A wall of white granite towered above a small team of engineers gathered in a California quarry. The ancient, ultra-hard material before them was, to most things, completely impermeable.
Then the rock-melting tunnel-boring machine (TBR) roared to life.
“It’s kind of like igniting a rocket,” says Troy Helming, founder and chief executive of EarthGrid, as he describes the initially loud process of lighting up three plasma torches at the front of his company’s machine.
Those torches, set within a spinning head, soon quieten down as they produce a stream of super-heated plasma reaching 27,000C – significantly hotter than the surface of the Sun.
During the California test this January, EarthGrid’s cigar-shaped boring machine chewed through three metres of granite. “We create, basically, a tornado – a violent vortex inside the tunnel,” says Helming, as he explains how this helps the machine to suck away debris, which at times takes the form of lava.
“I actually got a little bit emotional watching it,” adds the entrepreneur. “I’ve been waiting for this moment for 10 years.”
Emerging technologies like this could make tunnel boring quicker and easier. Putting electricity or telecommunications cables, substations, data centres and other critical infrastructure underground, while good for securing such equipment, has long been a very expensive and difficult option.
Engineering firms told BBC News they are seeing rising demand for undergrounding, in part due to Russia’s war with Ukraine, which has revealed just how vulnerable above-ground facilities can be to drone attacks.
Helming says he has fielded interest from companies that want to use his tunnel boring machine for power and fibre optic cables, or pipelines that could transport water, natural gas, or ammonia, for example.
One project the company has eyed up would involve boring tunnels for an underground freight-distribution system around airports and warehouses. “To take more trucks off the road,” says Helming.
The January TBR test went well, though the machine “over-bored” slightly to the top and left of the tunnel, says Helming. His team plans to adjust the machine so that it will create a vortex that spins in alternate directions every five minutes or so, in order to correct this, and they hope the TBR could see commercial deployment as early as next year.