1130 RAINIER AVE Geotech Report 2025-07-28

Everett Housing Authority JN 12080 May 16, 2012 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 3,000 pounds per square foot (psf) is appropriate for footings supported on competent soil and/or structural fill as noted above. 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, or on structural fill up to 5 feet in thickness, will be about one inch, with differential settlements on the order of one-half inch in a distance of 50 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, compact fill. If the ground in front of a foundation is loose or sloping, the passive earth pressure given above will not be appropriate. We recommend using the following ultimate values for the foundation's resistance to lateral loading: ti LTIMATE PARAN ETER At,t;E I i Coefficient of Friction 0.50 Passive Earth Pressure 300 pcf Where:(i)pcf is pounds per cubic foot,and(II)passive earth pressure is computed using the equivalent fluid density. 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. PIPE PILES Three-, 4- or 6-inch-diameter pipe piles driven with a 800-or 1,100-pound hydraulic jackhammer to the following final penetration rates may be assigned the following compressive capacities. INSIDE FINAL DRIVING ANAL DRIVING FINAL DRIVING ALLOWABLE PILE RATE RATE RATE COMPRESSIVE DIAMETER (850-pound (1,100-pound (2,000-pound CAPACITY hammer) hammer) hammer) 3 inches 10 sec/inch 6 sec/inch n/a 6 tons 4 inches 15 sec/inch 10 sec/inch 5 sec/inch 10 tons 6 inches n/a 20 sec/inch 10 sec/inch 2.0 tons Note: The refusal criteria indicated in the above table are valid only for pipe piles that are installed using a hydraulic impact hammer carried on leads that allow the hammer to sit on GEOTECH CONSULTANTS,INC. 1