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iii ~iniiiiiiiii iii ~ <br />STATE OF COLORADO <br />MINED LAND RECLAMATION DIVISION <br />Department of Natural Resources <br />1313 Sherman St.. Room 215 <br />Denver, CO 80203 <br />303 666-3567 <br />FA X. 303 832-8106 <br />DATE: March 2, 1990 <br />T0: Steve Renner <br />FROM: Jim Pendleton <br />RE: Battle Mou in Gold` San Luis Project Amendment - Material <br />Stre Analysis (Permit llM-88-112) <br />Nor .A~\9 <br />.~~~;$ <br />~ !9'!6 ~ <br />Roy FOmer. <br />Governor <br />Fred R. Barra. <br />Damon D~.recwr <br />In response to your request, I have completed a review of the letter submittal <br />from Battle Mountain Gold which you forwarded to my attention. This letter, <br />prepared by Steffen Robertson and Kirsten (SRK), consultants to Battle <br />Mountain Gold Company, presents the results of a material shear strength <br />analysis. The material represents the source material to be used in <br />constructing the earthen embankment at the San Luis Project tailings disposal <br />structure. This analysis was performed in response to one of my concerns <br />expressed in my adequacy memorandum of January 18, 1990, <br />In that adequacy memorandum I stated; <br />"In performing its original pseudostatic analysis of the tailings <br />structure, SRK assumed a material shear strength for the <br />non-tailings embankment with an angle of internal friction = 35 <br />degrees and cohesion = 0. This original analysis projected a <br />factor of safety (F OS) of 1,0 under a equivalent acceleration <br />factor of 0.15 g. The sensitivity analysis determined that if <br />the fill material's shear strength is increased by employing ,un <br />angle of internal friction = 38 degrees and cohesion = 200 psi, <br />the FOS (Factor of Safety) at 0.25 g is approximately 1.4. SRK <br />believes that this less conservative material strength is more <br />realistic for the sandy gravel source material located at the <br />embankment site than the original material shear strength <br />assumptions. In my opinion, Mr. Dorey's material strength <br />opinion is not unrealistic for the relatively granular native <br />materials of the site. However, my examination of the original <br />permit application's geotechnical appendices did not locate any <br />laboratory shear strength test results for those native <br />materials, The Division should stipulate that the materials <br />intended for construction of the embankment be tested to <br />determine their shear strength, prior to embankment construction, <br />in order to verify Mr. Dorey's opinion. Should the material <br />strengths prove less than expected the embankment design could be <br />amended to increase the factor of safety." <br />