Abstract
For composite mining coal-rock dynamic disaster, combining the theory of thermodynamics, damage mechanics, and other disciplines, the thermodynamic coupling mathematical model of composite coal-rock under an unloading condition is deduced, and the simulation model of composite coal-rock is established for numerical simulation. And the variation law of thermal infrared radiation under triaxial loading and unloading of composite coal-rock is analyzed and verified by experiments. The results show the following findings: (1) The distribution of thermal infrared radiation temperature of composite coal-rock is different in different stages of stress. The overall temperature of the temperature field is lower than the initial temperature field in the three-dimensional stress loading stage and the stage of stress-keeping pressure, but the internal temperature of the coal body is the highest. In the first stage of “loading and unloading,” the temperature of a coal seam increases slightly, and the temperature of other parts of the rock layer increases except for the circular low-temperature zone. In the second stage of “loading and unloading,” an alternating zone of high and low temperatures appears in the rock mass, and the temperature field is enhanced, among which the temperature field reaches the strongest after unloading the confining pressure. After jumping over the maximum stress, the temperature field decreases as a whole at the instability and rupture stage. (2) The variation of surface average thermal infrared radiation temperature ( T ave ) of composite coal-rock can be divided into the initial fluctuation stage, the linear heating stage, the local decline stage, the temperature sudden increase stage, and the fracture decline stage. At three different unloading rates of 0.003 MPa/s, 0.03 MPa/s, and 0.05 MPa/s, the T ave of coal body, floor rock, and roof rock reach the maximum before composite coal-rock instability and fracture, and the temperature change of the coal body is the most obvious. (3) Under different confining pressure unloading rates, the T ave of roof rock, coal body, and floor rock shows a strong linear relationship with stress after linear fitting. And the correlation between simulation and experimental results after fitting is above 0.89. The larger the confining pressure unloading rate is, the shorter the peak time of T ave arrives, and the larger the peak value. The comparison between the experimental results and the simulation analysis shows that the two results are consistent, and the research results can provide a theoretical basis for the prevention and control of dynamic disasters in coal and rock mining.
Highlights
With the increasing depth of coal mining, coal and rock dynamic disasters such as coal and gas outburst and rock burst are becoming more and more serious [1]
The comparison between the experimental results and the simulation analysis shows that the two results are consistent, and the research results can provide a theoretical basis for the prevention and control of dynamic disasters in coal and rock mining
During the loading-unloading process, when the thermal infrared radiation intensity of the composite coal-rock under the action of stress changes, the reason is that the external stress causes the change of the thermal field of the coal-rock, which leads to the alienation of the temperature field of thermal infrared radiation on the surface of the coal-rock
Summary
With the increasing depth of coal mining, coal and rock dynamic disasters such as coal and gas outburst and rock burst are becoming more and more serious [1]. Predecessors have studied the characteristics of thermal infrared radiation temperature and precursor laws of coal and rock under uniaxial loading, but there are few related studies on unloading failure of deep coal and rock mass. Aiming at the problem of effectively predicting and forecasting coal and rock mining dynamic disasters, this paper intends to study the distribution of thermal infrared radiation temperature during the unloading and fracture process of anisotropic composite coal-rock, and the relationship between thermal infrared radiation and stress on the surface of composite coal-rock and its changing law based on thermodynamics and damage mechanics. Joint early-warning simulations and experiments on coal and rock instability through multiphysics fields to explore the characteristics of infrared radiation temperature changes and coal and rock rupture precursor laws have important theoretical significance for the development of coal and rock mining dynamic disaster prediction and forecast
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