What happened in the Los Angeles tunnel collapse?

On Wednesday evening, a section of a massive tunnel under construction in Wilmington, Los Angeles, collapsed, trapping 31 workers deep underground. The collapse occurred just before 8 p.m. near South Figueroa Street and Q Street within the Clearwater Project, a $630.5 million wastewater infrastructure initiative spearheaded by Los Angeles County.

The affected tunnel, formally known as the Los Angeles Effluent Outfall Tunnel, is designed to carry treated wastewater from the Joint Water Pollution Control Plant to the Pacific Ocean. All 31 workers were safely rescued following an intense operation led by the Los Angeles Fire Department (LAFD) and specialized Urban Search and Rescue teams.

How were the workers rescued?

The collapse triggered an immediate response involving over 100 LAFD personnel, including Urban Search and Rescue (USAR) teams trained in confined-space emergencies. According to officials, the collapse occurred about 6 miles into the tunnel and 450 feet below the surface, which significantly complicated the rescue mission.

Trapped workers had to climb over a 12- to 15-foot mound of soil and debris to reach safety. LAFD chief Villanueva explained that a structural failure in the tunnel lining led to the incident, dumping tons of loose soil into the path of the workers.

“The workers had to climb through debris. They had to make themselves out through, and then rescuers actually came to them to assist them out,” said Chief Villanueva.

Despite the harrowing conditions, no serious injuries or fatalities were reported, a fact hailed as a testament to the effectiveness of the emergency response.

What caused the tunnel to collapse?

The workers were using a tunnel boring machine (TBM) — a giant mechanical excavator — when the collapse occurred. Preliminary assessments suggest that structural failure of the tunnel lining caused loose soil, more than 15 feet deep, to cave into the tunnel pathway.

This section of the tunnel was still under active construction and had not yet been reinforced, leaving it vulnerable to collapse. While no final determination has been made, experts will likely examine a combination of ground instability, equipment stress, and support failure as potential causes.

What is the Clearwater Project, and why is it important?

The Clearwater Project is one of Los Angeles County’s largest infrastructure efforts, aimed at modernizing aging wastewater systems dating back to the 1930s and 1950s. Once completed, the 7-mile-long, 18-foot-diameter tunnel will deliver treated wastewater to the ocean with minimal environmental risk, replacing older pipelines nearing the end of their functional lifespan.

The project is being developed by Flatiron Dragados, a major construction firm with expertise in large-scale tunneling. By using underground conveyance, the project minimizes surface disruption and strengthens long-term wastewater resilience for the region’s growing population.

How did city officials respond?

Los Angeles Mayor Karen Bass praised the rescue effort and spoke with several of the rescued workers shortly after their escape. In a post on X (formerly Twitter), she wrote:

“Thank you to all of our brave first responders who acted immediately. You are L.A.’s true heroes.”

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Mayor Bass also confirmed the City of Los Angeles mobilized immediate resources, coordinating across fire, safety, and engineering teams to ensure rapid extraction and safety assessment.

“The City of Los Angeles has mobilized resources to the tunnel collapse in Wilmington. More than 100 LAFD responders have been deployed,” she added.

Los Angeles Tunnel Collapse: What are the next steps?

With all workers safe, the focus now shifts to:

• Structural assessment of the remaining tunnel length
• Investigation into the precise cause of the collapse
• Repair and stabilization of the compromised section
• Delays in the construction timeline and potential cost overruns

Safety reviews will likely be conducted by OSHA (Occupational Safety and Health Administration) and Cal/OSHA, given the scale and seriousness of the incident.

The incident may also prompt wider scrutiny of tunneling safety protocols in high-density urban environments.

A tunnel under construction in Wilmington, Los Angeles, collapsed Wednesday evening, trapping 31 workers nearly 450 feet underground. The tunnel is part of L.A. County’s Clearwater Project, designed to upgrade wastewater infrastructure. All workers were safely rescued after climbing over debris. Officials are investigating the structural failure that caused the collapse.

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