Crossover TBM breakthrough a first for Albania 24 May 2018

On 3 May 2018, a 6.2m diameter Robbins Crossover XRE TBM broke through into an underground chamber to complete the first TBM-driven tunnel in Albania. The TBM, operated by contractor Limak, was also the first crossover machine to operate in Europe, boring through geology including ophiolite, sandstone, breccia and siltstone flysch to complete the 6.7km long Moglicë headrace of the Devoll hydropower project.

Field Service personnel assisted contractor Limak

“The cutterhead and cutters have achieved outstanding performance,” said Engin Gur, TBM Manager for Limak. The TBM achieved rates as high as 648m per month in April 2018, and 37.4m in one day. The crossover TBM did not encounter high-pressure water and was thus used in hard rock double shield mode throughout tunneling.

“The TBM performed well, as did a Robbins-supplied adit conveyor that operated in a 180-degree continuous curve,” said Max Walker, Robbins Field Service Superintendent. Several field service personnel remained onsite throughout operation of the TBM to provide guidance and trouble-shooting.

The machine was launched in November 2016 following assembly at the jobsite. The crew increased production slowly over the next 230m. “Ground conditions were good and we did very few cutter changes. Only 20 cutters were used during the bore,” said Walker. Two-stage grouting was carried out as the TBM bored and lined the tunnel in three 8-hour shifts/day. “The personnel on the project created a friendly work environment and made it enjoyable to come to work each day,” added Walker.

Completion of the first TBM-driven tunnel in Albania

While the TBM did not need to be sealed, the machine design took into account a predicted high risk of water inflows. The XRE machine used a belt conveyor, not a screw conveyor, for muck removal, as the muck chute needed to be able to be sealed off in the case of an inrush of water. The bulkhead was designed with a large sealing gate just above the belt conveyor. These pressure-relieving gates could also be used in a semi-EPB mode. As the pressure built in the excavation chamber, the gate would then be forced open by the pressure and material would spill onto the belt. As the pressure lowered, the gates would then automatically close, sealing off the chamber once again. In extreme cases, the gates could be sealed and the probe and grouting drills could be used to drill, grout, and seal off any excessive water inflow. In addition, the gripper shoes and inner telescopic shield were equipped with inflatable seals to further protect against inrushes of water.

Beakthrough of the 6.2m Robbins Crossover TBM

With the TBM drive now complete, grouting will continue behind the one-pass segmental lining. The tunnel is expected to become operational by May 2019.

The Moglicë hydropower project is part of a build-own-operate-transfer (BOOT) scheme to construct two hydropower plants along the Devoll River. The project is owned by the Norwegian power company Statkraft AS. The completed project will have an installed capacity of 242 MW and will increase electricity production in Albania by 17%.