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  Cost Comparison of NATM and Umbrella Arch Method

  The first construction of Istanbul metro network was started in 1992 and opened to public in October 2000. Uskudar-Umraniye-Cekmekoy metro project (UUCMP) is a part of this network and subjects this study. The project started on March 2012 and is still under construction. The project owner is Istanbul Metropolitan Municipality and contractor is Dogus Construction Corporation. UUCMP will integrate with Marmaray Undersea Metro Project in Uskudar station. UUCMP has total 20 km long main line tunnel and 16 stations (Fig. 1). At all tunnel project, especially at metro tunnel excavations, it is important to control of deformations observed before and after excavation, causing damages to the surface and subsurface structures. To ensure this, in tunnel excavations in soft soils and weak rocks, special reinforcement techniques such as umbrella arch method (UAM) is commonly used in order to secure the stability of tunnel (Ocak, 2008). Selection of UAM or NATM is related to some factors. These factors are cost comparison of NATM and UAM, allowable deformations, quality of rock or soil, application time of NATM and UAM, possibility of skilled worker and etc. Main line tunnels have been excavated using by 4 tunnel boring machines in UUCMP. But other tunnels except main line tunnels have been excavated using by new Austrian tunnelling method (NATM) in UUCMP and other metro project in Istanbul. But using of only NATM in weak rock and soil conditions not sufficient. Therefore, to controlling of surface and subsurface deformations in weak rocks and soils conditions, in addition to NATM, UAM has been used in UUCMP. In this study, cost of NATM and UAM are compared in sensitive regions. Geology in study region is composed of mudstone, claystone, limestone, sandstone. As a result of this study, it was found out that construction cost of UAM is 7.305,01 €/m and NATM is 3.472,64 €/m. In shortly, UAM is 2.1 times expensive than NATM.

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