Numerical modeling of surface settlements at the transition zone excavated by New Austrian Tunneling Method and Umbrella
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ORIGINAL PAPER
Numerical modeling of surface settlements at the transition zone excavated by New Austrian Tunneling Method and Umbrella Arch Method in weak rock Nazmi Erhan Yasitli
Received: 5 December 2011 / Accepted: 24 January 2012 # Saudi Society for Geosciences 2012
Abstract 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. Keywords Surface settlement . NATM . UAM . Numerical modeling . FLAC3D
N. E. Yasitli (*) Department of Mining Engineering, Aksaray University, Aksaray, Turkey e-mail: [email protected]
Introduction The metro tunnel for transport is considered as a sign of civilization in urban areas. Objective of the metro line construction is not only to mobilize people within the city but also to make the city life more livable. The metropolitan city of Istanbul is Turkey’s largest financial and industrial center. Present transportation system in Istanbul could not be sufficient due to the increasing population and new transportation projects preferably located in underground must be developed. Therefore, metro tunnel project is designed as an effective solution for transportation in Istanbul. The southern extension of the Metro line from Taksim to Yenikapi, which cross the Golden Horn on a bridge and underground through the historic peninsula, has thus far been completed up to the Sishane Station in Beyoglu, which also entered service on January 30, 2009. The TaksimYenikapı extension will be 5.2 km long, with four stations named Sishane, Unkapani, Sehzadebasi, and Yenikapi. Sishane, Yenikapi, and Sehzadebasi station are constructed by cut and cover method. Unkapani station will be located on the cable-stayed bridge named Golden Horn Metro Crossing Bridge. It will intersect with the
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