US contractor Affholder has set what is believed to be a single shift world record drive for a 3m diameter TBM.

On 14 September, tunnellers advanced 67m in eight hours on the Lower Canyon tunnel drive, part of the $24M Plateau Creek Pipeline Replacement (PCPR) project Phase 2 in Colorado, US.

The impressive advance rates were achieved using a Robbins Model 91-155 TBM, owned by Affholder. The machine has been used by the company on seven previous contracts totalling over 30km of tunnels.

The PCPR project consists of two 3m diameter tunnel drives constructed by the team using the same machine. The first is the 1km long Lower Messa tunnel, constructed through sandstone, siltstone and shale with compressive strengths of 50N/mm² 142N/mm² and 107N/mm² respectively. Construction commenced in July 1999 and was completed on 21 August 2000. Upon completion the TBM was disassembled, transported to another portal on the other side of the mountain, reassembled and set to face on the second drive, the 3km long Lower Canyon tunnel.

The tunnel is currently being driven through the same material, sandstone, siltstone and shale with respective compressive strengths of 70Nmm² and 162N/mm². Construction has advanced some 650m and it was during this that the record was set.

Tunnel spoil is being removed from the face by buckets on the cutterhead and placed directly onto an 450mm wide machine conveyor. This is then transferred to a train parked at the end of the TBM for transportation out of the tunnel.

Upon tunnel completion a 1.2m diameter steel pipe will be installed for the conveyance of fresh water. The oversized tunnel diameter has been specifically designed to allow maintenance access to the pipe and for future installation of other utilities. Tunnel completion is scheduled for the end of 2001.

A further 3km of pipeline is included in the project and this will be installed in open cut tunnel being constructed by contractor Barnard Construction Company.

The project client is the UTE Water Conservancy District with project consulting engineers, Camp Dresser & McKee and Lachel Associates.