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<br />BATTLE MOUNTAIN RESOURCES, SAN LUIS PROJECT <br />CMLRD ADEQUACY LETTER RESPONSES <br />Page 15 of 28 <br />As presented in the approved permit submitted to the MLRO 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 0.089. <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 0.159. In addition, the analyses <br />incorporated conservative estimates of the shear strength of the <br />embankment fill materials (yl = 35°, C = 0). 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 <br />to more accurately depict predicted stable conditions no refinement <br />the embankment was considered warranted. <br />In order to respond to MLRD concerns, however, a parametric <br />sensitivity 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 f rom this model. The results <br /> of the sensitivity analysis are presented in graphical farm as Figure <br /> D.6-17. <br />' <br /> A review of this figure shows that for a pseudostatic coefficient <br /> of 0.089, the FOS is approximately 1.7 if the embankment fill is <br />' assumed to have shear strength parameters of ~ 35° and L 0. If <br />the fill shear strength is increased by employing ~ = 38° and C = 200 <br />psf the FOS at 0.259 is approximately 1.4. The analyses indicate that <br />the embankment design is sufficiently conservative to provide a <br />stable condition. <br /> <br /> <br /> <br />1 <br /> <br />