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~ <br />'9P O1i09 18: 34 'd <br />~u3 <br />985 <br />9947 <br />SRK <br />DEN~~ <br />~1 <br />BATTLE MOUNTAIN RESOURCES, SAN LUIS PROJECT <br />CMLRD ADEQUACY LETTER RESPONSES <br />Page 15 of 28 <br />As presented 1n the approved permit submitted to the MLRD in November <br />1988 (File No. M-88-112) the pseudostatic coefficient for use in the <br />stability analysis of the heap and waste rock facilities was 0.08g. <br />For the amendment submitted to the MLRD in September 1989, design <br />the tailings facility was performed using a more conservative <br />pseudostatic coefficient of 0.15g. In addition, the analyses <br />incorporated conservative estimates of the shear strength of the <br />embankment fill materials (~l = 35°, C - O). These values are low for <br />the "dirty" sandy gravel material located at the site which will be <br />used for construction of the embankments. <br />If higher, less conservative, shear strength parameters are utilized <br />for the embankment fill the resulting factor of safeties (FOS) for <br />critical failure planes are raised considerably. The general approach <br />to the analyses was to evaluate a conservative model of the <br />embankment. As this model predicted stable conditions no refinement <br />to more accurately depict the embankment was considered warranted. <br />In order to respond to MLRD concerns, however, a parametric <br />sensitivlty analysis of the embankment when full of tailings <br />utilizing a detailed model of the embankment was developed. Several <br />conservative assumptions which were incorporated in the original <br />model used for the stability analyses presented in the permit <br />amendment application have been omitted from this model. The results <br />of the sensitivlty analysis are presented in graphical fora as Figure <br />D.6-1T. <br />A review of this figure shows that for a pseudostatic coefficient <br />of 0.08g, the F05 is approximately 1.7 if the embankment fill is <br />assumed to have shear strength parameters of ~ - 35° and C - 0. If <br />the fill shear strength is increased by employing JD - 38° and C - 200 <br />psf the FOS at 0.25g is approximately 1.4. The analyses indicate that <br />the embankmenk design is sufficiently conservative to provide a <br />stable condition. <br />~. ~~. <br />