ABSTRACT
The failure of underground structures such as tunnels, mines, oil caverns, etc. is a function of the magnitude of in-situ stress, the strength of the intact rock, and the conditions of discontinuities. In low in-situ stress environments, the continuity and distribution of natural fractures in a rock mass control the failure processes. Under high stress levels, however, the failure process is affected and eventually dominated by stressinduced fractures growing preferentially in a direction parallel to the excavation boundary. This fracturing is generally referred to as brittle failure by slabbing or spalling (Kaiser et al. 2000, Martin et al. 1999, Read et al. 1996, Hoek et al. 1995).
