2008-04-15_REVISION - M1980244 (193)

Home Browse Search

v' . J • MainCressonSlopeEvaluation Adrian6rown 6. SLOPE PERFORMANCE 6.7 Bench performance Bench performance has been monitored in the mine since the beginning of mining. Surveys have identified the amount of material on the benches, based on inspection of each bench on a periodic basis. Bench condition and utilized capacity has been mapped. Data on the bench performance are recorded as part of the regular slope surveys, which are performed by the CC&V Geological Division staff. The surveys disclose that the mine slopes are generally stable; little material moves from the slopes onto the benches, except when such material is blasted or pushed off a bench during pushback mining. Approximately 10% of the available bench capacity is currently used to catch material which has raveled from the walls in the period following the normal slope cleanup which is conducted at the end of each mining cycle. Up until 1995, no bench has been completely filled in the mine due to failure of material from above (T.R. Brown, 1995). A small number of failures of material from mined slopes and benches have been observed to occur in the last year, generally occurring where joints intersect on catch benches. The resulting block and wedge failures have been observed to involve less than 100 tons of material. There is no visual evidence in any mine wall of progressive movement of slopes, except for movement on • one "toppler" and on a clay-filled feature, both of which are discussed below. 6.2 Slope movement The movement of the slope has been monitored during operation at more than 20 locations, mostly in the South Kline, East Wall. Locations of the movement measurement prisms are shown on Plate 3. The results of these movement observations are presented below. 6.2.1 Toppling feature on Eas wall of the South Mine As noted above, on the east wall of the South Mine there has been evidence of movement on an in- dipping feature which was exposed by mining across most of the east wall (identified as a "toppler" on Plate 3). This location was monitored using four survey points for a period of three months, while mining was occurring on the benches immediately beneath the feature. Movement was measured by repeated Electronic Distance Measurement (EDM) readings across the mine, from a location at approximately the same elevation as the monitor prisms, and approximately normal to the slope. The results of the monitoring are presented in Figure 15, presented as a change in slope distance from the original slope distance. The movement rate is approximately 0.2 feet per month (0.08 inches per day). The monitors disclosed no differential movement across the in-dipping feature (Monitor 4 was located between the feature and the bench face, while the other monitor points were located between the feature and the mine opening). In addition to the EDM monitoring, direct measurement of movement across the feature was conducted. No differential movement was measured noted across the feature during the period when the EDM • measurement was being conducted. These EDM monitoring prisms have been relocaxed, since the "toppler" has been mined out as part of the Phase IIpush-hack on the East Wall of the South Kline. 1385D.980612 32