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Habitat for Humanity of Snohomish County ES-5168 <br /> April 26, 2017 Page 7 <br /> A one-third increase in the allowable soil bearing capacity may be assumed for short-term wind <br /> and seismic loading conditions. The above passive pressure and friction values include a <br /> factor-of-safety of 1.5. With structural loading as expected, total settlement in the range of one <br /> inch and differential settlement of about one-half inch is anticipated. The majority of the <br /> settlements should occur during construction, as dead loads are applied. <br /> Slab-on-Grade Floors <br /> Slab-on-grade floors should be supported on a firm and unyielding subgrade consisting of <br /> competent native soil or at least 12 inches of new structural fill. Unstable or yielding areas of <br /> the subgrade should be recompacted or overexcavated and replaced with suitable structural fill <br /> prior to construction of the slab. A capillary break consisting of a minimum of four inches of <br /> free-draining crushed rock or gravel should be placed below the slab. . The. free-draining <br /> material should have a fines content of 5 percent or less defined as the percent passing the <br /> Number 200 sieve, based on the minus three-quarters inch fraction. In areas where slab <br /> moisture is undesirable, installation of a vapor barrier below the slab should be considered. If <br /> used, the vapor barrier should consist of a material specifically designed to function as a vapor <br /> barrier and should be installed in accordance with the manufacturer's specifications. <br /> Retaining Walls <br /> Retaining walls must be designed to resist earth pressures and applicable surcharge loads, <br /> The following parameters can be used for retaining wall design: <br /> • Active earth pressure (unrestrained condition) 35 pcf <br /> • At-rest earth pressure (restrained condition) 50 pcf <br /> • Traffic surcharge (passenger vehicles) 70 psf (rectangular distribution) <br /> • Passive earth pressure 350 pcf <br /> • Coefficient of friction 0.40 <br /> • Seismic surcharge 6H* <br /> *Where H equals the retained height <br /> Additional surcharge loading from adjacent foundations, sloped backfill, or other loads should <br /> be included in the retaining wall design. Drainage should be provided behind retaining walls <br /> such that hydrostatic pressures do not develop. If drainage is not provided, hydrostatic <br /> pressures should be included in the wall design. <br /> Earth Solutions NW,LLC <br />