Numerical Investigation On The Longitudinal Flexural Behavior Of The Two-span Box Metro Tunnel

Metro box tunnel is applied for shallow tunnel in city, which is one of the common tunnel structure in metro tunnel. Because of large dimension and special section, the box tunnel flexural behavior can not be study by the elementary beam theory simply. Besides longitudinal reinforcement of the box tunnel is placed by detailing requirements, however, in bridge engineering, longitudinal reinforcement is placed by calculation, and sometimes the bridge may use prestressed steel if in need, so the flexural behavior of box tunnel is different from bridge’s. When the box tunnel takes place differential settlement arranged along the longitudinal direction of the tunnel, the crack will occur on the outside surface of the tunnel. Because the tunnel is covered in the soil, it is hard to judge the safety performance of the tunnel. But it is rarely to see the study about longitudinal deformation of the box tunnel especially the structure actual stress after the tunnel cracks. Therefore research on the longitudinal flexural behavior of the box metro tunnel and how to forecast and judge the tunnel’s safety performance by using the monitoring data about the tunnel’s deformation will be great importance in engineering practice.For this purpose, depending on one two-span box tunnel, numerical analysis is adopted to study longitudinal flexural behavior and the relationship between depth of crack to radius of curvature of longitudinal deformation in this passage. And then, control value of longitudinal deformation is obtained to evaluate the secure state of the box tunnel based on monitoring data in this project.The primary work in this paper as follows:(1) By considering the nonlinearity of concrete, 60 m two-span box tunnel model is established in MIDAS/FEA to study the longitudinal flexural behavior and to lay the foundation for follow analysis based on the design information of the box tunnel.(2) By means of the numerical analysis, the passage preliminary studies the longitudinal flexural behavior of the box tunnel which happens damage overall process because of the vertical loading and horizontal loading, including not only the stress distribution, but also the strain distribution and the laws of crack developing.(3) According to the tunnel state and monitoring data, the paper studies the relationship between the depth of crack and the longitudinal curvature radius, to obtain the control value of longitudinal deformation in different depth of crack. Finally, the control value of longitudinal deformation is used to estimate the safe state of the two-span box tunnel.