Weakening Mechanism and Infrared Radiation Characteristics of Coal with Different Moisture Contents in the Brazilian Test

Abstract

Water–rock interaction is an important factor affecting rock mass strength; water weakening of the coal pillar will affect the stability of underground storage. In this work, the Brazilian splitting strength weakening, splitting fracture characteristics, and infrared radiation characteristics of coal samples (CSs) with different moisture contents were studied. With increasing moisture content, the tensile strength of CSs decreases linearly, while the peak strain increases first and then decreases. The flatness of the splitting fractures on the sample surface after tensile failure decreases with the increase in moisture content, and the fractal dimension of the splitting fractures increases from 1.066 to 1.298 from the dry state to the saturated state. The temperature slowly increases during the loading process of CSs with low moisture content, and a sudden decrease in temperature is observed at the moment of fracture. However, the surface temperature of CSs with high moisture content decreases gradually during the splitting test, and the temperature changes are small. It can be concluded that the temperature change in the CS surface at the moment of failure is linearly related to the moisture content. After splitting failure, the stress on the CS is released and the surface temperature decreases gradually. The infrared radiation released by the CS during splitting failure decreases gradually with increasing moisture content. With the help of computed tomography, it is found that the primary fracture of a CS expands after water immersion, and the porosity increase after water immersion is 0.0255. The porosity increase accelerates damage development in the CS, leading to easier formation of penetrating fractures in the splitting process. The existence of water weakens the cementation strength of the primary fracture, so that it takes less strength for the splitting fracture to expand along the joint fracture surface. The reduction in new fractures also reduces the intensity of infrared radiation.