Taking Chongqing Huofengshan Tunnel as the engineering background, numerical simulation, model test and field monitoring are used to study the deformation and stress characteristics of the supporting structure at three different sections of Chongqing Huofengshan left-line tunnel. The influences of tunnel construction process on the uneven settlement of surface buildings before and after optimization were compared. The study results show that: (1) The deformation of the tunnel increases with the enlargement of the section, and the variable section has an effect on the deformation of tunnel front and back, the influence range is within 30 m. In the variable section, the settlement value of the vault varies greatly along the tunnel length, and the tunnel deformation is obviously affected by excavation. (2) The stress of the support structure in variable section is complex and distributed unevenly. There is a small range of stress concentration in the section changing zone. Arch waist position is the weak part, which should be properly reinforced. (3) The influence of gradual and abrupt expanding excavation on the settlement of tunnel vault is mainly shown in the vicinity of the changing zone of section. The influence range of the two schemes is similar, and there is no obvious adverse effect of the sudden excavation, the section transition distance can be appropriately shortened

To explore the directional pre-reinforcement method adapted to the bedding characteristics of large deformation tunnel, relying on Jiumian Highway large deformation tunnels, the parameters of surrounding rock were determined by rock test. The effect of directional reinforcement method was verified by adjusting the angle of bolt and advanced support and the spacing of small pipe under different large deformation grades and horizontal and longitudinal bedding angles in numerical simulation. Tunnel deformation in three large deformation levels field test section is significantly improved, which verifies the applicability of the method. The results show that: (1) The compressive stress in support structure is caused by the surrounding rock deformation and extrusion, bolt and the advanced support optimization affect the bolt and small pipe stress, and then change the support tension. The effect of bolt and small pipe optimization increases with the increase of large deformation grade. (2) Under plane bedding, the anchor rod angle directional reinforcement has a significant effect. Advanced directional reinforcement can be considered for strong large deformation when double-layered small pipes are used. Different bedding angles have different sensitivities to bolt and advance support optimization. (3) When the longitudinal stratification is inclined downward, insertion angle was optimized by increasing the angle between small catheter and longitudinal bedding; When the longitudinal bedding is inclined upwards, the turning point of surrounding rock deformation rate with the decrease of small pipe spacing is found to determine the optimal spacing. The optimal spacing decreases with the increase of large deformation grade and the longitudinal bedding angle.