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• Kathy Welt <br />August 31, 1994 <br />Page 3 <br />Slope stability was evaluated using PCSTABL5. This computer program was <br />developed at Purdue University and uses the simplified Janbu or simplified Bishop <br />method of slices. It compares the forces resisting slope failure to forces which cause <br />slope failure along a specified failure surface. The analysis utilizes a limit <br />equilibrium procedure to calculate the factor of safety against failure. The input <br />information for the analyses includes, but is not limited to, slope geometry, <br />groundwater conditions, soil strengths, and loading conditions. <br />The slope stability analysis is summarized in the following table. <br />Mine Development Waete Pile <br />(eroe~ section A•A) <br />o~~nal: 2.88 <br />popa~ea: 2.80 <br />• The calculated factors of safety for the pile is above the minimum factor of <br />safety of 1.50, as required by the State of Colorado Mined Land Reclamation Board, <br />1991. <br />Construction Requirements: <br />The mine development waste pile will meet all the requirements of section <br />4.10.4. The pile will be built in lifts not exceeding 24" and will be compacted <br />to 90% of standard proctor. The slope of the pile will not exceed 2.5h : lv. <br />Four feet of subsoil and one foot of topsoil will be placed on the pile during <br />reclamation. <br />Subdrainage System: <br />A series of subdrains meeting the requirements of section 4.09.2 is planned to <br />be installed underneath the mine development waste pile as shown on figures <br />LPG - 103G & 104G. The main drain will be installed along the natural <br />drainage and will extend to the toe and head of the fill. Two lateral drains will <br />be placed to intercept any potential drainage or seepage water directing it to <br />the main drain. The rock to be placed will be sized so that no more than 10% <br />of the rock will be less than 12" in size. The main underdrain will be 10' in <br />width and 4' in depth. The lateral drains will be 4' in width and 4' in depth. <br /> <br />