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Oskar Property Deck Limited CAO,Everett,WA MaterialsTesting&Consulting,Inc. July 17,2019 19B182 Deck Foundation Design and Construction Recommendations For general foundation design and construction considerations, MTC recommends referring to guidelines and parameters of the International Building Code (IBC, 2012/2015; or most recent edition at the time of construction). Assuming spread footings or pier blocks are employed for support of the isolated deck columns, we recommend excavating to remove the cover soils and upper loose or variable deposits until reaching generally dense or hard glacial till conditions and benching foundation pads flat. For these footing styles, a minimum embedment of 3.0 feet from final grade is recommended based on our field exploration results. Embedment should be increased as needed to reach the prescribed bearing soils, and to meet required lateral resistance per the foundation design using the parameters provided below. For spread or pier footings placed directly on generally dense or hard glacial till or advance outwash deposits, or on properly compacted imported structural fill used to level foundation grades, we recommend an allowable bearing capacity of up to 2,500 pounds per square foot (psJ). The bearing capacity may be increased by 1/3 for short-term transient loads such as due to wind or seismic loading contributions. In the event that a direct drilled shaft foundation is used (such as with sonotubes or caissons), we recommend all members be embedded fully through the upper loose soils and at least 18 inches into underlying dense soils, or greater as needed to achieve required lateral support, to ensure long term stability for the structure post footings. At all locations, placement depths shall be at least as deep as those depths penetrated by our DCP testing plus the additional prescribed embedment. For a drilled foundation style, a minimum typical embedment of 5.0 feet from final grade is recommended based on our field exploration results. Lateral loads can be resisted by passive pressure against buried portions of foundation elements and sliding resistance along its base. Allowable lateral bearing pressures and sliding friction coefficients include a factor of safety of 2. Values assume placement directly against undisturbed soil cuts or compacted structural backfill. For foundations backfilled with compacted structural fill of at least 18 inches lateral thickness, we recommend an allowable lateral (passive) pressure equal to that generated by a fluid with an equivalent unit weight of 250 pcf EFW. Footings embedded within dense or hard native glacial soils can also employ a passive bearing pressure of up to 250 pcf EFW for the embedded portion. For foundations placed directly against upper variable soils with little or no backfill, we recommend the passive pressure be reduced to 125 pcf EFW. This is a generalized bulk value that considers the range of shallow native soil conditions encountered on site for wide application. In all cases, the upper 18 inches of soil from adjacent exterior final grade should be ignored in terms of passive resistance, unless capped at the surface with concrete. 7/