Liner Behavior of a Tunnel Constructed Below a Caved Zone

Underground mining leads to deformation of the surrounding rock strata. Over time, this deformation tends to stabilize after mining has completed. However, ground movement can easily reactivated if another adjacent underground project is excavated nearby. When tunnelling underneath caved mining areas, the associated effects on load distribution and liner behavior of this caved zone can be significant. This paper presents a series of scale model tests to understand these effects. In these tests, various testing material compositions were used to simulate intact rocks, a caved zone, primary support and secondary liner based on similarity theory. Various caved zone-tunnel distances (d) and different buried depths were considered in the tests. Results such as deformation, thrust force and bending moment of the liner were recorded and compared. The results show that the caved zone has an obvious impact on the liner when it is located above and nearby the tunnel, but this influence decreases rapidly as a function of d. If the caved zone-tunnel distance is between 50% and 100% of the tunnel span, the bearing capability of the rock immediately surrounding the excavation is significantly reduced, which leads to more vertical load on the support of the tunnel compared to a tunnel without a caved zone. Furthermore, as the shape of broken rock is irregular and the arrangement is random, the caved zone creates an asymmetrical distribution of displacements if the tunnel is near the caved zone. Additionally, this may result in large moments and damage at the tunnel crown.