1208 50TH ST SW 2017-01-27 - Laserfiche WebLink

, ' ' ' , ' ' ' ' 1 , ' 1 ' ' ' ' ' ' Geotech�iical Engiiieering Letter Alhussaini Slope StabiLization and Retaiiling Walls �verett, Washington NGA File No. 867612 Decetnber 10, 2012 Page 4 to be the receutly placed till soils. Underlyiilg the new fill in Hand Auger-s 2 and 4, we encountered approxiniately LS feet o�T loose, dark browil silty fiiie to n�edium sand and abundant or�anics that we iiiterpi-eted as bui-ied topsoiL Underlying the new fill �naterial in Hand Augers 1, 2, 5, and 6 and the ground surface of Ha�ld Auber 3, we encountered loose to �nedium dense, brown to gray silty iine to �uediunl sand with �ravel aiid vaiying amounts of organics tl�at we iil�eipreted as olcier undocumented fiIl soils. 13elow the older undocumented lill in Hand Auger 3 and the buricd topsoil iu Hancl Auger 4, we encountered medium dense, brown-gray fine to mediuin sand with gravel interpreted to be wcathcred glacial till material. We also e�lcountered an approximate 2.0 foot� void in I-Iand Auger 4 extending from 5.0 to 7.0 fect below the existing ground surface. Hand Augers 1, 2, 5 and 6 were tenninated within the older undocu�nented fill soils at depths in the range of 7.5 to 10.0 feet below the existing ground surface Hand Augers 3 and 4 were tei�linated within the weathered glacial till soils at depths of 4.0 and 8.5 feet below the existing grouud surface, respectively. Hydrologic Conditions Groundwater seepage was not encountei-cd in the explorations, however any groundwater encouutered on this site would likely be intcipreted as a perched water condition. Perched water occurs when sw�face water infilU-ates through less dense, more permeable soils and accumulales on top of underlying, less permeablc soils. Perched water does not rcpresent a regional groundwater "table" within the upper soil horizons. I'erched water tends to vary spatially and is de�endent upon the ainount oP precipit�tion. We would expect the amount of �erched water to dccrease dui-ing clrier tiuzes of the ye�r aild increase duriiig wetter periods. SENSITIVE AREA EVALUATION Seismic Hazard We reviewed the 2009 Interil�tional Buildi�lg Code (IBC) for seisinic site classification for tlus project. We anticipate that medium dense to dense glacial soils underlie the site at depth and the site conditions best fit the IBC description for Site Class D. NELSON GEOTECHN/CAL ASSOCIATES, INC.