The critical tech staying safe by going underground. 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.

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.

Humans have long buried things in the ground to protect them. Doing it safely and cost-effectively with modern infrastructure is hard but sometimes, even in remotest places, it's an option worth taking. 'What we're seeing is that brutal materiality is still important,' says Alexander RE Taylor, senior lecturer in communications at the University of Exeter.