Case Studies : Current Projects
Three Robbins TBMs carve out hydroelectric tunnels in Iceland
- Machine Type: Main Beam TBM
- Diameters: 7.63 m (25 ft), 2 x 7.23 m (23.7 ft)
- Tunnel Type: Hydroelectric
- Tunnel Lengths: 14.3 km (8.8 mi), 14.1 km (8.7 mi), 11.4 km (7 mi)
- Owner: Landsvirkjun
- Contractor: Impregilo S.p.A. (Iceland branch)
- Location: Fljótsdalur Valley, Iceland
Project Overview
The Kárahnjúkar Hydropower Project will create the Kárahnjúkar Power Plant to provide 4600 GWh of electricity annually to a nearby aluminum smelting plant. Three dams feed the main Hálslón reservoir and several other dams join the outflow in a combined headrace tunnel to an intake. The intake water travels to the powerhouse through two steel-line vertical shafts and exits from a tailrace tunnel that empties into the Jökulsá i Fljótsdal River.
Project owner Landsvirkjun awarded the construction contract for the hydroelectric project to the Iceland branch of Impregilo S.p.A. The contractor awarded the contract to Robbins for three Robbins Main Beam High Performance TBMs for three lengths of tunnel. All TBMs are Main Beam machines with 19" (483 mm) cutters and feature a cutterhead with a variable frequency drive. All of the TBMs are equipped with probe and roof drilling capabilities.
The machines began boring between April and September 2004 in basalt, moberg, and pillow lava geology. By June 2006 the machines had made good progress despite difficult geologic conditions in the tunnels. TBM 1 finished its drive on September 9, 2006 after achieving impressive advance rates with a best month of 864.6 m (2,755 ft) in March 2006. On the same day, TBM 2 tied a world record in its size class after excavating 92 m (302 ft) in 24 hours. The TBM tied the record with another TBM that bored on the Epping to Chatswood Rail Link. TBM 2 finished its initial drive in Fall 2006 and will be disassembled and transported to bore an additional 8.7 km (5.4 mi) long section of the Jökulsá Diversion Tunnel in the first quarter of 2007. The tunnel, to be finished in 2008, will add to the water supply capacity of the powerhouse by connecting the Ufsarlón Reservoir to the main headrace tunnel.
The third TBM finished its drive on December 5, 2006. All of the TBMs have achieved impressive monthly advance rates despite troublesome rock conditions.
Updates of this project will be posted as boring continues.
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