4518 SEAHURST AVE Geotech Report 2022-10-25

Naranjo JN 15186 May 18,2015 Page 5 Depending on the final site grades, overexcavation may be required below the footings to expose competent native soil. Unless lean concrete is used to fill an overexcavated hole, the overexcavation must be at least as wide at the bottom as the sum of the depth of the overexcavation and the footing width. For example, an overexcavation extending 2 feet below the bottom of a 2-foot-wide footing must be at least 4 feet wide at the base of the excavation. If lean concrete is used, the overexcavation need only extend 6 inches beyond the edges of the footing. An allowable bearing pressure of 2,500 pounds per square foot (psf) is appropriate for footings supported on competent native soil. A one-third increase in this design bearing pressure may be used when considering short-term wind or seismic loads. For the above design criteria, it is anticipated that the total post-construction settlement of footings founded on competent native soil will be about one-inch, with differential settlements on the order of one-half-inch in a distance of 30 feet along a continuous footing with a uniform load. Lateral loads due to wind or seismic forces may be resisted by friction between the foundation and the bearing soil, or by passive earth pressure acting on the vertical, embedded portions of the foundation. For the latter condition, the foundation must be either poured directly against relatively level, undisturbed soil or be surrounded by level, well-compacted fill. We recommend using the following ultimate values for the foundation's resistance to lateral loading: i vt \\il ri Iz t i 11\1 \ 11 \ \i t i Coefficient of Friction 0.45 Passive Earth Pressure 300 pcf Where: pcf is Pounds per Cubic Foot, and Passive Earth Pressure is computed using the equivalent fluid density. If the ground in front of a foundation is loose or sloping, the passive earth pressure given above will not be appropriate. We recommend maintaining a safety factor of at least 1.5 for the foundation's resistance to lateral loading,when using the above ultimate values. FOUNDATION AND RETAINING WALLS Retaining walls backfilled on only one side should be designed to resist the lateral earth pressures imposed by the soil they retain. The following recommended parameters are for walls that restrain level backfill: P\R \II 11R \ \I.t I Active Earth Pressure* 35 pcf Passive Earth Pressure 300 pcf Coefficient of Friction 0.45 Soil Unit Weight 130 pcf Where: pcf is Pounds per Cubic Foot, and Active and Passive Earth Pressures are computed using the equivalent fluid pressures. *For a restrained wall that cannot deflect at least 0.002 times its GEOTECH CONSULTANTS,INC.