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specifications. Given that a rock free subgrade is anticipated and that a capillary <br />break is not required, sand below the barrier is not required. <br />The allowable bearing pressures presented above may be increased by 1/3 when considering <br />short duration wind or seismic loads. Additional rigidity may be necessary for structural <br />considerations, or to resist the effects of the liquefaction-induced differential settlements <br />discussed above. The actual design of the mat foundation, including the steel reinforcement, <br />should be determined by the structural engineer. <br />Spread Footing Foundation Design Parameters <br />As discussed previously, it is recommended that that proposed building be supported on a mat <br />foundation. Minor improvements such as retaining walls less than 3 feet in height and site walls <br />may be supported on shallow foundations. New square and rectangular footings for these minor <br />improvements may be designed as follows: <br />• Maximum, net allowable soil bearing pressure: 2,500 lbs/ff. <br />• Minimum wall/column footing width: 14 inches/24 inches. <br />• Minimum longitudinal steel reinforcement within strip footings: Four (4) No. 5 rebars <br />(2 top and 2 bottom). <br />• Minimum foundation embedment: 12 inches into suitable structural fill soils, and at <br />least 18 inches below adjacent exterior grade. Interior column footings may be <br />placed immediately beneath the floor slab. <br />• It is recommended that the perimeter building foundations be continuous across all <br />exterior doorways. Any flatwork adjacent to the exterior doors should be doweled <br />into the perimeter foundations in a manner determined by the structural engineer. <br />The allowable bearing pressures presented above may be increased by 1/3 when considering <br />short duration wind or seismic loads. The minimum steel reinforcement recommended above is <br />based on geotechnical considerations; additional reinforcement may be necessary for structural <br />considerations. The actual design of the foundations should be determined by the structural <br />engineer. <br />Foundation Construction <br />The foundation subgrade soils should be evaluated at the time of overexcavation, as discussed <br />in Section 6.3 of this report. It is further recommended that the foundation subgrade soils be <br />evaluated by the geotechnical engineer immediately prior to steel or concrete placement. Soils <br />suitable for direct foundation support should consist of newly placed structural fill, compacted to <br />at least 90 percent of the ASTM D-1557 maximum dry density. Any unsuitable materials should <br />be removed to a depth of suitable bearing compacted structural fill, with the resulting <br />excavations backfilled with compacted fill soils. As an alternative, lean concrete slurry (500 to <br />1,500 psi) may be used to backfill such isolated overexcavations. <br />,> .SOUTHERN <br />CALIFORNIA <br />' GEOTECHNICAL <br />G&M Convenience Store #72 - Santa Ana, CA <br />Project No. 16G123-1R <br />Page 22