This article is part of a three-part cover package on the Music City Loop. Read the rest here.
Many questions went through Nashvillians’ minds when Elon Musk’s The Boring Company announced plans for the Music City Loop — a tunnel from downtown to the airport serviced only by Tesla vehicles. Chief among them: “Is that safe?”
Nashville’s limestone bedrock is susceptible to forming sinkholes, and the 2015 “Nashville Next” report declared building a subterranean subway “cost-prohibitive” due to the city’s geology. So letting a private entity loose underground seemed unwise — especially when the company racked up almost 800 environmental violations for its Tesla tunnel in Las Vegas. (And you can get into the politics of this project elsewhere in this cover package.) The Boring Company hired an outside group to conduct an evaluation of the project and its environmental impact. The report was released in December but did little to satiate the skepticism of the Metro Council.
Middle Tennessee State University professor of geoscience Mark Abolins notes that engineers have surmounted similar geological challenges in countries like China and South Korea. But such projects are expensive. “Often it comes down to the economics you’re dealing with,” Abolins tells the Scene. “Engineers can design to overcome all sorts of challenging situations, but then actually building out what they’re designing and planning — that requires a certain amount of money.”
The Scene spoke with the MTSU professor about the challenges of working with Nashville’s limestone bedrock and what other information he’d like The Boring Company to make available. The following has been edited for length and clarity.
What was your reaction to the initial announcement about the Music City Loop?
I was probably a little surprised. “Wow — big project potentially happening in Nashville.” I am a geoscientist, so of course my interest was piqued. I started wondering, “How is this going to work? How are they going to design for the geology that we have around here?”
The Boring Company has been criticized about their lack of transparency, communicating mostly through their own website and press releases. Were they addressing your concerns throughout that process?
They have not put out a huge amount of information. … The first release of meaningful information to me as a technical person came in December when the environmental impact work by people external to The Boring Company was made public, and that allowed me and others to learn a little bit more about what they’re actually doing to make this work in this area.
And what did you think of that December report?
It has a lot in it that is what I would expect to be in it. For example, The Boring Company is using very sophisticated seismic techniques to look underground at the geology along the tunnel route. They’re also doing a lot of test drilling along the route, and they’re taking advantage of drilling [and] coring that’s been done by others in the past, so all of that was very much in line with what I would expect. And some of the details, like the seismic techniques that send vibrations down into the ground and allow engineers to get essentially sort of like an ultrasound of the earth. … Those sorts of details were in the information that came to light in December, as well as plans to divert water away from the tunnel at the surface, and also, as best as they can, to seal the tunnel using grout and other materials to keep water out of the tunnel, and also to keep anything that’s in the tunnel out of the surrounding environment.
Was there anything that left you wanting, or that you still wish had been addressed?
No, the report is very general. It does contain some technical detail. …. But there’s a lot more that they’re doing that they’re not going to make public.
Speaking of challenges, a lot of people bring up limestone.
It’s the limestone. Yeah, that’s exactly it. This kind of rock, which is likely to be encountered along parts of the tunnel route — it gets water in it. It has cracks in it. Naturally, water gets in the cracks, and it hollows out the limestone — has hollowed out the limestone over long amounts of time — resulting in fissures through which water can move. There’s some potential to encounter caves along the route. Tennessee has more caves than any other American state. That said, Davidson County would be one of the places where there are fewer caves, as opposed to other places — say, the Cumberland Plateau. …
[It’s] especially important when you’re dealing with limestone to use grout and other materials to seal the tunnel, keep water out of the tunnel, keep what’s in the tunnel out of the surrounding environment. … With limestone, you have potential for subsidence, for the ground surface to go down, potentially forming sinkholes. And over long amounts of time that has happened in the Nashville area.
Is there any information you’re particularly interested in seeing come out next from the company?
It would be great to know [if] they are able to do any sort of environmental testing inside the tunnel demonstrating that water is not coming in; environmental testing in the surrounding area, to demonstrate that anything involved in construction of the tunnel is not getting into the surrounding environment. … If they’re able to make some measurements of the ground surface along the tunnel route and make that sort of information available to the public, that would again address some of these concerns that people have. And just more information about the geology that they’re encountering as they work their way through the subsurface; to the extent that they can make that public, that would probably be helpful as well.
In terms of the level of information that has not been made available, is this unusual? Or is this common for projects of this kind of magnitude?
That’s difficult to gauge. Different projects have taken different approaches. Certainly, this one is very proprietary. They’ve released a relatively small amount of information, and I think that’s been very vexing to members of the Nashville city council, for example, and some residents … And while I can speak to this in relative terms like this project versus other projects, I would characterize this one as very proprietary, very, very private, only releasing the information that they have to release. At least thus far, that has been the approach they’ve taken, to a large extent.
As The Boring Company tunnels forward, we explore the company’s track record, the tunnel’s environmental impact and the politics surrounding the project
