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<br />GEOTECNIA <br />Project Number: 060805 <br />2888 Darius Way, San Leandro <br />October 27,2006 <br /> <br />Page 9 <br /> <br />are poured directly over the expansive subgrade soils, the width of the grade beams should be as <br />small as possible and the additional uplift load on the grade beams should be resisted by the <br />piers. <br /> <br />The above-recommended void may collect water that could add to the expansion of the soils or <br />highly weathered bedrock. Therefore, it may be necessary to construct a drain system that would <br />dewater the void under the grade beams. Grade beams and piers should be formed above grade <br />to prevent overpours. <br /> <br />A passive equivalent fluid weight of 300 pef may be used to estimate the maximum passive <br />pressures acting against the piers. It may be assumed that those pressures would act over two <br />pier diameters. However, we recommend that the actuallateralpi~r capacities be estimated <br />based on the allowable lateral deflections at the tops of the piers, as discussed below. <br /> <br />R,~sistance to lateral loads will be provided by passive earth pressure against each pier and by the <br />bending strength of the pier itself The estimated lateral capacities and maximum moments in <br />the piers are tabulated below as a function of the allowed deflection of the top of the pier <br />assuming "free head" conditions, and that the piers are 18 inches in diameter and at least 16 feet <br />deep. The pier top lateral deflections for loads between the tabulated values may be interpolated <br />from the values given. The tabulated data include a safety factor of 1.0 and depend on the <br />allowable deflection at the top of the pier. For different pier diameters and depths, the lateral <br />capacity as a function of lateral deflection will be different than the values tabulated below. <br /> <br />Lateral Deflection <br />(in.) <br />~ <br />1 <br />2 <br />3 <br />4 <br /> <br />Lateral Load <br />(kios) <br />13 <br />22 <br />39 <br />50 <br />56 <br /> <br />Maximum Moment <br />(ft-kips) <br />50 <br />85 <br />150 <br />193 <br />216 <br /> <br />The estimated depths to the maximum moment and zero lateral deflection below the tops of the <br />piers are 6Y2 and 12 feet, respectively, assuming 18-inch-diameter piers at least 16 feet long. <br /> <br />For lateral loading in pier groups or in the longitudinal direction (along the length of grade <br />beams), a Group Reduction Factor (GRF) should be applied to the capacity of each individual <br />pier as tabulated below. <br /> <br />Center-to-Center Pier Spacing GRF <br />(Pier Diameters) <br />2 0.4 <br />3 0.6 <br />4 0.8 <br />5 1.0 <br />