3-D global–local finite element analysis of shallow underground caverns in soft sedimentary rock

We present a realistic approach for a 3-D finite element analysis of shallow underground openings excavated in soft and discontinuous rock mass. We address the stability analysis on two different scales, local-discontinuous and global-continuous, and promote 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 case of the ancient caverns of the BetGuvrin National Park in Israel. Well preserved damage zones indicate that local instabilities are associated with exposure of pre-excavation joints and development of tensile stresses exceeding the tensile strength of the rock. Global stability is compromised when supporting pillars within the caverns are diminished. Results of the local-discontinuous analysis were compared with a well-documented local failure, and were found to be in agreement with the ground truth. Following, we performed a comprehensive global stability analysis using a linear analysis of a large-scale global model (6.3 � 10 6 DOF). We modeled different scenarios of supporting pillar integrity, thus gaining comprehensive understanding of possible stress fields otherwise requiring excessive computational resources. We conclude this article with simple guidelines for performing local-discontinuous and global-continuous analysis.