Mechanical responses of a shallow-buried super-large-section tunnel in weak surrounding rock: A case study in Guizhou

With the gradual increase in traffic demand, the cross-sectional sizes of tunnels are increasing. Consequently, significant attention has been given to the complexity of the mechanical responses of super-large-section tunnels. Based on a super-large-section tunnel of 21.6 m (four-lane) in Qichong Village, Guizhou Province, China, the mechanical responses of the tunnel construction process in the weak surrounding rock were studied using on-site monitoring. The mechanical responses were summarized through the deformation analysis of vertical displacement and horizontal convergence, as well as through the comparison with the existing case of the lon-gitudinal displacement profile. The surrounding rock pressure, shotcrete stress, steel set stress, and axial stress of the bolts were also analyzed. The unique mechanical construction characteristics of the super-large-section of the tunnel with a low flat ratio were observed, and the corresponding technical suggestions for super-large-section tunnels were proposed. This study enriches the database and provides a reference for similar super-large-section tunnels.