Model experiment study on the stability mechanisms of box culvert excavation faces under the effect of pipe roof in a shallow bury

The pipe roof box culvert construction method is widely used in short-distance crossing projects. The shallow buried tunnel can reduce the wiring length, thus saving on the project's construction costs. However, if not handled properly, roof collapse may occur in the tunnel. In this study, we created a model experiment design based on the Tianlin Road pipe roof box culvert project and conducted an experiment involving a pipe roof box culvert excavation surface stability model under different bury depths and pipe roof stiffness levels as well as a support plate moving forward or backward. This was done to explore the process of the excavation face instability and the development mechanism of ground deformation. The excavation face support plate was moved during the experiment to simulate the failure process of the excavation face limit equilibrium state. The DIC binocular camera and the fiber Bragg grating fiber were used to monitor the surface deformation and pipe roof deformation, respectively. The experiment results reveal the environmental influence law of the supper shallow buried pipe roof box culvert construction method and the failure shape of the excavation surface. The results further indicate that the development of the surface deformation of the under-excavation gradually changes from "straight" to "parabolic" with the change of the stiffness of the pipe roof. Furthermore, without the pipe roof, both the deformation value and the ground deformation under the over-excavation do not exceed 63.4% and 20.6%, respectively. The maximum vertical deformation of the over-excavation pipe roof is located at about 1 H of the excavation surface, and the maximum deformation of the under-excavation occurs at a distance near 2 H. The results of the model experiment can provide guidance in the application of the pipe roof box culvert construction method under supper shallow buried conditions.