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KLE/NFELOER �Bright People.Right Solutions. 5.5 STRUCTURE FOUNDATION DESIGN 5.5.1 Allowable Bearing Pressure The structures may be supported by shallow spread foundations constructed of reinforced concrete. Due to presence of potentially expansive near surface soils, the footings should be founded at least 24 inches below adjacent finished subgrade. In addition, perimeter continuous foundations would serve as a horizontal moisture break, reducing the potential for seasonal or man-made wetting and drying below the structure. Accordingly, continuous foundations should extend the entire perimeter of the building, including door, bay and garage openings. Continuous footings should have a minimum width of 12 inches. Isolated footings should have a minimum width of 24 inches. Spread foundations may be designed with a net allowable bearing pressure of 2,500 psf for dead plus sustained live loading. The allowable bearing pressure provided above is a net value. Therefore, the weight of the foundation that extends below grade may be neglected when computing dead loads. The allowable bearing pressures apply to dead plus live loads, includes a calculated factor of safety of at least 3, and may be increased by one-third for short-term loading due to wind or seismic forces. A modulus of subgrade reaction (for a 1 ft. by 1 ft. foundation) of 90 pci may be used for footing design for foundation subgrade prepared as presented above. This modulus may need to be modified accordingly to reflect differences in foundation size and shape. To maintain the desired support, foundations adjacent to utility trenches or other existing foundations should be deepened so that their bearing surfaces are below an imaginary plane having an inclination of 1.5HAV (horizontal to vertical), extending upward from the bottom edge of the adjacent foundations or utility trenches. 5.5.2 Lateral Load Resistance Lateral loads may be resisted by a combination of friction between the foundation bottoms and the supporting subgrade, and by passive resistance acting against the vertical faces of the foundations. An allowable coefficient of sliding friction of 0.30 between the foundation and the supporting subgrade may be used for design. For allowable passive resistance, an equivalent fluid weight of 350 pcf acting against the side of the foundation may be used. This value generally corresponds to a lateral deflection of less than about 1/2-inch. Passive resistance in the upper 12 inches of soil should be neglected unless the area in front of the footing is protected from 20210067.001A/ST020R111447 Page 18 of 37 May 11, 2020 ©2020 Kleinfelder www.kleinfelder.com