Application of mechanical and groundwater-flow models to predict the hydrogeologic effects of longwall subsidence -- A case study
- Weir International Mining Consultants, Des Plaines, IL (United States)
- Monterey Coal Co., Carlinville, IL (United States)
An investigation was undertaken to determine hydrogeological effects of subsidence over a longwall coal mine in the Illinois Basin. At this mine, approximately 200 ft of bedrock overburden is overlain by up to 150 ft of glacial till and localized water-bearing glacial sediment within a buried bedrock valley that overlies the longwall panel. A finite-element mechanical model of the subsided longwall panel shows sufficient strain to enhance permeability throughout the bedrock portion of the overburden. However, examination of the actual surface subsidence profile indicates that the overburden deformation is localized in narrow zones at the panel edges. The aquifer units at the base of the glacial sediments are confined by glacial clays (above) and weathered shales (below). Elevated water levels were observed in the glacial aquifers during subsidence, which indicates that the clays and shales maintained confinement as the overburden subsided and deformed. A three-dimensional ground-water flow model was used to simulate the effects of subsidence on the hydrogeologic system and to estimate inflows into the mine. Longwall retreat was simulated by several mod3el runs, each representing a new longwall face position. Simulated heads and mine inflows were calibrated with recorded water levels and observed inflow conditions by modifying the hydraulic conductivity of particular model layers. Model calibration indicates that the permeability of certain lithologies, such as plastic underclays and weathered shales, is not significantly enhanced by subsidence. A worst-case scenario was simulated by inserting a deeply incised, sand-filled valley into the model, which had only minimal impact on the simulated mine inflows.
- OSTI ID:
- 124692
- Report Number(s):
- CONF-950811-; ISBN 0-930284-56-9; TRN: IM9548%%282
- Resource Relation:
- Conference: 14. conference on ground control in mining, Morgantown, WV (United States), 1-3 Aug 1995; Other Information: PBD: 1995; Related Information: Is Part Of 14. International conference on ground control in mining: Proceedings; Peng, S.S. [ed.] [Univ. of West Virginia, Morgantown, WV (United States). Dept. of Mining Engineering]; PB: 330 p.
- Country of Publication:
- United States
- Language:
- English
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