4945 OCEAN AVE 2018-01-02 MF Import

GEOTECHNICAL ENGINEERING STUDY Mr. Rick Remsing May 5, 2003 E-10558 Page 7 Horizontal loads can be resisted by friction between the base of the foundation and the supporting soil and by passive soil pressure acting on the face of the buried portion of the foundation. For the latter, the foundation must be poured "neat" against the competent native soils or backfilled with structural fill. For frictional capacity, a coefficient of 0.35 can be used. For passive earth pressure, the available resistance can be computed using an equivalent fluid pressure of three hundred fifty (350) pounds per cubic foot (pcf). The passive pressure should be neglected on the downslope side of the residence. These lateral resistance values are allowable values, a factor -of -safety of 1.5 has been included. As movement of the foundation element is required to mobilize full passive resistance, the passive resistance should be neglected if such movement is not acceptable. Footing excavations should be observed by a representative of ECI, prior to placing forms or rebar, to verify that conditions are as anticipated in this report. Retaining and Foundation Walls Retaining walls and foundation walls that act as retaining walls should be designed to resist lateral earth pressures imposed by the retained soils. Walls that are designed to yield can be designed to resist the lateral earth pressures imposed by an equivalent fluid with a unit weight of thirty-five (35) pcf. If walls are to be restrained at the top from free movement, the equivalent fluid weight should be increased to fifty (50) pcf. These values are based on horizontal backfill and that surcharges due to backfill slopes, hydrostatic pressures, traffic, structural loads or other surcharge loads will not act on the wall. If such surcharges are to apply, they should be added to the above design lateral pressure. The passive pressure and friction coefficients previously provided in the Foundations section are applicable to retaining walls. If design against earthquake loading is desired, a rectangular pressure distribution equal to six times the wall height (6H) should be added to the above lateral earth pressure values. In order to reduce the potential for hydrostatic forces building up behind the walls, retaining walls should be backfilled with a suitable free -draining material extending at least eighteen (18) inches behind the wall. The remainder of the backfill should consist of structural fill. The free -draining backfill should conform to the WSDOT specification for gravel backfill for walls (WSDOT 9-03.12(2)). A perforated drainpipe should be placed at the base of the wall and should be surrounded by a minimum of one cubic foot per lineal foot with three -eighths inch pea gravel. Earth Consultants, Inc.