Global continuous-local discontinuous approach for the analysis of shallow underground caverns in soft and discontinuous rock

We present a realistic approach for 3-D Finite Elements analysis of shallow underground openings excavated in soft and discontinuous rock mass. We promote stability analysis on two different scales, local-discontinuous and global-continuous, and the use of computationally effective linear analysis and multiple loading scenarios as a trade off for elaborate non-linear analysis. The research was performed using the well documented ancient caverns of the Bet-Guvrin National Park, Israel. Well preserved damage zones within the caverns indicate that local instabilities are associated with exposure of pre-excavation joints and development of tensile stresses exceeding the tensile strength of rock. Global stability is compromised when supporting pillars within the caverns are damaged and diminished. Local discontinuous analysis was compared with a well documented local failure. The results of the model were found to be in good agreement with the ground truth Global continuous analysis showed that the stresses within the supporting pillars are close to the limiting uniaxial strength of the rock. Following the present state analysis we have performed a comprehensive stability analysis considering different scenarios of pillars integrity. For a large scale global model (6.3 × 106 DOF) linear analysis enables us to attain comprehensive understanding of possible stress fields and different failure paths, otherwise requiring excessive computational resources.