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28 <br /> ,%We .i — <br /> Provided the reinforcing extends down from the base of the footing to a depth of <br /> at least 2 ft or one-fourth the minimum footing width, whichever is greater, the <br /> allowable and maximum allowable bearing pressures for seismic loads can be <br /> increased by 500 psf. <br /> Sliding. Sliding resistance can be computed based on the values of passive <br /> pressure and base friction provided in the discussion for the turbine and boiler <br /> foundations. <br /> Settlement. Estimated settlements for various combinations of footing <br /> sizes, applied net pressure, and subsurface conditions are provided on Plate 43. <br /> Note these values are approximate and are additive to values of settlement due to <br /> the planned grade raise at the site. Settlement considerations were discussed <br /> more completely in the previous Foundation Considerations of this report. <br /> Minor Foundations and Structure <br /> Minimum Footing and Overexcavation Requirements. Small, lightly loaded, <br /> settlement-insensitive equipment and structures can be founded on shallow foot- <br /> ings. A minimum footing width of 2 ft and a minimum footing embedment of 1.5 ft <br /> are recommended. <br /> A relatively nominal thickness of compacted soil should underlie the footing <br /> and slabs. This thickness can either be comprised on new fill placed above the <br /> existing ground surface or by overexcavating and recompacting soils below the <br /> existing ground surface. Minimum overexcavation requirements below footings and <br /> slabs bearing on unimproved fill are shown on Plate 45. <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 /> q = 150B + 570D gmax < 1500 psf <br /> a a — <br /> in which: q = allowable bearing pressure (psf) <br /> max maximum allowable bearing qa = g pressure (psf) <br /> B & D = footing or pad width and depth (ft) <br /> 1144A/CC-28 :i McClelland <br />