Seismic events associated with catastrophic fracture propagation in rock under compression

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.

 

Our previous experiments on brittle transparent samples with an internal initial crack under biaxial compression showed that a small magnitude of the intermediate principal stress, around 5% of the major principal stress, is sufficient to ensure extensive fracture propagation [1- 3]. The catastrophic fracture propagation is then 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. We present a simple model that allows the determination of the conditions of unstable fracture propagation and the energy of the associated seismic event. The results of this research contribute to the understanding of the nature of seismic events and the mechanics of skin rockburst.

 

1. Wang, H., Dyskin, A.V. Pasternak, E Dight, P Sarmadivaleh, M. 2018. Effect of the intermediate principal stress on 3-D crack growth. Engineering Fracture Mechanics, 204, 404-420.
2. Wang, H., Dyskin, A.V. and Pasternak, E. (2019) Comparative analysis of mechanisms of 3-D brittle crack growth in compression, Engineering Fracture Mechanics220, 106656.
3. Wang, H., Dyskin, A. Pasternak, E., Dight, P. and Sarmadivaleh, M. (2019) Experimental and numerical study into 3D crack growth from a spherical pore in biaxial compression, Rock Mechanics and Rock Engineering, doi.org/10.1007/s00603-019-01899-1.

 

Acknowledgements. AVD and EP acknowledge support from the Australian Research Council through project DP190103260. The first author acknowledges financial support from the Australian Centre for Geomechanics. The authors are grateful to Mr. Frank EE How Tan for his assistance with specimen preparation. AVD acknowledges the support from the School of Civil and Transportation, Faculty of Engineering, Beijing University of Civil Engineering and Architecture.