A Mechanical Model and Parameter Analysis for Pipe-Roof Considering the Arch Effect

In order to better study the actual stress state of the tunnel pipe-roof, according to the tunnel construction process and construction influence, the lining segment of the pipe roof tunnel was divided into five segments: the second lining section, the primary support section, the excavation section, and the disturbed and undisturbed section in front of the palm face. Considering the whole pipe-roof arch effect formed after pipe-roof grouting, a Winkler elastic foundation beam model of the five-sections tunnel pipe-roof is established. The flexure and internal force calculation formula of the five-paragraph tunnel pipe-roof model are deduced and compared with existing engineering cases. At the same time, different excavation footage, pipe diameters and elastic modulus of reinforced area are analyzed. The results show that: The maximum deflection of the pipe-roof obtained by the new model and the corresponding position are closer to the on-site monitoring results, which can solve the problem of pipe-roof deformation in the disturbance section caused by the unreasonable setting of boundary conditions in the existing pipe-roof model. The arching phenomenon at the end is more in line with the actual deformation of the pipe-roof. Changing the excavation footage has a greater impact on the deflection of the pipe-roof. When the diameter of steel pipe is 108 mm and 114 mm, the pipe-roof support effect are similar; when E_c(elastic modulus of converging) is greater than 40.0 E_g(elastic modulus of ground rock), the excavation footage and the diameter of the steel pipe have little effect on the deflection and bending moment of the pipe-roof. Therefore, increasing the elastic modulus of the reinforced area is the most effective method for reducing pipe-roof deflection and internal force.