Investigation of the soil arching evolution in the ground with or without a tunnel

Abstract

The soil arching effect has been widely observed in geotechnical engineering. Despite extensive studies on this topic, there is still a lack of research on the effect of an existing tunnel on the evolution of the soil arching effect, which is investigated in this study via trapdoor tests. Digital image correlation was used to visualize the displacement and shear information of the sand. The effect of the backfill burial depth was considered. The results showed that the same load–displacement curve characteristics can be obtained with four stages (initial arching, maximum arching, load recovery, and ultimate stages), whether an existing tunnel is present or not. The ultimate soil arching ratio is degraded in ground with a tunnel, and most evident with H/B = 4.0, compared to the results without structures. A shield region was generated above the existing tunnel. A double-groove-shaped displacement was formed in the sand above it in the presence of an existing tunnel; it was symmetrical along the central axis of the trapdoor. The shear band gradually expanded from the inside to the outside as the trapdoor slid downward. New shear bands formed at the tunnel shoulder when the shear band exceeded the trapdoor width range. Two deformation patterns, parallel flow over a tunnel and cross-flow over a tunnel, were identified based on development of shear bands in the sand within the existing tunnel.