Dive Brief:
- The Los Angeles County Metropolitan Transit Authority has completed tunneling for the D Line Subway Extension Project, also known as the Purple Line, the agency announced on April 2. The total cost of the extension is $9.5 billion, per the Los Angeles Times.
- Metro will continue to work with two joint ventures — one of Skanska-Traylor-Shea, and another made of Tutor Perini and O&G Industries — to complete seven new underground stations, per the release. The first section of completed work is slated to open in 2025.
- Metro referred to the tunnel, which took five years to complete, as a feat of modern engineering, and said the areas builders drilled under were among the densest and most geologically challenging in the Los Angeles region and nation.
Dive Insight:
This milestone didn’t come without hurdles, however. In October 2022, the project ground to a halt after LA Metro shut down the work Tutor Perini and O&G Industries were performing due to safety issues on a section of the extension. Work was allowed to resume that November following additional safety training.
Contractors used the latest tunnel boring machine technology to excavate approximately 40-60 feet per day, per the release. Four-hundred-foot-long, 21-foot-diameter earth digging machines use closed face, pressurized technology to minimize ground settlement during excavation. The devices also lined the tunnel with precast concrete segments, bolted together to form secure rings, which makes them water- and gas-tight and prevents related risks.
This is not LA Metro’s first time with the process — the same TBM technology was used on its 2009 Eastside Extension Project.
Challenging terrain
The contractors’ work was compounded by the difficulties of the environment they toiled in — the team had to work around abandoned oil wells, gassy ground and the La Brea Tar Pits, which exposed the team to tar sands.
To deal with this problem, teams used horizontal directional drillings to probe the earth, which allowed the pros to identify and remove potential objects before any damage to the TBM equipment occurred, per the release. They also used the same method to navigate and avoid unmapped, abandoned oil wells underneath Beverly Hills High School.
“The D Line Subway Extension is one of the most complex engineering feats that Metro has undertaken,” said Lindsey Horvath, Chair of the LA County Board of Supervisors and Metro Board Member, in the release.
The second and third section of the project are scheduled to open in 2026 and 2027, respectively.
Correction: In a previous version of this article, the total cost of the D Line extension project was incorrect. It is $9.5 billion.
