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AUG. 1.2000 4.13PM DIViMINERRLS&GEOLOGY <br />u <br />N0.330 P.3i4 <br />r1 <br />U <br />6, Th Opuator has proposed 40 foot highwalls with 20 foot wide benches. It is an important safety <br />co sideration that the benches aze capable of catching falling rock. Call (1986) prepared a series of <br />co servative catch bench widths that will almost always produce a catch bench that will prevent <br />ra ling rocks from reaching the bottom of the pit. Based on this work, the Operator should commit <br />to a installation of 3 foot high berms on the catch benches as illustrated on the attached figure 2. <br />This emo provides a fairly rigorous discussion of the procedures necessary to design a safe and stable <br />pit w Howevu, if a stepwise procedure is followed, the amount of field work, physical testing, and <br />analys s required can be minimized. For example, if the operator can demonstrate that there aro no <br />advus fracture onmtations dipping out of the quarry, and that the rock has a moderately high <br />comp sslve strength, then no further infotrnation would be required for approval of the pit wall, If <br />there a adverse fracture sets, then some degree of physical tasting and limiting equilibrium slope <br />stabili analyses maybe required. Tbc Division can provide the Opttator with examples of pit wall <br />eval 'ens and designs upon request if the Operator will agree to pay for any copying costs. <br />Abel, ~F., 1996, Preliminary Open Pit Slope Design, Kelsey Lake Mine:~+ Division of Minerals and <br />Geolo Files, Denver, Colorado, 46 p, plus appendices. (Source of table and figures). <br />Call, D„ 1986, Cost-benefit design of open pit slopes: ire Annals 1" Colloquium on Open Pii Mining, <br />Antof asta, Chile, l8 p. <br />pie.aoc <br />