If you’ve watched a tunnel boring machine go into the ground, you’ve probably watched a crane lower one very large steel cylinder into one very large hole, after which the thing vanishes into the dirt and nobody sees it again for a year. Melbourne did the first half of that back in July. The second half is happening in installments.
TBM Alice started cutting on September 7, heading from Burwood toward Glen Waverley in Melbourne’s eastern suburbs. The Victorian Government announced it that Monday. A second machine, Hacia, sits in the same box and should open the parallel tunnel within a few weeks.
Neither of them went into that box as a finished machine. Alice still isn’t one.
So what is an umbilical launch?
The launch box at Burwood isn’t long enough to hold a complete machine, so nobody tried to put one in there. Crews bolted together the front section of each machine on the surface, and a heavy-lift crane dropped it into the shaft in July. That front section is the shield, and on its own it weighs 551 short tons (500 metric tons). Everything the shield needs to run, power and hydraulics and the rest of it, comes down from ground level through a bundle of cables and hoses. The bundle is the umbilical. That’s the whole reason for the name.
Alice cuts on that leash. As it pushes forward it opens up tunnel behind itself, and crews install the trailing gantries into the space it just made, one section at a time. Keep that up long enough and you end up with a complete machine standing inside a tunnel it dug before it was finished being built, which is a pretty neat trick if you’ve got more patience than room.
Victoria’s Big Build calls the technique a state first, and I’d hold onto that exact wording, because it isn’t a first for tunneling. An earth pressure balance machine called Chris went in the same way under Washington DC on the Northeast Boundary Tunnel, a 26-foot machine started out of a 66-foot shaft. Dragados ran an umbilical launch under Los Angeles on the effluent outfall tunnel. There’s one happening under the Thames right now.
So Melbourne hasn’t invented anything. It ran out of room the way plenty of cities have, and it borrowed the fix.
Why not dig a bigger hole?
Because the hole’s the expensive part. A launch shaft eats concrete, makes its own spoil, and sits on a chunk of somebody’s suburb for as long as it exists. Burwood is across the road from Deakin University, acoustic sheds are going up to keep the noise off the neighbors, and a second launch box is already being dug at the northern end of the site for the two machines that head toward Box Hill next year. They’re short of space, not steel.
So how long is this machine?
Alice’s cutterhead measures just under 24 feet across, which isn’t remarkable for a metro tunnel and is a lot smaller than the road-tunnel machines that finished under the other side of Melbourne earlier this year. The shield weight is agreed everywhere at 551 tons. The assembled length is where the sources stop agreeing.
Victoria’s Big Build puts a fully built machine at approximately 120 meters, or 394 feet. Clough, part of the joint venture actually digging the tunnel, says approximately 100 meters, which is 328 feet. The Tunnelling Journal reported 103 meters.
I had to check that twice.
That’s a 66-foot spread between the owner and the builder on the length of their own machine, and I can’t find anywhere the two get reconciled. So treat the finished length as somewhere between 328 and 394 feet, and don’t trust anyone who quotes you a precise one.
Seven more machines, and a crew that doesn’t start until 2027
Alice is one of eight. Victoria’s Big Build lists four machines from Herrenknecht working the southern tunnels out of Clarinda, and four from China Railway Engineering Equipment Group, built in Zhengzhou, working out of Burwood. All eight run on renewable electricity bought from Yurringa Energy, which Clough describes as Australia’s first Indigenous-owned energy retailer. I’d normally leave a supplier out of it, except one of these machines pulls an industrial amount of power and somebody had to sell it to them.
The third machine, Aayushi, is being assembled at Clarinda and starts toward Glen Waverley before the end of the year. More launch next year from Heatherton to Cheltenham, and from Burwood toward Box Hill.
You’ve seen the naming convention even if you’ve never thought about it. Boring machines get women’s names, a habit that’s older than the machines themselves and goes back to miners praying to Saint Barbara, and Seattle gave you Bertha. The project handed the job to students at eight local primary schools, who picked from a shortlist of Victorian women. Kerrimuir Primary School chose Alice, after the Melbourne music producer Alice Ivy, whose reaction on the project’s own site was “I absolutely dig it.” Glen Waverley Primary School chose Hacia, after Hacia Atherton, who founded Empowered Women in Trades.
We covered the eight machines and the all-women crew back in July. That crew, 18 women led by Isolde Piet, the first female TBM pilot in the world, doesn’t work as a single unit until 2027, and it’s assigned to the southern tunnels out of Clarinda. Alice isn’t its machine.
Alice has 6.2 miles to cut
Terra Verde, the joint venture of Webuild, GS Engineering and Construction and Bouygues Construction Australia, holds the northern contract. That’s almost 6.2 miles of twin tunnel between Glen Waverley and Box Hill, plus two station boxes, a ventilation shaft, two launch sites and 39 cross passages to cut between them. A separate consortium’s got the 9.9 miles between Cheltenham and Glen Waverley. Together they make up SRL East, 16 miles of twin tunnel and the first stage of a planned 56-mile orbital line.
The tunnels average 85 feet down and reach roughly 197 feet at the deepest, which Victoria’s Big Build compares to a 16-story building. On good ground a machine covers up to 295 feet a week. A crew runs around ten specialist roles, and anyone working the pressurized end trains in a hyperbaric chamber first.
When Alice finishes, it doesn’t come back out the way it went in. These machines are designed to be taken apart from inside the tunnel and carried up in pieces, and the shield stays buried where it stops. The pair that dug the North East Link left town the other way, in night convoys with traffic lights coming down ahead of them. Hacia opens its tunnel in the coming weeks, Aayushi launches from Clarinda before the end of the year, and nobody rides a train through any of it until 2035.
