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Rockcrv I:valu,rtion Lcltcr <br />f3clmontc Ilcights Rcsidcntial Dc�:lopmcnt <br />livcrctt, Washington <br />August 2R, 200G <br />CG I�ile No. �098 <br />I'agc 2 <br />DF,SIGN <br />R'c analyzc�l glubal :,�abilily ol thc fill in thc vicinity u( ihc rockcry using Vcrsion '�.2 af <br />aS'fA13L computcr progiam. a:S7'Af3L is a Iwo-dimcnsional, limit-cyuilibnum, slopc stability <br />program. XS'fA13L genc�atcs random potcn�ial failure surfaces and Jctcrmincs thcir <br />corresponding factors of safcty with respcc: to lailurc. Thc factor of satcty is dcfincd as th� ratio <br />o!'the in�emal soil strength divided by the gravity driving forces �hat cause failure. [3y generating <br />a largc numbc� of randoir� surfaccs, thc lactur of salcty can hc uhlamcd as ihe I�iwcst nu�.nhcr <br />calculalcd. <br />Wc cstahlishcd a dcsign strengih o(thc fill soii bchind thc rockcry hascd on our sitc obscr��ations <br />and cxpericncc with similar matcrials. Soil paramctcrs and results arc shown on I�igures 1 and 2. <br />I'hc factor of safcty against dccp-sca�cd failures thst would impact thc planncd �csidatcc <br />fi�undations unJcr static conditions is ahout 1.9. 'fhc factor of safcty against similar failures that <br />would impac� yard arcas hul not thc residcncc foundations i�, aho�r 1.3. Our analysis did not <br />includc ticismic in�lucnecs. <br />c�c�vc�i.usu>Ns ANU RF.('O�11111?YU���riovs <br />\V. rccummcnd Ihat timndation dcpths comply with �hc ('ore Dcsign dcl:ul, tiuch ihat thc <br />foundations cxtcnd bclo��• a linc that hcgins at thc back of !hc basc of thc rockcry, and coniinucs <br />upward ��ith an inclination of 211:IV. '1'his will rcducc thc potrntial for any rockcry failurc to <br />nnpact thc planncd residcncc �bundations. Wc czpcct thal dccpcncd fowidations will bc rcquircd <br />�iir thc cast sidc ul' I�uildings A, R, and C and ihc nor1hcrn sidc of Building C Wc havc prcparcd <br />a dc�ail illu,traun�: ihc rockcry coic:truc�iun anJ thc planncd fuunJation location. prescnted in <br />Pigurc ?. <br />In uur upmion, failures of �hc lill slup� bet��cen thc ruckery and thc linmdations of [3uildings A, <br />li, anJ (' arc unlikcly. 7�hc tactor of safcly a�ainst tailures Ihat would impact thc structures is <br />❑ppropriatc litt resiJcntial conswction. Rockcrics arc not cansidcrcd rctaining structures. 7'hccc <br />Icauircs arc t}�ically installcd tn facc slopcs that arc inhcrenAy stable (as generally indicated by <br />our plohal stahility analysis). 'fhe perfomiance of ihc rock facing unJer certain conditions, such <br />as thosc prudurcd during scismic cvcnis, is �iifficult to prcdict. <br />�� <br />,; i \Dl <br />Cornerstone Geotechnical, Inc. � <br />