Fastest tunnel boring
Robbins Mk 12C
Australia (Katoomba)

The fastest tunnel boring machine (TBM) is the 3.4-m-diameter Robbins Mk 12C, a machine built to excavate a sewage redirection tunnel called the Katoomba Carrier in the Blue Mountains of Australia. In August 1994, this TBM achieved a single-day distance record of 172.4 m (565 ft), removing 1,565.3 m3 (55,278 cu ft) of rock in the process.

The Blue Mountains National Park is a UNESCO World Heritage Site that covers some 2,680 km2 (1,034 sq mi) of forested mountains to the North and West of Sydney, New South Wales. The park is divided by the Great Western Highway (the main route connecting Sydney to the Australian interior) and the settlements that have grown up alongside it. In the 1980s, it was realised that the sewage systems of these growing communities could not handle the volume of waste produced, and so a plan was put forward to transport sewage away from the national park to areas where it could be treated properly.

The most important part of this civil engineering project was the 13.4-km (8.3-mile) Katoomba Carrier tunnel, a 3.4-m (11-ft 1-in) diameter sewer designed to handle waste from the towns of Katoomba, Leura, Wentworth Falls, Bullaburra and Lawson. It was designed to connect Katoomba with the inflow of an existing sewer tunnel at Hazelbrook, and from there to sewage treatment plants closer to Sydney.

To dig this tunnel, which would mostly pass through relatively soft Sydney sandstone, the contractor brought in a custom-ordered tunnel boring machine designed by American engineering firm Robbins. The TBM's record-setting speeds were aided by a muck conveyor system (faster than hauling the spoil out in trucks) and favourable geology, which required very little shoring up and lining.