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' layout of Subsidence Monitoring Net <br />The surface subsidence mpnltoring net installed for the DOE rock mechan- <br />ics study consists of three lines of surveying monuments placed along an <br />orientation approximately perpendicular to panel centerlines and r1b- <br />sides. Short lines of surveying monuments rare constructed parallel to <br />panel centerlines at or near the Intersection of the panel centerlines <br />and the perpendicular lines. <br />The perpendicular lines rare Intentionally located to provide data on <br />the effects of overburden thickness and topographic slope orientation on <br />subsidence phenomena. One tine is located along the ridge crest There <br />overburden thickness is greatest and slope togography should have a min- <br />• imal effect of subsidence. The tro remaining lines are located on oppo- <br />site sides of the ridge There overburden thicknesses are about equal but <br />slope orientations are different. One of these lines has the general <br />slope trend dipping torards the advancing mining face and the other line <br />has the general slope trend dipping allay from the advancing mining face. <br />The layout_of the surface subsidence monitoring net 1s illustrated on <br />Map A. <br />A total of 98 surveying monuments are installed over the three-panel <br />area. Perpendicular lines are extended out beyond the rlbsldes of the <br />three-panel area to altor for the determinations of dray ang}es. <br /> <br />28 <br /> <br /> <br />