Abstract: A scaled model test is conducted to clarify the development of structural collapse induced by seepage in tunnel entrances/exits.Model soil and shield tunnels are established using a similarity relation. In tunnel entrance/exit construction, seepage was triggered in the model shield tunnel, causing structural collapse. The response of the stratum, the change in the external load of the tunnel, the deformation of the tunnel, and the development of the tunnel collapse are observed. Finally, the structural response caused by seepage at different locations in the tunnel entrance/exit and the influence of different seepage locations on the collapse development are analyzed and compared. The experimental results demonstrate the following: (1) After seepage of the tunnel entrance/exit, unstable soil caves appear due to seepage erosion, experiencing a formation, destabilization, and reappearance cycle. (2) The impact of the unstable soil causes the tunnel to collapse structurally. (3) The mechanism of external soil erosion development in the tunnel due to tunnel crown and waist seepage varies, and the shapes of soil caves induced by seepage at different locations differ, resulting in collapse at different locations.

Key words: shield tunnel; entrance/exit construction, seepage, structural collapse, seepage erosion of soil