The interconnector project involves the construction of 48 km of underground, reverse-flow water pipeline from the Noosa Water Treatment Plant, located at Cooroy, to the Northern Pipeline Interconnector (NPI) – Stage 1,
in Eudlo.
The NPI – Stage 2 potable water pipeline, a key component of the South East Queensland Water Grid, is being designed and constructed by the Northern Network Alliance (NNA). The alliance comprises of LinkWater Projects, McConnell Dowell, Abigroup and KBR.
The pipeline alignment includes a section through Pringle Hill, in Nambour. Tunnelling through the area was a significant construction challenge given the length of the 1,032 m tunnel, its height difference of 60 m from the launch position to the final target, and the design requirement for a significant vertical curve.
Usually a microtunnel of comparable length would be divided into sections with one or more intermediate shafts. However, the steep slope and topography of the area made this option impossible. So the Pringle Hill tunnel had to be one long, continuous tunnel.
The 2,100 mm internal diameter pipe-jack, from Humes, was integral to the successful completion of the tunnel and was a significant accomplishment for tunnel engineering in Australia. Ten inter-jacking stations were deployed inside the tunnel to enable the pipe-jack to achieve this significant length.
By successfully installing jacking pipes over a distance of more than 1 km, NNA and Humes have demonstrated a greater scope for infrastructure designers to choose more economical routes, which may also deliver benefits to residents and the environment.
The design of the pipes and intermediate jacking stations has been based on overseas standards and experience with the view to providing a world-class jacking pipe, ideally suited for use with modern, closed-faced micro-tunnelling equipment.
Construction on the NPI – Stage 2 began in February 2010. The conclusion of major construction activity is expected to occur in mid-2011 and commissioning is expected by December 2011.