Deformation Behavior of Topographic Unsymmetrical Loaded Tunnels and Their Pre-Reinforcements after Excavation

Abstract

This study used FLAC to simulate the excavation of unsymmetrical loaded tunnels with various transversal gradients, surrounding rock grades, and thicknesses of side covering soil by considering all factors that affect these unsymmetrical loaded tunnels. The deformation behavior and displacements of key points were analyzed. The effects of unsymmetrical loading are negligible when the thickness of the side covering soil exceeds 21 m, and pre-reinforcement is needed prior to excavation when the thickness of the side covering soil is less than 15 m. These data were used in simulating tunnel pre-reinforcement in different conditions. Results indicate that in the condition of surrounding rocks V, a main problem is insufficient counter pressure in the shallow buried side when the thickness of the side covering soil is less than 7 m. By contrast, overpressure in the deep buried side needs to be addressed when the thickness of the side covering soil is more than 7 m. These findings were verified in actual practice. The conclusions of this study can be used as references to design and construct similar engineering projects.