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Dive brief:
- The Los Angeles County Metropolitan Transit Authority has completed tunnel construction $2.4 billion D Line subway expansion projectalso known as the Purple Line, the agency announced on April 2.
- Metro will continue to work with two joint ventures, one from Skanska-Traylor-Shea and another from Tutor Perini and O&G Industries, to complete seven new subway stations, the statement said. The first section of the completed works is scheduled to open in 2025.
- Metro hailed the tunnel, which took five years to complete, as a feat of modern engineering, saying the areas the builders drilled were among the densest and most geologically challenging in the region and the nation of Los Angeles.
Diving knowledge:
However, this milestone did not come without obstacles. In October 2022, the project was subsequently halted LA Metro shut down the work Guardian Perini and O&G Industries were acting over safety concerns in a section of the extension. The job was allowed to resume that November after additional safety training.
Contractors used the latest tunnel boring technology to excavate approximately 40-60 feet per day, according to the release. The four-hundred-foot-long, 21-foot-diameter earthmoving machines use closed-face pressure technology to minimize soil settlement during excavation. The devices also lined the tunnel with precast concrete segments, bolted together to form secure rings, making them water and gas tight and preventing related risks.
This isn’t LA Metro’s first time with the process — the same TBM technology was used 2009 Eastside Expansion Project.
Challenging terrain
The contractors’ work was made worse by the harsh environment they were working in: the team had to work around abandoned oil wells, gas fields and the La Brea tar pits, which exposed the equipment in tar sands.
To address this issue, crews used horizontal directional drilling to probe the ground, allowing professionals to identify and remove potential objects before any damage to the TBM equipment occurred, according to the release. They also used the same method to navigate and avoid abandoned, uncharted oil wells beneath Beverly Hills High School.
“The D Line subway extension is one of the most complex engineering feats Metro has ever undertaken,” said Lindsey Horvath, Chairwoman of the LA County Board of Supervisors and Metro Board Member , in the statement.
The second and third sections of the project are scheduled to open in 2026 and 2027, respectively.
