A Robbins 7.2-m- (23.6-ft-) diameter tunnel boring mach-ing (TBM) operating on the remote Karahnjukar hydroelectric project in Iceland has entered new territory. The machine, operated by contractor Impregilo SpA, beat its own world record for the second time when it bored 115.7 m (380 ft) in 24 hours on Aug. 25,2007. It then set another record in its size class of 7 to 8 m (23 to 26 ft) by boring 428.8 m (1,400 ft) in one week. The previous record was also held by a Robbins TBM that excavated the TARP project in Chicago, IL. These feats are all the more remarkable considering the machine is on its second tunnel, having bored more than 15 km (9 miles) so far in very hard rock up to 300 MPa (43,500 psi) UCS. The machine previously bored an 11.1-km- (6.9-mile-) long section of the main headrace tunnel at Karahnjukar, breaking through in September 2006.
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