Elon Musk's The Boring Company has unveiled its first hard-rock tunnel boring machine, designed to drill through Nashville's limestone terrain, The Tennessean reported. The machine is a major engineering leap for the company as it prepares for this challenging project.
The company announced on X that its hard-rock TBM has entered final acceptance testing before it's shipped to Tennessee. The machine can generate up to 4 million pounds of grip force and 1.5 million pounds of maximum thrust load, and it has a 15-filter dust removal system.
Final acceptance testing of TBC's first hard-rock TBM before it ships to Nashville! The TBC tunnels built in Vegas, Austin, Bastrop and Los Angeles were in mostly soft soil, while Nashville is hard rock. Shown is:
— The Boring Company (@boringcompany) November 10, 2025
-Dust removal system, equipped with 15 high capacity… pic.twitter.com/oW2QGvPMBn
Previous Boring Company projects in Las Vegas; Los Angeles; and Austin and Bastrop, Texas, used machines designed for soft soil — but Nashville's geology requires different technology.
"It's a tough place to tunnel, Nashville. If we were optimizing for the easiest places to tunnel, it would not be here," Boring Company CEO and President Steve Davis told The Tennessean. "You have extremely hard rock, like way harder than it should be. It's an engineering problem that's fairly easy and straightforward to solve."
The Music City Loop will run beneath the Outer Nashville Basin, made up of cherty Mississippian-age limestone. The rock can feature underground caves that complicate construction processes.
"Limestone is generally a stable sedimentary bedrock material with strength parameters that are favorable for tunneling," Jakob Walter, founder and principal engineer of Haushepherd, said. "Limestone is, however, fairly soluble when compared to other rock materials, and can dissolve over long periods of time when exposed to water."
Walter added that "unexpected encounters" with dissolved rock during tunneling can result in major delays and instability.
"In urban locations, structures at the ground surface should also be constantly monitored with robotic total stations or similar surveying equipment to identify any early signs of movement or distress," he said.
Residents stand to gain a new transportation option that reduces surface-street traffic congestion and commute times. The company's hard-rock boring technology could also expand tunnel transit options to other cities with challenging geology, bringing electric vehicle-based transportation systems to more communities.
The Boring Company's progress comes as Tesla, Musk's EV company, continues facing headwinds. Its deliveries have declined this year, though the company remains the top-selling EV brand in the United States.
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