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Memo to Dave Berry <br />Bowie No. 2 Geotechnical Adequacy Responses <br />page 7 <br />Paragraph 2 <br />BRL concurs with the Division's observation that it will be important to <br />establish the effectiveness of pillar recovery in retreat early in the <br />operation of the Bowie No. 2 mine. BRL, however, failed to respond to the <br />Division's suggestion that it may be necessary to place high resolution <br />monuments above early panels to determine the actual character of ground <br />subsidence manifested, if recovery proves to be less than projected. The <br />Division's resolve in this regard has not changed. <br />1.3 SUBSIDENCE MAGNITUDE AND PROFILE <br />Paragraph 1 <br />In my earlier adequacy comments I related what I believed to be a mistake <br />in BRL's use of an NCB method for projecting the maximum subsidence <br />above a panel of sub-critical width. The author had stated that Figure 15- <br />3 of the Subsidence Engineer's Handbook (SEH) was used to reduce the <br />projected maximum super-critical panel subsidence of Smax =subsidence <br />factor of 0.472 x 12.0 feet extracted height = 5.7 feet, to 23% of that <br />projection, or 1.3 feet. In attempting to recreate this graphical reduction <br />myself I could not recreate the BRL result. I concluded that the SEH <br />technique had been mistakenly applied. BRL now <br />In my preface to my discussion of Exhibit 1 S in my earlier adequacy <br />comments, I recognized that the analysis presented within the application <br />employed empirical methods of prediction. The empirical methodology <br />applied by BRL is based largely upon the proven methods developed by <br />Britain's National Coal Board (NBC), published in 1975 as "The Subsidence <br />Engineer's Handbook". The NBC's empirically derived predictive <br />relationships were developed predominantly for subsidence above longwall <br />underground extraction. During the past two decades a myriad of authors <br />in the USA have developed correlation factoring to correct for mechanical <br />differences between overburden response of the USA and England, as well <br />as the mechanical differences between subsidence above longwall and <br />room & pillar extraction. Dr. John F. Abel, Jr, previously a professor at the <br />Colorado School of Mines, has been instrumental in developing one of these <br />