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• (3) A minimum pier depth of 5 feet is recommended for the conveyor foundations. Any <br />buildings or other structures founded on drilled piers should have piers of a depth at least <br />10 times the diameter. Minimum pier diameter should be 12 inches. <br />(4) Drilled piers should be designed to resist lateral loads using a modulus of horizontal <br />subgrade reaction in the clay soil of 50 tcf below 3 pier diameters. The modulus value <br />given is for a long one-foot wide drilled pier and must be corrected for pier size. <br />(5) Drilled piers should be reinforced their full length with at least one No. 5 reinforcing rod <br />for each 16 inches of pier perimeter to resist tension by the swelling materials. <br />(6) A 4-inch high void form should be provided beneath any required pier-supported grade <br />beams or pier caps to concentrate drilled pier loadings and to prevent the expansive soil <br />from exerting uplift forces on the grade beams. <br />• (7) Concrete used in the drilled piers should be a fluid mix with sufficient slump so it will <br />fill the void between reinforcing steel and the pier hole. We recommend concrete have <br />a slump in the range of 5 to 7 inches. <br />(8) Drilled pier holes should be properly cleaned prior to placement of concrete. <br />(9) The lack of water within the anticipated depth of drilled piers indicates that drilling will <br />generally be in the dry. The above criteria do not consider the presence of water and <br />we do not recommend piers be drilled into water. <br />(10) Scattered to frequent cobbles and boulders of weakly to strongly cemented fine-grained <br />sandstone were encountered in the borings. Generally, they were fairly easily penetrated <br />with our drilling equipment advancing a 3 to 4-inch diameter hole, but some additional <br />effort will be necessary to drill larger diameter holes, possibly necessitating the use of <br />~• 22 <br />