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• WHEXSIopeEvaluation AdrianBrown <br />location, blasting pattern and practices, drilling equipment, and other factors. The critical design <br />requirements are that the overall slope be achieved, and that the catch benches be mined to the specified <br />widths. <br />Table 9 -Bench Designs for WHEX Walls <br />Wall NE SE W, N <br />Overall angle deg 45 50 60 <br />Berm width feet 35 30 20 <br />Inter bench angle deg 90 90 90 <br />Bench height feet 35 35 35 <br />Holding capacity cu.yd/ft 6 13 18 <br />Holding mass tons/ft 13 28 39 <br />7.4 Wall Excavation <br />The structure of the rock and the occasional presence of water in the WHEX mine will result in <br />significant volumes of material being released from the mine walls after excavation. This has not been a <br />significant problem in the other mines in the Cripple Creek district. The construction of effective slopes <br />• at WHEX requires care during excavation to ensure that bench capacity is created. This will require that <br />the bench crests are maintained, which in turn requires avoiding undue disturbance of the rockmass <br />during blasting. <br />To achieve good catch capacity on a safe wall, the following blasting practices will be required: <br />1. Trim Row. A closely spaced trim row is essential to creating a stable, vertical wall. Past <br />experience and testing indicates that an effective trim can be achieved in this rock with the <br />following approach: <br />a. Trim row holes no more than 5 feet apart (4 feet is better). <br />b. Trim row holes lightly loaded, preferably air decked. <br />c. Trim row detonated last in the row, to blast to an open face. <br />To facilitate comminution of the material at the toe, it is recommended that the trim row be <br />drilled five feet below planned grade. This will not disturb the crest, but will likely lead to an up- <br />slope from toe to crest, which will facilitate catch. It will also help avoid leaving a sloping toe <br />wedge, which can kick falling rocks off the bench if they remain. <br />2. Bench Rows. Blastholes on the (future) bench, and the first row beyond the bench, should be <br />drilled to grade. This will facilitate preservation of the rock integrity of the future bench crest that <br />is immediately below these holes. Row location should be arranged so that no blasthole is located <br />within 4 feet of the future crest. Ideally, the future crest should be midway between blastholes. <br />3. Outer Rows. These rows should be drilled to 5 feet subgrade. <br />• <br />Report 1385L.200309017 <br />19 <br />