An integrated study of physical and numerical modelling on the stability of underground tunnel influenced by unloading rate

Abstract

Excavation of tunnel is the unloading process of surrounding rock, and the unloading rate is one of the important factors affecting the stability of underground tunnel. Through the combination of large-scale physical model test and numerical simulation, combined with the water bag filling technology to simulate high-speed unloading excavation, the influence of unloading rate and unloading magnitude on the stability of surrounding rock of underground tunnel is quantitatively analysed according to the crack depth, displacement and stress concentration of surrounding rock. The results show that low-speed unloading produces closed arc-shaped cracks on both sides of the tunnel, while high-speed unloading produces closed circular cracks around the tunnel surrounding rock. Tunnels excavated with low-speed form wedge-shaped cracks and flaky destruction. The cracks distribute on the left and right sides of the tunnel, and form closed arcs. Tunnels excavated with high-speed form wedge-shaped closed cracks, which are circularly distributed around the tunnel. The crack depth of tunnel surrounding rock caused by low-speed unloading is larger than that caused by high-speed unloading, and the local stress concentration of low-speed unloading is also more obvious in the sidewall of the tunnel. However, the overall stress of the surrounding rock of the high-speed unloading is more significant, which means it accumulates much energy, and dynamic disasters may occur. High-speed unloading is more suitable for projects in low ground stress or soft rock mass stratum, which may cause less damage to the surrounding rock. In contrast, low-speed unloading can reduce the possibility of dynamic disaster for projects in high ground stress or hard, brittle rock mass.