On Nov. 21, 2013 a cutterhead turning ceremony and champagne celebration marked the return of TBMs to Norway. The 7.2-m (23.6 ft) Robbins Main Beam Machine, dubbed “Iron-Erna” after the country’s Prime Minister, Erna Solberg, will bore sections of the Røssåga Hydroelectric Project.
Attendees of the ceremony included the founder of contractor Leonhard Nilsen & Sønner (LNS), Malvin Nilsen, as well as officials from project owner Statkraft and Robbins Field Service personnel. “I am most proud that LNS has been able to bring TBMs back to Norway after 22 years since the last TBM project! And the reason we managed to do that was because of a very close and good cooperation with Robbins,” said Frode Nilsen, Managing Director of LNS.
Located in northern Norway less than 100 km from the Arctic Circle, the Røssåga Hydroelectric Project involves an overhaul and addition to existing power stations. A new powerhouse, headrace and tailrace tunnel will be added, increasing annual generating capacity by 70 MW.
A 450-m (1,500-ft) access tunnel and 7.40-km (4.6-mile) long headrace tunnel through hard rock were awarded to Norwegian contractor Leonhard Nilsen & Sønner (LNS). The project was originally tendered as drill-and-blast. However, once LNS submitted an alternative TBM solution, the project owner identified the benefits of the TBM method, and asked for alternative TBM solutions from all bidders, eventually leading to the contract being awarded to LNS.
The TBM was assembled using Onsite First Time Assembly (OFTA) in order to expedite the project schedule, and was set to begin boring in January 2014. For Nilsen, getting the equipment to site was a challenge: “The logistics were complex for bringing the TBM, conveyor system, spare parts and cutters from all over the world to almost ‘the top of the world.’” However, he said, Robbins Field Service were instrumental in the process: “The crew from Robbins on site have been very professional, efficient and skilled. They have a lot of experience in working under condition where the logistics have been challenging.”
The TBM was designed with 19-in. back-loading cutters for excavation in limestone, mica schist, mica gneiss, and granitic rock. Depending on the quality of the rock, the TBM may also excavate an additional 4.30-km (2.7-mile) tailrace tunnel.
In preparation for the difficult ground, the TBM has been equipped with a powerful probe drill, and has the capability to install an additional probe drill if needed. The machine also has an integrated Measurement While Drilling (MWD) system, which provides electronic visualization of probe drill data. Primary rock support during tunneling will consist of two roof drills dedicated to rock bolting and mesh installations, the McNally roof support system using steel slats, and shotcrete systems.
LNS is expecting the tunneling to be complete in summer of 2016, and the newly renovated power station to go online in spring of 2017. They are confident in their choice of a TBM: “We think that more project owners will consider the use of a TBM as interesting after seeing that we’ve got the technology back in Norway again. We are already seeing it for upcoming projects in both infrastructure and hydropower. We think TBMs are here to stay in Norway.”