Mechanical Characteristics of Super-Large Variable-Section Tunnel

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