The underground excavation industry is exploring mini-robots, plasma torches and superheated gas to replace the massive drilling machines currently in use.
Engineers seeking to build underground tunnels relied on huge tubular machines armed with a fearsome set of cutting wheels at one end—blades that eat dirt for breakfast. These behemoths, called tunnel boring machines, or TBMs, are expensive and often custom-made for each project, just like the TBMs used to excavate track for London’s newly opened Elizabeth Line railway. The machines involved in this project weighed more than 1,000 tons each and cut tunnels with a diameter of more than 7 meters under the capital of Great Britain.
But British startup hyperTunnel has other ideas. The firm envisions a future in which much smaller, roughly 3-meter-long half-cylinder-shaped robots fly underground through pre-drilled pipes. These pipes, approximately 250 millimeters (10 inches) in diameter, will follow the contours of the proposed tunnel walls. Once inside, the bots used a robotic arm with a milling head to penetrate the surrounding ground and carve out small voids, which were then filled with concrete or other durable material. Piece by piece, the structure of the new tunnel will thus come together.
“We’re talking about thousands of them,” says HyperTunnel’s director of development Patrick Lane-Knott. “Just like an ant or termite colony works in swarms.”
Videopublished by the company, features 3D animation of robots racing around some imaginary underground structure of giant proportions. But that would be like building tunnels in reverse. With a TBM, you first dig a hole and then add piers or walls to hold the remaining earth around the void. “We put a tunnel in the ground and then we dig a hole,” Lane-Knott says. Once the structure is built, the material filling the tunnel chamber can be removed.
One of the benefits of this, he claims, is the use of fewer building materials. Instead of placing standardized tunnel wall sections throughout the length of the project, the outer thickness of the structure can be varied according to the actual geology and pressures surrounding the tunnel at any given point.
Tunneling experts agree that the industry needs technological solutions to reduce costs and improve efficiency — for example, it can take years to design and build a TBM and then actually dig a tunnel with it. A number of new companies are emerging that promise to change the situation — from Elon Musk’s Boring Company to HyperTunnel and firms developing new high-temperature methods of blasting the hardest rocks on Earth.
“There’s a lot going on, and I think that’s a good thing, because the tunneling industry has to improve,” says Jasmine Amberg, project manager at Amberg Engineering, the underground construction company founded by her grandfather. In her opinion, the tunneling business needs to become faster and more sustainable.
There is no shortage of work there either. China recently completed a 20-kilometer railway tunnel in the Longmen Mountains after a decade of construction. In Great Britain, there is the HS2 railway project, which will connect London with cities in the north of the country and is supposed to lay more than 100 kilometers of tunnels along the proposed route. And Peter Vesterbacka, formerly of Angry Birds developer Rovio, is behind an ambitious plan to build an underwater tunnel between Finland and Estonia. These are just a few examples.
Amberg predicts an increase in demand for underground infrastructure in the future — not least as a means to avoid rising temperatures above ground due to climate change. “Maybe it’s not so bad to have a place where we have a more stable temperature,” she says.
Tunnels are not only for transportation. Troy Helming, founder and CEO of San Francisco-based startup EarthGrid, emphasizes the need to run power lines underground, which is what his company aims to do. The vast majority of transmission cables run above ground in the United States and Canada, he notes, leaving them vulnerable to hurricanes and other storms and, increasingly, wildfires.
“Our plan is to put a supergrid across North America,” he says, holding up a map with colored lines showing the grid stretching from the East Coast to the Pacific Ocean and future offshore wind farms to the west. It’s a plan that could help unify the U.S.’s fragmented energy system — and perhaps one day even extend as far as Europe to tap the vast potential of offshore wind energy there. “It’s crazy and daring, and we know it,” says Helming.
One obstacle is the extremely hard rocks, such as granite and quartzite, which make traditional excavation difficult or impossible at some of these sites. Helming is betting on plasma torch technology, which heats the stone to about 6,000 degrees Celsius, tearing it apart. He speculates that this would allow tunneling in hard rock 100 times faster than with current technology. EarthGrid is developing a prototype robot with five plasma torches, which Helming says should be ready for testing in March 2023. The firm also plans to complete its first small commercial project by the end of this year.
Helming notes that in the case of EarthGrid, the tunnels will not be circular in shape, but rather a traditional horseshoe—think square with an arch at the top instead of a flat ceiling. This, he claims, makes it easier to install cable trays or, in large traffic tunnels, a road surface on a flat tunnel base.
Competing company Petra is also looking to drill through hard rock with heat, albeit with a thermal cutting device that uses superheated fluid rather than a plasma torch. The idea is to cut through “nightmare geologies” with relative ease, says CEO and co-founder Kim Abrams.
We finished a 34-foot-long, 30-inch-diameter granite tunnel last week, she says, adding that the firm hopes to begin commercial operations next year. And she notes that the company is also working on a separate solution to deal with the other end of the spectrum — the extremely soft or waterlogged soil often found under and near coastal cities.
These tunneling technologies have yet to prove that they can be successful at scale, Amberg notes. She says the concept of the HyperTunnel is interesting, but adds that she’s not sure how the robots will cope with more difficult geological conditions or, for example, wetlands.
Jian Zhao is a professor in the Department of Civil Engineering at Monash University in Australia. He and his colleagues explored the use of laser, microwave, and high-pressure water-abrasive technologies, among other things, for tunnel boring. He is skeptical, for example, that Petra’s heat-based method will be sufficient on its own for large tunneling projects, but he wonders whether it can be used alongside mechanical excavation.
“I think the seed funding, the angel investment and all the things that drive some of the innovation are fantastic,” says Michael Mooney, who is a professor in the Department of Underground Construction and Tunneling at the Colorado School of Engineering. He agrees that “the jury is still out” on whether any of these new tunneling technologies can achieve large-scale commercial success, but he stresses that faster, cheaper methods are in high demand in the industry.
He also claims that the Boring Company, which is developing its own type of TBM that can be launched from the surface to dig underground tunnels (by default, you dig a hole first and then move the TBM into it to create a tunnel), has also implemented innovation in a commercial sense, as the firm plans to standardize tunnel boring equipment across projects.
“Building a new tunnel boring machine for a specific project makes it difficult and expensive every time,” explains Mooney.
Finally, Amberg mentions that there are many existing tunnels around the world that are now aging and in need of maintenance and repair—many of which are in her country, Switzerland. New technologies are needed to effectively perform this work.
Among those targeting such markets is HyperTunnel. Lane-Knott says his firm’s robots will be able to lower pipes to service the exterior structure of the underground tunnels without operators having to stop road or rail traffic inside. And this revolution is already beginning. Network Rail, which owns and operates a large part of the UK’s rail network, brought HyperTunnel into the project in this vein, adds Lane-Nott.
It’s a small step toward a vision of thousands of robots working in concert to create vast underground structures—what he calls “swarm power.”
The specified technological developments are extremely important and have a high investment potential – Kostyantyn Kryvopust notes.
