LA Metro Finishes 5 Years of Tunneling for D Line Subway Extension Project

Courtesy of LA Metro

LOS ANGELES – LA Metro has finished five years of tunneling. The Tunnel Boring Machines (TBMs) added nine additional miles to the D Line.

LA Metro announces it has completed five years of tunneling, therefore adding nine miles on its D Line. The work was part of its D Line Subway Extension Project to connect downtown Los Angeles with West Los Angeles.

Tunnel Boring Machines (TBM) were used to excavate 40-60 feet daily. The machines measure at 400 feet long and 21 feet in diameter. They utilize “closed face, pressurized TBM technology that minimizes ground settlement during excavation.” In addition, they line the tunnel with precast concrete segments that were bolted together. This is to form secure rings to make them water-tight and gas-tight to reduce risks. This TBM technology was also used on Metro’s 2009 Eastside Extension Project. Over the last five years, there were a plethora of challenges that Metro had to face which include “gassy ground, tar sands and abandoned oil wells.” 

L.A. City Mayor and Metro Board Chair Karen Bass said “This safe completion of tunneling through this part of Los Angeles is a milestone in Metro’s work to expand fast and reliable public transit across the region. . . When completed, the D Line extension will make Metro transit available to 53,300 more weekday riders traveling between Downtown Los Angeles and the Westside. Thank you to all of the construction workers who have given their time and talent to successfully complete the tunneling.”

Chair of the LA County Board of Supervisors and Metro Board Member Lindsey Horvath said “The D Line Subway Extension is one of the most complex engineering feats that Metro has undertaken. . . Its complexity is matched by the immense value the project will bring to Los Angeles when it opens and carries 30,000 daily riders through one of our densest and most job-rich regions.”

“The end of tunneling work on this project is a triumph of engineering, planning and execution. Our construction team undertook a painstaking process that helped us keep everyone in these communities safe and deliver a better project for the people of L.A. County,” said Stephanie Wiggins, Metro CEO. “We have proven yet again our capability to safely tunnel underneath a range of different structures as well as sensitive and historic sites.”

While the tunneling is complete, Metro says it will continue to work with two contractors “as part of a joint venture with Skanska-Traylor-Shea and Tutor-Perini/O&G to complete seven new underground stations in Section 1 between Wilshire/Western and Wilshire/La Cienega, Section 2 between Wilshire/La Cienega and Century City, and Section 3 between Century City and Westwood.” Metro says the forecasted openings for Section 1, 2 and 3 are 2025, 2026, and 2027, respectively. Funding for the project came from the 2008 Measure R and 2016 Measure M voter-approved transportation sales tax measures which “were then matched by federal funding, which ultimately amounted to approximately half of the project’s overall cost.”

Metro states that once the project is completed, riders will be able to travel between downtown Los Angeles and Westwood within 25 minutes.

As previously mentioned, Section 1 has a projected opening of 2025. It spans three stations and 3.92 miles. From the Wilshire/La Brea station site, the TBM began digging eastwards toward the existing D Line station at Wilshire/Western, which it reached in June 2019. After, the TBM was removed from the ground, transported back to the La Brea Avenue site, and it was launched westward. This is because “launching a TBM at the Wilshire/Western site would have required a large, time-consuming, and costly additional excavation.”  In April 2021, it broke through to the Wilshire/La Cienega subway station site in Beverly Hills. The second TBM followed the next month.

Section 2 includes 2 stations and spans 2.59 miles. The tunneling for this stretch began back in April 2020. Both TBMs started “at the staging yard at the future station at Century City/Constellation and then headed east.” The first TBM reached Wilshire/Rodeo station box in January 2021 with the second TBM following a few weeks later. By January of the next year, the TBMS “pulled into the excavation for the future station at Wilshire/Rodeo.” The first reached a future station at Wilshire/La Cienega in November 2022, with the second TBM following in January 2023.

Section 3 includes 2 stations and spans 2.56 miles, making it the shortest section. Two TBMs launched into the ground at the future Westwood/VA Hospital station on the west side of the VA campus in October 2020. For section 3, Metro states it used two contractors at once. “One team of contractors operated the TBMs while another team created the station boxes.” (For sections 1 and 2, contractors dug out the stations first.) Metro connected the tunnels to the future station box by digging down and meeting the existing tunnels “by bursting through precast segments.”

Now that tunneling is complete, Metro says crews will begin concrete work in said tunnels to support tracks. In addition, they’ll create cross passages of twin tunnels for emergency use. After, crews will build the stations.