Major braced excavations for Los Angeles Subways

Major braced excavations for Los Angeles Subways designed with DeepEX

Los Angeles underground is expanding and DeepEX is instrumental in getting the city forward. Support of excavation systems for the new subways stations for the Regional Connector and the Purple line expansion projects have been and are designed with DeepEX. These projects involve excavations of up to 100 ft that require lateral bracing to be designed according to strict specifications.

The joint venture by Skanska – Traylor – Shea, with PB&A won contracts for the subway stations. PB&A, based in San Rafael, CA, has been using DeepEX for the last five years. The project presented some challenges in incorporating the specified apparent earth pressure diagrams as well as the specified passive lateral earth pressures. Given the number of conditions that had to be examined, we at Deep Excavation, went into high gear and implemented options that would give the ability to easily match the lateral pressure specifications.

Apparent earth pressures were defined as a trapezoidal diagram with a maximum pressure of 24 H in psf, with the top and bottom triangular portions of the pressure diagram set at 20% of H (H= excavation height in ft).

Regional_Transit_Subways_Apparent_lateral_earth_pressures.jpg

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The designers (PB&A), with the help of DeepEX, were able to quickly model all construction stages and determine the most critical conditions. This included not only the final excavation but also the construction stages after the permanent station walls are constructed and struts are removed.

The following stations are also to be designed with DeepEX:

Regional Depth Length Width - ft (Approx.)

2nd & Hope Station 97 ft 75 X 470

2nd & Broadway Station 100 ft 75 X 470

Westside Depth Length Width - ft (Approx.)

Wilshire - La Brea 85 ft 75 X 1,000

Wilshire - Fairfax 85 ft 75 X 1,000

Wilshire – La Cienega 85 ft 75 X 1,000

Project background

Regional Connector

The Regional Connector Transit Corridor is an under construction light rail subway corridor through Downtown Los Angeles to connect the Blue and Expo Lines to the current Gold Line and Union Station. When completed, the connector will become part of the Los Angeles County Metro Rail System. The project is being implemented by the Los Angeles County Metropolitan Transportation Authority (Metro).

Purple line extension (Westside)

The long-awaited Metro Purple Line Subway Extension is now under construction. From the current terminus at Wilshire/Western, the Purple Line Extension will extend westward for about nine miles with seven new stations. It will provide a high-capacity, high-speed, dependable alternative for those traveling to and from LA’s “second downtown,” including destinations such as Miracle Mile, Beverly Hills, Century City and Westwood.