Abstract
Gas-induced geodynamic phenomena can occur during underground mining operations if the porous structure of the rock is filled with gas at high pressure. In such cases, the original compact rock structure disintegrates into grains of small dimensions, which are then transported along the mine working space. Such geodynamic events, particularly outbursts of gas and rock, pose a danger both to the life of miners and to the functioning of the mine infrastructure. These incidents are rare in copper ore mining, but they have recently begun to occur, and have not yet been fully investigated. To ensure the safety of mining operations, it is necessary to determine parameters of the rock–gas system for which the energy of the gas will be smaller than the work required to disintegrate and transport the rock. Such a comparison is referred to as an energy balance and serves as a starting point for all engineering analyses. During mining operations, the equilibrium of the rock–gas system is disturbed, and the rapid destruction of the rock is initiated together with sudden decompression of the gas contained in its porous structure. The disintegrated rock is then transported along the mine working space in a stream of released gas. Estimation of the energy of the gas requires investigation of the type of thermodynamic transformation involved in the process. In this case, adiabatic transformation would mean that the gas, cooled in the course of decompression, remains at a temperature significantly lower than that of the surrounding rocks throughout the process. However, if we assume that the transformation is isothermal, then the cooled gas will heat up to the original temperature of the rock in a very short time (<1 s). Because the quantity of energy in the case of isothermal transformation is almost three times as high as in the adiabatic case, obtaining the correct energy balance for gas-induced geodynamic phenomena requires detailed analysis of this question. For this purpose, a unique experimental study was carried out to determine the time required for heat exchange in conditions of very rapid flows of gas around rock grains of different sizes. Numerical simulations reproducing the experiments were also designed. The results of the experiment and the simulation were in good agreement, indicating a very fast rate of heat exchange. Taking account of the parameters of the experiment, the thermodynamic transformation may be considered to be close to isothermal.
Highlights
It is difficult to indicate any work that examines the operation of the gas during its sudden decompression, experimentally or by modeling. This results in frequent presumptions as to the nature of the thermodynamic transformation
A fundamental problem in such cases is determination of the energy balance, which enables a proportional comparison of the factors affecting accumulation of energy in the rock–gas system and the work that must be done during phases of the event [18]
To determine the parameters at which a rock and gas outburst is possible it is necessary to establish the nature of the thermodynamic transformation taking place during decompression of the gas from the rock pores
Summary
It is difficult to indicate any work that examines the operation of the gas during its sudden decompression, experimentally or by modeling. This results in frequent presumptions as to the nature of the thermodynamic transformation. The novelty described in the article is the analysis of the nature of the transformation taking place during a sudden gas decompression [6]. This problem is most often associated with coal mining [7,8,9,10]. Reports were made on both incidents, and investigations showed the main cause of the outbursts to be the presence of gas in dolomite [16,17]
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