By Lynda Myer
Using the 8m diameter Robbins single shield TBM, the excavation process of the second tunnel for Turkey’s Bahçe-Nurdaği railway has been completed.
While the drive of this TBM comprised over than 18km through hard rock to form Turkey’s longest twin tunnels, it completed the first bore of 9.2km in 2020, and broke through in June to finish the second, 9.6km tunnel.
According to Deniz Sahin, TBM chief for contractor Intekar Yapi Turizm Elektrik Insaat San ve Tic Ltd Sti: “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.”
Considering that the geology for both tunnels included incredibly hard and abrasive metasandstone with quartz, with an average of 220MPa (31,900psi) UCS and a Cerchar abrasion value of 3.87 and that the rock is some of the hardest and most abrasive ever measured in Turkey, after its first bore in the difficult ground, the TBM required 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,” added Sahin.
February 2021 was the date of commencing machine’s second bore, whereas its progress was 411m per month.
Sahin also asserted: “During tunneling we performed a normal maintenance program as given in the TBM manual, and the machine had minimum downtime”
Due to providing an economic boost to a region recovering from two devastating earthquakes in February, this twin rail tunnels for owner Turkish State Railways Directorate (TCDD) is important.
Although the location of project site is very close to the intersection of two large active fault zones, the East Anatolian Fault and Dead Sea Fault, after the earthquakes the tunnels were found to have sustained only minor cracking in a few segments.
As a part of the TCDD’s plan to overhaul the railway connection in south-east Turkey by providing a shorter, faster route in one of the country’s busiest railway corridors, this new rail line is slated to provide service between the towns of Bahçe and Nurdagi.
