Numerical investigation of mechanized shield tunnels cross-cut

In parts of constructing east-west t lot of line 7 Tehran subway, the excavating machine (EPB-TBM) passes from the top of the Abouzar’s wastewater conveyance tunnel with clear distance of 2.25 m. The FLAC 3D has been used to model this problem and find the deformations and forces of ground and linings. The modeling results show that after excavating subway tunnel, lining of Abouzar tunnel will be moving upward due to the increasing plastic zones and stress relaxation. This rate of displacement induced the internal force more than allowable designed amount in concrete lining of Abouzar tunnel. Generally, excavation a tunnel near another tunnel may lead to significant interaction effects, which mainly dependent on tunnels position relative to each other (parallel or cross), the distance between two tunnels, tunnel dimensions, lining rigidity, stress and boring environment condition as well as the method of tunnel boring. The interaction between adjacent tunnels have been investigated by different researchers using methods such as analytical and empirical, field observation, physical modeling and numerical modeling. In the current project, the tunnel of Tehran metro line 7 passes with a distance of 2.25 meters from the top of the Abuzar tunnel. Because of the nature of three-dimensional problem of interaction between underground spaces, numerical modeling is an appropriate tool for the analysis of these complicated problems. Therefore, FLAC3D software have been used in order to investigate into the interaction analysis. The purpose of modeling is study on stability of support system of Abuzar tunnel during tunnel excavation of Tehran metro line 7. Methodology and Approaches: In this paper, the finite difference method (FDM) is used for modeling and solving the problem. FLAC 3D program which uses FDM was selected in order to study the interaction between the two tunnels, in construction stage. For this purpose, at first Abouzar tunnel modeled and excavated, then impact of stepwise excavating of line 7 Tehran subway on lining system of Abouzar tunnel is investigated numerically. History of Internal forces, bending moments and structural displacement of Abouzar’s tunnel lining have been provided and studied. Engineering recommendations have been proposed in different-leveled intersecting tunnels. Results and Conclusions: The results of modeling show that after excavation of metro tunnel, the support system of Abuzar tunnel will be uplifted because of increasing the plastic zone and stress relaxation. This displacement causes internal forces in Abuzar tunnel lining which are more than allowed values.