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overall stability, all sections were stable except section GH-2 in the south end of the (North) <br /> Globe Hill mine. Recent drilling of hole GTl1-4 indicates a zone of low quality rock in this <br /> portion of the mine. This is probably related to the poor quality rock in the north end of the <br /> (South) Globe Hill mine. To arrive at reasonable stability for this section, the interramp angle <br /> had to be lowered from the MLE2 design of 52 degrees to 45 degrees. <br /> All slopes are assumed to be completely depressurized by underground workings. If <br /> phreatic water pressures are encountered, the inputs to these analyses will need to be revisited. <br /> A complete description of results in the cross sections follows. <br /> 7.3.1 Section Cres-1 <br /> Section Cres-1 is on the northeast side of the Main Cresson mine. The cross section has a <br /> total wall height of 1790 feet, which is the highest wall analyzed for the MLE2 study. The <br /> overall slope angle is 48°. Porphyritic phonolite is the only rock type that will be exposed on the <br /> final mine wall. RQD data for the section are relatively sparse (Figure 7-6). The RQD in the <br /> final wall is estimated to be 70% based on the closest RQD model blocks. <br /> The June 2011 design of the Cresson MLE2 mine shell yields a FOS of 1.91 and a <br /> probability offailure of 0.2% (Figure 7-7). <br /> 7.3.2 Section Cres-2 <br /> Section Cres-2 is on the northwest side of the Main Cresson mine. The cross section has <br /> a total wall height of 1100 feet and an overall slope angle of 46°. Cripple Creek brecica is the <br /> main rock type that will be exposed on the final mine wall. RQD data for the section are <br /> relatively sparse (Figure 7-8). The RQD in the final wall is estimated to be 40% based on the <br /> closest RQD model blocks. Anisotropic rock-mass strengths were considered for this section <br /> based upon the rock fabric data presented in Chapter 3. <br /> The June 2011 design of the Cresson MLE2 mine shell yields a FOS of 1.42 and a <br /> 0 <br /> probability offailure o 0.1/o 7-9 . <br /> P h' .ff f (Figure ) <br /> 7.3.3 Section Cres-3 <br /> Section Cres-3 is on the south wall of the South Cresson mine. The cross section has a <br /> total wall height of 550 feet and an overall slope angle of 58°. Cripple Creek brecica is the main <br /> rock type that will be exposed on the final mine wall, with porphyritic phonolite near the crest. <br /> RQD data for the section appears to be bimodal(Figure 7-10). The RQD is estimated to be 30% <br /> for the upper half of the slope, and 40%for the lower half of the slope. <br /> The June 2011 design of the Cresson MLE2 mine shell yields a FOS of 1.93 and a <br /> probability offailure of 0.4% (Figure 7-11). <br /> 27 <br />