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1 Sanborn Creek Subsidence Page 3 September 2, 1997 <br />1 inside the panel group boundaries projected upward to the ground <br />surface. These ridges will approach a maximum height of 1-ft above <br />the subsided ground surface. <br />Panel #1 (Plate 1), the potential single longwall panel with <br />its long axis east-west, is the shallowest planned longwall panel, <br />ranging from 480-ft depth at its southeast corner to 1080-ft at its <br />northwest corner. The predicted maximum vertical surface <br />subsidence over Panel #1 is 9.72-ft, the predicted maximum <br />1 horizontal ground surface tensile strain is 12100µe and the <br />predicted maximum horizontal surface compressive strain is 10050µe. <br />1 The maximum predicted tensile strain will probably result in <br />greater than 1-ft wide open fractures at the ground surface. <br />Planned Panel #1 underlies a short, approximately 500-ft long <br />section the old alignment of State Highway 133. Predicted maximum <br />1 subsidence of State Highway 133 from planned longwall mining of <br />Panel #1 will lower the right-of-way approximately 9-ft. The <br />predicted maximum tensile strain and the associated widest surface <br />fractures are predicted to cross State Highway 133. In addition, <br />approximately 700-ft of the north-side highway cut slope to the <br />west and 150-ft to the east of the panel will be subjected to less, <br />but still potentially disruptive, vertical subsidence and <br />horizontal tensile strain. The North Fork of the Gunnison River <br />should not be subsided or strained by planned longwall mining Panel <br />#1. <br />The central part of the possible landslide area that overlies <br />a portion of Panels #5 - #7 (Plate 9) will be subsided by longwall <br />1 mining of that group. Typical features of a sliding mass of rock, <br />1 i.e. a headwall scarp or a hummocky ground surface, were not <br />identified when inspected on July 25, 1997. An approximately 9-ft <br />1 high toe buttress will result from lowering of the central portion <br />of the possible slide. The present stability of the possible <br />landslide mass should increase as the result of the subsidence <br />~ accompanying longwall mining of Panels #5 - #7. <br />Some portion of all thirteen planned longwall panels are <br />overlain by abandoned Hawksnest Mine workings, approximately 369-ft <br />overhead. The Hawksnest Mine E Seam workings are present over the <br />shallower southern one-third or less of Panel #2 and Panel #3, the <br />1 extreme northern and southern ends of Panel #9 and most of Panels <br />#5 - #13. The shallowest southernmost 900-ft to 800-ft of Panels <br />#9 - #12 are overlain by abandoned Oliver No. 1 Mine D seam <br />workings that are 238-ft overhead. Roughly the northern third and <br />western half of Panel #1 is overlain by Hawksnest Mine workings. <br />Planned longwall mining in the Sanborn Creek Mine should not be <br />adversely impacted by stress concentrations under barrier pillars <br />1 in the overlying workings because the stress concentrations should <br />J be laterally distributed and dissipated by the thickness of the <br />interburden and the weighted average 56~ sandstone in the <br />3 <br />