The Plateau Creek Pipeline was built to replace a pre-existing pipeline that supplied fresh water to rural and urban areas of Mesa County, Colorado, USA. The new tunnel provides water to 70,000 customers and has four times the hydraulic capacity of the old pipeline, which was unable to meet the District’s peak water demands.
The project owner, UTE Water Conservancy District, awarded the construction contract for the entire 21 km (13 mi) pipeline to the Barnard-Affholder Joint Venture. Affholder was solely responsible for the two sections of tunnel that were bored by TBM. The contractor used a 3.3 m (10.8 ft) diameter Robbins Main Beam TBM to bore two tunnel lengths of 1.0 km (0.6 mi) and 3.1 km (1.9 mi).
The geology consists of sandstone, shale and siltstone with an Unconfined Compressive Strength (UCS) of 69 – 172 MPa (10 – 25 ksi). The rock required immediate support including rock bolts, wire mesh, and shotcrete.
Robbins rebuilt and modified the Affholder-owned Robbins Main Beam TBM specifically for the project. The machine had been a workhorse for Affholder, who has used the machine on nine different projects totaling over 30 km (19 mi) since purchasing the machine in 1993.
Modifications included a new cutterhead, cutterhead power increase by 25%, a new high capacity main bearing and a thrust increase to allow a loading of 267 kN (60,000 lb) per cutter. The machine was capable of up to 4,893 kN (1,100,000 lb) of cutterhead thrust and could generate up to 455,738 N-m (336,135 lb-ft) of torque at the cutterhead.
Boring began on the 1 km (0.6 mi) long tunnel in June 2000 and the machine holed through in August, just 1 month later. The machine was then disassembled and re-launched in only 2 weeks to bore the longer 3.1 km (1.9 mi) tunnel.
Excavation on the second tunnel began in September 2000. The machine set a world record in its size class on September 14th when it advanced 67 m (219 ft) in a single eight-hour shift. The TBM holed through ahead of schedule on March 16, 2001.