June 2023 saw an 8m diameter Robbins Single Shield complete its second tunnel on Turkey’s Bahçe-Nurdaği Railway. The machine completed 9.6km of tunnelling, adding on to the 9.2km it completed in its initial railway tunnel in 2020 – for a total of more than 18km bored.
“We are very proud to complete this tunnel in difficult rock formations with our excellent team by utilizing an extremely powerful and strong Robbins Single Shield TBM,” said Deniz Şahin, TBM Chief for contractor İntekar Yapı Turizm Elektrik İnşaat San. ve Tic. Ltd. Şti.
Geology in the second tunnel was comparable to the first, including incredibly hard and abrasive metasandstone with quartz, with an average of 220MPa (31,900 psi) UCS and a Cerchar abrasion value of 3.87. The rock has some of the most extreme hardness and abrasiveness ever measured in Turkey.
After its first bore in the difficult ground, the machine required some inspection and repairs. “The biggest repairs we undertook with Robbins Field Service technicians were the main bearing seal change and checking and repairing of the TBM before launching it on the twin tunnel after the completion of the first tunnel. Both operations were completed in a short time due to good planning with Robbins technicians,” said Şahin.
The machine began its second bore in February 2021, achieving a best monthly advance rate of 411m. “During tunnelling we performed a normal maintenance program as given in the TBM manual, and the machine had minimum downtime, which shows the durability of Robbins TBM in very hard and abrasive rock,” said Şahin.
The twin rail tunnels, for owner Turkish State Railways Directorate (TCDD), will provide an economic boost to a region recovering from two consecutively devastating earthquakes with magnitudes of 7.8 and 7.6 that occurred in February 2023. The project site is located very close to the intersection of two large active fault zones, the East Anatolian Fault (EAF) and Dead Sea Fault (DSF). The tunnels were inspected after the event and were found to have sustained only minor cracking in a few segments. The new rail line will provide service between the towns of Bahçe and Nurdağı, and is part of the TCDD’s plan to overhaul the railway connection in southeastern Turkey by providing a shorter, faster route in one of the country’s busiest railway corridors.