Numerical investigation of the interaction of adjacent tunnels - Influence of excavation sequence (Case: East access tunnels of Iran Mall)

Today, due to the development of cities and the lack of space on the ground, as well as the increase in traffic problems, has resulted in increase of the need to build underground spaces to develop urban transportation systems. This study also examines the effect of the sequence of excavation of adjacent tunnels. The case study used in this study is the access tunnels of Iran Mall collection. For numerical modeling, the Midas GTS finite element software is used in 3D mode, and the effect of the sequence of tunnel excavation on the surface settlement and the internal forces of the structures of these tunnels have been investigated. The results showed that successive excavation of adjacent tunnels resulted in lower settlement values ​​than the simultaneous excavation of tunnels and had a significant effect on the temporary support of the tunnels in the values ​​of forces and bending moment. Finally, in order to validate the results of the surface settlement obtained from the numerical model, the monitoring data of the surface settlement of Iran Mall project were used, it was determined that the numerical results are close to the monitoring data.   Summary In this study, the effect of the sequence of adjacent tunnel excavation was investigated and the study sites of access tunnels of Iran Mall collection located in 22nd district of Tehran were studied. In this study, Midas GTS finite element software was used for design and simulation in three dimensions and the effect of tunnel excavation sequence on axial and shear forces and bending moment on the temporary support of these tunnels and surface settlement were investigated.   Introduction Evaluating the interaction between underground spaces with each other and also between these spaces with existing structures and providing appropriate solutions is one of the most important topics of tunneling in urban environments, which is of particular importance. In some cases, it is necessary to excavate tunnels in the vicinity of each other, which leads to significant impact effects. These interactions depend on the distance between the tunnels, the size of the tunnel cross section, the rigidity of the support system, and the method used to excavate the tunnels.   Methodology and Approaches Since numerical methods can be used to model the tunnel in different and complex conditions of soil mass and rock, and the stresses and displacements created around the tunnels as well as the forces and bending moment on the tunnel support system can be predicted with high accuracy. This research is designed and simulated using 3D Midas GTS finite element software.   Results and Conclusions The results showed that successive excavation of adjacent tunnels resulted in lower settlement values at the ground level than simultaneous excavation of tunnels and had a significant effect on the temporary support of the tunnels in the values of forces and bending moment. Finally, in order to validate the results of the surface settlement from the numerical model, the monitoring data of the surface settlement of Iran Mall project were used, it was determined that the numerical results are close to the monitoring data.