Study On The Collapse Mechanism Caused By The Combination Of Shield Tunnel And Connecting Passage

Shield tunneling method has the advantages of fast construction speed and small environmental disturbance,and has become the main choice of urban underground rail transit construction.Considering the needs of disaster prevention,mitigation and rescue evacuation for long-distance Metro tunnels,it is generally necessary to build a connecting passage in the middle of each tunnel.Connecting passage is a key project in metro tunnel construction,which directly affects the safety of the whole structure and rescue ability in case of accidents.Especially,the connecting structure between connecting passage and main tunnel of metro is likely to be damaged and destroyed under various external loads,which leads to the collapse of connecting passage and main tunnel.This paper focuses on the analysis of the stress and deformation of the connecting structure between the connecting passage and the main subway tunnel,and further studies on the collapse mechanism of the shield tunnel.A three-dimensional numerical model comprising of the main tunnels and the connecting passage is established by ABAQUS.Geometric nonlinearity and material nonlinearity are introduced into the model.The local stiffness reduction method is used to consider the effect of the ring head on the overall structural stiffness of the tunnel,and the boundary effect is eliminated by extending the length of the main tunnel.According to the actual engineering situation,different stratum conditions are set up in the middle and both sides of the main tunnel including the connecting passage to highlight the stress and deformation characteristics of the weak joint between the connecting passage and the main tunnel.The influence of external earth pressure and high-water pressure on structure is mainly considered in the analysis process.Analysis of the model in different geological strata and soil-water load conditions is performed and calculation results presented,the following conclusions are drawn: when the external water pressure increases,the stress and deformation of the connecting structure between the connecting passage and the main tunnel increase;when the stratum conditions of the connecting passage area are different from those of other areas of the main tunnel,the connecting structure between the connecting passage and the main tunnel is more prone to local damage;The structural stiffness of the connecting part can be improved as an important measure to ensure the safety of the connecting passage and the main tunnel.Compared with the traditional reinforced concrete segment,the composite segment has higher strength and stiffness,so it can be used to replace the traditional segment in the construction of the connecting part of the main tunnel and the connecting passage.