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1 <br />lJ <br /> <br /> <br />recoveries cvere on the order of 100b with RQD's (Rock Quality <br />Designation) ranging from 87.58 to 99.2 in the immediate roof area. <br />She have been given to understand that existing procedures for <br />roof reinforcement now used in the mining of the ~~" seam consists <br />of the use of resin bolt units. We understand that these units are <br />typically 9 feet in length with 6-foot and 8-foot units being used <br />occasionally. S4e further understand that the maximum roof span is <br />on the order of 20 feet. Bolt patterns are typically 4 feet by 4 feet <br />to 9 feet by 5 feet. SOe have been given to understand that these <br />procedures have been very successful in tunnel drifts with only <br />sporadic problems with .roof fall in intersection areas. <br />~ ~ <br />The ';F" seam and "E" seam both lie in the upper coal member of <br />the Mesaverde formation and are typically separated by something on <br />the order of 90 feet. Therefore, one would anticipate that roof <br />conditions might not vary greatly betcaeen the two seams. Hocrever, in <br />such highly variable sedimentary rock, differences can occur and we <br />would like to briefly discuss our approach to the analysis of roof <br />conditions. Prior to the beginning of mining, the amount of infor- <br />mation available is e•ctremely limited. We have a general idea of roof <br />rock type and condition from two test borings located near the proposed <br />entry area. In such sedimentary rock conditions, the litholooy, <br />thickness, and character of the various strata in the roof area can <br />change significantly and rapidly as one moves laterally within the <br />formation. We have taken the samples of the strata at the one location <br />(Test Boring No. 3) and performed physical property tests enabling <br />us to model roof rock conditions. Such a model was developed util- <br />izing beam theory techniques for predicting deflections and stresses <br />4 <br />