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Record-Setting Large Diameter Mixed Ground Tunneling in Turkey: The Eşme-Salihli Railway Tunnel

Large diameter tunneling has historically been seen as a challenge. Add into the equation mixed ground conditions, and it becomes a task that may seem insurmountable. How-ever, a recently completed tunnel in Turkey is a flagbearer for changing the mindset towards these challenging tunneling scenarios that are becoming more frequent. A 13.77 m diameter mixed ground Rock/EPB TBM bored the Eşme-Salihli Railway Tunnel at rates of up to 721.8 m in one month, making it the fastest TBM ever recorded over 13 m in diameter. The machine began its bore in altered gneiss, then passed through mélange consisting of gneiss, sandstone, claystone, mudstone, quartz, and silt. By the end of the bore the machine was excavating in mainly mudstone. Core drillings were taken every 200 m prior to boring.

In this paper, we detail the project as well as analyze factors contributing to the fast advance rates. The factors include TBM choice and system design, ground conditions, TBM utilization rates and downtimes, as well as maintenance practices, crew expertise and technical support, all of which have a part to play in the overall advance rates and successful outcome. Recommendations are made as to best practices in order to achieve good advance rates on similar large diameter, mixed ground tunnels.

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