Numerical Simulation and Analysis of the Causes and Distribution of Secondary Lining Cracks in Overlapping Railway Tunnels

Abstract

The construction of new tunnels above existing tunnels has become increasingly common to optimize underground space utilization. However, such construction may pose potential engineering hazards due to cracking in the secondary lining of the lower tunnel. This study investigates the occurrence and evolutionary characteristics of longitudinal cracks in the secondary lining of the lower tunnel during the construction of the upper tunnel adjacent to the pre-existing lower tunnel. Our findings demonstrate that the construction of the upper tunnel has a significant impact on the lower tunnel, as confirmed by on-site monitoring and numerical simulation results. The redistribution of surrounding rock pressure alters the stress distribution of the secondary lining of the lower tunnel, which is the primary reason for the observed cracking. To mitigate the risk of cracks, two different methods are recommended based on the density of the cracks. In areas with less dense cracks, the method of chiseling and grouting is adopted to improve the strength of the secondary lining, while in relatively dense areas, resin anchor rods with saddle joints are used to enhance the stability of the surrounding rock. Long-term monitoring, classification, and early warning of cracks are also recommended.