1992-02-10_GENERAL DOCUMENTS - C1981017 (2)

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-2- calculated using the slope-angle-corrected angle-of-draw formula, rather than '!simple angles, as follows : x 0 = tan-1------ Hcos2§ where x = horizontal distance between the point of interest and the edge of the ined-out area, H = depth of cover at the edge of the mined-out area, and § = surface slope angle between the point of interest and the edge of the mined-out area; for all slope angles greater than zero and less than 900, 0 will be greater than § . The first crack, barely noticeable, starts between monitoring points MC-15 and MC-16 and extends about 500 feet northwesterlyon the (west side of the ridge, parallel to the MC-10-MC-16 line of _m_1lonitoring points as projected in this direction (MC-16 being the most northwesterly point ) , and to the centerline of Longwall 102 . This crack, evident in soil cover only, varies from 0 to an inch or so in width, with no apparent offset . At its origin it is about 450 feet northwest of the Longwall 102 stopline, and at its terminus approximately 1, 000 feet ahead; no coal has been removed from any point closer than the 102 stopline . While the southeast end at 9 . 230 is well within the projected maximum angle of draw of 18 , the northwest end is in excess of this figure at 18 . 930 (see discussion of angle of draw below) . The distance ahead of the 102 stopline, coupled with the fact that the crack i virtually parallel to the centerline of the panel, as oppo ed to perpendicular to it as would be expected for an angle-of-draw panel-end subsidence feature, suggests that this fe ture, which is also parallel to the second crack, is sympathetic to the latter and is a natural ridge-line slumpage f acture . The second crack is m ch more evident. It starts at the southeast end of the addle between the south fork of Coal Creek and Rock Creek, is parallel to the first crack, and extends almost without interruption for approximately 3, 500 feet, along or closel on either side of the ridge line to the saddle between th south fork of Coal Creek and South Twin Creek . While st rting as a barely detectable feature similar to the first crack, it varies up to 3 to 6 inches in width in places, with an offset down to the northeast of from 0 to 12 inches (�ostly 0 to less than an inch) . The crack strikes through soil cover and rock slopes, including the upper slip plane of an old slump block, alike . This crack is approximatel 475 feet from the upper end of the 103 startline at its and is also about 600 feet from the edge of the Long�aiginj ll 207 panel at its stopline . At the crack 's maximum development, about 1, 700 feet from its origin, it is nearly , 000 feet from the edge of the mined- out Longwall 207 panel, while at its disappearance it is only about 250 feet f om the 207 startline . The angles