Experimental Study on the Segmental Tunnel Collapse Induced by Water and Sand Inrush in the Connecting Passage
Several tunnel collapse accidents caused by water and sand inrush during the construction of shield tunnels have resulted in significant economic losses.Due to the sudden and concealed nature of these accidents,research on the development process and mechanism of shield tunnel collapses is still in its early stages,making it challenging to propose effective preventive measures.To explore the mechanism of segmental tunnel collapse induced by water and sand inrush in connecting passages and provide a theoretical basis for subsequent prevention measures,a model test was designed and conducted,using the accident case of Shanghai Metro Line 4 as the research background.The development process of tunnel collapse was reproduced,and the responses of the strata and tunnel during the collapse were analyzed.The study proposed the development process and causes of structural collapse induced by tunnel leakage.The results indicate that:① Seepage erosion following tunnel leakage creates soil caves in the external strata,which develop to the ground through a process of formation,destabilization,and reproduction;② The soil arching effect causes load redistribution outside the tunnel,leading to significant deformation of the tunnel structure;③ When the soil caves reach a critical height,the top soil destabilizes and falls,and the impact load causes the tunnel structure to collapse.The maximum impact load observed in the test was 13 times the normal soil and water load;④ A preliminary theoretical formula for calculating the impact load on the tunnel is proposed.