Theoretical and experimental investigation on fracture response of coal impacted by high-velocity water jet

Abstract

This paper adopted theoretical derivation and experiments to investigate the stress wave propagation characteristics in rock under water jet impact and fracture response of coal. The evolution model of stress and displacement was presented to analyze the formation, propagation and attenuation of stress wave during rock fragmentation. The rock failure criterion for shear and tensile failure under dynamic impact loads, and crack propagation criterion under quasi-static pressure of water jet were established. And the broken pit range formed by shear component of stress wave and the damage range caused by tensile stress were obtained. Based on scanning electron microscopy and binarization method, experiments on water jet impinging coal under various velocities were conducted to study the failure patterns and fracture characteristics of coal. It is indicated that during the water-hammer pressure and its unloading stage, the radial stress and tangential stress decrease first and then increase, accompanying the occurrences of the radial and tangential tensile stresses peaks and the maximum compression displacement. In the subsequent stagnation pressure stage, the radial and tangential stresses trend to be the stable compressive stress and tensile stress, respectively. The peak values of radial stress and tangential stress at different stages all decay exponentially with the propagation distance. Moreover, the broken pit surrounded with radial and annular cracks is formed on coal when the jet velocity exceeds the threshold value, while the split fracture of coal will occur for the high impact velocity. The rock-breaking specific energy consumption decreases first and then increases with the increasing jet velocity. Besides, the theoretical damage scope is verified and close to the experimental value before the splitting fracture of coal. Combined with fracture morphology of coal debris with different sizes, two microscopic damage-failure modes of coal impacted by water jets are revealed, namely shear failure and tensile failure.