve sctback" of at lcast 2� lcet from the slopc face. The "effectice <br /> setback" is the horizontal distancc measured from the nearest edge of the footing, or from the bottam of <br /> the pier or pile in the case of a deep foundation system, to the slop� face, as illustrated in Pigure 8. This <br /> � measurcmcnt should be takcn to the Pace of thc native soils, and not to the face of��egetation or debris <br /> resting on thc slopc. It is our opinion that the rccommcndcd cficcti��c sctback and cmbedment criteria <br /> � <br /> � Cornerstone Geotechnical, Inc. <br /> �'lz s <br />� ----- <br />