On the Kárahnjúkar Hydroelectric project in Iceland, Robbins is claiming a world record advance for the class of machine of 92m in 24 hours for one of its TBMs, while another Robbins TBM on the project has notched up the first bored tunnel breakthrough on the scheme.
On 9 September, TBM2 tied a world record of 92m bored for a 7-8m diameter machine with a similar Robbins TBM that achieved the same feat on the Epping to Chatswood rail tunnel s in Australia in 20005. In what must have been a competitive push between rival crews, on the same day the Robbins TBM designated TBM1, a main beam machine, broke through a 14.6km long section of the headrace tunnel on the project.
Robbins said the performance of these machines has been especially impressive given the nature of the ground conditions they have had to traverse. The company supplied three TBMs to the project and all experienced heavily fractured ground and water inflows into their sections of the headrace tunnel. Nevertheless, the TBMs are on schedule and TBM1 finished its bore on time with Robbins informing it maintained an average advance of 643m per month in 2006. The company said the TBM suffered only minimal machine wear despite boring through hard basalt, moberg and pillow lava geology of up to 300Mpa.
The 7.23m diameter TBM2 finished its 11.1km long bore at the end of September and advanced 137.6m in its final week. It is currently being transported and reassembled to begin boring a 8.7km long section of the Jökulsá Diversion Tunnel for the scheme in the first quarter of next year. Once completed in 2008, this tunnel will add to the water supply capacity of the powerhouse by connecting the main headrace tunnel to an additional reservoir.
In total the Kárahnjúkar project includes 73km of tunnels to transfer water to its powerhouse complex. The 690MW scheme is being built by Impregilo SpA for Landsvirkjun to provide a power supply to the Alcoa aluminium smelting plant.
