Experimental study of the dynamic mechanical responses and failure characteristics of coal under true triaxial confinements

Abstract

Investigations on the dynamic mechanical properties and failure mechanisms of coal under in-situ stress is essential for the prevention of dynamic disasters in deep coal mines. Thus, a modified true triaxial Hopkinson bar was employed to explore the dynamic mechanical behaviors of coal at different confining pressures (0–20 MPa) and strain rates (40–220 s−1). The results show that the dynamic peak stress is positively correlated with lateral static pre-stress σy and σz, but negatively correlated with axial static pre-stress σx. At approximate strain rates, increasing the lateral static pre-stress facilitates increasing the dynamic peak stress, but the minimum lateral static pre-stress is the primary factor limiting a significant increase in dynamic peak stress of coal. Furthermore, the dynamic differential stress is linearly related to the logarithm of strain rate, and the peak strain varies linearly with strain rate. However, there is no significant correlation between confining pressure and peak strain. Moreover, X-ray CT images and photographic fracture observations of coal samples show the failure patterns under uniaxial and triaxial conditions are splitting failure and shear failure, respectively. The device provides a viable approach for fully comprehending the dynamic mechanical behaviors of rock-like material in complex stress conditions.