A numerical study of rock burst development and strain energy release

We consider rock burst to be a dynamic disaster similar to earthquakes, rapid land sliding, or coal mine gas dynamic disasters. Multi-scale mechanical principles imply the same mechanism of damage evolution proceeds the catastrophe. Damage may occur at various scales from a meso-scopic scale to a macroscopic, or engineering scale. Rock burst is a catastrophe at the scale of the engineering structure, such as a tunnel cross section or the work face of a long wall mine. It results from dynamic fracture of the structure where microscopic damage nucleates, expands, and finally propagates into a macroscopic sized fracture band. Rock burst must, therefore, undergo a relatively long development, or gestation, time before its final appearance. In this paper, a study of rock burst within a deeply buried tunnel by numerical methods is described. The results show that during rock burst gestation the distributed microscopic damage in the rock surrounding the tunnel localizes, intersects, and then evolves into a set of concentrated “V” shaped damage bands. These concentrated damage bands propagate in the direction of maximum shear as shearing slide bands take shape. Rock burst happens within the wedge separated by the shear bands from the native tunnel rock. An analysis of the wedge fracture shows that the unloading effects result in rock burst and rapid release of the strain energy. The implications for rock burst prediction in tunnels are that: (1) rock burst develops in the upper arch corners of in the tunnel cross section prior to developing in other zones, so good attention must be paid there; (2) all monitoring, prevention, and treatment of rock burst should be done during the gestation phase; (3) the shear bands contain abundant information concerning the physics and mechanics of the process and they are the foundation of physical and mechanical monitoring of acoustic emission, micro seismic events, stress, and the like. Thus a special study of the shearing mechanism is required.