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Dickerson Pit Wall Stability 3 July 31, 2000 <br /> 6. The Operator has proposed 40 foot highwalls with 20 foot wide benches. It is an important safety <br /> consideration that the benches are capable of catching falling rock. Call (1986)prepared a series of <br /> conservative catch bench widths that will almost always produce a catch bench that will prevent <br /> raveling rocks from reaching the bottom of the pit. Based on this work, the Operator should commit <br /> to the installation of 3 foot high berms on the catch benches as illustrated on the attached figure 2. <br /> This memo provides a fairly rigorous discussion of the procedures necessary to design a safe and stable <br /> pit wall. However, if a stepwise procedure is followed, the amount of field work,physical testing, and <br /> analysis required can be minimized. For example, if the operator can demonstrate that there are no <br /> adverse fracture orientations dipping out of the quarry, and that the rock has a moderately high <br /> compressive strength, then no further information would be required for approval of the pit wall. If <br /> there are adverse fracture sets, then some degree of physical testing and limiting equilibrium slope <br /> stability analyses may be required. The Division can provide the Operator with examples of pit wall <br /> evaluations and designs upon request if the Operator will agree to pay far any copying costs. <br /> References: <br /> Abel, J.F., 1996, Preliminary Open Pit Slope Design, Kelsey Lake Mine: in Division of Minerals and <br /> Geology Files, Denver, Colorado, 46 p.plus appendices. (Source of table and figures). <br /> Call, R.D., 1986, Cost-benefit design of open pit slopes: in Annals P Colloquium on Open Pit Mining, <br /> Antofagasta, Chile, 18 p. <br /> attachment(s) <br /> cAwindows\personalUckerson pit.doc <br />