Industry NewsTransportationTunnel Boring

First tunneling machine reaches future Wilshire/La Cienega subway station

The first of two tunnel boring machines (TBM) working on the D Line (Purple) Extension project in Los Angeles, CA broke through to the Wilshire/La Cienega subway station in Beverly Hills.

Metro announced that tunneling for the first 6.4-km (4-mile) section of the subway project is now two-thirds complete. More than 90 percent of the tunnels have been mined safely and Metro anticipates completing tunnel mining this summer. Excavation for all three subway station boxes beneath Wilshire Boulevard has been completed.

Elsie, the 910-t (1,000-st), 122-m (400-ft) long TBM, started west at the Wilshire/Fairfax station on May 29, 2020, and broke through to the Wilshire/La Cienega station site about 1.6 km (1 mile) away on Feb. 25.

Reaching this milestone is a significant win for Metro. Section 1 of project tunneling has presented challenges that have been successfully overcome by the project. En route to Wilshire/La Cienega, the agency’s modern, high-tech TBMs have mined through a unique combination of soils and geologic conditions, including tar sands and methane gas.

Metro’s TBMs were first lowered into the ground at Metro’s Wilshire/La Brea station site in the Miracle Mile area of Wilshire in October 2018. While advancing, the TBM tunneled about 18 m/d (60 ftpd). They worked five days a week, 20 hours a day.

Metro’s TBMs are pressurized, closed-face machines that minimize ground settlement during excavation. The tunnel is lined with precast concrete segments that are bolted together to form a ring. Segments are also gasketed to make the joints between segments water- and gas-tight.

When tunneling is finished for this project section, both of Metro’s TBMs will have mined nearly half a million cubic yards of earth — the equivalent of filling 2.3 million bathtubs with dirt.

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.

The $9.3-billion Metro Purple Line Extension is a nine-mile underground subway project that will extend the Metro Purple Line from its terminus in Koreatown to Westwood/VA Hospital in West Los Angeles. Section 1 is expected to be completed in 2023, Section 2 in 2025 and Section 3 in 2027.

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