Damage evolution mechanism of coal rock under long-term soaking

The deterioration of the mechanical properties of water-rich coal rock is a predisposition to many mine geologic hazards. To explore the progressive damage characteristics of coal rock under long-term soaking, the weakly caking coal of the Shenmu region is selected as the research object. Firstly, the long-term soaking tests on coal rock are carried out without pressures for 15, 30, 60, 120 and 240 days. Then, the uniaxial compression tests with acoustic emission (AE) monitoring are carried out on the dry and then soaked coal rock to analyze its water-softening characteristics. Finally, the evolution of pore structure of coal rock under different soaking durations is studied using the scanning electron microscope (SEM) and nuclear magnetic resonance (NMR). The results show that: ①The water saturation of coal rock increases with the duration of soaking, and the increase rate continuously decreases, and tends to a constant. ②In the process of saturation, the mechanical properties of coal rock deteriorate, and those of saturated coal rock still deteriorate with the increase of the soaking duration, characterized by the decrease of the compressive strength and elastic modulus, and an increase in the cumulative AE ringing numbers. ③A surface shrink may occur after the drying process, and during the soaking tests, the small pores of samples gradually increase, and the pore structure becomes more complex with the increase of the soaking duration. The research results can provide useful prevention for the instability and failure of coal rock under water-rich conditions.