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GeoTest Services, Inc. December 9,2016 <br /> 3313 Oakes Avenue,Everett,WA Job No. 16-0659 <br /> the weight of the footing or any backfill placed above the footing. The net allowable <br /> bearing pressure may be increased by one-third for transient wind or seismic loads. <br /> Foundation Settlement <br /> The settlement of shallow foundations depend on foundation size and bearing pressure, <br /> as well as the strength and compressibility characteristics of the underlying soil. <br /> Assuming construction is accomplished as previously recommended and for the <br /> maximum allowable soil bearing pressure recommended above, we estimate the total <br /> settlement of building foundations should be less than about 1 inch and differential <br /> settlement between two adjacent load-bearing components supported on competent soil <br /> should be less than about one half the total settlement. The soil response to applied <br /> stresses caused by building and other loads is expected to be elastic in nature, with <br /> most of the settlement occurring during construction as loads are applied. <br /> Concrete Slabs-on-Grade <br /> Conventional slab-on-grade floor construction is considered feasible for the planned site <br /> improvements. All floor slabs are recommended to be supported on properly placed and <br /> compacted structural fill placed over properly prepared native soil as described above. <br /> Prior to placement of the structural fill, the native soil should be proof-rolled as <br /> recommended in the Site Preparation and Earthwork section of this report. <br /> We recommend that interior concrete slab-on-grade floors be underlain by a minimum of <br /> 6 inches of compacted, clean, crushed free-draining gravel with less than 3 percent <br /> passing the U.S. Standard No. 200 sieve (based on a wet sieve analysis of that portion <br /> passing the U.S. Standard No. 4 sieve). The purpose of this layer is to provide uniform <br /> support for the slab, provide a capillary break, and act as a drainage layer. GTS <br /> recommends that material conforming to Washington State Department of <br /> Transportation Standard Specification 9-03.12(4), "Gravel Backfill for Drains", with the <br /> added requirement that the material consist of a crushed, angular aggregate material be <br /> used as capillary break material. <br /> To help reduce the potential for water vapor migration through floor slabs, a continuous <br /> 10-mil minimum thickness polyethylene sheet with tape-sealed joints should be installed <br /> below the slab to act as a vapor retarder. The vapor retarder should be installed, and <br /> sealed in accordance with the manufacturer's instructions. 15-mil vapor barriers are also <br /> available and can be obtained from manufactures such as Stego and others if moisture <br /> control within the building is more critical. <br /> The American Concrete Institute (ACI) guidelines suggest that the slab may either be <br /> poured directly on the vapor retarder/barrier or on a granular curing layer placed over the <br /> vapor barrier depending on conditions anticipated during construction. We recommend <br /> that the architect or structural engineer specify if a curing layer should be used. If <br /> moisture control within the building is critical, we recommend that the vapor barrier be <br /> inspected to confirm that openings have been properly sealed. Use of a curing layer is <br /> generally only recommended during drier months of the year and/or when limited rain is <br /> expected during the slab-on-grade construction process. If the slab will be constructed <br /> during the wet season, exposed to rain after construction or the site may be potentially <br /> wet, we do not recommend the use of a curing layer as excessive moisture emissions <br /> through the slab may occur. <br /> Page 9 of 17 <br />