2008-01-16_APPLICATION CORRESPONDENCE - C2008086 (3)

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DRAFT height ranges from 10 to 11 feet. The 11-foot maximum planned mining height was used as a conservative maximum thickness in the subsidence analysis. 3.2 Gateroad Pillar Configuration and Design The currently planned gateroads will generally follow the example on Figure 2. Plan View of Three Adjacent Longwall Panels, where the gateroad pillars involve one row of yield pillars and one row of rigid pillars. The advantage of this design is that it should minimize stress levels at the headgate and tailgate ends of the longwall face. The centerline distance between the planned 20-foot wide gateroad entries will be 100 feet for the planned 80-foot wide rigid pillars. The centerline distance between the 20-foot wide gateroad crosscuts will be 200 feet for the 180-foot long rigid pillars. The centerline distance between the gateroad entries adjacent the 30-foot wide yield pillars will be 50 feet and 100 feet between the crosscuts adjacent to the 80-foot long yield pillars. Every other crosscut for the yield pillars will line up with a rigid pillar crosscut. Figure 3. Estimated Gateroad Pillar Loads From Mining First Adjacent Panel indicates the estimated minimum load and average stress that must be supported by the 30-foot wide by 80-foot long yield pillars, if the yield pillar is not to potentially crush. Figure 3 also indicates the estimated rigid pillar load that must be supported by the planned 80-foot wide rigid pillars, after the longwall face of the first adjacent panel has been advanced roughly one Load Transfer Distance, approximately 329 feet, past any location. The Load Transfer Distance is how far from active mining that deformation or loading in response is measurable or otherwise detectable, and shown on Figure 4. Load Transfer Distance Data (compiled by Abel, 1988). Figure 5. Estimated Gateroad Pillar Loads From Mining Second Adjacent Panel indicates the estimated minimum load and average stress that must be supported by the planned 80-foot wide by 180-foot long rigid pillars, if the rigid pillar is not to potentially crush, after the longwall face of the second adjacent panel has been advanced roughly one Load Transfer Distance past any gateroad location. It is not essential that the central gateroad entry remain open for ventilation through the gob to the bleeder entries. Two of the active panel tailgate entries will be open to the bleeder entries at all times during mining of the panel. See Figure 2. The disadvantage of a line of rigid gateroad pillars through the gob is the potential for higher horizontal tensile strain at the ground surface overlying the gateroad because the overburden initially bends toward the first adjacent panel as it is mined and then in the opposite direction when the second adjacent panel is mined, i.e. the tensile strains are additive over rigid gateroads. The optimum situation is for the 80-foot wide rigid pillar to be only temporarily rigid as the second longwall face passes. The rigid pillar can safely be allowed to yield and then crush after it is roughly 100 feet out from the longwall face between collapsed gob on both sides. This, in effect, reduces the tensile strain, and fracture opening, that is directly proportional to the differential vertical subsidence between the gateroad and the maximum subsidence (Smax) over the center of the adjacent panels. 3.3 Previous Mining There is no known previous mining within the proposed coal lease. However, the McClave Canyon Mine is operating in the immediately adjacent existing coal lease on most of Sections 15, 16, 21 and 22, T. 7 S., R. 102 W., 6 P.M. A small coal operation, the Munger Mine now closed and reclaimed, operated in adjacent Section 27. Figure 1. Red Cliff Mine Project and Coa/Lease Areas shows the location of these workings. Page 7 of 57