LA Metro TBM makes "break through" for Purple Line Extension

Marking a new construction milestone for the Metro Purple Line Extension project, the Los Angeles County Metropolitan Transportation Authority (Metro) announced that its first Tunnel Boring Machine (TBM) has officially broken through to connect with the Wilshire/Western subway station in Koreatown.

The 1,000 ton, 400-feet long TBM named “Soyeon” burrowed through the last remaining cluster of soil 50 to 70 feet below busy Wilshire Boulevard Tuesday afternoon, June 11. The TBM is one of two TBMs to mine approximately two miles of parallel subway tunnels between the future Wilshire/La Brea Station and the existing Wilshire/Western Station.

The breakthrough marks an early triumph in the decades-long effort to extend L.A.’s subway farther west underneath Wilshire Boulevard, one of the busiest and most congested urban thoroughfares in the United States.

“Our last TBMs at Wilshire/Western were powered down over 23 years ago, so we are definitely going ‘back to the future’ in our modern-day mission to extend this subway,” said L.A. County Supervisor and Metro Board Chair Sheila Kuehl. “I’m glad that this enormously complex operation has gone off without a hitch. It’s a testament to the ways in which Metro and its contractors meticulously plan and execute their tunneling work.”

Soyeon was originally lowered into the ground at Metro’s Wilshire/La Brea station site in the Miracle Mile area of Wilshire last October. While advancing, the TBM burrowed about 60 feet per day. It worked five days per week, 20 hours a day. The digging has taken eight months to reach the bulkhead — the retaining wall at the face of the Wilshire/Western subway terminus. Metro anticipated future westward subway expansion and built the bulkhead wall as part of station construction. The station originally opened in 1996.

A second TBM named “Elsie” that launched six weeks after Soyeon is also expected to break through to Wilshire/Western later in June. When done tunneling this project section, both TBMs will have mined nearly half a million cubic yards of earth — the equivalent of filling 2.3 million bathtubs with dirt.

“Our tunneling achievements to date prove that we can successfully mine through some of the most challenging conditions that any subway project anywhere in the world is likely to face,” said Metro CEO Phillip A. Washington. “We are fortunate to have an international, industry-leading team of tunneling experts who know how to tunnel safely. We also have a project team with a laser-like focus on reducing construction impacts to local communities.”

After tunneling this first leg, both TBMs will be partially disassembled. Some pieces will be trucked back to their Wilshire/La Brea insertion point while most of the TBMs will be pulled back through the new tunnels. The TBMs will then be reassembled and will then tunnel west to future station sites at Wilshire/Fairfax and Wilshire/La Cienega. The TBMs are expected to reach the end of the four-mile subway section in Beverly Hills by mid-2020.

Following the tunneling operation, Metro will focus on completing construction of its first three subway stations over the next three years. This first section of the Purple Line extension is scheduled to open in 2023. 

The name Soyeon is Korean for “bright” and “beautiful” and was named after female astronaut and mechanical engineer Yi Soyeon. The name Elsie is a tribute to Elsie Eaves, the first female to be elected as a member of the American Society of Civil Engineers. Metro held a contest for local students to name the TBMs in 2018. The winning names were chosen by Marianne Gutierrez, a local Fairfax High School student.

The TBMs were manufactured in Germany by Herrenknecht AG. Metro has contracted with Skanska Traylor Shea (STS), a joint venture to design and build the first section of the project.

“We’re pleased to celebrate this major project milestone,” said Mike Aparicio, Executive Vice President of Skanska USA, lead partner of the Skanska Traylor Shea (STS) design-build joint venture team. “The project will deliver immediate benefit to the community and long-term benefit from its award-winning, environmentally sustainable construction.”

The $9.8-billion Metro Purple Line Extension is a nine-mile underground subway project that will extend the Metro Purple Line from its current terminus in Koreatown to Westwood/VA Hospital in West Los Angeles. Section One is expected to be completed in 2023, Section