ABSTRACT: Pillar recovery in deep coal mines with competent roof and floor can concentrate stresses and generate hazardous bumps. Actual calculation of the geologic strain energy released in association with these coal bumps has been rare, although energy release values have been utilized successfully for indicating burst potential in numerous hard-rock mines. This paper advances the current knowledge of energy release calculations as applied to coal bumps through an extensive analysis of an actual bump occurrence. The U.S.B.M, displacement-discontinuity code, MULSIM/NL, is used to produce a numerical model which generates stress, displacements and energy values associated with a pillar retreat section. This model is calibrated with actual field data, and then several alternative energy release values from the model are examined as to their suitability for indicating bump potential. Ultimately, it is determined that prudent application of dissipated energy calculations can be used as a tool to investigate the coal bump potential of a mining plan or cut sequence.
1 INTRODUCTION
On October 18, 1983, two miners were killed by a bump on a continuous miner section in which a barrier pillar was being extracted at the Olga Mine in McDowell County, West Virginia (Blankenship and Castanon 1983). Because of these two coal-bump fatalities and a dozen others in the Appalachian area in the time period between 1959 and 1986, the Bureau of Mines established a major research effort to alleviate the safety hazards associated with coal bumps. As part of this effort, an investigation of the geologic strain energy released in association with coal bumps was initiated.
It was hypothesized that calculated energy release values may provide better insight, or even a certain predictive capability, regarding the occurrence of coal bumps. For many years, it has been understood that energy changes occur in the rock mass during mining. aPart of this redistributed energy goes to increasing the elastic strain energy of the nearby rock mass while another part of the redistributed energy is dissipated or released. This released energy can take a passive form such as heat, sound, etc, or it may appear as dynamic energy driving a damaging rock burst or coal bump.
It is not surprising, then, to find that in the past the energy re- lease rate (ERR) has been found to correlate with the incidence or risk of damaging rock bursts. In the 1960's, the concept of ERR as an indicator of burst potential was pioneered in deep hard-rock mines in South Africa (Cook et al., 1966; Salamon, 1963; Hodgson and Joughin, 1966). More recently, energy release rate computation and application have improved (Salamon, 1984; Gay et al., 1984), and use of the ERR concept at burst-prone hard-rock mines has become common.
However, the application of energy concepts to bump-prone coal mines has been limited. Crouch and Fairhurst (1973) applied a displacement- discontinuity model with an energy release calculation to simulated coal mining sequences and demonstrated a technique for selecting an optimum cut sequence for bump control based on the energy values.
