Skin rockbursts and microseismicity in underground mining

Fracture growth produced by compressive stress is typically restricted to the sizes of the pre-existing defect seeding the fracture. However the biaxial compression acting near a free surface (e.g. a wall of an opening or at a large scale, the Earth’s surface) can change the fracture growth mechanism. Our experiments demonstrate that in the presence of the second, intermediate principal stress (the minor principal stress is nearly zero in the vicinity of free surface) leads to extensive fracture propagation. Furthermore, the interaction of the propagating fracture with the free surface makes the growth unstable (catastrophic). This produces a seismic event and can lead to such a dangerous and hazardous dynamic rock failure such as skin rockburst. We found that a small magnitude of the intermediate principal stress, around 5% of the major principal stress, is sufficient to ensure extensive fracture propagation. The catastrophic fracture propagation is induced by the interaction between the fracture and the free surface as the presence of the free surface imposes additional tensile stresses on the growing fracture. The type of the associated seismic event is the Compensated Linear Vector Dipole (CLVD) source.