3606 W MUKILTEO BLVD 2016-01-01 MF Import

Gcotechnical Enginecring EvTluation Mukiltco Boulcvard Dcvelopmcnt Evcrctt, Washington March 31, 2003 NGA Pilc No. 3((�03 Pagc G sprcad footings. }lowcvcr, founJations should catcnd through any topsoil, fill, or loose soils and bcar on thr undcrlying (irm nativc soils or structural fill supportcd on thcsc soils. Perched ground water was cncountercd in several of our subsurfacc explorations. Ne cspcct thc amoimt of this perched water to decrcase during the dry senson. Howevcr, project budget and schcduling should allow for addition�l expenses to control ground watcr if cncountered in structure, vault, or utility excavations. We have providcd prcliminary recommendations for ground water control in t�ie Site Drainngc subse,:tion of this report. Qascd on the composition and high moisture contents of thc matcrial cncountcred in our esplorations, using thc majority of thc on-site soils as stnichiral fill would bc extremcly difficult, even during dry weathcr. Thc contracror would likcly nced to moisture-condition thcse soils to near-optimum moisture content prior to using this materinl �s structunl fill. This may cntail sprcading the material in thin lifts ovcr n largc arca during extended periods of dry wcather and working thc matcrial until thc desired moisturc content is �chicved. Anolhcr nitem�tive would bc to mix the on-site material with cement or kiln dust for moiswrc conditioning purposes. For planning purposes, the usc of the on-site material for structurnl fill should bc limited to selected areas. 7 he contractor should be prepared to import material to thc silc for usc as structural fill. \Vc understmid thnt an c�cavation up to 12 fect deep is planncd for detention vault installation. Rccomnundntions for workcr safcry and maxinwm cscavation inclinations can be found in thc Temporary :mcl Permancnt Slopcs subscetion of this rcport. If thc excavation approaches existing structures or sitc boundarics, it may bc nccessary to install tcmporary shoring for nll or poAions of thc e�cavation. Ne are available to providc shoring design for the excavation. Shallow pe�ched ground ��nter was encowitcred in our subsurface csploration locntcd in the area of the proposcd vault. 1t is likcly that ground watcr secpagc will bc encowuered in the vatdt e�cavation during construction, which could c�use erosiou and inst�bility of the excavation. If seepage is encountered, sump pumps and/or cutoff drains should be installcd around thc ��ault e�cavation to reduce the amount of seepage entering the cscavation. '1'his rccommcndation is furthcr discusscd in thc Subsurfacc Drainagc subscction of this rcport. NELSON GEOTECHN/CAL ASSOC/ATES, INC.