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<br /> 2.5 Subsidence predictions (RULE 2.05.6(6)(e)(i)(D)-(F)) <br /> Predictions of the maximum subsidence and horizontal tensile <br /> and compressive strains for the proposed Dorchester No. 1 Mine <br /> are presented on Table 1.0. Maps, presented in Appendix A, show <br /> the locations of the areas where subsidence calculations were <br />performed. The predictions are based on results of subsidence <br />studies made by the British National Coal Board (NCB, 1975) and <br />by other independent engineers, throughout the United States and <br />within Colorado (Singh, 1979; Dunrud, 1976; and Abel and Lee, <br />1980). The NCB model is based on studies involving long wall <br />panels and not room and pillar. They involve primarily areas <br />which have been extensively mined prior to the monitoring and <br />observation of subsidence, leading to the published correlations. <br />• Therefore, the overburden materials for mines involved in the <br />National Coal Board studies tend to be more highly fractured with <br />a much stronger tendency toward clastic behavior as opposed to <br />elastic behavior. The coal seams found in Colorado and <br />specifically at the Dorchester No. 1 Mine commonly contain <br />massive sandstone units and are more competent, stronger <br />materials and can have considerable load carrying capacity. <br />These materials have a tendency to behave much more elastically <br />during subsidence and will commonly produce lower actual surface <br />subsidence than that predicted and lesser atlgles of draw. In <br />similar bedrock materials, it is not uncommon to observe actual <br />surface subsidences on the order of one-half to one-third of <br />those predicted by the National Coal Board equations. The <br />. relationship of the subsidence to panel width, depth to coal, and <br />~ mine seam height is presented in Figure 1. In addition, the NCB <br />13 <br />