A 3m-diameter boring machine nicknamed Ms Colleen has holed through the final 2m of a 3022m tunnel that will carry part of a 23.3m-long replacement water pipeline in Plateau Creek, Colorado.

The Plateau Creek project involves boring two 3m-diameter tunnels through a sandstone and shale mesa to replace an existing water pipeline that was constructed in the 1960s to supply water to rural and urban areas in Mesa County, western Colorado. The new line will have four times the capacity of the old line, which was unable to meet the district’s demand for 60M litres a day and was badly deteriorated in several sections. Construction of the new pipeline is scheduled for September 2001.

The recent hole-through milestone was for the second and longest tunnel of the project. At one point, tunnel contractor Affholder advanced 67m in a 12-hour shift. GEI, Massachussetts-based consultant on the project says that this is a world record for this diameter tunnel in hard rock. The tunnels are sized to permit access to the 1.2m-diameter steel water pipe being placed inside.