Study on the Mechanical Properties of TBM Crossing Composite Strata with Large Longitudinal Slopes

Relying on the Dujiangyan Irrigation Project, the Siguniang Mountain Rail Transit project, and the Balang Mountain No.1 Large Longitudinal Slope Tunnel Project, this paper systematically studies the mechanical response of the surrounding rock and support structure induced by TBM tunneling in composite stratum by using the methods of indoor test, similar model test and numerical simulation. In model tests with different rock dip angles (0°, 10°, 20°, 30°), the main findings are as follows: (1) The maximum settlement of the arch crown reaches −4.89 mm (monitoring surface 2, 20° dip angle), the displacement of the arch waist is smaller than that of the arch crown, and the deformation of the soft rock section is more significant. (2) The peak radial surrounding rock pressure generally occurs at a distance of 5 cm from the tunnel wall, with the highest pressure in the soft rock area of the arch waist reaching 16.807 kPa (monitoring surface 4). (3) The lining stress increases with the increase in rock dip angle, and the stress distribution on the same monitoring surface shows as arch waist > arch crown > arch shoulder, with the maximum stress concentrated in the soft rock area of the arch waist. Then, the finite difference method is used for numerical simulation to analyze the convergence deformation mechanism in the composite formation. The results indicate a strong consistency between the simulated displacement/stress patterns of the surrounding rock and lining structure and the experimental data. The research results provide a theoretical basis and experimental reference for the design and construction of similar projects.