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lUR-17-BB 15:12 From:CCiV GOLD ~ 1719EB9G2E4 • T-317 P DB/10 Job-647 <br />Analytic wac performed using the method of Hoek, E., and Bray, J.W. (1981. Rock Slope <br />Engineering, Institution of Mining ati~iyletallurgy, London, Third Edition). It assumes dry <br />slopes. The results of Utis evaluation azea•sented below. <br />`r <br /> <br />Intact Rock Within <br />Potential Failure Pathway None 1 % 10 % 100 % <br />Effective Friction Angle <br />(degrees) 40° 40° 40° 40° <br />Effective cohesion (psi) 0 100 1,000 10,000 <br />Ground-Water Pressure (psi) 0 0 0 0 <br />Factor of Safety 0.5 1.75 7.0 60.0 <br />This evaluation indicates that the only significant failure mechanism for this slope is if the entire <br />failure envelope is comprised of pre-existing fracture surfaces (where "no intact rock" exists <br />throughout the projected failure plane). This phenomenon is not observed to occur, except in <br />very localized azeas, where the appropriate block and wedges are removed during blasting, or <br />by the highwall sealing and bench clearing process that follows blasting. <br />Based on the extensive mapping of joints and fractures in the Mine highwalls, it is estimated that <br />abou[ 10 percent of the critical potential failure pathway will pass through intact rock. <br />~ Accordingly, the factor of safety for the 60° slopes is computed to be 7.0. This agrees with the <br />pre-mining projections. <br />Comparison between original and present slope designs <br />The reduction in the number of mine benches between catch benches in the current configuration <br />(four in the past; three now), the wider range in the width of these catch benches, and the <br />steeper interramp slope result in the wider range of overall slopes in the present operations. <br />These highwall relationrhipc are summarized in the following tabula ion (next page). <br />~ ~ <br />