Effects of Round Length and Excavation Phases in the NATM Induced Surface Settlement- Line 4 of Tehran Metro

In order to control settlement induced by tunneling in urban area, effective parameters in the excavation procedures should be determined with respect to the geotechnical properties and construction methods. In NATM, round length and sequence of excavation phases are the significant parameters that affect on tunneling economically and technically. These two factors have a great relationship with time and cost of tunneling projects. Therefore, determination the optimum amount of those parameters is the main challenge in such projects. In this paper, the effects of round length and excavation phases on surface settlement in line four of Tehran metro, still in construction, were evaluated. To do the analyses, a three-dimensional finite element package was used to simulate the tunnel operations for different number of round length. The results showed that, regarding to the geotechnical properties and tunnel dimensions in line four areas, the round length was determined conservatively. Therefore, it can be suggested that in order to improve efficiency, the round length is determined 2 and 3 meter in upper and lower parts of tunnel cross-section, respectively.