The TBM, or Tunnel Boring Machine, is a very special machine that does not limit itself to milling mountains or scratching clay to dig a tunnel for a railway or a road.
“It’s like a submarine,” says Andrea Dolcini, Webuild Vice Plant Manager for the underground project Grand Paris Express being realized in Paris. The TBM is like a train, with toilets and a mess hall, in addition to, of course, control panels, carts, conveyor belts and even a so-called spaceship, the equipment used to grab the pre-compressed arches that coat the inside of the tunnel and bring them to the erector, which positions and glues them to the wall of the tunnel.
Submarine, train, mechanical mole, it is a machine that moves thanks to the work of a crew of between 80-100 people, who work in 8 hour shifts to keep the TBM operating 24/7.
Webuild: being a leader in mechanical digging
The Webuild group, which in the last 50 years has put about 200 TBMs to work, has built more than 1,500 kilometers of tunnels. That’s equivalent to traveling from Milan to Copenhagen entirely in beautiful, wide and safe underground railways or roads. In fact, in both Milan and Copenhagen, Webuild constructed acclaimed subway systems.
Today there are 40 Webuild TBMs operating, of which half are in Italy. During 2023 and 2024, the number of Webuild TBMs at work will progressively increase, exceeding 45 units, a number destinated to grow with the new projects that will be acquired in the meantime.
“No other company in the world reaches that level, they might have 10, not more,” says Remo Grandori, Director Plant and Equipment, Webuild – “It’s an unparalleled contribution of experience for the entire sector. We build is implementing a platform, called WeView, thanks to which the data collected during the various phases of the dig and evacuation of the material are accessible by the various TBMs in real time.”
The data collected by WeView is exploited by a software called Smile, which analyzes them and processes the predictive maintenance program.
Thanks to Smile, therefore, maintenance interventions are optimized and the efficiency of the TBM is increased, reducing downtime and breakdowns.
Webuild also developed “Green” TBMs to achieve an energy efficiency of at least 20%.
Usually TBMs are custom-built for each project, depending on the diameter of the milling head, or shield, which can reach 19 meters in diameter. To dig a highway tunnel the diameter of the head will be at least 15 meters, enough for three lanes plus a fourth for emergencies. To get an idea, that’s as high as a five storey building. For railways it’s usually 9-10 meters, while a single channel subway tunnel has a diameter of 7 meters, and hydraulic tunnels are narrower still. The head of a TBM alone can weigh 500 tons and is equipped with concentric rows of cutters or rippers depending on the terrain. The body can be as long as 100 meters or more.
Genesis and journey of the great TBMs
These enormous mechanical moles are built in a factory (Germany and China are the major producers) and, once they have passed all the tests, are taken apart, transported to the entrance of the dig and re-assembled piece by piece. Once all the tests are passed once more, the TBM starts turning and the material it digs is removed via the conveyor belt that runs along the body of the machine. As the dig progresses, so does the coating of the gallery. Once the dig is completed, the TBM is take apart and, usually with a buy-back operation, resold to the maker to be rebuilt and renovated for a new job.
The crew is made up, on average, by 60 miners, experts in underground work, and 20 specialized technicians and staff who, during the dig, maintain contact with the operations headquarters outside the tunnel. The digging speed can reach 100 meters a day. Until about 20 years ago the speed was even greater, but now safety and quality take precedence over speed. New TBM designs and production techniques have been introduced to minimize the environmental impact as well.
The team of technicians that run a TBM
There are 2,300 tunneling specialists currently working on Webuild projects, a team of professionals with tens of different nationalities, on work sites in Australia and the United States, Europe and South America. There are workers specialized in tunnel work as well as mechanical, mining, mechatronic and electrical engineers. It’s a job that sometimes is passed on from father to son, as is the case of Andrea Dolcini, Vice Plant Manager, Webuild. He followed in his father’s footsteps, entered his first TBM in 1999 when he was 22 years old, and today he is responsible for the electrical work on the Grand Paris Express 16.2 Line, on which Webuild is working after completing line 14.
“When I got my first job I was a little scared,” Dolcini said. “But my father (Giorgio Dolcini, former Direttore Tecnico SELI Overseas) encouraged me with a confident tone saying: ‘Behave properly, you know what you need to do. All will be well.’ The control panel was enormous, full of relays and cables for the electromechanical control of the machine, from which you could program, for example, the power and oil necessary to make it work.”
“In Paris there are 11 km of tunnels to dig,” Dolcini adds, “with two 9,84 meters TBMs digging toward each other in the same channel, carving ground that is mostly clay. The second TBM needs a few more months to reach its goal, while the first one needs a little longer. The TBM must never be without power. There are safety and backup units, but everything must work in unison.”
Gentile Travaiani, currently working with Webuild on the Brescia-Verona railway line, agrees. He is responsible for the conveyor belts of the TBM and previously worked on the dig for Milan’s M4 subway line, another Webuild project.
“Crossing Milan over 30 meters below street level,” he explains, ” is not easy. Above us are historical buildings, homes, offices, monuments, vehicles and other subway lines. It was one of the most challenging experiences, but we did it. I say, we did it, because it’s the team that counts, alone with the TBM you get nothing done.”
The M4 tunnels are terminated and now the stations are being completed. The TBMs that were used have already been disassembled and shipped back to the factory.
“In Milan,” Travaiani said, it’s one curve after the other. First the bed of a river, full of sand and gravel. The conveyor belt must be at the right tension, the material must flow smoothly to be evacuated. And the head must be handled with experience: foam, soap, water, rotation, pressure. The TBM is a machine in constant motion, 24/7, where organization is essential. You advance making sure nothing above you moves. In the TBM team work is everything!”