Multiple fault zones and groundwater pressures of up to 23 bars were some of the challenging ground conditions that had to be overcome during the drive of the Gerede Water Transmission Tunnel which has just achieved breakthrough.
Robbins, which supplied the successful tunnel boring machine (TBM) to main contracting joint venture Kolin Limak, on the project said that the project was probably one of the most demanding tunnelling projects ever undertaken in Turkey.
The project for the State Water Department of Turkey started in 2010 and originally used three double shield earth pressure balance TBMs from Herrenknecht but two became irretrievably stuck following massive inflows of mud and debris. The Robbins Crossover XRE TBM was launched to drive the final 9km section of the 31.6km water supply tunnel that will overcome draught issues in the capital city Ankara.
Concerns over the ground conditions were known at the outset of tunnelling with the route passing through ground influenced by the Anatolian Fault Zone and ground investigation showing a mix of volcanic rock including tuff, basalt, and breccia, giving way to sedimentary formations like sandstone, shale, and limestone, all punctuated by fault zones that contained clay and alluvium.
The Robbins TBM was launched in November 2016 and has just completed the drive.