Tunneling often proves a hard nut to crack. Civil engineers tasked with making new tunnels for a highway or subway station will often encounter rocks that will break even the sturdiest drill bits. When this inevitably happens, the demo squad is called in since only dynamite can save the day. But Petra, a startup hailing from sunny San Francisco, claims to have a solution.
The company has developed a thermal drilling semi-autonomous robot, aptly named “Swifty”, that can bore through the hardest geologies on earth by pulverizing rock. Rather than using mechanical drills, the robot employs a hot, high-pressure head that displaces rock without any direct contact.
In a recent demonstration, Swifty made tunnels between 18 and 60 inches (45-152 cm) in diameter, blasting through all sorts of rock. This includes a 24-inch tunnel through 20 feet of sioux quartzite, widely considered the hardest rock on earth that only dynamite can break. The robot made the tunnel at a rate of about an inch a minute.
“No tunneling method has been able to tunnel through this kind of hard rock until now. Petra’s achievement is due to Swifty’s thermal drilling method which efficiently bores through rock without touching it,” Ian Wright, Petra CTO and a Tesla co-founder, said in a statement.
Petra’s robot uses machine vision, an AI system that essentially is supposed to allow a robot to ‘see’ and make decisions based on the obstructions it encounters. When the robot is put to work, it blasts rock with a mixture of hot gas above 1,000 °C (2,000 °F), breaking the rock into smaller fragments. Once the rock is broken into bits, a powerful vacuum sucks in the fragments, clearing the way for more drilling.
“Petra is able to bore through the hardest geologies on earth, enabling customers to [install] underground utilities in difficult geographical regions most at-risk for wildfires and hurricanes. In addition, we can simplify urban utility projects in cities by allowing engineers to navigate below the maze of existing grid infrastructure,” according to a company statement.
The startup’s technology is inspired by experiments performed in the 1960s by scientists at Los Alamos National Laboratory, who imagined a nuclear-powered tunneling machine that could travel through Earth’s upper mantle or even the Moon’s crust. The rock-melting drill devised there never amounted to anything, but Petra picked up where others left off and conducted its first tests in an industrial park in Oakland, California in 2018. These initial tests used a plasma torch but it was soon abandoned in favor of gas and heat, which proved a less cumbersome setup.
Although Swifty could theoretically be used successfully in boring operations for tunnels serving transportation, there are already economically feasible solutions for this industry. Instead, Petra’s product aims to make tunneling through bedrock cheap enough to provide the right incentive for utilities to bury their electricity, broadband, and other lines underground.
According to Wired, burying power lines costs at least five times more than running them above ground while hard-rock installations can cost up to 20 times more. The advantage is that maintenance costs are much lower since the cables are sheltered from the elements, something that is particularly appealing in extreme weather-prone areas. Local citizens can enjoy a nice view of their city without having to see dangling spider webs overhead.
Petra claims that Swifty’s thermal drilling can cut the cost of tunneling through bedrock by 50% to 80%. But that remains to be proven before the industry can climb aboard the Swifty train. The startup is now testing its heat-based drilling method in a variety of settings and geologies from granite to limestone ranging from California to the Appalachian Mountains.