Research on Suitable Construction Method Parameters for Large-scale Mechanical Tunnelling

To fully utilize the advantages of large-scale mechanical construction and address the matching problem between such construction and bench height/length in tunnels, this study, based on the Qixingping Tunnel project of the Xi'an-Chongqing High-speed Railway, investigated the construction process of corresponding machinery and proposes a configuration scheme suitable for large-scale mechanical tunnelling. Based on the operational space requirements of mechanical construction, the bench length and height are adjusted, and the influence of construction on surrounding rock stability and structural safety was analyzed via numerical simulation. The results shown that: (1) Although increasing the bench length can effectively reduce the horizontal displacement and minimum principal stress of the lower bench, its control effect on the stress at critical locations and the volume of the plastic zone was limited. (2) With the increase of bench height, the concentration area of the minimum principal stress in the secondary lining significantly shrinked, and the peak stress decreased, indicating optimized structural compressive performance. However, the maximum principal stress increases markedly and tends to concentrate, especially at the junction of the upper and lower benches, where the tensile stress area expands, and its magnitude rised, posing a potential cracking risk. (3) Considering both structural mechanical performance and construction safety, it is recommended to control the tunnel bench length within 3~5 m and the bench height within 1~5 m.