The fracture of composite coal-rock under load is the process of energy conversion. As the dissipative energy composition, there is a correlation between the infrared radiation energy and the coal-rock states. Based on theories of theoretical mechanics, modern quantum mechanics, thermodynamics, and other disciplines, first, this paper explained the causes of infrared radiation energy in the process of coal-rock fracture by using the microanalysis method. After that, the mathematical model of dissipation energy−infrared radiation energy coupling was deduced and established, and the experimental analysis was carried out under different loading conditions. The analysis shows that the conversion of mechanical energy and internal energy in the process of loading caused constant collisions between molecules in coal-rock, which led to a temperature rise. After entering the excited state, molecules have to transition to a lower energy level, which generates infrared radiation. The experimental results show that there was a strong correlation between energy characteristic parameters, which is consistent with the established relationship. In addition, the energy conversion and dissipated energy changes in the loading process had stages. Before the elastic−plastic stage, the dissipated energy obtained by coal-rock energy conversion was less, but it increased rapidly in the later stage, which eventually led to the fracture of coal-rock. In the early elastic−plastic period, infrared radiation energy was the main component of the dissipated energy and its variation trend was consistent with the dissipated energy. After that, the infrared radiation energy remained stable, but the dissipation energy still increased. At this time, infrared radiant energy was no longer the main component of dissipated energy. And the infrared radiation energy dropped rapidly before coal-rock fracture, which had certain precursory characteristics. The coupling mechanism of dissipated energy−infrared radiation energy can be used to explain the failure reason of composite coal-rock under different loading conditions from the perspective of energy, which will provide a new idea for assisting the prediction of coal-rock dynamic disasters.

The nature of composite coal and rock fracture under load is the process of energy conversion inside it, and to explore the coupling mechanism of dissipated energy (DE) and electromagnetic radiation energy (ERE) during the deformation and fracture process of loaded composite coal and rock, based on theoretical mechanics, electromagnetics, and other subject theories, the stress–charge induction signal coupling relationship is deduced and established. On this basis, a coupled mathematical model of dissipated energy–electromagnetic radiation energy (DE–ERE) is established, and uniaxial loading experiments under different loading rates are carried out. The research results show that the energy of the composite coal and rock increases, and the internal free charge transitions from the high-concentration area to the low-concentration area, accumulating charges on the fractured surface, forming a regional electric field, and generating electromagnetic radiation. The change of the charge-induced signal on the surface of the loaded composite coal and rock is phased and has a corresponding relationship with each mechanical phase. Its peak appears earlier than the stress peak. There is a linear relationship between the charge induction signal and stress, and they have a strong correlation, which is consistent with the established mathematical model. The energy conversion characteristics of the composite coal and rock under load have stage characteristics. The elastoplastic period is mostly converted to dissipative energy release, and the increase of plastic deformation leads to rupture. ERE is one of the components of DE. In the early stage of elastoplasticity, the dissipated energy mainly exists in the form of electromagnetic radiation energy, and the change trends of the two are the same. After the peak value, it drops rapidly, and the DE is mainly composed of other destructive energy that causes deformation. The changes in ERE can be used to determine the DE and stress state, providing a new method for preventing coal and rock dynamic disasters.

To further study the problem of spontaneous combustion of coal gangue mountains, a multifield coupled simulation model was established based on the mathematical models of temperature field, gas concentration field, and seepage velocity field. In addition, the dynamic development law of these three physical fields in the process of spontaneous combustion is numerically simulated, and the relationship between gas concentration and temperature is studied and verified by experiments. The results show that in the initial stage of the thermal storage and heating process of the coal gangue mountain, the overall heating rate is small. With the passage of stacking time, a high-temperature area will gradually form inside, and the high-temperature area is concentrated near the windward side first and then spread to the leeward side. The oxygen on the windward side keeps a high concentration all of the time and gradually attenuates after entering the interior, and the overall concentration decreases with the extension of stacking time. The distribution law of carbon monoxide concentration is opposite to that of oxygen concentration. The variation law of carbon dioxide concentration is the same as that of temperature, that is, the concentration near the windward side is the highest, and then, it shows a distribution trend of first concentration and then divergence. The vortex phenomenon formed on the leeward side of the mountain outside and the chimney effect inside will aggravate the gas convection inside the gangue mountain, which makes the reaction continue so that the temperature of the gangue mountain keeps rising until it spontaneously ignites. There is a correlation between temperature and gas concentration. Among them, the concentration of carbon monoxide and carbon dioxide can well reflect the temperature change inside the coal gangue mountain, and the effect of carbon dioxide is better in the high-temperature area. The research results provide a theoretical reference for the prevention and control measures of spontaneous combustion of coal gangue mountains and have certain guiding significance.

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.

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