Ground Reinforcement Method for Closely Spaced Overlapping Tunnels Passing beneath High-Speed Railway Bridge

There is a high risk of ground collapse during the construction of closely spaced overlapping metro tunnels in sensitive environments. When overlapping tunnels pass beneath important structures such as high-speed railway (HSR) bridges whose deformation controlling standard is extremely strict, special ground reinforcement measures should be implemented. This paper investigated stability control measures for closely spaced and overlapping metro tunnels passing beneath the HSR bridge based on the engineering project of the Jinan R1 Metro line in China. The risk sources and engineering difficulties were analyzed. Further, special reinforcement measures including isolation piles and a postgrouting method were proposed. A three-dimensional model was built by a finite element program, and the deformation characteristics of ground and bridge piles were calculated. Subsequently, their deformation characteristics were analyzed and compared with monitoring results. The deformation of an HSR bridge was successfully controlled within permissible value during the shield tunneling process, indicating the effect of ground reinforcement measures is satisfactory.