Even Arch Tunnel The Karst Segment Construction Mechanical Behavior And The Basal Accumulation Of Deformation Study

With the further development of infrastructure construction, such as the special lines for passenger trains and the highway, more and more tunnels needs in the west karst region. Twin-bored tunnel is widely available because of its unique advantage. The existence of karst makes changes to the structure of the soil around the tunnel, which may reduce the soil strength, and then, kinds of problems are encountered during the construction and operation. Therefore, study on the mechanic state during construction and the accumulated deformation caused by the repeated train load in the karst region has important realistic signification.The karst part of the twin-bored tunnel which located in the entrance of the Baiyunshan, Yichang-Wanzhou railway is studied in this thesis. With the aid of the numerical simulation approach, site monitoring and the simplified method based on the experience formula, the appropriate order of excavation, mechanic state of rock and support system, accumulated deformation caused by repealed train load in karst filling basement were studied. The main contents are as following:1. The appropriate order of single tunnel excavation of the twin-bored tunnel is studied means of 3-d explicit finite difference method. Through comparative research on the rock deformation,rock stress,central division wall deformation,central division wall stress and so on, the conclusion that under such working condition the tunnel which run across the carst region should be excavated with the first priority, were obtained.2. With the aid of the three-dimensional finite element simulation method, the distribution of the rock plastic region,the stress of the supporting system,the deformation and the stress of the central division wall were studied when excavating the main tunnel in the karst region.The results show that the roof and the bottom,the side wall and basement of the tunnel without the karst region are the weak positions which can influence the tunnel stability; During the excavation, the central division wall deflects and twists which cause the middle part of the wall bending to the side without the karst. 3. Using the method of the site monitoring, the inner rock displacement,stress of the supporting system,basement subsidence of the carst region were measured and analyzed, the corresponding changing law concluded.4. With the 3-d explicit finite difference method, dynamical computation of the karst region in the twin-bored tunnel under train load was finished, the displacement and dynamic response of supporting system was also analyzed; according to the results and applying the simplified method based on the experience formula, the accumulated basement deformation law and the subsidence during the operation period were predicted and studied.