Resilient TBM completes tough drive in Turkey 27 Aug 2020

It was a jubilant ceremony that marked completion of the first TBM drive for the arduous Bahçe-Nurdaği high speed railway route in Turkey in July. The 8m diameter single shield Robbins TBM completed the 8.9km drive through some of the hardest and most abrasive rock ever encountered in the country ranging from abrasive, interbedded sandstone and mudstone with quartzite veins, to highly weathered shale and dolomitic limestone. Rock strengths were recorded at UCS 136 to 327 MPa (19,700 to 47,400 psi). The TBM teams also had to cope with water ingress with fines anticipated in the expected fault lines and shear zones affected by the East Anatolian Fault.

TBM bored through some of the hardest rock in Turkey at up to 327 MPa UCS

“The TBM crews acted rapidly to conditions and were well organized to overcome the challenges,” said Deniz Sahin, TBM Chief for contractor Intekar Yapi A.Ş. “In fault zones water inflows of 10 liters/sec on average were managed by the dewatering system; we encountered excessive material flow and the TBM had to be stopped while ground had to be stabilized with chemical injections and the cutterhead was cleaned out,” said Sahin. “On three occasions the TBM became stuck in different fault zones, which we got through by building bypass tunnels.”

The majority of tunnelling, said Sahin, was in metasandstone with quartz, with an average of 220 MPa UCS and a Cerchar abrasion value of 3.87. In such regions, the 19in back-loading disc cutters had to be changed frequently and there was high vibration. Despite the challenges, Sahin was impressed by the overall capacity of the TBM. “The Robbins single shield TBM motor power, hydraulic power and cutterhead torque were quite strong, the secondary ventilation and air suction systems inside the TBM were powerful and the connections between the gantries, scaffolding systems, walkways and working areas were good.”

Single shield TBM erected a segmental lining

The TBM ultimately achieved up to 456m (1,500ft) per month, a result achieved in conjunction with a Robbins continuous conveyor muck hauling system. “The electric motor and gearbox capacity of the conveyor system was quite enough for a 10km tunnel and we had no failure on them. The conveyor performed well even under excess material and the whole system was quite robust,” said Sahin.

Project owner, Turkish State Railways Directorate, is aiming to overhaul the railway connection in southeastern Turkey by providing a shorter, faster route in one of the busiest railway corridors in the country. The new rail line between the towns of Bahçe and Nurdağı includes twin 9.8km tunnels that are being excavated 850m by both NATM and 8.9km with TBM.