DJ Mac Cormick has completed another large diameter microtunnel project on a stormwater drainage concrete jacking pipeline in the Northern Territory.
The project took place at the Larrakeyah Defence Base in Darwin, on a 1,950 mm pipeline with a 1,650 mm internal diameter.
DJ Mac Cormick used its Herrenknecht AVN 1600 control container and 24 t tunnel boring machine, equipped with a closed face laser guided steerable and a slurry spoil removal system.
The contractor said it encountered groundwater and ground conditions at 6–8 m of rock up to 150 MPa, with a rock cutting wheel used to cope with the high strength.
The project’s tunnelling involved two drives of 330 m and 354 m with an 850 t jacking system in the launch shaft.
Due to the length of the drive, several intermediate jacking stations were necessary – powered by an intermediate jacking unit – as well as a lubrication system to minimise friction on the outside of the pipe.
DJ Mac Cormick said the jacking unit allowed for jacking of more than 1 km drives, as there are four intermediate jacking stations from the control container and four more that can be housed inside the tunnel line.
The contractor said man entry was also possible from inside the microtunnel boring machine (MTBM) due to the pipe diameter if cutter changes were required along the drive.
Additionally, the long drive lengths and high humidity in Darwin meant a ventilation system was necessary not only at the shaft locations, but also inside the tunnel.
DJ Mac Cormick said it undertook detailed temporary design including thrust block, entrance wall, base pad, entrance and exit rings, plates and more, all of which were independently checked and signed off as the project was completed.
For more information visit the DJ Mac Cormick website.
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