Abstract
Mining disturbances may cause fissure water in the sandstones of a coal seam roof to link up with the coal seam, further causing changes in the moisture conditions of coal–rock systems such as immediate roofs, coal seams, and immediate floors. The varying moisture content influences the mechanical properties and failure precursor symptoms of coal–rock systems. In this study, we carried out uniaxial compressive experiments on coal–rock combinations under dry, natural moisture, and saturated conditions and measured the acoustic emission (AE) and infrared radiation (IR) data. The results show that the combinations can be classified according to the varying water absorption capacities of coal, mudstone, and siltstone with intrusion time. We classified them into a rapid water absorption stage (0 to 2 h), a slow water absorption stage (> 2 to 14 h), and a stable stage (> 14 h). At the same stage, the water absorption capacities can be ranked as coal > mudstone > siltstone. From dry to saturated, the uniaxial compressive strengths, modulus of elasticity, and peak strain of the coal–rock combination specimens is reduced by 37.5, 8.9, and 35.2% respectively. Cracks produced by coal–rock combinations were concentrated mainly on the surface of the coal portions. Before and after the peak failure, the IR temperature of the dry coal–rock combination increases first and then decreases, while the IR temperature of the natural moisture and saturated coal–rock combinations decreases first, then increases, then decreases again. From dry to saturated, the time interval and stress-level interval between the AE precursor point and IR precursor point of the specimens increases by 1.68 times and 4.5 times, respectively. These outcomes provide a useful reference for studying monitoring and early warning of coal and rock interactions and coal and rock pillar instability under the effect of water–rock interaction in engineering practice.
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