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2401 Taylor Drive Geotechnical Engineering Study <br /> Everett,Washington <br /> moisture-sensitive soil in structural fills should be limited to favorable dry weather and dry <br /> subgrade conditions and should not be used beneath foundation elements. The on-site soils <br /> contained substantial amounts of silt and are considered highly moisture-sensitive when <br /> excavated and used as fill materials. Construction equipment traversing the site when the soils <br /> are wet can cause considerable disturbance. <br /> If fill is placed outside of foundation areas during wet weather or if proper compaction cannot be <br /> obtained, a select import material consisting of a clean,free-draining gravel and/or sand should <br /> be used. -Free,draining fill consists of non-organic soil with the amount of fine-grained material <br /> limited to 5 percent by weight when measured on the minus No.4 sieve fraction and at least 25 <br /> percent retained on the No.4 sieve. <br /> Slab-on-Grade Floor Support <br /> Slab-on-grade floors may be constructed either directly on the undisturbed, native soil or upon <br /> structural fill placed over these sediments. Areas of the slab subgrade that are disturbed <br /> (loosened).during construction should be recompacted to an unyielding condition prior to placing <br /> the capillary break,as described below. <br /> In order to control moisture vapor transfer through the slab; slab-on-grade floors should be <br /> constructed atop a capillary break consisting of a minimum thickness of 4 inches of washed pea <br /> gravel,washed crushed rock or other suitable material approved by the geotechnical engineeror <br /> engineering geologist. The capillary break should be overlain by,a 10-mil (minimum thickness) <br /> plastic vapor retarder. <br /> Foundation Walls <br /> All backfill behind foundation walls or around foundation units should be placed as per our <br /> recommendations for structural fill and as described in this section of the report. Horizontally <br /> backfilled permanent walls, which are free to yield laterally at least 0.1 percent of their height, <br /> may be designed to resist active lateral earth pressure represented by an equivalent fluid equal <br /> to 35 pounds per cubic foot(pcf). Fully restrained, horizontally backfilled,rigid permanent walls <br /> that cannot yield should be designed for an equivalent fluid of 50 pcf. Permanent walls with <br /> sloping backfill up to a maximum gradient of 2H:1V should be designed using an equivalent fluid <br /> of 55 pcf for yielding conditions or 75 pcf for fully restrained conditions. If parking areas are <br /> adjacent to walls, a surcharge equivalent to 2 feet of soil should be added to the wall height in <br /> determining lateral design forces. <br /> •As.required:by,the•2015 IBC, permanent retaining wall design should include a seismic surcharge <br /> pressure in addition to the equivalent fluid pressures presented above. Considering the site soils <br /> and the recommended wall backfill materials,we recommend a seismic surcharge pressure of 8H <br /> and 10H psf,where H is the wall height in feet for the"active"and "at-rest" loading conditions, <br /> November 6,2019 SONDERGARRD GEOSCIENCES,PLLC <br /> 9 <br />