Experimental study on soil erosion induced by leakage of circumferential joints in shield tunnels

Leakage at shield tunnel joints is a primary cause of soil erosion and ground collapse. In this study, model tests were conducted to investigate the development of soil erosion under different leaky joint locations, and the effect of overlapped tunnels on erosion was investigated. The results revealed a three-stage evolution of soil erosion: internal erosion, surface collapse, and stabilization. For leakage at the tunnel crown and waist, the sand erosion region was limited to a narrow area above the joint, with ground surface collapse widths ranging from 1.0R to 1.3R. In contrast, leakage at the tunnel invert led to an expanded erosion region extending to both sides of the tunnel, exhibiting a “U”-shaped distribution. The width of the surface collapse reaches 5.3R, which is 4–5 times leakage at the tunnel crown or waist. The presence of an existing upper tunnel significantly mitigated the evolution of soil erosion. Regardless of leakage positions, soil erosion was confined to narrow regions on one side of the tunnel. The surface collapse width decreased by 50%–70% compared to the single tunnel case.