We Asked Geotechnical Engineers If Elon Musk’s Crazy Underground Tunnel Dream Is Realistic
They're like a "subway system on steroids."
When Elon Musk announced The Boring Company and his plan to build labyrinthine freeways under cities like Los Angeles, I was reasonably skeptical.
What does a network of tunnels, descending up to 30 layers deep, do to a city's structural integrity? What happens if there's an earthquake? Can you perforate a city's subterranea so tremendously without risking a terrible collapse?
I spoke to a few geotechnical engineers about my admittedly unfounded fears, and asked if it's possible, geologically speaking, to dig too far and too deep.
"The short answer is that this is absolutely something that is 'engineerable,'" Matthew Evans, an associate professor at Oregon State University's School of Civil and Construction Engineering, told me. "Excavating giant caverns would be difficult, though not impossible. Drilling tunnels would, I think, be more straightforward."
Ben Mason, another assistant professor of civil and construction engineering at the university, told me 30 layers of tunnels seems ambitious.
"I could likely spend the next 30 years with a team of five full-time research associates studying the challenges surrounding this problem," Mason said. "My initial gut reaction is: how would this be constructed? How would you regulate the temperature in the tunnels? How would you keep the lower tunnels dewatered?"
Right now, The Boring Company's biggest challenges are digging at a monstrous scale, and quickly. In the future, the project's most prohibitive barrier will likely be its astronomical cost, ranging in the billions.
"I am having a very hard time imagining a situation where this is the most cost-effective way to facilitate transportation around a large urban area," Evans said, "Put another way, how many more people would we need to be moving per day in order to efficiently use such an underground system? That's a question for the transportation engineers, urban planners, and economists, of course."
We know, from the company's video, the tunnels are meant to work like conveyor belts—propelling cars along a predetermined route at a constant speed. The Boring Company has already broken ground on a test trench that's 30 feet wide, 50 feet long, and 15 feet deep in Los Angeles, according to Bloomberg.
But digging can have its downsides, which is why no sane engineer would start boring without taking necessary precautions. "It really depends on the geologic condition that underlies a given city," said Armin W. Stuedlein, an associate professor at Oregon State University's School of Civil and Construction Engineering. "Any time there's a tunnel, there's the potential for movement of soil, and anything supported by that soil."
All of the geotechnical engineers I spoke to assured me that Musk's tunnels aren't so different from regular subway tunnels. A "subway system on steroids," Evans remarked.
Still, if this exact type of infrastructure already existed, Musk wouldn't be pursuing it. In an interview with Bloomberg, he pictured thousands of miles of tunnels, 30 levels deep, zipping people across metropoli like Los Angeles. Engineering-wise, vast networks of underground tubes are doable, even where challenges like seismicity—the potential for earthquakes—exist. San Francisco's $267 million earthquake retrofitting for its Transbay Tube is proof of that.
"Seismicity does complicate the tunnel building process. In particular, the rock is usually low quality, because many years of tectonic processes has broken it up and weakened it. However, weakened rock is usually not something that time, careful engineering, and money can't handle when building tunnels," Mason said.
Most nightmare scenarios, my sources told me, can be mitigated for. But one potentially novel aspect is the depth at which Musk might need to dig to make this a reality.
Since we have few details regarding the tunnels themselves, it's impossible to know how deep he intends to go. London's "Chunnel," for instance, which runs beneath the English Channel to Paris, is 250 feet deep at its lowest point. And the world's deepest rail tunnel belongs to Switzerland's Gotthard Base Tunnel, whose maximum depth is 8,040 feet underneath the Swiss Alps.
Other criticisms, like the possibility that Musk's tunnels will further segregate poorer urban communities, are worth considering. But tunnels, especially those used for public transit, will probably be our best bet when it comes to sustainability—a value that's going to become increasingly more important in the future. "Buried," Stuedlein said, "is a lot better for the environment."