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14r~entymile Coal Company - Rockfall Hazards Analysis <br />• Table 4 states that the likelihood of failure increases from "low-medium" <br />prior to mining to "very high" after mining for zones 5 and 6. This increase <br />is inferred to be due to fracturing associated with mine subsidence. <br />• No mining related increases in the likelihood of failure were recognized for <br />SAIC Zones 1, 2, 3, and 4 (Zones 1 and 2 in this study) <br />The report contains the following hazards summary and recommendations: <br />For SAIC Zones 1 and 2 (Zone 1 in this Study <br />• H z r :: although subsidence can be expected to have a detrimental <br />effect causing an occasional block to slide or fall, the overall impact will <br />hardly be noticeable. <br />• Recommendations: None in text <br />For SAIC Zones 3 and 4 (Zone 2 in this Study <br />• Hazards: <br />- already shows a high degree of instability due to sliding of narrow <br />blocks and toppling of blocks. <br />- subsidence will make the situation worse, but not much worse. <br />- massive failures are not expected. <br />- some blocks will topple, slide, and/or roll. <br />- hazards to the road are expected due to the steepness of slope and <br />proximity to road. <br />- remedial measures may be required to protect people on the <br />highway <br />- zone 4 is inherently weaker than either zone 3 or zone 5. <br />- zone 4 may be a combined arcuate and toppling failure <br />• Recommendation <br />- ameliorative measures should be considered due to the proximity to <br />the road <br />- construct a wire mesh fence approximately 3 or 4 feet high and 1000 <br />feet long <br />- different fence designs need to be considered <br />u <br />z <br />