Laboratory Studies of Electric Current Generated during Fracture of Coal and Rock in Rock Burst Coal Mine

Experiments show that electric current would be produced in uniaxial compression of coal and roof rock. The electric current of coal shows a rapid increasing tendency when the loading stress is greater than or equal to 0.75 σmax which can be regarded as an omen for coal failure. The current of roof rock shows reversal tendency while loading stress is greater than or equal to 0.91 σmax and revised from negative to positive at the main fracture and the reversal of current can be regarded as the omen of rock fracture. There are obvious differences in physical and mechanical properties, composition, and failure process between coal and rock. The dominant mechanism of electric current generated by coal is triboelectrification of coal particles and charge separation during crack propagation. The mechanism of electric current of roof rock is piezoelectric effect of quartz materials in the early stage and charge separation during crack propagation in the later stage of loading. It can be found that the rapid increasing and reversal characteristic of electric current can reflect the failure process of coal and roof rock, respectively. Thus, it can be considered the omen of coal and rock failure.