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Dickerson Quarry sl• s Page 4 • October 31, 2000 <br />sheared for the block of granite above the adverse block to <br />slide. The shear strength of intact granite ranges from <br />about 2,000 psi to 7,000 psi (Farmer, 1983). Very little <br />intact granite along the worst-case potential sliding surface <br />would prevent sliding, as shown on Figures 6 or 7. <br />5) If the adverse 38° dipping joint set was continuous and planar <br />the granite overhang would have slid into the existing quarry <br />as soon as one of the first adverse 38° dipping joint was <br />undercut in the existing quarry. <br />6) The southwest corner of the ultimate planned quarry wall is <br />reinforced by the curvature of the quarry wall. The degree <br />of reinforcement is impossible to quantify but the presence <br />of this phenomenon is well documented (Piteau, 1974). Figure <br />8 presents the Piteau's data on long-term stable residual <br />slope angles and radius of curvature of the slope toe for the <br />same shale unit at four open pit diamond mines. Piteau's <br />data that the radius of curvature of the recommended slope <br />toe in the southwest corner is approximately 340 feet should <br />result in an increase in the long-term stable residual slope <br />angle of about 14° above the northeast 38 dip of the <br />potentially adverse joint set. <br />CONCLUSION <br />The planned 2 vertical to 1 horizontal (53°) ultimate overall <br />quarry wall slope angle is predicted to be long-term stable. <br />Flattening of the southwest corner of the quarry is recommended to <br />essentially eliminate any potential for sliding on the one adverse <br />joint set present in the area of the planned quarry extension. <br />Sincerely, <br />~.~.~~ <br />John F. Abel, Jr. <br />Colorado P.E. 5692 <br />