Experimental study on dynamic mechanical characteristics and fracture behaviors of coal under water–gas-temperature coupling conditions

Abstract

The stability of underground spaces in abandoned coal mines is affected by water, gas, temperature, and other dynamic disturbances. Thus, it is important to understand the dynamic behavior of coal in a complex environment for reusing abandoned mines. To this end, a multi-field coupled test system was independently developed to investigate the dynamic behaviors of coal under water–gas-temperature coupling conditions. The results revealed that in the presence of water and gas, the upper part of the coal sample was surrounded by gas, while the lower part was soaked in water. The dynamic stress–strain curve of the coal samples in the coupled water–gas-temperature environment includes a linear elastic deformation stage, rapid crack propagation stage, and post-peak fracture stage. The presence of the water–gas mixing pressure changes the failure of coal from ductile to brittle, whereas an increase in temperature changes the failure of coal from brittle to ductile. The dynamic strength of the coal samples increased linearly with an increase in the impact velocity, strain rate, and water–gas mixing pressure but decreased with an increase in temperature. The failure strain of the coal samples increased linearly with an increase of impact velocity, strain rate, and temperature, but decreased with an increase in the water–gas mixing pressure. In addition, the fracture process of the coal was captured using a high-speed camera, and the results indicated that the cracking degree of the gas part was greater than that of the water-soaked part. Moreover, the influence of various factors on the impact fracture behavior and deterioration mechanism of coal under water–gas-temperature coupling conditions were revealed.