What happens to our metro tunnel boring machines when they hit the end of the line? When these massive mechanical behemoths, weighing 1200 tonnes each and measuring 170 meters in length, have completed their arduous task of digging through millions of tonnes of rock, their journey doesn't end there. These tunnel boring machines, like Betty and Dorothy, are carefully dismantled underground, with each piece weighing up to 110 tonnes. The main drive units, electrical systems, and other moving parts are sent back to the manufacturer, Herrenknecht, for repair and potential reuse. However, the cutterheads, the massive circular saws at the head of these machines, cannot be reused due to exceeding their wear limits. They are dismantled and recycled into new parts. Betty and Dorothy, named after record-setting Olympians and human rights advocates, were the first in Australia to use artificial intelligence software for steering and digging, requiring a crew of 15 people to operate each machine. Their work was relentless, cutting 800 meters of tunnel per month and installing over 57,900 segments of concrete tunnel lining. As tunnelling on the Metro West network nears completion, other borers like Jessie and Ruby are also winding down their operations. Jessie and Ruby, mixed shield (slurry) machines, were designed for the challenging conditions under Sydney Harbour and the CBD. They mix slurry fluid with excavated rock and soil to maintain pressure at the cutterhead, requiring additional systems for slurry management. Despite their slower progress, at about 90 meters per week, they have excavated a significant amount of rock. The cost of building and maintaining these tunnel boring machines is substantial, with all six used for Metro West costing tens of millions of dollars. The challenge of retrieving Jessie, once it reaches the finish line, will be a complex overnight operation in the cramped space of Sydney's CBD.
