The underground tunneling industry is exploring various solutions such as mini robots, plasma torches, and superheated liquids to replace the massive drilling machines currently in use.
For decades, engineers seeking to construct underground tunnels have relied on gigantic cylindrical machines, equipped with a series of cutting wheels to handle the rock and soil at one end. These colossal machines, known as Tunnel Boring Machines (TBMs), are very expensive and often custom-built for each project. In the recently inaugurated Elizabeth Line railway in London, the deployed machines weigh over 1,000 tons each and can create tunnels with diameters exceeding 7 meters beneath the UK capital.
However, the British startup hyperTunnel has different ideas. The company proposes a future scenario in which much smaller robots, only about 3 meters long and shaped like half-cylinders, will be launched underground through existing pipes. These pipes, approximately 25 cm in diameter, outline the walls of the proposed tunnel. Once inside, the robots will use a robotic arm with a milling head to penetrate the surrounding soil and carve out small voids, which will then be filled with concrete or other solid materials. With each of these pieces, the structure of a new tunnel will be created and assembled.
“We’re talking about thousands of such robots,” said Patrick Lane-Nott, the technical director of hyperTunnel. “Like a swarm of ants or termites working in unison.”
Our future will be filled with tunnels.
The company has released a 3D video illustrating its concept. However, it contrasts with conventional tunnel construction. With TBMs, you first dig a hole and then place supports or walls to hold the remaining earth surrounding the void. In hyperTunnel’s technology, they create the tunnels underground and then excavate afterward. Once the structure is completed, the materials filling the tunnel’s void can be removed.
He argues that one of the significant advantages of this approach is the reduced use of construction materials. Instead of placing standard sections of tunnel walls along the entire length of the project, the outer thickness of the structure can vary to suit the actual geology and surrounding pressure at any point.
According to tunneling experts, the industry is calling for technological solutions to reduce costs and enhance efficiency. Currently, it can take years to design and build a TBM, and then you can only excavate one tunnel with it. A range of new companies promising to shake things up is gradually emerging, from Elon Musk’s Boring Company to hyperTunnel and others, all developing new methods to break through the hardest rocks on Earth.
Pipes are drilled into the rock surface (in blue), and from within them, countless robots (in orange) will build the tunnel walls before the central section is excavated.
Jasmin Amberg, project director at Amberg Engineering, a company founded by her grandfather specializing in underground construction, stated: “There is a lot going on, and I think that’s good because the tunneling industry needs to improve.” In her view, the tunneling business needs to develop faster and more sustainably.
At the same time, there are many projects waiting for them out there. China recently completed a 20 km railway tunnel in the Longmen Mountains after a decade of construction. In the UK, the HS2 railway project will connect London with towns in the north and will feature over 100 km of tunnels along the proposed route. Additionally, Peter Vesterbacka, who previously worked for Rovio, the developer of Angry Birds, is behind an ambitious plan to build an underwater tunnel between Finland and Estonia. These are just a few notable examples.
Amberg Engineering predicts that the demand for underground infrastructure will continue to rise in the future. And these tunnels are not just a means of escaping the rising temperatures on the surface due to climate change. “It might not be so bad to have a place with more stable temperatures,” she said.
Tunnels are not just for transportation. Troy Helming, founder and CEO of the San Francisco-based startup EarthGrid, emphasizes the need to place power lines underground. This is what his company aims to achieve. He notes that most transmission cables are above ground, exposing them to gusty winds, storms, and increasingly frequent wildfires.
“Our plan is to create a supergrid across North America, providing a map with colored lines showing the power grid extending from the East Coast to the Pacific and future offshore wind farms in the West. It’s a plan that could help link America’s fragmented power systems and potentially expand to Europe one day to harness the enormous offshore wind potential there,” Helming said. “It’s crazy and bold.”
One obstacle in tunneling is extremely hard rocks, such as granite and quartz, which make traditional drilling difficult or impossible in some areas. Helming is betting on a technology called “plasma torch”, which can heat rock to around 6,000 degrees Celsius, causing it to explode into glass shards. He suggests that this could allow for tunnel creation in hard rock at speeds over 100 times faster than current technology. EarthGrid is developing a prototype robot using five plasma torches, and Helming stated they are ready to conduct testing by March 2023. The company also aims to complete its first small-scale commercial project by the end of this year.
However, Helming notes that in the case of EarthGrid, the tunnels will not be circular but will take on a traditional horseshoe shape. It will be a square with an arch on top instead of a flat ceiling. He argues that this makes it easier to install cable supports.
EarthGrid technology utilizes plasma torches.
A competing company, Petra, also aims to tunnel through hard rock using thermal power, but they propose a thermal cutting device that uses a gas mixture and heat instead of plasma torches. Co-founder and CEO Kim Abrams stated that the idea is to overcome “geological nightmares” relatively easily.
“We completed a 10-meter long, 76 cm diameter tunnel through granite last week,” she said, adding that the company hopes to begin a commercial project next year. This company is also researching a separate solution to address other challenging cases, such as tunneling in extremely soft or flooded areas in coastal cities.
Of course, these tunneling technologies have yet to prove that they can succeed on a large scale. Jasmin Amberg commented that hyperTunnel’s concept is intriguing, but she is unsure how the robots will handle areas with hard or flooded geology.
Jian Zhao is a professor in the Department of Civil Engineering at Monash University in Australia. He and his colleagues have explored the use of laser, microwave, and high-pressure water technologies, among others, for tunneling applications. He is skeptical that Petra’s heat-based method will be sufficient for large tunneling projects, but he wonders if it could be used alongside conventional machinery.
Michael Mooney, a professor of construction and tunneling at the Colorado School of Mines, stated that investment sources are driving innovation. While it remains uncertain whether any of these new tunneling technologies will breakthrough to large-scale commercial success, he emphasized that faster, cheaper techniques are highly sought after in the industry.
He also argued that the Boring Company, Elon Musk’s venture developing its own type of TBM that can be activated from the surface to excavate underground tunnels, represents an innovation. Typically, you would need to dig a hole first and then lower the TBM into it to start creating the tunnel.
“Building a new tunnel boring machine for a specific project each time complicates and increases costs,” Mooney explained.
Elon Musk recognized the future of tunneling early on when founding the Boring Company.
Finally, Amberg noted that there are many aging tunnels worldwide that need maintenance and repair. New technologies are also required to carry out this work efficiently.
One of the companies targeting such markets is hyperTunnel. Lane-Nott stated that the company’s ultra-small robots will be able to dive into old tunnels to reinforce the outer structure without requiring operators to halt road or rail traffic inside.
The future of humanity will be filled with tunnels; this is an inevitability that has been acknowledged. The race is on to determine who will excavate them and how to do so in the fastest and most efficient way.
