Second bore completed for tunnel on Turkey’s Bahçe-Nurdaği Railway

The tunnel is the second bore driven by the 8m diameter Robbins single shield TBM through challenging geology by contractor İntekar Yapı Turizm Elektrik İnşaat San on the Turkish State Railways Directorate (TCDD) project.

The tunnel is the longest on the new rail route, which is part of the larger 286 km railway construction project between Mersin city and Baspinar station, passing through Adana, Toprakkale, Bahce and Nurdagi.

The TBM started driving the second bore in February 2021 but experience gained on the ground conditions during the first 9.2km drive for the project, which was completed in 2020, aided the work. Geology in the second tunnel was comparable to the first, including incredibly hard and abrasive metasandstone with quartz, with an average of 220MPa compressive strength and a Cerchar abrasion value of 3.87. The rock has some of the most extreme hardness and abrasiveness ever measured in Turkey.

As well as challenging ground conditions the tunnelling work was also in progress when Turkey suffered from two earthquakes with magnitudes of 7.8 and 7.6 in February 2023. The project site is located very close to the intersection of two large active fault zones, the East Anatolian Fault and Dead Sea Fault. The tunnels were inspected after the event and were found to have sustained only minor cracking in a few segments.

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