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GeoTest Services, Inc. April 15, 2021 <br /> 3617 Upland Avenue, Everett,WA Project No. 21-0375 <br /> Nonyielding walls under drained conditions should be designed for an equivalent fluid density of <br /> 55 pcf for structural fill in at-rest conditions. Design of walls should include appropriate lateral <br /> pressures caused by surcharge loads located within a horizontal distance equal to or less than <br /> the height of the wall. For uniform surcharge pressures, a uniformly distributed lateral pressure <br /> equal to 35 percent and 50 percent of the vertical surcharge pressure should be added to the <br /> lateral soil pressures for yielding and nonyielding walls, respectively. <br /> For structures designed using the seismic design provisions of the International Building Code, <br /> GeoTest recommends that retaining walls include a seismic surcharge in addition to the <br /> equivalent fluid densities presented above. We recommend that a seismic surcharge of <br /> approximately 8H (where H is the height of the wall) be used for design purposes. This surcharge <br /> assumes that the wall is allowed to rotate or yield. If the wall is restrained, GeoTest should be <br /> contacted so that we can provide a revised seismic surcharge pressure. <br /> Passive earth pressures developed against the sides of building foundations, in conjunction with <br /> friction developed between the base of the footings and the supporting subgrade, will resist <br /> lateral loads transmitted from the structure to its foundation. For design purposes, the passive <br /> resistance of well-compacted fill placed against the sides of foundations is equivalent to a fluid <br /> with a density of 325 pcf. The recommended value includes a safety factor of about 1.5 and is <br /> based on the assumption that the ground surface adjacent to the structure is level in the direction <br /> of movement for a distance equal to or greater than twice the embedment depth. The <br /> recommended value also assumes drained conditions that will prevent the buildup of hydrostatic <br /> pressure in the compacted fill. Retaining walls should include a drain system constructed in <br /> general accordance with the recommendations presented in the Foundation and Site Drainage <br /> section of this report. In design computations, the upper 12 inches of passive resistance should <br /> be neglected if the soil is not covered by floor slabs or pavement. If future plans call for the <br /> removal of the soil providing resistance, the passive resistance should not be considered. <br /> An allowable coefficient of base friction of 0.35, applied to vertical dead loads only, may be used <br /> between the underlying imported granular structural fill and the base of the footing. If <br /> foundations will bear directly on the native soil, an allowable coefficient of 0.30 should be used. <br /> If passive and frictional resistance are considered together, one half the recommended passive <br /> soil resistance value should be used since larger strains are required to mobilize the passive soil <br /> resistance as compared to frictional resistance.A safety factor of about 1.5 is included in the base <br /> friction design value. GeoTest does not recommend increasing the coefficient of friction to resist <br /> seismic or wind loads. <br /> Temporary and Permanent Slopes <br /> The contractor is responsible for construction slope configurations and maintaining safe working <br /> conditions, including temporary excavation stability.All applicable local, state, and federal safety <br /> 12 <br />