Stability Assessment and Support Design for Underground Tunnels Located in Complex Geologies and Subjected to Engineering Activities: Case Study

A good understanding of rock mass behavior around underground tunnels is necessary for stability assessment and support design. This paper presents a three-dimensional (3D) numerical analysis to support the aforementioned statement for an underground mine by using the distinct element method. Geological and engineering complexities simulated in the numerical model include large-scale faults and a nonplanar weak interlayer, as well as open and backfilled tunnels. Sequential excavation, backfilling, and delayed supporting were simulated according to the field construction process. Numerical analysis investigated the effect of complex geologies and engineering activities on tunnel stability. Deformations and strength degradation areas around the tunnels are illustrated and analyzed at different locations. Based on the rock mass behavior and the failure conditions of the applied rock supports, useful suggestions are made on the selection of appropriate tunnel support for this underground mine. These suggestions shared similarities and slight differences with the guidelines suggested by an empirical method. The accuracy of the numerical results is verified by comparing with the field deformation data. This study provides a comprehensive procedure for stability assessment and support design for similar underground rock mass projects.