Subway tunnels are an essential part of urban sustainable development in this era. They are mostly excavated in low depth and one of their most apprehensive engineering challenges is the resulting surface subsidence. So, understanding the factors that play role in surface subsidence and forecasting the size and mechanisms of subsidence, and in some cases reducing the fatal effects of subsidence on surface buildings and structures are the most important concerns in developing these projects.

In this study, tunnel-induced surface subsidence in Tehran subway line 6, as a case study, was modeled and investigated. This project is the last part of the Tehran Line 6 subway development. It passes under the old buildings and structures of Ray City in southern Tehran. To evaluate the subsidence, the data of soil layers of the site, the specifications of the tunnel, and its supporting elements were modeled in FLAC 2d soft. Then, the amount of subsidence near the last station of this line, the eastern yard of holly shrine of Abdulaziz was provisioned.

The study showed despite the weak quality of soil layers, surface subsidence is in a favorable range and this is because of the medium diameter of the tunnel, the method of digging, and the good quality of the supporting system. The study also showed that the E modulus of soil is more responsible for surface subsidence than the cohesion of soil is.