4703 GLENHAVEN DR 2016-01-01 MF Import

IPmliminary Gcotechnical Lcttcr Landslidc Evaluation and Repair I 4703 Glcnhavcn Drive Evcrett. Washington February l, 2007 � NGA Filc No. 75570G Pagc 6 wi�h sand lenscs. Wc intcrpreted this matcrial to bc native soil. Borings I through 6,and 8,9, I I, and 12 Iwere tcrminateJ in thc nalivc soil at dcpihs ranging betwecn IGA to 20.5 fect below the cxisting ground surfacc. I Qorings 7 and 10 were drilled adj,icent to �he nortliwestern corner of thc house. At the surface, ��c encountered approximately one to two fect of fill with crushed rock and gravel. [3elow the fill, we cncountcred gnry-brown, sil� with varying �mounts of sand. We interpreted this material ro be native � soil. Borings 7 and 10 wcre �erminated in the nativc soil at depths of 8.5 and 12.5 feet bclow thc existing gromid surfacc, respeclivcly. Hydrologic Condilions 1 Groundwatcr seep:�ac w.�ti encountered in Qoriogti 3. 3. �1. 5, 8, and 9 at dcpths ranging bchveen SA and 14.0 feet. A perched watcr condi�ion could occur on the site. Perched water occurs when surface �ti•ater I infiltratcs through lass dcnsc, morc pernmablc soils, such at topsoil loosc fill, and accumulates on top of l a relatively low penneabiliiy nmterial, such as �he dense silty sand at depth. Perched water does not Ircpresent a regional groundwuter "table" within the upper soil horizons. Perched watcr tends to vary spatially and is depcndent upon thc amomu of rainfall. We would expect the amount of crowidwater to Idecrease during drier times of thc year and incre:ise durina wctter periods. I LA130RATORY T�STING Nc perfonncd ninc Graiu-siu analyscs and two Attcrbcrg Limits tcsts on sciccted soil s.unples from �hc i borings for usc iu soil classification. Thc results of thc sicvc analyscs arc presentcd as Figures IS through 2G. Thc grain sizc analyscs gencrally indicated silt and ciay soils. One of thc grain size analyses indicated silty sand wi�h vace gravcl. The Atterberg tcsts both indicated inorganic clay of inedium plasticity with a liquid limit (LL) of approaimatc;y dG and a plastic limit (PL) of approsimately 24. yiclJing .� plasticity indc� (PI) of approximaicly 22, as shown on Floure 27. I NELSON GEOTECHNICAL ASSOC/ATES, INC. 7