An 18 -section of the Los Angeles Outfall Tunnel effluent diameter partially collapsed at the end of Wednesday, briefly trapping 31 construction workers about six kilometers from the only access to the Axis.
The crews of the Urban and Paramedic Search and Paramedic Rescue units of the Los Angeles Fire Brigade entered the tunnel and found that the colleagues of the trapped men had already climbed on a pile of soil and remains of 12 to 15 feet to reach and evacuate them through a tunnel transport vehicle.
According to a statement from the Los Angeles county sanitation districts, the incident took place at 19.45; At 21.20, the 31 workers returned to the surface, without injuries and were released after a medical evaluation.
“What started as a very frightening evening … I just have to tell you that we are all blessed today in Los Angeles. No one was injured. Everyone is sure,” said Bass mayor, at a press conference at the beginning of the morning.
The incident took place within the Los Angeles effluent tunnel of the Clearwater Set program, a $ 630.5 million duct, seven kilometers long, designed to carry wastewater treated from the hyperion water claim plant to Ocean exits near San Pedro, about 7.5 miles north of Long Beach. The tunnel coating consists of prefabricated concrete segments in snails and joints that are installed after the TBM.
The temporary head of firefighters, Ronnie Villanueva, added that more than 100 firefighters, drones, search canines and dangerous material specialists were staged by what was quickly climbed at a major emergency tunnel rescue at 19:58.
The Clearwater project replaces existing wastewater tunnels built in the 1930’s and 1950’s.
Map courtesy of the Los Angeles County Sanitation Districts
In a statement, the Sanitation District said that the collapse was not an environmental risk, as the tunnel was not in service.
Cal/Osha and the Los Angeles County Sanitation District have launched joint research on collapse, which engineers say may have been precipitated due to the conditions of “esprescom terrain”, when mild or fractured soils exert an interior pressure on the TBM shield.
The Department of Health said that Clearwater’s tunnel operations have stopped while this investigation occurs and there is no deadline for the time the process will take.
Construction operations
The LAFD said that trapped men worked on the tunnel face: driving the tunnel boring machine controls, removing the excavated soil and guiding new segments of rings, when the collapse took place. Four additional crew members had a backup just behind, helping -with the removal of the muck and the manipulation of equipment.
The TBM head mounted before the release by 2021.Photo courtesy of the Los Angeles County sanitation districts
Flatirondragados is the main contractor, who uses a TBM Herrenknecht called “Rachel”, for the sections of an internal diameter of 18 feet at 450 feet below the existing roads.
According to the LAFD, the failure occurred at the gentle part of the alignment in the city of Wilmington. The alluvi of the port area is more susceptible to “tightening the ground” when punctured by a TBM.
As the TBM progresses, it installs a segmental concrete coating prefabricated in 5 -foot rings immediately behind the head. This “Construct AS You Go” approach provides continuous support for the recently excavated terrain and limits deformation, according to the agency.
According to the Sanitation District, the TBM is expected to end the tunnel this year and the construction will be completed in 2027. The new line is planned operational in 2028. The tunnel will replace the aged pipes installed in 1937 and 1958, the seismic risks of cross -failure and overflow during major storms.
Parsons Corp. and McMillen Jacobs associates directed the geotechnical and design phases, using deep and soil analysis to map the conditions of land.
The Flatirondragados Safety Plan includes recurring inspections of segmental coating, emergency shelter areas every 1,500 feet and rescue exercises in coordination with LAFD.
Construction work engines work exclusively underground, with daily pre-torn security information and continuous atmospheric monitoring in trapped entrance areas. Continuous atmospheric monitoring and call rescue drills with LAFD are integrated into the construction calendar, which limits all the interruptions on the surface on weekdays and restores the places to the pre-construction conditions once completed.
