Contents lists available at ScienceDirect Tunnelling and Underground Space Technology journal homepage: www.elsevier.com/locate/tust Assessment of the factors affecting the advance rate of the Tunnel Gerede, the longest and one of the most problematic water transmission tunnels of Turkey Murat Alp a, ⁎ , Ahmet Apaydin b a Fifth Regional Directorate of State Hydraulic Works (DSI), Turkey b Civil Engineering Department, Giresun University, 28200 Giresun, Turkey ARTICLE INFO Keywords: Tunnel Advance rate Water ingress Turkey ABSTRACT The Gerede Tunnel, with approximately 31.6 km in length, is Turkey's longest water transmission tunnel as of 2018. The tunnel will transmit the water from the Gerede River to the Camlidere reservoir, providing drinking water to Ankara. The tunnel is divided into three sections as Umitkoy, Havullu and Camlidere, and excavations started in each section with separate tunnel boring machine (TBM-1, TBM-2 and TBM-3 respectively). The ex- cavation, started in 2012, completed within 508 days without significant problem in the Umitkoy section having 9588 m length. In Havullu and Camlidere sections, TBMs were blocked due to high pressure water and also material ingression. This caused the progress in the tunnel to be delayed repeatedly. In addition, the harsh conditions forced to be drilled upwards after 6061th m in the Havullu section, and to be drive with another type of TBM after 7235 m in the Camlidere section. Finally, the last 8821 m was completed with the EPB machine. The daily average advance rates of TBM-1, TBM-2 and TBM-3 are respectively 18.77 m, 6.13 m and 9.37 m. For the modified EPB type TBM-4, which takes over the task of TBM-3 and TBM-2 in the last 8821 m, the advance rate is 9.56 m/day. According to the analysis, the tectonic structure, hydrogeology and TBM type are the most effective parameters on the advance rate of the Gerede Tunnel. Experiences obtained from the tunnel show that geological-tectonic-hydrogeological studies should be carried out in detail in project phase and TBM selection according to these conditions, particularly against collapse and high pressure water ingress, have vital im- portance. 1. Introduction In recent years, long tunnels are constructed for highway, railway, water transmission and hydroelectric purposes in many parts of the world. (Matsuo, 1986; Kassana and Nilsen, 2003; Shang et al., 2006; Holmøy, 2008). Most of the times in the tunnels drilled with the Tunnel Boring Machine (TBM), often have frequent or long stoppages due to some problems (such as high pressure water ingression and material flow), therefore the progressive performance decreases. By a majority, the tunnel cannot be completed in the predicted or promised period in the tender contract. Detailed geological research and well documented reporting in planning and project phase have vital importance for de- termining the most appropriate route, selection the most appropriate TBM type, predicting the possible problems that may be encountered during the progression and minimizing the risk of unpleasant surprises. The most important problem for submerged tunnels is the ingression of high pressure water to the tunnel (Jun and Xiangyu, 1982, Tsenga et al., 2001, Turkmen and Ozuguzel, 2003, Panthi and Nilsen, 2005, Holmøy, 2008). When passing through loose cemented or non-ce- mented formations with fault breccias, it is possible to be exposed to collapses and mud flow. Since the pressure and quantity of the water coming into the tunnel is dependent on hydraulic head and hydraulic conductivity, it is crucial to know, lithologic and tectonic features along with the hydrogeological structure which is under their control, in advance. High hydraulic head with weak zones above the tunnel cause instability and the ingression of intense water and material to the tunnel. These events, which may cause the TBM to be jammed or even damaged, may result in a delay in completion of construction. In fact, there are examples where the TBM is completely out of use and the remaining part has to be completed by a conventional method (Lui and Chang, 2005; Lin and Yu, 2005). TBM selection is an important factor affecting the advance rate in https://doi.org/10.1016/j.tust.2019.04.001 Received 13 November 2018; Received in revised form 1 April 2019; Accepted 6 April 2019 ⁎ Corresponding author. E-mail address: muratalp@dsi.gov.tr (M. Alp). Tunnelling and Underground Space Technology 89 (2019) 157–169 0886-7798/ © 2019 Published by Elsevier Ltd. T