Affholder, the US contractor, has holed through on the second and final drive of the $24M Plateau Creek Pipeline Replacement (PCPR) project Phase 2 in Colorado, US. Breakthrough, using a 3m diameter Robbins TBM, comes in the wake of a claimed record drive for a 3m hard rock TBM in September last year of 67m in eight hours (News, Nov 2000).

The TBM, nicknamed Ms Colleen, finished boring the Lower Canyon tunnel on March 16. Affholder began boring in September last year and was quick to set impressive advance rates, the machine coping well with sandstone, siltstone and shales along the tunnel alignment. The tunnel is the second on the project and, at 3km, the longest.

The first tunnel to be constructed on the project was the 1km long Lower Messa tunnel. Using the same TBM, Affholder began boring the tunnel through similar geology in July 1999 and completed on the 21 August 2000. Both tunnels are sized to permit access to the 48" diameter steel water pipe being placed inside.

The tunnels will house part of a 4.8km long water transmission pipeline designed to replace an existing water pipeline constructed in the early 60s. The new system will provide the rural and urban areas in Mesa County, western Colorado, with the 13 million gallons of water a day required at peak times. This is four times the hydraulic capacity of the old system.

The pipeline is scheduled for a September completion. The client for the job is the Ute Water Conservancy District who worked with the team of GEI Consultants, Inc, LACHEL & Associates, and West Water Engineering who designed both tunnels for the project.