Abstract
After long-term oxidation and energy storage, broken coal body borehole walls and drainage shaft walls may cause spontaneous combustion during gas extraction. The high-temperature thermal shock caused by the spontaneous combustion of coal incurs thermal damage on adjacent coal, which, in turn, causes changes in the mechanical properties of the coal. However, only a few studies have been conducted in this context, which has limited our understanding of the thermal damage characteristics of coal bodies in such situations. This study aimed to experimentally investigate the correlation between the crack evolution law and the mechanical properties of coal bodies at different temperatures (50-300°C) using heat-force loading considering Ping Mei No. 10 coal mine as the research object. The results suggest that the coal body experiences a large amount of visible damage, and becomes increasingly complex. At 50-300°C, some indexes (such as longitudinal wave velocity, Poisson's ratio, compressive strength, elastic modulus, impact energy index, and pre-peak strain) are positively correlated with temperature. In addition, the dynamic failure time and temperature show a negative correlation, and the overall change slope is small. The relationship between each index and temperature at 200-300°C is opposite to that at 50-200°C, and the overall change slope is larger. Moreover, when the oxidation temperature exceeds 200°C, the destruction of the coal body changes from elastic brittleness to ductility-plasticity. High-temperature oxidation incurs irreversible thermal damage of coal. Hence, it is necessary to focus on the changes in mechanical properties of coal after a spontaneous combustion process is extinguished.
Highlights
Because external resources of coal mines are increasingly being depleted, and the state of deep mine mining is gradually shifting, coal seam storage environments are presenting new characteristics [1]
The high temperature generated by combustion causes thermal damage to the coal near the extraction rotary hole, which causes changes in the mechanical properties of coal
Huang et al [19, 21] studied the effects of thermal shock on the compressive strength, elastic modulus and wave speed of deep rocks after they were subjected to different temperatures, and discussed the rock deformation and fracture mechanism after rock materials were subjected to a high-temperature treatment
Summary
Because external resources of coal mines are increasingly being depleted, and the state of deep mine mining is gradually shifting, coal seam storage environments are presenting new characteristics [1]. The high temperature generated by combustion causes thermal damage to the coal near the extraction rotary hole, which causes changes in the mechanical properties of coal. The high-temperature oxidation effect results in changes in the physical and mechanical properties of coal, which affects its stability. Song et al [10] studied the heating rate and macroscopic spontaneous combustion characteristics of different coal particle sizes during high-temperature oxidation. Huang et al [19, 21] studied the effects of thermal shock on the compressive strength, elastic modulus and wave speed of deep rocks after they were subjected to different temperatures, and discussed the rock deformation and fracture mechanism after rock materials were subjected to a high-temperature treatment. A reference for the stability evaluation of high-temperature oxidized coal, together with a reference for the prevention and control of the instability of ignited coal in coal drilling and extraction wells
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