Train induced tunnel-structure interaction analysis using the scaled boundary method

In this paper, train induced tunnel-structure interaction problem is analyzed using the coupled scaled boundary finite element (SBFE)-finite element (FE) method. Scaled boundary method is a relatively novel approach, which enables us to model bounded and unbounded domains accurately. Effects of adjacent buildings and effects of double tunnel on the train-induced vibrations are evaluated using this method. Construction and development of underground transportation lines like metro tunnels in urban areas is a suitable choice to reduce volume of the traffics especially in large cities. Train induced vibrations in these tunnels can affect adjacent structures. Train induced vibrations can make some damages to the adjacent structures and these structures can also affect vibrations of the tunnels. To analyze train induced vibration problems numerically, a special numerical method should be used to model unbounded soil media. The numerical methods, used for this purpose, are grouped in two classes of global and local. Local methods cannot model radiation-damping effect of unbounded soil media completely and accurately. SBFE method is a global approach with semi analytical formulation, which can model unbounded media precisely. In this paper, this novel approach is used to analyze tunnel-structure interaction problem. Methodology and Approaches: In this paper, the coupled SBFE-FE method is used to model train-induced vibrations in tunnels. The semi analytical SBFE method is used to model unbounded soil media where conventional finite element method is used to model near field soil media and contained structures. A MATLAB code, based on the coupled SBFE-FE method, has been developed in this research work. The written code is verified by comparing its results with the results of the finite element-boundary element method mentioned in the available published papers. As train induced vibrations cannot make large displacements, linear elastic behavior is considered for both soil and structures. Results and It is shown that the buildings in the vicinity of train induced tunnels can make an increment on displacement time history of tunnels and it can reduce radiation-damping effect of the considered soil media. In the case of a double tunnel, it is also shown that adjacent tunnel can increase horizontal dynamic stiffness of the trapped soil between two tunnels. Furthermore, it is demonstrated that simultaneous movement of the second train can magnify vertical displacements of the domain. In the case of the horizontal displacement, it is indicated that displacements of the domain between two tunnels are decreased but displacements of the other areas are magnified.