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SubTerra, Inc. C1fVCC-Foidel Creek Mute-Subsidence...:...- ....::. March 23, 1993 <br />i <br />• ~ Fracture Zone: This zone is mechanically characterized by significant frachrring and <br />extends approximately 30.60 times the mined coal thickness. <br />Intermediate Zone: Referred to as the "aquiclude" zone by Rauch (1989) and the zone of <br />"composite beams" by Hasenfus (1988). This zone is mechanically characterized by minor <br />bed separation and the absence of vertical fracture dilation and extends from the fracture <br />zone to within 50 feet of the surface. <br />Surface Zone: This uppermost zone is mechanically characterized by vertical fracturing <br />(or existing fracture dilation) associated with tensile strains induced by mining. The exact <br />nature of the deformation is a function of the surface geology and the magnitude of <br />mining induced displacements (e.g., see Whittaker and Breeds, 1977). <br />l.2 A~tproach to Predicting Subsidence in the Study Area <br />Our approach to Subsidence prediction for the study area has involved: <br />1. A review of the original Subsidence predictions for the initial mine permit. <br />2. Analysis of survey data collected for three monitoring lines representing panel <br />start and transverse profiles; <br />Line 12000E: This line extends from 900 feet north of Panel No.l's tailgate <br />• (Monument SM72) a distance of 2400 feet south to a point ]00 feet <br />beyond Longwall Panel No.2's maingate (Monument SM50). This <br />line was used to analyze subsidence over Longwall Panels 1 and 2 <br />due to Panel 1, Panel 2, and Panel 3 undermining. <br />Line bLCL: This line extends from 1200 feet west of Panel No.l's start room <br />(Monument SM98) a distance of 2000 feet east along Panel No.l's <br />centerline (to Monument SM78). <br />Line 4LCL: This line extends from 650 feet west of Panel No.3's start room <br />(Monument P92) a distance of 2800 feet east along Panel No.3's <br />centerline (to Monument P120) <br />3. Development of transverse, start, end, and travelling subsidence, displacement and <br />strain profiles for the selected survey lines. <br />4. Comparison of measured profiles with the Subsidence Engineefs Handbook (NCB, <br />1975). <br />5. Prediction of subsidence profiles for First and Subsequent Panels. <br />6. Preparation of subsidence predictions along the road, power line, creeks and <br />railway line, using the predicted profile data. <br />u <br />2 <br />