Numerical modeling of surface settlements at the transition zone excavated by New Austrian Tunneling Method and Umbrella Arch Method in weak rock

As a result of urbanization all over the world, complicated transportation system have been constructed to supply the need of the public transport. Metro tunnel is the most important effective solution method for public transportation. However, the surface settlement around the metro line in urban areas should be within the allowable limits and it should not damage nearby structures. The tunnel excavation and the support system have to provide a reliable working condition for the workers and the people living along the metro line. Although New Austrian Tunneling Method (NATM) is a very useful method in tunnel excavation, it may be insufficient in weak rock condition. Umbrella Arch Method (UAM) has been recently a viable alternative in various important areas. In this paper, the results of 3-D numerical modeling of surface settlement at the transition zone in Istanbul Metro excavated by NATM and UAM are presented by using a finite difference code called FLAC3D. The results showed that umbrella arch pipe is very effective to minimize the surface settlement. According to the actual measurement result and numerical modeling result, umbrella arch pipe reduced the surface settlement by 71% and 63%, respectively. In addition, the numerical modeling result represented 79.5% of the actual value obtained from in situ for NATM region and 86.0% of in situ value for UAM region.