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;,.~ <br />static <br />Memo to B. Keffelew <br />May 21, 1997 <br />Page 2 <br />factor of factor of safety was determined to be 1.2. The operator states that no modified <br />structural fill will be used in this part of the pad so the material properties were not included in <br />the stability analysis. You need to make it very clear that modified structural fill cannot be used <br />in this area of the pad unless it can be demonstrated that the material will not de-stabilize the pad. <br />A static factor of safety of 2.5 and pseudo-static factor of safety of 1.7 were calculated for section <br />B-B'. Since this is the expanded area of the pad the modified structural fill material properties <br />were included in the stability analysis. It appeazs, since the FOS's aze greater that one, the <br />probability that a slope failure will occur in these sections of the leach pad is very small even <br />during a moderate seismic event. <br />Pursuant to existing specifications, the structural fill material will be sufficiently conditioned to <br />allow compaction to the required density that will result in a firm, unyielding surface. If placed <br />on slopes steeper than 3.1, horizontal benches shall be excavated into the slope to allow fill to be <br />placed in horizontal lifrs in order to minimize potential weak interfaces between the fill and <br />native ground. <br />I[ does not appear that the proposed modified structural fill material will create a stability <br />problem in the expanded azea so I recommend accepting the revised specifications. <br />m:\oss\memo.jd <br />