Failure characteristics and meso-deterioration mechanism of pre-stressed coal subjected to different dynamic loads

Abstract

The study of dynamic fracture mechanism of pre-stressed coal is of great importance to the coal bursts prevention and the coal pillar reinforcement subjected to the dynamic disturbance. In this paper, the effect of pre-static load and dynamic load on the initiation fracture evolution and destruction states of coal were studied using experimental and theoretical approaches. The results show that the coal usually splits into several blocks along the dominant fractures when subjected to the static load. The increase of pre-static load can make the post-peak dynamic stress–strain curve of the specimen gradually transform from type II to type I. The dynamic load plays the same role as that of pre-static load in terms of the effect on the dynamic stress–strain curve, but different in dynamic failure state of the coal. The enhancement of the former will make the dominant fracture expansion and leading the dynamic failure of coal gradually transform from the surface peeling to failure into several large pieces along the dominant fractures, while the increase of the latter will provid increasing kinetic energy to activate the internal fracture expansion of the specimen, and causing the failure state of the specimen transform from the surface peeling to the complete destruction into pieces. For the specimen with the surface peeling failure form, the peeling degree of the specimen depend on both the length of the fracture and the distance of the fracture to the free surface. Based on these results, the dynamic instability mechanism and protection focus of coal pillars under coupled static and dynamic loads were further discussed.