Abstract:Southwest arduous mountain tunnel construction faces severe challenges in terms of plateau alpine, large terrain height difference, complex geological conditions, etc. The application of a full-section tunnel boring machine (TBM) is one of the effective ways to efficiently complete the Sichuan-Tibet Railway tunnel, but the conventional TBM can no longer meet the complex geological and variable tunnel construction requirements. To ensure the safe and efficient construction of TBMs, a new dual-structure TBM was proposed to adapt to the extremely complex geological environment. Through the research and practice of TBM engineering under complex geological conditions, firstly, the adaptability of different models of TBMs under adverse geological conditions was discussed, and the tunnel deformation mechanism of open type TBMs under high ground stress rock explosion stratum, dense zone of joints and altered rock stratum was analyzed in depth; furthermore, based on the conventional open TBM structure, a series of innovative designs have been developed, such as advance geological forecasting interface, mainframe structure enhancement, reinforced support capability and slag removal capability, advance ground stress release, safety protection measures, anti-seize, and extrication, etc. In view of the limitations of single-structure TBM in facing complex geology, a conventional geological "net-spray-anchor" design has been established. Finally, based on the Sejila Mountain project, we evaluated the adaptability of dual-structure TBMs in poor geological conditions by combining the application of dual-structure TBMs in the field. Finally, based on the Sejila Mountain project, we evaluated the adaptability of dual-structure TBMs in adverse geological conditions, and the overall tunneling rate results in the field showed that the dual-structure TBM was effective in the construction of geologically variable tunnels.