Instability and collapse of shield segment ring in sand foundation induced by shield tail sealing failure
The cases of instability and collapse of shield segment ring are extremely rare.It is of great significance to explore the conditions of instability and collapse for preventing serious accidents.Based on Midas GTS,a load-structure calculation model of 30 rings considering the effect of ring joint bolts was established.The instability failure process and the occurrence conditions of instability collapse of shield segment ring structure were discussed from two aspects,which were foundation hollowing at the shield tail and the shield tail attitude mutation.The results are drawn.Shield tail leakage causes the shield tail shell to lose the effective restraint from the surrounding foundation,and the shield tail attitude changes is forward and backward.The tunnel structure undergoes lateral"duck egg"and longitudinal deflection deformation,which eventually causes the collapse of some segment rings.The shield tail subsidence displacement is the main factor inducing the instability and collapse of the segment ring.The longitudinal deformation of the tunnel develops more rapidly than the longitudinal deformation caused by the foundation hollowing around the segment ring due to shield tail leakage.When the shield tail subsidence displacement exceeds 0.50 m and the hollowing range exceeds 5 rings,when the shield tail subsidence displacement exceeds 0.45 m and the hollowing range exceeds 10 rings.When the shield tail subsidence displacement exceeds 0.40 m and the hollowing range exceeds 11 rings,the maximum opening of the ring seam exceeds the maximun stress limit of a single bolt,and the ring seam opening is 47.43 mm,causing some longitudinal bolts to break.Injection of water and soil outside segment accelerates rapid loss of sand outside segment ring.When the shield tail subsidence displacement exceeds 0.5 m and the hollowing range exceeds 9 rings,the maximum opening of the ring seam exceeds 65.2 mm,the ellipticity of the segment ring exceeds 46.1‰,which eventually induces the collapse of multiple segment rings.The research results can provide reference for the evaluation of major safety risks induced by shield tail leakage.
万方数据
维普
