LA Metro’s Westside Purple Line Extension Section 2 Construction

The year 2024 was a busy one for the Los Angeles County Metropolitan Transportation Authority’s (LA Metro) Westside Purple Line Extension (WPLE) Section 2 Project. After successfully completing the tunneling of the 2.59 miles (4.17 km) of twin-bore tunnels on January 12, 2023, significant progress was made to advance the project toward its goals. Key achievements include the completion of the excavation, initial lining, and permanent cast-in-place (CIP) concrete work for all 14 cross passages and the completion of all first-stage inverts and CIP concrete walkways within the running tunnels. Also of note are the efforts made on the difficult task of disassembling and removing both tunnel boring machines (TBMs) from within the tunnel.

CIP Invert & Walkway Construction

The first stage of the CIP invert and CIP walkway work began in late February 2024, with completion scheduled for January 2025. The first stage of the CIP invert placement averaged 240 feet per day, while the CIP walkway placement averaged 150 feet per day utilizing a traveling form system.

Cross Passage Excavation

Cross passages were excavated utilizing the sequential excavation method (SEM). Cross passage excavation commenced at the west end of the tunnels in September 2022, at cross passage 40, and progressed to the far east end of the tunnels, to cross passage 27, which was completed in December 2024. Excavation of the cross passages presented significant challenges, including:

• Excavation beneath busy streets in a densely populated urban environment
• Excavation below the groundwater table
• Excavation through coarse-grained sands and gravels at some locations

The contractor initially installed dewatering wells at each cross passage as their only means of ground improvement. When it became apparent that dewatering alone would not suffice to allow for safe SEM excavation, the contractor also chose to treat the ground with chemical grout. The choice of whether chemical grout was needed at each cross passage was based on an observational approach using probe drilling.

TBM Disassembly & Removal

TBM disassembly started in May 2024. Disassembly and removal of the first machine (leaving the TBM shield in place for ground support at the connection to WPLE Section 1) was completed in early November 2024 with the contractor now focusing efforts on completing the structural tie-in work necessary to make the final connection to the Section 1 tunnel. Disassembly and removal of the second TBM is ongoing and should be completed
in February 2025.

Progress at Underground Stations

Both underground stations—Century City and Wilshire/Rodeo—also saw considerable progress in 2024. Concrete placement progressed from the platform to concourse levels and up to the arched roofs. By the end of 2024, the arched roof at Century City Station was nearly complete, while backfilling above the arched roof at Wilshire/Rodeo Station had begun. The only remaining excavation work at the stations is now the various appendages, e.g., exhaust air shafts and traction power supply shafts, which were at various stages of completion by the close of 2024. Mechanical, electrical, and plumbing installation commenced at both stations.

Looking Ahead in 2025

In 2025, the focus will shift to stations and tunnel MEP systems installation, and the installation of the permanent track. These efforts will bring the project closer to its anticipated completion in late 2026.

Project Background

The design-build contract for Section 2 was awarded in 2017 to a joint venture between Tutor Perini and O&G Industries. The Purple Line 2 CM Partners Joint Venture—led by AECOM, SafeworkCM, Morgner and TEC, with Delve Underground as the lead tunneling and geotechnical consultant—is providing construction management support to LA Metro.