Mechanical mechanism of piperoofs with variable coefficient of subgrade reaction in shallow tunnels

In order to improve the elastic foundation beam model for piperoofs with constant coefficient of subgrade reaction, the distribution law of coefficient of subgrade reaction in front of the excavation face is discussed. Furthermore, the new elastic foundation beam model with variable coefficients of subgrade reaction is established, in which the lateral deformation effect of the excavation face is taken into account. And it is calculated by finite difference method. The forces and deformations of piperoofs are compared under different conditions. The results show that it is necessary to take the lateral deformation effect of excavation face into account during the analysis, and that the deflection deformation of piperoofs can be effectively reduced by reinforcing the excavation face. Simultaneously, the results also indicate that mechanical behaviors of piperoofs colsely relate to the location of the excavation face, the footage of the tunnelling cycle and the Poisson’s ratio. The conclusions can be reference for the design parameter optimization and the construction scheme selection of piperoofs.