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IPrclimin��ry Gcotcchnical Lctter �I <br /> LandsliJc Evaluation and Rcpair <br /> I 4703 Glcnh;n�en Drivc <br /> Gvcrett, �Vashington <br /> Fcbn:ary I, 2007 <br /> I NGA Filc No. 75570G <br /> Page 2 <br /> slope at this timc. You have infonned us that, ,it this time, you prefcr to rcpair only the upper portion af <br /> Ithc slopc in thc arca wcst of thc residcncc and not thc rem�ining portion of the slide adjacent to the <br /> existing concrcle driveway. You havc requested our recommendations for repairs tu thc upper portion of <br /> Ithe slope adjacent to thc housc only. Qased on that undcrstanding, our recommendations includc <br /> rcmoving thc soft soil from thc slope and rebuilding Ihe slope with rock spalls. �Vc note that the repair to <br /> Iihis arca of thc slidc is not our prefcrrcd mcthod of slopc stabilization and that thc cxcavation, and <br /> subsequent fill placement on the unstable slope, will be difrcult to implement. <br /> � Without a soldicr pilc wall to slabilizc thc slidc matcri:�ls in-placc, repairs to thc upper portion of thc <br /> I slopc will rcquirc removul of all of thc sau•ratcd and loosc/soft soil from thc slop�, and constn�ction of a <br /> rock spall slopc supportcd on Icvcl benches in lhc undcrlyina competcnt native soil. Our borings on thc <br /> f slopc indicatc that thcrc may �e approximatcly S !0 12 fect of loose soil :hat will nced to bc removed <br /> I <br /> l from �hc slopc to cxposc suitablc compctcnt nativc soil for support of thc ,lopc repairs. This excav:uion <br /> Iwill gencmtc a large volume of soft soils that will necd to bc rcmoved frem the site. <br /> T��is e�cavation will also result in a steep excavation wall that will c�tend to the top of the landslide <br /> ! scaq�, which is .ipprosinm�ely Gve feet �vest of�he western wall of d:e residence. Our explorations near <br /> I <br /> Ihe westem wall of thc residence encountercd very sliff to harJ silt soil in this area; however. the natural <br /> � slapc anglc for this matcri:d is not vertical and thcrc is a potcnti.�l for additi;�,al soil loss in this arca. <br /> With a steep exca��ation planned extremcly close to �hc residence. wc reconunendcd that the foundations <br /> Incar ihc cxcavatinn bc undcrpinncd as :� prccaution against furUicr slopc failures during excavation. You <br /> have infurmcd us that you do not plan to underpin the residen�c founJations prior to the excavation and <br /> ircpairs to the slope. �Vc cannot accept responsibility or liability for damage to thc residcnce due to thc <br /> cxcavation and repairs if you choosc not to undcrpin thc fomidatians. If thc residencc foundations arc <br /> not unJerpinned, tl�e e�cca��ation stability ���ill necd to L e mc,nitored closely by the contractor. <br /> hi the area below thc residence, wc recommend ihat the excavation «all be immediately buttressed by <br /> b:tckfilling each scctioir of the escavatiun with rock spalls be(ore the ncat section of soft soil is removed. <br /> I This can hr accomplished in stages with the excavation of small sections of soil, with the sections <br /> � <br /> � <br /> � NELSON GEOTECHNICAL ASSOCIATES, INC. 3 <br /> � <br />