| Land subsidence is an environmental geological disaster caused by excessively pumping groundwater,resulting in a slow and uneven reduction of ground elevation.It is widely distributed in major cities in China.According to incomplete statistics,there are more than 50 cities with land subsidence disasters in China.In recent years,with the acceleration of the process of urbanization in China,the construction of urban rail transit develops rapidly and the construction of urban rail transit inevitably encounters the problem of land subsidence and geological disasters.The intensification of uneven land subsidence will lead to the longitudinal deformation of subway tunnels,which will lead to cracks in tunnel structures,secondary disasters such as water leakage and sand leakage,and will eventually threaten the safe operation of urban rail transit.Therefore,land subsidence has become one of the major engineering geological problems that seriously restricts the construction and safe operation of urban rail transit in China.This paper takes Xi'an Metro Tunnel as a research background through the land subsidence area,and clears the basic characteristics of land subsidence along the Xi'an Metro on the basis of the investigation of land subsidence in Xi'an.Based on theoretical analysis and finite element numerical simulation,the ground settlement law under the ground settlement environment and its influence mechanism on the longitudinal deformation of metro tunnel structure are systematically studied.The main conclusions and results are as follows:(1)The basic laws and activity characteristics of the land subsidence area along the Xi'an Metro have been ascertained,the future development trend of land subsidence along the subway line has been analyzed,and the maximum settlement of land subsidence under extreme conditions has been predicted.(2)Analyze the groundwater overdrawing mechanism caused by overdrawing groundwater.Based on the Mindlin displacement solution of elastic semi-infinite space,quantify the relationship between surface settlement displacement and soil settlement displacement in a certain depth,and reveal the ground settlement under ground settlement environment and the spatial distribution pattern.(3)The mechanics and deformation modes of the tunnel deformation under ground settlement are clarified.Based on the theory of Vlastov foundation elastic foundation beam,a theoretical analytical model of the interaction between land subsidence and tunnel deformation is established,and the longitudinal structure of the tunnel under the action of ground settlement is analyzed.The characteristics of subsidence deformation and internal forces of structures and the intrinsic link between the width of the sedimentation tank and the internal force of the tunnel structure are discussed.At the same time,the empirical formula of the ground settlement and the maximum bending moment of the tunnel in the land subsidence environment is given by the normalization method.(4)Based on the finite element theory,a three-dimensional numerical model of the interaction between land subsidence and tunnel deformation is established,and the tunnel response law under ground subsidence is numerically simulated.The rationality and applicability of the theoretical analytical model are verified by the longitudinal deformation characteristics of the tunnel.The response characteristics of land subsidence to the internal force and strain of the longitudinal structure of the subway tunnel are analyzed. |
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