Laserfiche WebLink
IPrcliminary Gco�echnical Lc�tcr <br /> Landslidc Evaluation and Rcpair <br /> ( 4703 Glcnha��en Drivc <br /> G��crctt. Washington <br /> Fcbruary 1, 2007 <br /> I NGA Filc Nu. 75570G <br /> Pagc 1 I <br /> immediately as they are excavated. Also, runoff generated within the site shoulJ be collected and routed <br /> ( to a pennancnt dischargc location at the bottom of thc slopc and not be allowed to ilow over thc slope. <br /> Under no circumslances should water be allowed to concentrate or(lo�v uncontrolled over the slope. Thc <br /> fvcgctation covcr on thc slope should bc e�:�luatcd I'or compatibility wilh desircd slope stabiliry <br /> conditions, and a vcgctation memagcment plan should bc devised to cnhancc slope stability. <br /> IThe slope should be monitored on an on-going basis after conswction, especially during Ihe wet season. <br /> I for any signs of instabili�y, and corrcctivc :iGions taken promptly if any signs of instability arc obscrvcd. <br /> Lawn clippings or any othcr dcbris should ncvcr bc cast ovcr thc slopc. <br /> , Our explorations indica�e that the competcnt n:uive soils at depth consist of silt, day, and silty sand, and <br /> thesc soils arc also considcrcd extremcly moisture scnsitivc. Thc nativc soils will bc casily disturbcd and <br /> Idifficult to work �vith in wct condilions. Wc rccomnunJ diat thc contractor usc an cxcav�tor equippcd <br /> with widc Iracks and a smooth buckct to complc�c sile grading to minimizc disturbancc ro thc moisturc <br /> � scnsitivc nativc soils. Thc cxposcd sub,�radc .hould bc immcdiatcly covcrcd wilh thc recommended <br /> laycr of rock spalls for protcction. Thc prep:ircd sub�radc should bc protcetcd from construction traffic <br /> ( and surfacc water should be divcrtcd around prep,ircd subgrade. �Vc rccommcnd that the site bc <br /> dc� :lopcd only during cxicnded periods of dq� wcathcr. A cross scction illustraling thc conccptual plan <br /> Ifor thc slopc repair and drainagc instnllation is shown on Pigurc 28. Cross scctions illustrating possiblc <br /> cscavation gcomcUy based un our cxplurations are shown on Fi�,ures 29 and 30. <br /> � Urainage Improvements <br /> ( �Ve recommend that drains be insialled to collect groundw:uer in the slope and direct water to the bottom <br /> of the west-facin� slope in tighiline pipes. The drains shoulJ consist of rigid, four-inch diameter <br /> perforated PVC drainpipe cmbedded in a minimum of ono-foot of washed rock and wrapped in a (ilter <br /> i fabric. The drains should be placed directly on the benches in the native soil and then be covered with <br /> the rock fill. The drainpipes should be sloped to drain to a tightline collection pipe along the northern <br /> cdgc of the slopc rcpair. The tighUine collection pipe should drain to :� suitable outlet at lhe bottom of <br /> ihc slopc, such as thc cxisting storm drain along Glcnhavcn Drivc. <br /> NELSON GEOTECHNICAI. ASSOCIATES, INC. <br /> � I�- <br /> � <br />