Evolution of Soil Arching–Induced Deformation and Stress Redistribution in the Ground with an Existing Tunnel

The mechanism of an existing tunnel on the evolution of soil arching effect is not fully understood. This study systematically investigates the issue via a validated FEM with consideration of the distance between the existing tunnel and the trapdoor, the burial depth, and the tunnel diameter. The results indicated that when the normalized distance (the distance between the tunnel and the trapdoor was normalized by the trapdoor width, L) was below 2.0, the influence of tunnel excavation on the pressure above the trapdoor cannot be disregarded, which can be described with a logarithmic function for the relationship between normalized initial stress and normalized distance. The soil within the ranges of 0.17B below the invert of tunnel and 0.5B above the crown of tunnel was significantly influenced by the shadowing effect of the tunnel. Analyzing the principal stress trajectories and soil deformation patterns revealed three distinct regions: the loosened zone, stress transfer zone (comprising friction arch and end-bearing arch), and undisturbed zone. Depending on whether the footings of friction arch and end-bearing arch fell within the tunnel (i.e., whether L exceeded 2.0B), they were categorized as interaction arch or independent arch. The burial depth significantly influenced the load–displacement curve above the trapdoor, whereas the tunnel diameter had a comparatively minor effect.