Westside Subway Extension Project, Section 1

As part of a joint venture, Traylor is constructing the $1.6 billion design-build construction of the Westside Subway Extension, Section 1, in downtown Los Angeles. This is the first of three projects to extend the Purple Line from Wilshire Center to Westwood.

This project will add 3.92 miles to the Purple Line, beginning at the Wilshire/Western Station. The twin tunnel alignment will travel beneath Wilshire Boulevard, and underground stations will be constructed at Wilshire/La Brea, Wilshire/Fairfax, and Wilshire/La Cienega. The tunnel, mined by two Herrenknecht Tunnel Boring Machines (TBMs), will be 35,750 linear feet long with an inner diameter of twenty feet, seven inches. The project also includes train control and signals, communications, traction power supply and distribution, and fare collection systems.

Due to the gassy conditions along the alignment, Traylor’s Equipment Division retrofitted stock electric excavators to meet stringent code requirements.

The largest and most complex of the three major excavations is La Brea Station, which is 1,000 feet long, sixy-five feet wide, and nearly eighty feet deep, located down the center of busy Wilshire Boulevard. The work is also on the critical path, as it is the location from which the TBMs will be launched.

Dewatering has proven to be a challenge at the La Brea site. With a flow rate much larger than expected, the treatment plant was expanded both in size and in capability to treat the hydrogen sulfide. The originally planned dewatering configuration, has been supplemented with a wellpoint system.

At Fairfax Station, near the La Brea Tar Pits, the presence of methane and hydrogen required an extra-large, extra-robust ventilation system operating twenty-four hours a day, seven days a week to remove contaminated air. Because of the risk to archaeological finds, all excavation at this site takes place six inches at a time; the excavator ‘combs’ through a layer while the on-site paleontologist examines for fossils.

The project’s twin TBMs are supported by a complex conveyor system critical to meeting Traylor’s traditionally high levels of TBM productivity. Traylor’s underground group worked closely with Robbins to design a conveyor system for both tunnels that could make the complicated trip up and out of the south shaft. The one-of-a-kind conveyor system utilizes four types of belts and a three-story vertical storage cassette. It is running successfully in both tunnels, moving an average of 2,000 tons of material from the two TBMs every day.

Client: Los Angeles County Metropolitan Transportation Authority
Location: Los Angeles, CA


•First of three phases
•Twin tunnels in soft ground
•Equipment innovations to mitigate highly gassy conditions