The Sydney Urban Train System was extended with the addition of The Epping to Chatswood Rail Link. The extension consists of two twin parallel tunnels 12.5 km (7.7 mi) in length. The New South Wales Government awarded the contract for the project to the Theiss Hochtief Joint Venture (THJV), a collaboration of Australian and German construction firms.
In 2002, THJV awarded the contract to Robbins to build two 7.2 m (23.6 ft) diameter Main Beam TBMs. The TBMs excavated the two tunnels in two sets of drives beginning at Delhi Road Station (about the center of the tunnels), and advanced at impressive rates throughout the project.
Both tunnels pass through Hawkesbury sandstone and deposits of Ashfield shale. One fault line exists along the route, near Macquarie Park Station, about 2 km (1.2 mi) into the first drive.
The two Main Beam TBMs had a cutterhead power of 2300 kW (2957 hp) and a maximum thrust force of 1400 metric tons (1500 US tons). Robbins designed both machines with innovative features for the project. A unique rolling back-up system allowed concrete roadbed to be poured while the machines excavated the tunnels. This construction method enabled the use of rubber-tired vehicles during excavation and the rapid installation of train tracks.
Robbins also designed custom conveyors consisting of five integrated systems: two horizontal conveyors, two vertical conveyors, and one stacker conveyor. The crown-mounted horizontal conveyors ran for 6 km (3.7 mi) with more than 80 percent in curves.
The TBMs began boring the tunnels in August and September 2003. Both machines broke through the tunnel at Epping in July 2004. Boring began a second time in November 2004 and the machines broke through at Chatswood in June and July 2005. During the excavation, one machine set an advance rate world record for its size class by boring 92 m (302 ft) in one day. Their best week was 368 m (1,207 ft) and the average advance rate for the project was 200 m (656 ft) per week. The TBMs ran into few problems and were available for 80% of the total project time.