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2015 IBC Parameter Recommended Value <br /> Seismic Coefficient, FA 1.0 <br /> Seismic Coefficient, Fv 1.3 <br /> 4.1.2.Liquefaction Potential <br /> Liquefaction is a phenomenon where soils experience a rapid loss of internal strength as a consequence <br /> of strong ground shaking. Ground settlement, lateral spreading and/or sand boils may result from soil <br /> liquefaction. Structures supported on liquefied soils could suffer foundation settlement or lateral <br /> movement that could be severely damaging to the structures. <br /> Conditions favorable to liquefaction occur in loose to medium dense, clean to moderately silty sand that is <br /> below the groundwater level. Based on our evaluation of the subsurface conditions observed in the <br /> explorations completed at the site, it is our opinion that liquefiable soils are not present below the site. <br /> 4.1.3.Surface Fault Rupture <br /> Based on United States Geologic Survey(USGS) maps of active faults in the Puget Sound region,traces of <br /> the South Whidbey Island Fault are mapped roughly 11/2 miles west of the site. However, in our opinion the <br /> risk for surface fault rupture at the project site is relatively low considering the recurrence interval of the <br /> fault (on the order of 1,000 years). In our opinion, the risk of surface fault rupture is comparable to other <br /> sites in this area. <br /> 4.2. Shallow Foundations <br /> 4.2.1.Allowable Bearing Pressure <br /> We recommend an allowable soil bearing pressure of 3,000 psf be utilized for design of the proposed <br /> building addition footings anticipated to be founded within the upper 2 feet of site grade.This value can be <br /> increased to 8,000 psf where footings are founded on very dense glacial till (footings founded below a <br /> depth of 21/2 feet or on CDF extending to the very dense soils). We recommend the exposed subgrade be <br /> compacted following excavation. Footing subgrade should be evaluated by a representative from our firm <br /> to confirm conditions are as assumed during design. <br /> The above design value has a factor of safety of at least 3 for dead plus long-term live loads. For short-term <br /> transient loads (e.g., seismic, wind loads), the allowable bearing capacity can be increased by one-third if <br /> permitted by the design standard. <br /> All exterior footings should be founded at least 18 inches below the lowest adjacent finished grade, while <br /> interior footings may be founded a minimum of 12 inches below top of slab. We recommend minimum <br /> footing widths of 16 inches and 3 feet for continuous and isolated footings. <br /> 4.2.2.Foundation Settlement <br /> Provided that all loose soils are removed, and that the subgrade is prepared as recommended under <br /> "Construction Considerations" below, we estimate that the total settlement of shallow foundations will be <br /> less than 1 inch.The settlements will occur rapidly,essentially as loads are applied. Differential settlements <br /> between adjacent footings is estimated to be half of the total settlement, or less. Note that smaller <br /> GEOENGINEERS November 14,2019 Page 5 <br /> File No.2095-019-07 <br />