ASSESSING THE EFFECTIVENESS OF EXCAVATING LARGE SECTION TUNNELS FOR SUBWAY STATION CONSTRUCTION (CASE STUDY: TEHRAN SUBWAY LINE 7)

One important factor in the urban areas is the selection of suitable excavation method which has a significant effect on the stability of the structures surrounding the tunnel during excavation, surface settlement induced by excavation and long-term stability of the excavated space (subway station).In this paper, considering the geotechnical properties of the ground and geometry of the investigated station, three methods of pre-supporting concrete arch, side drifts and German method are evaluated for the execution of underground stations for space stability, tunnel peripheral displacements and ground surface settlement due to excavation operations. In other words, the main objective of this study is to evaluate the application of different excavation methods (with the inclusion of support structure or not) on the peripheral tunnel deformations, ground surface settlement and other parameters and finally, to propose the appropriate excavation method for the desired station. Numerical modeling of different execution methods of the desired space is performed using finite element method. Maximum surface ground settlement is occurred by applying side drifts method while the minimum value is occurred by applying pre-supporting concrete arc method.