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<br /> STATE OF COLORADO <br />DIVISION OF MINERALS AND GEOLOGY <br />Department of Natural Resources <br />1313 Sherman Sl.. Room ?15 <br />D I V I S I O N O F <br />Denver, Colorado 80203 <br />Phone: (30 31 866-3 567 MINERAL S <br />FAY: (3031 832-8106 & <br /> GEOLOGY <br /> RECLAMA710N <br /> MINING•SAFETY <br />MEMO 9111 Owens <br />Governor <br />DATE: August 24, 2000 ereg t walcner <br />E.ecuuve D~re<lor <br />TO: Tom Schreiner <br />Cc: Carl B. Mount Micnzel e. Long <br />t/ Divisw~ D~reclor <br />FROM: Christina Kamnikaz C~ <br />RE: Stability Analysis for Milliken Pit application, #M-2000-087 <br />Having reviewed the stability analysis for this project, I found several gaps in the document that need to be <br />remedied before [his stability analysis can be accepted as technically adequate. These include the following: <br />1) A copy of the data input for the factor of safety calculations. This would include the strength, <br />cohesiveness, and internal angle of friction for the soils as inputted into the softwaze program, as well as <br />which analysis, Spencer or Bishop, was used, and whether any internal or external loading was applied or <br />friction factors inputted. <br />2) What is the slurry wall thickness? This is stated nowhere in the document, and the validity of the results <br />can not be checked without this information. <br />3) Will the site be dewatered through in-place wells, or with a dewatering trench at the toe of the slope? How <br />far away will these wells or trenches be from the excavation slope? <br />4) How were the soil parameter values for the "mud lens" layer arrived at? This is not a ASTM classification <br />for soils. Please explain how this label was applied. <br />5) How far away is the irrigation ditch `immediately to the west of the mine? At this point, several <br />structures are within IO' to 30' away from the slurry wall. <br />6) Finally, how will the slope of 2H:1 V be guaranteed? What equipment will be used to excavate this slope? <br />It might be wiser to calculate a minimum setback from the edge of the excavation face to the slurry wall, <br />and maintain that setback, the excavation slope allowed to retain whatever grade is convenient for the <br />operation. <br />While the preliminary analysis indicates that mining at an angle of 2H:1 V with a 20' setback from the slurry <br />wall does guarantee a minimum factor of safety of 1.5, this analysis can not be considered final until the above <br />questions are answered, and the data results re-examined in light of the new information. <br />Until these questions are answered, this stability analysis can not be accepted as it is. <br />C.L. Kamnikar <br />