Laserfiche WebLink
IPrcliminary Gcotcchnical Lettcr <br /> Landslidc Evalua�ion :md Rcpair <br /> I d703 Glenh.rvcn llrivc <br /> L=vcrett, Washin�ton <br /> Febnciry 1. 2007 <br /> � NGA 1 ilc No. 7�i70G <br /> Pagc 3 <br /> CONCLUSIONti AND RGCOMMENUAI'IONS <br /> IGcncral <br /> Bascd on our obscrvations and subsurfacc explorations, it is our opinion that thc slopc movcnunt that <br /> � was cxpericncul at this sitc was duc to samration of loosc m;uerial that was placcd along thc up�r <br /> portion of the slope in the past. ll appcars that during rccent hcavy rainfall, thesc loose soils bcecune <br /> Ioversaturated and, in turn. experienced a significant rcduction in she,ir strength, which Ied to the slide. <br /> Our explorations indicatc th�u thc soft fill on thc upper portion of the slope is up to 12 feet thick. <br /> IAlthough, it is our opinion that the slide only affceted loose surficial soils rather than the core of the <br /> slope, it is likely that Uie slope movement will continue and will evenlually impact the residence abo��e <br /> Iand thc strcet bclo�v if adcquatc mcasures for stabilizing tlic affecicd arcas arc not implemcnte.l. <br /> ( Bascd on our cxplorations and sitc obscrvat�ons, it is our opinion that permanent stabilization of thc sitc <br /> slopc and prcvention of further movemcnt would rcquire m:�ssivc rctaining walls. After diswssions with <br /> you and your contractors, wc undentand that you dcsirc �o only improvc thc slopc stability cnnditions in <br /> � the area adjacent to the residence and a portion of the driveway using more surficial and less costly <br /> Imeasures. l'ou have chosen not to repair the entire Iength of Ihe failure adjacent to the concrete <br /> driveway. <br /> IThe goal of the slidc rep.iirs is to reduce the polenlial and rate of future slope movetncnt to Iessen the <br /> adverse impacts un the yard :md rcsidence, without incurring the major espenses th:u woiild othcnvise be <br /> Iassociated with tlie more elaburate stabiliration methods. Based on this, we rccommend the removal of <br /> all of the saturated and soft soil from the slope, and constniction of a rock spall fill slope supported on <br /> I Icvcl benches in thc underlying compctent n:uive soil. Our borings on the slope indicatc that there m;�y <br /> t <br /> bc 3 to 12 fcct of soR soil that will necd to L:, removed from thc slope lo czpose suitablc competent <br /> ' nativc soil for support of tlic slopc rcpairs. This excavation will gencratc a large volume of soft soils that <br /> will nced io bc removed from the site. �Ve anticipate that and that the excav.uion and fill placement on <br /> thc unstable slope will bc difficult to implcment and will rcquire c:u�cful planning and st.�ging by the <br /> contractor. <br /> I <br /> � NELSON GEOTECHN/CAL ASSOCIATES, INC. <br /> � <br /> ( <br />