Excavation of Turkey’s longest water tunnel came to an end in December 2018. To get there, a 5.56 m diameter Robbins Crossover (XRE) TBM and the contractor JV of Kolin/Limak had to overcome dozens of major fault zones and water pressures up to 26 bar. After the breakthrough the completed national priority water line was scheduled to go into operation in March 2019.
The 31.6 km long Gerede Water Transmission Tunnel is an urgently needed project due to severe and chronic droughts in the capital city Ankara. Its final leg, a 9.0 km section of extremely difficult ground including sandstone agglomerate, limestone and tuff, was just one section in the middle of a tunnel widely considered to be the most challenging ever driven by TBMs in Turkey. The Kolin/Limak JV called in the Robbins XRE Dual-Mode TBM to complete the tunnel, which was at a standstill. The three Double Shield TBMs that had been excavating the tunnel had encountered incredibly difficult geology including massive inrushes of mud and water.
The Crossover machine was assembled underground in spring 2016 and began boring in summer. Within the first 50 m of boring it had successfully passed through the section that buried the original Double Shield TBM. The machine was required to be used in EPB mode as it encountered water pressures up to 26 bars, alluvium, flowing materials, clay and a total of 48 fault zones. Together with the difficult geological conditions the travel time to reach the TBM within the tunnel had effects on TBM performance. Despite this constraint, the tunnel excavation achieved a best day of 29.4 m, best week of 134.6 m and a best month of 484 m.