Investigation of effects of distance between tunnels, depth and excavation stages on surface settlement in twin tunnels

In recent years, with the relocate of city rail system to the underground, also highways are started to built up in underground especially in high traffic jam areas. In cities, underground transportation has many advantages. On the other hand, it brings a subject that can affect the overground construction such as surface settlement. In future, it would be occur that, the necessity of construction of side by side tunnels which provide different infrastructure. That situtation will make surface settlement even more critical. Therefore in this study, it is aimed that; surface settlement that will be occur at two existing building located above the tunnels (Building A – Building B) which are affected by twin tunnels construct in large span with New Austrian Tunneling Method (NATM), will be investigated through some parameters like space between tunnels (1D, 2D, 3D), depth of the tunnels (1H, 2H, 3H and 5H) and number of excavation stage (2, 3, 4, 5, 6, 7, 8, 9 stages). Parameters will be evaluated by 2D numerical modelling programme (Phase2) in this study. Result of that study, it is determined that; when depth of tunnels (1H….5H) which are investigated with modelling increase, settlement amount which will be occur at buildings also increase. On the other hand, with the rising of the space between tunnels (1D…3D) there is a decreasing at amount of settlement. In tunnels which construct in different depth and distance, with the increasing of excavation stage 2 to 9, it is determined that, the settlement amount was decrease until stage 4 and than it started to increase again and it stabilized for last 3 stage. It is also ascertained that when comparison of calculation the model with building loaded and unloaded, there is an increase at settlement amount in shallow tunnels in loaded model and when the depth of tunnels increase, settlement amounts come close to each other.