The conventional approach to refurbish this tunnel was to shotcrete the existing precast segments, but it was considered that a more robust liner was required:
- The precast liners were constructed using fibre reinforced concrete. They were transported into the tunnel on a 600mm gauge railway track, rotated 90 degrees and lifted into place using a purpose built hydraulic machine mounted on a railway bogey.
- The tunnel had deteriorated to such an extent in places that a timber ‘heading’ had to be constructed prior to installation of the liner segments.
- Confined space tunnelling and robust health and safety systems were required.
- The existing watermain in the tunnel was live and had to be protected at all times.
- The remote location in the Waitakere Ranges provided difficulty of access.