Experimental study on the leakage-induced structural collapse of segmental tunnels

During the construction of segmental tunnels, unexpected leakage poses a significant safety hazard to the tunnel structures, potentially leading to collapse. Worldwide, accidents caused by leakage during the construction of shield tunnels have resulted in substantial losses. However, existing studies have not clearly elucidated the mechanism behind tunnel collapse induced by leakage, making it challenging to propose effective prevention or control measures. To address this issue, a series of model tests on tunnel collapse induced by leakage were designed and conducted. These tests replicated the tunnel collapse process and revealed three stages: seepage erosion, soil cave formation and destabilization, and soil impact. The soil caves develop upward, leading to a redistribution of external pressure on the tunnels. Ultimately, the structural collapse of the tunnel occurs due to soil impact from the unstable soil cave. Comparing tunnel entrance/exit accidents with connecting passage accidents highlights that both accident types share the same underlying mechanism but differ in boundary conditions.