The new main is replacing the century old pipe that is still in operation and, once up and running, will supply more than 20 per cent of Melbourne’s water.
Using a trenchless solution was a priority for Bothar Boring as the alignment of the new watermain was through a peak in the catchment area. With the area also environmentally sensitive with a large population of protected flora and fauna, mitigating damage from significant excavation was vital.
A global fleet
To complete the project, Bothar used one of the many microtunnel boring machines (MTBM) in its fleet: the Herrenknecht AVN1800-TB M2150 fitted with a DA2225 extension kit that gives the machine an outside diameter of 2225 mm.
The machine has a maximum torque of 554 kNm, a permanent torque of 424 kNm and is fitted with four drive motors, making it the perfect selection for this particularly challenging project. During the bore, the MTBM jacked through more than 250 MPa basalt ground conditions via a DN1800 RCJP, supplied by the John Holland–KBR Joint Venture.
Bothar, which is believed to own the largest global fleet of Herrenknecht MTBM’s, shipped this particular machine in from Kuwait, where it had completed its most recent project.
Planning is the key to success
Bothar says the project was successfully completed on time and on budget which, owed to some significant material issues hindering the tunnelling operations, is a testament to the continual commitment of the team involved.
The total length of the drive was 425 m with more than half of that distance in the 250 MPa basalt; this proved a great challenge to the project as the disc cutters needed to be changed every two to three pipes.
To overcome this, Bothar monitored the machines parameters and kept the machine within its optimum tunnelling conditions by regularly entering the cutting chamber and redressing the cutting head with new tooling.
Bothar says it worked very closely with Baroid to mix the best face slurry and lubricating mud for the ground conditions encountered. The bentonite product was mixed meticulously and then pumped into the face at premium pressures allowing for optimum operation, jacking forces and cutter longevity.
Additionally, Bothar says the remote site meant there was no telephone reception, so the project’s logistics needed to be precisely timed and planned. To do so, communication was managed with satellite phones, UFD radios and through forward planning programming and management.
Teamwork makes the dream work
Bothar Boring Australia’s General Manager David King says not only did the project present material challenges in the extreme geological conditions, but the exit target was to be within 50 mm of tolerance as the MTBM was required to exit within an existing structure.
“Thankfully, the drive throughout was well within these tolerances rendering the drive a complete success,” says Mr King.
“The integrated efforts of all our staff worked safely and seamlessly to ensure the safe and successful completion of this project. I commend every one of our team involved – from labourers to supervisors and management – for their hardworking efforts.”
Bothar worked collaboratively with the John Holland-KBR Joint Venture and client Melbourne Water to successfully complete the project.
This article was featured in the June 2020 edition of Trenchless Australasia. To view the magazine on your PC, Mac, tablet or mobile device, click here.
For more information visit the Bothar Boring website.
If you have news you would like featured in Trenchless Australasia contact Journalist Sophie Venz at svenz@gs-press.com.au