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AirTouch Cellular <br />3 October 1997 <br />7-91 M• 11905-0 <br />Pape 9 <br />subgrade reaction (n,,) multiplied by the depth iz) below the ground <br />surface and divided by the pier diameter (61; expressed as kh= nh(z/B). <br />► ifSt f CLAY: For soil layers consisting of stiff clay deposits, the <br />coefficient of horizontal sutgrade reaction (k.) remains uniform with <br />depth and is considered din:ctly proportional to the coefficient of <br />vertical subgrade reaction (k,i divi�ed by 1'/: pier diameters (B); <br />expressed as kh=k,/11.56). <br />Our recommended constants of horizontal subgrade reaction (nh and k.) for the soil layers <br />encountered at this site are presented in Table 5, below. These values do n�c [ include a <br />factor of safety since they model the relationship between contact pressure and <br />displacement. Therefore, the structural engineer or tower manufacturer should select an <br />appropriate allowable displacement for design. In any case, we recommend that the <br />maximum allowable displacement not exceed 2 inches at the ���oundline. <br />TABLE 5 <br />RECOMMENDED HORIZONTAL SUBGRADE REACTION VALUES <br />Depth Intervel nh k. <br />(feet) (pci) (pci) <br />0 to 5 75 N/A <br />5 to 12%: g5 N/A <br />12'/a to 28 95 N/A <br />28 to 40 100 ry�A <br />Coefficient of Horizo�tal Subgrade kh= nhlz/B) kh=k.!(1.5B) <br />Reaction (pci) (Sand & Soft Clay) (Stiff Clay) <br />Settlements: For the given pier diameters, we estimate that total post-construction <br />settlements of properly desiyned and constructed drilled piers could approach 1 inch. <br />Differential settlements between foundation elements may approach approximately half of <br />the tota! settlement. <br />�onstruction Considerations: Construction activities for drilled piers could encounter caving <br />sidewalls, groundwater, and other physical difficulties. We offer the following comme�ts <br />and recommendations regarding these issues. <br />7•BiM•11806-0 <br />