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Sanborn Creek Subsidence Page 36 September 2, 1997 <br />presents the incremental and cumulative worst-case vertical <br />subsidence for four east-west cross sections through the third <br />panel group made up of Panel #8, Panel #9 and Panel #10 and <br />1 cumulative worst-case vertical subsidence for four east-west cross <br />J sections through the third panel group made up of Panel #8, Panel <br />#9 and Panel #10. Plate 5aN graphically presents the worst-case <br />vertical subsidence for the northern two-thirds of the third group <br />_ of panels and Plate SaS for the southern two-thirds. Plate SbN <br />presents the location of the worst-case horizontal strains for the <br />northern two-thirds of the third group of panels and Plate SbS for <br />the southern two-thirds. The greater length of the third and <br />fourth panel B Seam groups necessitated dividing the worst-case <br />subsidence and strain graphs in order to maintain the 1-in equals <br />500-ft scale of the enclosed mine map. Table 10 presents the <br />incremental and cumulative worst-case vertical subsidence for four <br />east-west cross sections through the final panel group made up of <br />Panel #11, Panel #12 and Panel #13. Plate 6aN graphically presents <br />the worst-case vertical subsidence for the northern two-thirds of <br />the third group of panels and Plate 6aS for the southern <br />1 two-thirds. Plate 6bN presents the location of the worst-case <br />_ horizontal strains for the northern two-thirds of the third group <br />of panels and Plate 6bS for the southern two-thirds. <br />1 Table 11 presents the worst-case maximum predicted horizontal <br />tensile (+E) and compressive (-E) strains for each of the four <br />panel groups. The predicted maximum worst-case compressive strains <br />will produce compression ridges at the ground surface within the <br />projected outlines of the panel groups, at the locations indicated <br />on the plates. The height of the worst case compression ridges, <br />less than 1-ft, in relation to the hillside slopes at the ground <br />surface should not impede the normal seasonal runoff. The absolute <br />maximum predicted compression strain is 15060µe, at the southern <br />end of Panel #11. <br />The magnitude of the predicted tensile strains would result in <br />I tensile fractures at the ground surface. These fractures will be <br />most pronounced at the shallower southern end of the panel groups. <br />The absolute maximum predicted tensile strain is 9080µe, also at <br />the southern end of Panel #11. The predicted open surface <br />fractures will approach 1-ft in width. Outside the northern and <br />southern panel mining limits these open fractures will intercept <br />seasonal runoff water and divert it toward the east or west, <br />depending on the local hillside slope direction. In effect, these <br />open surface fractures will facilitate the flow of runoff toward <br />the nearby natural drainages. The predicted north-south open <br />surface fractures will tend to channel runoff water downslope, <br />generally toward the south.' The channelization of the seasonal <br />I surface runoff will probably temporarily increase erosion along the <br />subsidence fracture channels. The impact should, however, be <br />temporary as indicated by the absence of any drainage channel <br />diversions from the previous advance-and-retreat high-extraction <br />38 <br />