Dynamic response and failure mechanism of fractured coal under different soaking times

The soaking time plays an important role in the engineering practice with respect to coal stability and failure. In the present study, 36 coal specimens were prepared and soaked in water for 0-240 h (h). A series of laboratory tests, including X-ray diffraction analysis, static load uniaxial compression test, and Split Hopkinson Pressure Bar test, were conducted. The results show that the dynamic mechanical properties of coal can be divided into several stages based on the critical soaking times. The dynamic mechanical properties of coal in stage I are mainly dominated by cohesive forces due to the Stefan effect; in stages II and III, they are mainly influenced by water-coal interactions. The dynamic failure process of the coal specimens was recorded with a high-speed camera in each stage. The dynamic mechanical model of coal specimens with different soaking times was established based on water-bearing wing fracture and spheres models. The effects of the soaking time on the fracture expansion and dynamic mechanical properties of coal at different stages were further discussed.