Assessment of strain bursting using a Voronoi-based breakable block model: A case study of 2400-m-deep tunnels

Strain bursting around deep underground excavations is a complex phenomenon. The velocity of the failed rock mass and the depth of the excavation damage zone (EDZ) are the important support design parameters that depend on the failure mechanism of strain bursting. The advanced numerical models have the potential to assist in the evaluation of rockbursts. In this study, based on the proposed Voronoi-based breakable block model (VBBM), which can accurately characterize the stress-induced tensile and shear fracture mechanisms of surrounding rock, a quantitative analysis method for determining the energy resulting from the hard rock rupture process is developed to analyze the excavation of cave 7 at the China Jinping Underground Laboratory Phase II (CJPL-II). The results indicate that most of the strain energy is transformed into fracture energy for new ruptured surfaces. The kinetic energy of the moving rock blocks accounts for approximately 16% of the strain energy released by the collapsed surrounding rock. The in-situ stress ratio (K) and rock mass strength significantly affect the depth and range of the EDZ. Compared with the semi-empirical energy demand for support system, the numerical results are more conservative.