Investigation of collapseexcavation and support studies on the routeof İzmir metro tunnel(Üçyol-Üçkuyular)

In this study, the mechanisms of collapses occurred in 2009 and 2012, and their economical-practical impacts that took place during the construction of second phase metro route between Üçyol-Üçkuyular districts of Izmir were investigated. The project was planned between the years 2005 and 2014 according the principles of New Austria Tunnel Construction Method (NATM). The route of the Second Phase Izmir Subway between Üçyol-Üçkuyular is 5203.5 m long with five stations. The 47% of the main tunnel passed through Upper Kretase Aged Bornova Philish formations, the 16% Neojen Aged Altındağ Formation and the 37% Yamanlar Volcanite formations constituted the remaining part of the tunnel. The 47% of the tunnel is characterized as a shallow tunnel with weak rock properties. The collapse that occurred during the construction caused delays and cost increases in the project. The sites where collapses took place were modeled using Phase2 (v.7.0) software. The improved alternatives of the excavation support systems are analyzed in this study in order to provide an answer to the question of "Had the project been planned with respect to more adequate support system, would it had been realized in a more productive manner?"