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Dickerson Pit Wall Stability 3 Julv 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 aze capable of catching falling rock. Call (1986) prepazed 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 aze 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 aze 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 Is` Colloquium on Open Pit Mining, <br />Antofagasta, Chile, 18 p. <br />c:\windows\personal\dickerson pit.doc <br />