Distance improvement between non-level crossing tunnels by numerical method - case study of Tehran crossing subways line 6 and 7

In non-level crossing tunnels, optimization of distance between tunnels is one of the most important factors. In theory, the more distance between the tunnels, the more appropriate it is, but in terms of operation, the closer the tunnels are to each other and to the surface, as long as there is no damage to other subsurface structures, the more suitable it is. The main objective of this study is to optimize and determine the minimum allowable distance in intersecting of non-level tunnels. To achieve this objective, three dimensional numerical models were developed by MIDAS GTS NX (a finite element numerical analysis software) and the geometry and the initial distance of tunnels were considered according to the basis of information received from the intersection of Tehran subway tunnels, no 6 and no 7. In this research, two main scenarios have been examined: in the first, a deep tunnel getting closer to a shallow tunnel and in the second, a shallow tunnel to a deep tunnel. In each scenario, several numerical models were developed where each tunnel get closer to each other for 40 cm. This process continued until ground subsidence or strain in the models exceed the permissible level and where there is no need to change any of designed properties of the lining of the tunnels. The results show the second scenario is more suitable, especially in the case of ground subsidence. In this scenario the distance between the tunnels can be reduced to 80 cm without any change in the structural parameters of lining of both tunnels. The results of this study can be considered in designing and excavating of non-level crossing tunnels.
Summary First, all the assumptions considered is intended. Then, literatures were reviewed and the project is introduced precisely. Finally the 3D model by finite element software was done, and improvement of distance between tunnels in two scenarios was investigated. At last after investigating a different parameters the best distance between tunnels has been chosen.
Introduction This research has been done by numerical finite element method. According to subway networks development, constructing the underground structures has always been a challenge. In this research one of the most important challenges (improvement the distance between tunnels) has been answered.
Methodology and Approaches Because there are a various factors affecting the interaction of non-level crossing tunnels, so the best method for investigating these problems, are numerical models. And because the medium that tunnels are constructed in, is continuum, the finite element method for solving the problem is used. Due to 3D nature of the problem, 3D modeling is used.
Results and Conclusions As mentioned before, the best scenario is to move the shallow tunnel downward toward the deep tunnel.