Momentum

23 December 2019 (Last Updated July 30th, 2020 15:11)

The City of Los Angeles has seen several milestones this summer for its Purple Line extension, Nicole Robinson reports on the progress for each phase

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Divided into three sections, the Purple Line extension will add nine miles and seven stations to Los Angeles’ subway network. In June alone the Los Angeles County Metropolitan Transportation Authority (Metro) announced a series of milestones – the signing of the final major contract, the first TBM breakthrough, and unveiling the next set of TBMs.

Specifically the USD 9.8bn project will extend Metro’s subway to Century City and Westwood, two areas it describes as high density, as well as UCLA. The alignment largely follows Wilshire Boulevard, an important east to west road. Poised to open in advance of hosting the 2028 Olympics, these milestones are part of a very significant infrastructure project for residents and visitors alike.

Section 1

Connecting Koreatown to Beverly Hills, this first 3.9-mile (6.2km) stretch of twin tunnels includes three stations and is more than halfway through construction.

Design-build contractor Skanska Traylor Shea (STS), is using two 21ft- (6.4m-) diameter Herrenknecht EPBMs. Launched at the site of the future Wilshire/La Brea station, they mined east to a bulkhead at Wilshire/Western. Anticipating future expansion to the west, Metro had the bulkhead built as part of station construction in the 1990s.

The first TBM broke through on June 11 and the second on June 27. Metro says this was roughly an eight-month journey, with the first TBM averaging 60ft (18.2m) per day (five days per week/20 hours a day). Lining comprises precast segments for a finished diameter of 18ft (5.4m).

“Reaching the ‘halfway there’ mark is an exciting milestone in this critical transit project,” said Paul Ryan, Stantec’s administrative project manager overseeing the construction support services contract. “We are honoured to collaborate with Metro as we work to provide greater transit options for residents of Los Angeles. It’s exciting to see how far we’ve come.”

Geology along the whole of the extension comprises sands, silts, stones and boulders, as well as slightly weathered silt- and claystones.

Currently STS is dismantling both TBMs, which will be trucked back to the La Brea site for reassembly to mine the western drives of this first section. STS is in association with Parsons Transporation Group as lead designer and L.K. Comstock National Transit as sytems design and installation subcontractor.

Section 2

This contract concerns the 2.59-mile (4km) stretch of twin tunnels to the west of Section 1 and two stations. Tutor Perini/O&G (TPOGJV) is the design-build contractor, a joint venture between Tutor Perini Corporation as the managing partner, and O & G Industries, Inc.

Over the last decade this particular portion of the alignment has seen controversy and the threat of legal action from local residents who opposed tunnel construction beneath Beverly Hills High School.

The section is moving forward. On June 17, Metro officials and other Los Angeles politicians held a TBM unveiling ceremony to showcase two more, 21.75ft- (6.6m-) diameter Herrenknecht EPBMs. They are currently being staged at the Century City Station site for an early 2020 start. The first drives will be eastbound toward Wilshire/La Cienega in Beverly Hills at depths ranging from 50 to 120ft (15 to 37m).

The TBMs will tunnel five days per week, 20 hours per day and take approximately two years to complete the drives, with averages of 60ft mined per day expected.

Section 3

Metro awarded the third and final major work contract for the Purple Line Extension this spring. TPOGJV also has the design-build contract for this third section, which comprises 2.5 miles (4km) of twin-bored tunnels and two underground stations located at Westwood/UCLA and Westwood/VA Hospital.

Preconstruction activities including a subsurface investigation are underway for this portion of the project. Construction for the launch shaft and other infrastructure to enable tunnelling is scheduled to start this year.

Sections 1 and 2 are funded primarily by Measure R—a half-cent sales tax approved by Los Angeles County voters in 2008—and federal grants. In 2016 Los Angeles voters passed another sales tax, Measure M, that will fund infrastructure repair and development including expanding rail, subway and bus systems, including the third leg of the Purple Line extension.

Metro says it expects this newest measure to generate USD 860M million a year, in 2017 dollars, to build projects over the next 40 years.