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27 <br /> Minimum Footing Dimensions. We recommend all footings be founded at least <br /> 2 ft below finish grade. A minimum footing width of 2 ft is recommended. The <br /> base of foundation pads should be at least 1 ft below finish grade. <br /> Allowable Bearing Pressure. Foundations should be proportioned so that the <br /> maximum gross contact pressure under dead, live, and transient loads (including <br /> wind and seismic loads) does not exceed the gross allowable bearing pressure. <br /> Based on the anticipated properties of improved soil or compacted structural fill <br /> and the standard bearing capacity equations, the net bearing pressure can be <br /> computed in accordance with the following equations: <br /> DDC improved soil: <br /> qa = 430B + 960D gaax < 4000 psf <br /> Native soil excavated to at least 8-ft depth and replaced with compacted <br /> fill: <br /> qa = 4308 + 960D qmax < psf <br /> a — 3500 <br /> Native soil excavated, to between 4 and 8-ft depth, and replaced with <br /> compacted fill: <br /> q = 360B + 820D gmax < 2200 psf <br /> a a — <br /> in which: q = allowable bearing pressure (psf) <br /> gaax = maximum allowable bearing pressure (psf) ` <br /> B & D = footing or pad width and depth (ft) <br /> These equations are applicable for vertical loads applied at the center of <br /> the footing and include a factor of safety in excess of 2.5. A 33 percent <br /> increase in allowable bearing pressure can be used for seismic design. <br /> If compacted structural fill is reinforced with geotextiles in accordance <br /> with previous discussions, the allowable bearing pressure can be increased. <br /> 1144A/CC-27 'OMcClelland <br />