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The $630 million tunnel that no one in Los Angeles knew existed collapsed at a depth of 137 meters and trapped 31 workers — all climbed over the debris and emerged alive in less than an hour
On the night of July 10, 2025, the Los Angeles tunnel of the Clearwater Project partially collapsed 137 meters below the surface of Wilmington, California.
At that moment, 31 workers were operating a tunnel boring machine nearly 9 kilometers from the only vertical exit.
In a matter of seconds, the ceiling gave way. Additionally, a 4-meter pile of soil and debris blocked the way back.
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Even so, all 31 workers climbed over the debris, reached the internal transport vehicle, and made it to the surface unharmed before 9:20 PM — less than an hour and a half after the collapse.
No one required hospitalization. On the other hand, the $630 million project was put on indefinite hold.
What is the Clearwater Project — and why did no one know about it
The Clearwater Project is one of the largest infrastructure works in Los Angeles County. However, the Los Angeles tunnel flew under the public radar for over a decade.
In practice, the project will replace two old tunnels — built in 1937 and 1958 — that transport treated wastewater from the Hyperion Water Reclamation Plant to ocean discharges near San Pedro.
The new tunnel is 11.2 kilometers long and 5.5 meters in diameter. Thus, it runs 137 meters below entire neighborhoods without the residents ever knowing it existed.
Construction began in late 2019. Consequently, the actual tunneling began in 2021, with completion expected by the end of 2025.
Until the night of July 10, the project had never recorded a serious accident.
How the Los Angeles tunnel collapsed — and what the workers faced
Around 8 PM, the soil around a segment of the Los Angeles tunnel exerted extreme pressure on the lining rings.
According to chief engineer Robert Ferrante of the Los Angeles County Sanitation Districts, the phenomenon is known as “squeezing ground” — when layers of soft or fractured soil compress the tunnel structure beyond its designed limit.
The result was the partial collapse of a section, dumping tons of soil and debris inside the tunnel.
At that moment, the 31 workers were at the excavation front — operating the TBM (Tunnel Boring Machine), removing soil and installing lining segments.
The collapse point was about 1.6 kilometers behind them. In other words, the way back was blocked, but the workers were physically unharmed.
The escape inside the Los Angeles tunnel: climbing 4 meters of debris in the dark
Instead of waiting for external rescue, the workers themselves took action. They climbed the pile of 4 to 4.5 meters of soil and debris that blocked the tunnel.
Colleagues positioned on the other side of the barrier had already begun digging to create a passage. Additionally, the internal transport vehicle — a train used to move teams within the tunnel — was waiting on the other side.
Thus, one by one, the 31 men crossed the debris, boarded the vehicle, and traveled the remaining kilometers to the vertical access shaft.
By 9:20 PM, everyone was on the surface. The Los Angeles Fire Department (LAFD) assessed each one medically. None required hospital transport.
Mayor Karen Bass stated at the press conference: “What started as a very scary night… We are all blessed today in Los Angeles. No one was injured. Everyone is safe.”
The numbers of a project few knew about
Despite being the largest construction project in LA County, Clearwater never made headlines — until the collapse. To give an idea of the scale:
- Total cost: $630.5 million (~R$ 3.5 billion)
- Tunnel length: 11.2 km (7 miles)
- Diameter: 5.5 meters (18 feet)
- Depth: 137 meters (450 feet)
- Workers at the front at the time of the collapse: 31
- Evacuation time: less than 1h30
- Construction start: late 2019
- Contractor: Flatiron Dragados (joint venture)
County Supervisor Janice Hahn stated after the incident: “We will investigate exactly what caused this and do everything we can to prevent something like this from happening again.”
The invisible enemy beneath the Los Angeles tunnel: the soil that crushes structures from within
The phenomenon of “squeezing ground” is not uncommon in deep tunnel projects. However, predicting where and when the soil will compress the structure beyond its limit remains one of the greatest challenges in underground engineering.
The route of the Los Angeles tunnel passes through two active fault zones — the Palos Verdes Fault Zone and the Cabrillo Fault Zone. In other words, the tunnel was excavated through one of the most geologically unstable areas in California.
When the collapse occurred, the boring machine had advanced 1,250 meters beyond the initial high soil pressure zone. In practice, engineers believed the most dangerous section was already behind them.
This situation is similar to other tunnels at extreme depths like Rogfast in Norway, which advances 392 meters beneath a fjord.
Investigation opened and work halted indefinitely
Cal/OSHA — California’s occupational safety agency — opened an investigation immediately after the incident. Additionally, the Sanitation Districts initiated an internal analysis together.
Operations in the tunnel remain halted indefinitely. Consequently, the expected completion by the end of 2025 has become impossible, and there is no new estimated date.
In comparison, underground projects like the neutrino detector at 1,520 meters depth in South Dakota require years of drilling under equally dangerous conditions. However, the difference is that DUNE operates in stable rock, while Clearwater faces soft soil and active seismic faults.
The additional cost of the delay could significantly raise the $630 million budget. Nevertheless, no official estimate of financial impact has been released so far.
The paradox of building beneath a city that doesn’t know the project exists
According to ABC7, communities in the Harbor Area — including Wilmington and Carson — barely knew that an 11-kilometer tunnel was being excavated beneath their feet.
Indeed, the project “flew under the radar” for over a decade. The irony is that the Los Angeles tunnel will transport treated wastewater that keeps the region’s beaches clean — an essential service that no one notices until something goes wrong.
For the 31 workers who climbed over debris at a depth of 137 meters and walked out, the question that remains is different: will the next time the soil compresses the tunnel, everyone have the same luck?
As reported by Newsweek, the training and safety protocols — refuge shelters, LAFD on standby, internal evacuation vehicles — were crucial for the incident to end without casualties.
Still, the collapse exposed how much a city’s invisible infrastructure relies on workers who risk their lives in conditions that few can imagine.
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