Los Angeles, CA: New 18' Outfall (Effluent) Tunnel Collapsed, All 31 Workers Escaped Unharmed

(Satellite)

lacsd, p1

The yellow cylinder to the left of the opening is the basket that the crane used to bring up eight workers at a time. The workers had to climb over a 12-15' pile of loose soil leaving just 3' at the top of the tunnel. Only minor injuries were reported among the 27 workers and 4 rescuers.

ABCnews

ABCnews @ 1:14

The old tunnels were built in 1937 and 1958. The tunnels dump treated wastewater into the ocean. [lacsd, p2] If I remember correctly, they were 8' and 12' in diameter. The new tunnel is 18'.

lacsd, p3

In this view, we can see in the lower-left corner a stockpile of the segments that the Tunnel Boring Machine (TBM) uses to line the tunnel. This news report said the workers had to walk 5 miles to the entrance. Other reports indicated that they had to walk about a mile to get to the shuttle that would take them the last 5 miles to the entrance. The tunnel's planned length is 7 miles.

ABCnews
"There was a location that squeezed the tunnel and forced it to partially collapse." [Robert Ferrante, Chief Engineer & General Manager, LA County Sanitation Districts @ 0:45]

Satellite

"The cave-in apparently happened between the tunnel boring machine, 5 miles in from the only entrance, and the construction crew working 6 miles in, said Michael Chee, spokesperson for the Los Angeles County Sanitation Districts, which is in charge of the nearly $700 million project. The workers were about 400 feet underground....Firefighters said workers had to climb over 12 to 15 feet of fallen dirt and debris to reach the tunnel boring machine and then were transported by vehicle back to the opening. Some people had to be pulled out....The workers were operating the boring machine when the collapse occurred said Robert Ferrante, chief engineer and general manager for the sanitation districts. 'A section that they have already built had squeezing ground and had a collapse, a partial collapse,' he told reporters." [Associated Press article by Damian Dovarganes and Julie Watson in the July 11, 2025, edition of Chicago Tribune]

The first sentence confused me when I read it because a TBM works at the end of the tunnel. Given Robert's comment, I think the TBM was six miles in, and the collapse happened around the 5-mile mark. It is scary to learn that the soil pressure could cave in the concrete segments that are installed to hold the ground up. Perhaps grouting hadn't reached its full strength.

lacsd, p5

This diagram makes me appreciate that the Deep Tunnels dug in Chicagoland were through competent rock.

lacsd, p7

The contract for the Clearwater Project was awarded for $630,500,000 in Jan 2019 with a "notice to proceed" in Apr 2019. The main shaft was dug Jan-Jul, 2020. The TBM was delivered in Oct 2020, and mining began in Jan 2022. As of July 24, 2024, 4.4 miles had been dug, and completion was expected to be in 2Q 2025. [lacsd, p4,5] (I'm writing this July 12, 2025, so that schedule has already slipped.)

FlatironDragados

"Today [I could not find a date on the webpage], the Sanitation Districts of Los Angeles County (Sanitation Districts) awarded a $630 million construction contract for the Clearwater Project to Dragados USA, Inc....Dragados brings extensive tunneling expertise to the Clearwater Project. The firm has completed more than 530 underground projects in 20 countries, totaling over 800 miles of tunnel. For a recent project in Seattle, Washington, Dragados utilized a 57‐foot diameter tunnel boring machine, which was the largest tunneling machine in the world at that time. “We look forward to working on this important infrastructure project,” said Tom Robertson, Vice President of Dragados. “Our vast experience in tunneling through a wide range of geological conditions will be an asset for the Clearwater Project.”" [cwea]

The Seattle tunnel project was a disaster. The TBM got stuck. They had to dig an access shaft, bring the TBM head up for repair, then lower the head back down to the machine. I had started detailed notes on the tunnel project while it was still in progress, but I got so depressed that I quit following the project. I would not be surprised if lawsuits are still in progress. They were very lucky that it got stuck below vacant land rather than under downtown buildings.

Dec 14, 2020: Mammoet posted
#MilestoneMonday: After a year of meticulous planning, #Mammoet liberated the 1,700t tunnel boring machine, "Big Bertha", in just 16 hours after it had stalled approximately 36m (120 ft.) underground in #Seattle.