Work on a new sewer outfall tunnel drive in New Zealand has achieved breakthrough to set a new world record for the longest direct pipe drive.
Contractor McConnell Dowell launched the Herrenknecht microtunnelling machine – named Blanche – four months ago on the 1,930m drive for the outfall as part of Watercare’s Army Bay Wastewater Treatment Plant project.
The drive will form part of a 2.9km long sea outfall which is part of scheme to increase capacity at the Army Bay facility.
The direct drive technique developed by Herrenknecht was selected for the work in order to minimise the impact on the marine environment but the drive was significantly longer than the previous record for a tunnel of this type which was 1,496m long.
The direct drive technique used a micotunnelling machine with a pipe string attached to simultaneously insert it during the tunnelling process and uses a pipe thruster to aid the installation.
With breakthrough achieved, the microtunnelling machine has been lift from the seabed and towed back to shore.
The new discharge point is expected to be put into service early next year.