investigating the effect of twin tunnels excavation sequence on the surface subsidence: isfahan subway line 2 as a case study

During the tunnel construction surface subsidence is very probable. the applied method to excavate the twin tunnels of isfahan subway line 2, iran is epb tunneling. therefore, in this research, applying 3d numerical simulation, geotechnical characteristics of soil layers and construction parameters of the twin tunnels, the surface subsidence was analyzed. three scenarios were assumed for the sequence of twin tunnels excavation and the subsidence profile variation were examined in each scenario. in the first scenario, the distance between the working face of tunnels is more than 3 times of tunnel diameter (3d) and for the second and third scenarios, the distance is 0.5d and 1d, respectively. according to the results, the total subsidence was not affected by the distance between working faces of twin tunnels, and it increased only 3 percent by increasing the distance. however, the rate of subsidence occurrence was increased by reducing the distance between working faces.