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11 <br />L` <br />minimum factor of safety of 2, it can be concluded that limiting maximum height for the <br />SDR 15.5 HDPE pipe is 250 feet. <br />6.3 Design of Pipes for Future Modules 5 through 11 <br />A comparison of the base grading plan in Figure 1 and the final grading plan Figure 2 <br />shows that the maximum waste height above the most critical leachate collection pipes <br />within Modules 5 through 11 is approximately 255 feet. Based on the pipe loading <br />calculations for Module 4 discussed above, an SDR 15.5 HDPE pipe will not have <br />adequate factor of safety against wall crushing for a waste height of 255 feet. Therefore, <br />a greater pipe thickness would be required. Accordingly, the pipe loading calculations <br />have been performed for a -4 -inch diameter, SDR 13.5, perforated, HDPE pipe. A gravel <br />bedding material both below and around the pipe is assumed in the calculations. Again, <br />the pipe loading calculations are presented in Attachment E. These calculations show <br />adequate factors of safety against ring deflection, wall buckling, wall crushing, and <br />circumferential strain for the SDR 13.5 pipe. <br />Geotechnical Analyses for NCRCSL Department of Public Works/Solid Waste <br />Shaw Environmental, Inc. County of San Joaquin, December 12, 2007 <br />6-3 <br />