53rd U.S. Rock Mechanics/Geomechanics Symposium,
New York City, New York
2019. American Rock Mechanics Association
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ABSTRACT: This study has analyzed 3D stress and displacement distributions around a retreating longwall face intercepted by a geological fault. Analyses considered longwall set-up and development entries, and the longwall face. Linear elastic rock mass behavior was used for analysis except in areas adjacent to the fault where non-linear Hoek-Brown failure criterion was used. Data analyses along several lines in the roof and floor included roof-to-floor displacements and stress concentration factors. The displacements across the face in set-up entries were 35% larger with the fault present. Similar data parallel to the face advance varied with the face location. Vertical displacements were similar for this specific fault orientation. Similar analyses are also included for development entries and T-junctions. These data were compared with field measurements in longwall set-up and development entries.
1. BACKGROUND AND PROBLEM STATEMENT
Longwall mining is an underground coal mining method where a long face or wall of coal is mined (Fig. 1) in a single slice (typically 0.6-1.0 m thick). The longwall panel (the block of coal that is being mined) is typically 4-6 km long and 250-450 m wide. It is developed by driving one or more entries on either side of the block to carve out the panel. Longwall mining of coal is a highly productive mining system with very large initial capital investment ($ 75-100 million for a single face). It is not uncommon today to produce 5-6 million metric tons of clean coal from a single face with advance rate of over 30 m per day. The technology is particularly suited for mining deeper, thicker, and inclined coal deposits where partial extraction mining systems would not be economic. Due to large initial capital outlay and high production rates, this technology requires mining areas with large reserve base, few geologic anomalies and good mine planning based on sound science. Mining under adverse conditions presents challenges, particularly in regions where geological anomalies such as faults, folds, and dipping seams are present. A scientific understanding of ground behavior and control particularly around geologic anomalies is required to achieve high rates of production while providing safe environments for workers. This study focuses on understanding redistribution of stresses and displacements around faults that are not uncommon. Most of the longwall mining in the USA in the past has been done in the Appalachian Basin (Pennsylvania, West Virginia, Virginia) and in the Western states of Colorado and Utah. Within the Illinois coal basin, most of the coal mined now also comes from six (6) operating longwall faces. Due to economic pressures, several mines have determined that longwall mining is preferred for economically mining deeper reserves in southern Illinois that has a large concentration of faults (Fig. 2).
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