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JOHN F. ABEL, JR. 3~aLOOKOUrvlEwcouRr MINING ENGINEER GOLDEN, CO 80401 • ]01279.4801 F!~(278.818~ JF4BELQCompu54M.mm October 19, 1998 Mr. Tom Anderson Oxbow Mining Inc. P.O. Box 535 Somerset, CO 81434 REFERENCE: "D" Seam portal area slope stability Dear Tom: The stability of the slide mass above and to the west of the "D" Seam portal area in the Elk Creek drainage will be improved by excavating the portion of slide material shown on the portal area plan map and indicated between the "1976 Ground Surface" and the "Cut Surface" on Section 7300 (Figure 1) and on Section 7450 (Figure 2). Excavating the indicated parts of the slide mass increases the preliminary calculated factors of safety for all • Roman numeral indicated cut slope segments (slices) along the potential sliding surfaces. The increased stability is primarily the result of reducing the weight of overlying slide rock, as shown on Tables 1 and 2. The planned fill, shown at the slide mass toes of the two cross sections, provides an additional minor increase in the slide resisting forces. The thrust components along the poten- tial slide surface, tending to drive the slide mass in each slope segment to failure, are reduced more than the normal component across the potential slide surface, providing proportionally more frictional resistance to further downslope movement. The cohesive resistance along the potential sliding surface was assumed to be constant, i.e. independent of the shape of the overlying ground surface, because cohesion is shear resistance under no normal load. The planned cutting and filling of the slide mass above the "D" Seam portal area applies the two traditional methods of stabi- lizing a moving soil or rock slope, 1) removal of slide material from the crest of the slope and 2) buttressing (loading) the toe of the slope. Figure 3, modified from Golder (1971), demonstrates one similar previous instance of slope stabilization by applying these methods, •