Launch support system and its design and construction method for super-large diameter TBM

To meet the growing demands for high traffic capacity, large conveyance, and specific functional requirements, the use of super-large diameter Tunnel Boring Machines (TBMs) has become increasingly widespread. However, providing a stable and reliable reaction force for TBM launching without a secondary lining remains a significant engineering challenge. Focusing on the TBM-10 excavation section of Contract Lot 8 in the Yangtze-to-Han River Diversion Project, this study proposes a composite launch support system consisting of a cast-in-place concrete lining combined with anchor bolts or prestressed cables. A design and calculation method based on load combinations and structural mechanics analysis was established, and finite element simulations were performed to investigate the stress and deformation characteristics of the system under maximum thrust conditions. The proposed system was further validated through an engineering case study. Numerical results show that the maximum deformation of the composite system under TBM launching thrust was 9.35 mm, accounting for only 39% of the limit specified by the code. The maximum stress on the lining reached 2.5 MPa, satisfying both code-specified and allowable stress requirements. Field monitoring indicated that the maximum displacement of the reaction frame during launching was 4.3 mm. These results demonstrate that the proposed system enables the safe and stable launching of a super-large-diameter TBM without a secondary lining, significantly improving construction efficiency and economic performance. The findings provide valuable theoretical and practical references for the design and optimization of TBM launch support systems under similarly complex geological and construction conditions.