Study on Reasonable Reinforcement Range of Starting End of Overlapped Shield Tunnel in a Water-Rich Soft Stratum

Taking the construction of the composite shield tunnel of Suzhou (China) Rail Transit Line 8 as an example, the reinforcement range of the overlapped shield launching end is calculated by Japanese elastic thin plate theory, static theory and slip instability theory, respectively. The finite element modeling analysis is used to obtain the soil displacement curve of the shield launching end in different reinforcement ranges, and then the simulation results are compared with the engineering-measured data. In the engineering example, the reinforcement area is 13.75 m wide and 6 m long. The three construction techniques of triaxial mixing, TRD wall forming and MJS all-round jetting are combined to fully ensure the quality of foundation reinforcement. The longitudinal reinforcement length calculated by the slip instability theory is similar to the longitudinal reinforcement length determined by simulation analysis and engineering measurement. The slip instability theory can be used to preliminarily determine the reasonable reinforcement range of the starting end of the overlapped shield.