Laserfiche WebLink
• GHMXSIopeEvaluation <br />3.1.4 GHMX Analvsis <br />The stability analysis is performed on a factor of safety basis, and the analysis is shown on Plate 9. <br />The results of the analysis for the three rock zones evaluated are as follows: <br />1. Very Poor Rock: The overall stability of the wall in "Very Poor Rock" is generally poor. For the <br />planned slope height on this wall of 400 feet, a maximum overall slope angle of 40° is <br />recommended. This will have a factor of safety of 1.1, which is appropriate due to the high <br />probability that the strength parameters used in the analysis will be met in the field. <br />2. Poor Rock: The overall stability of the wall in "Poor Rock" is generally good up to a height of <br />600 feet, the maximum currently planned in this material. The slope will be stable (FOS>1.3) at <br />an angle of 60°, the maximum slope angle that it has been found practical to mine in the Cripple <br />Creek Diatreme materials. However, the material in this rock zone is highly fractured and <br />weathered, so the practical overall slope angle will be determined by bench conditions. Bench- <br />scale raveling will limit usable bench width and catch capacity, creating a requirement for wider <br />than minimal benches, resulting in a reduced overall slope angle. <br />3. Fair Rock: The overall stability of the wall in "Fair Rock" is good up to the planned maximum <br />slope height in the mine of 600 feet, with a factor of safety in excess of 3 for an overall slope <br />angle of 60°. Practical overall slopes in this material will be determined by bench conditions. <br />• 4. Good Rock: The overall stability of the wall in "Good Rock" is also good, with vertical slopes to <br />600 feet depth being stable. Overall slopes will be limited by mining considerations. <br />3.2 Block Failure Analysis <br />The northeast portion of the GHMX will be excavated in very weak material, comprising almost entirely <br />weathered and very closely fractured volcanic breccia. A total of 11 shear strength tests were performed <br />in this material to closely determine the strength of this material. A check slope stability analysis was <br />performed, taking advantage of the statistical distribution of the strength parameters, to confirm the <br />selected slope angle for this zone of the mine. <br />3.2.1 Method <br />The analysis of the northeast portion of the slope was performed as follows (Plate 10): <br />1. Direct shear data was analyzed to determine the statistical parameters of the shear strength of the <br />friable material. The parameters were determined to best fit alog-normal distribution2, which <br />was used in the analysis. <br />2. A simple block failure analysis was selected, and an algebraic formula for the factor of safety of <br />the block was developed. <br />z The log-normal distribution cannot have negative values, which is consistent with the data being characterized here (cohesion and friction <br />• angle. The data fit less well to an arithmetic normal distribution, which also produced a significant percentage of values with unrealistic <br />negative cohesion when used in the stochastic analysis. <br />Report 1385E.20071126 <br />