What happens to our metro tunnel boring machines when they hit the end of the line? When these colossal machines, weighing 1200 tonnes each and measuring 170 meters in length, have completed their task of digging through millions of tonnes of rock, they undergo a meticulous dismantling process. 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 front of these mechanical worms, are not reusable due to exceeding their wear limits. Instead, they are carefully dismantled into sections and recycled. These tunnel boring machines, Betty and Dorothy, were the first in Australia to utilize artificial intelligence software for steering and digging, requiring a crew of 15 people to operate each machine. The machines worked tirelessly, cutting around 800 meters of tunnel per month and installing over 57,900 segments of concrete tunnel lining. Betty and Dorothy were named after record-setting Olympians and human rights advocates, respectively, following a worldwide tradition of naming underground tunnelling machines with female names. As the tunnelling on the Metro West network nears completion, other borers, Jessie and Ruby, are also finishing their work. Jessie and Ruby are mixed shield (slurry) machines 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 and enable safe digging. Their progress was slower, excavating 460,000 tonnes of rock at a rate of about 90 meters per week. Despite their slower pace, all six tunnel boring machines used for the Metro West project cost tens of millions of dollars to design, manufacture, and commission. The dismantling and retrieval of these machines present a complex challenge, especially for Jessie, which will require a meticulous overnight effort in the cramped space of Sydney's CBD once it reaches the finish line.
