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k/m, 29, 'Illy) <br />.1 r <br />Y? <br />ptwe 20 <br /> <br />Fir 4*JM • f1 r ° tt <br />• r <br />dmL <br />IL, <br /> <br />' Figure 23. <br />And <br />Natural Segregation of Coarse Durable Rock at Toe of G-Dip Pit Dragline <br />Spoil Pile <br />4.3 Drain Design <br />Based on the materials observed on-site, the review of the core logs and the surface <br />hydrology, this drain should be designed for a predominantly sandstone till. However. due to <br />sonle uncertainty with regard to the degree of overburden rubblization from the G-pit landslide, <br />AAI recommend's that the initial length of drain be constructed as if the overburden were <br />predominantly shale. This conservative approach will allow evaluation of' the effectiveness of' <br />the filter system placement with little risk of failure due to tines infiltration. <br />A schematic drawing of the proposed underdrain is shoxvn in Figure 24 and additional <br />drain design details are presented in Appendix A. A trench is cut to contain the very coarse drain <br />core material. The base width is a function of the dozer used in cutting the trench to grade. The <br />dragline spoil is allowed to drape over the core to torn the filter system. The extents of the <br />underdrain are shown in Figure 25 and additional drain design details are presented in <br />Appendix A. AAA added the underdrain location to the dragline casting diagram provided by <br />Tlvll (Figure 26). <br />Agapito Associates, Inc.