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<br />David Berry -23- June 20, 1996 <br />Paragraph 2: The DMG notes that it will be important to <br />establish the effectiveness of pillar recovery in <br />retreat early in the operation of the Bowie No. 2 <br />Mine in order to determine if subsidence <br />predictions will be accurate. <br />BRL hopes that more specific rock mechanic testing <br />and evaluation can be done in the early stages of <br />mine development at the conservatively designed <br />Bowie #2 Mine. This evaluation has the potential <br />to increase recovery by adjusting panel geometry, <br />panel and development pillar size, barrier pillar <br />size, recovery ratios, and main and sub-main <br />configuration. Consequently, accomplishing the <br />most efficient pillar recovery possible for the <br />mining conditions and a rate of subsidence <br />comparable to subsidence rates experienced above a <br />longwall panel advancing at the same rate as the <br />pillar line retreats. <br />1.3 SUBSIDENCE MAGNITUDE AND PROFILE <br />Paragraph 1: The DMG's reiteration of the modified NCB method <br />clearly illustrated in this section is incorrect, <br />for the following reasons: <br />1) The subsidence factor (0.472) is determined from <br />equation derived from Figure 15-2. Figure 15-2, a <br />reproduction of the graph representing the data <br />collected by Abel and Lee (1980), is the <br />modification to the NCB method for partially <br />extracted room and pillar panels. When the <br />subsidence factor is multiplied by the mining <br />height it produces a prediction for the maximum <br />possible subsidence that can occur for a partially <br />extracted, super-critical width panel. <br />2) The panel correction factor (0.23) is determined <br />from Figure 15-3. Figure 15-3, is a reproduction <br />of Figure 3 of SEH and reduces the super-critical <br />panel width prediction to a sub-critical panel <br />width prediction. <br />3) Figure 4 of SEH is not applicable and is never <br />used in the analysis. If Figure 4 was applicable <br />to this analysis it would further reduce the sub- <br />critical panel width prediction for maximum <br />subsidence. <br />Paragraph 2: The DMG has suggested that there is a comparison to <br />the geometry and layout of panel #36 in the Bowie <br />#2 mine (B2M) and 1st West and 2nd West panels in <br />