C+S September 2020 Vol. 6 Issue 9 (web)

compensation grouting; abandoned soldier piles and tieback anchors were encountered within the public right-of-way; the existing LA Metro heavy rail Re Line (B/D) was underpassed with a clearance distance as low as one quarter of the tunnel diameter (nominal 20 feet) without interrupting the B/D Line operations; sensitive stakeholders were coordinated for the ground borne noise and vibration; and Angeli precisely advanced with minimal clearances to existing bridge founda - tions and sanitary sewer manhole structure without disturbing. After both tunnels were fully excavated, “Angeli” was dismantled and removed from the site. Since that time WSP’s services have supported the completion of tunnel work and transitioned to focus on rail transit systems. WSP staff has been involved in the process leading to rail ac - tivation and will provide technical assistance after the start of operations. Three cross-passages in the bored tunnels were excavated and had the final concrete lining placed along with comprehensive water/gas proofing process using hydrocarbon resistant membranes and chemical grout. Construction of tunnel walkways has also been completed. Work has also progressed on the construction of three new under- ground stations, an underground crossover, cut-and-cover concrete box tunnels and U-structures: View on Hope Street. The glass building is the high-speed elevator. It shows a pedestrian bridge connecting the station to The Broad museum. This station is about 100 ft deep from this location. Photo: LA METRO

This station will be integrated with a new high-rise building by LA Times. The ticketing area shown will be inside the new building. Photo: LA METRO

would be the last technically difficult underground challenge, accord - ing to Hansmire, was completed in March 2019 nine months after the commencement from the final grade of the Historic Broadway Station. In addition, the Grand Av Arts/Bunker Hill Station, with a maximum depth of 105 feet, completed its excavation in February 2017. The 1,350-foot-long cut-and-cover excavation along the Flower Street was completed in July 2019. Concreting the final structures within those excavations has been substantially advanced, and the backfill and sur - face restoration works are expected to begin later this year. “Among those stations, the construction of Historic Broadway Sta - tion would be considered as the most challenging one,” Choi said. “The station excavation was hugging the basement of an adjacent historic building, which had a portion vacated into the excavation to be underpinned. The existing 10-foot-diameter storm drain running the entire length of the station had to be replaced and protected in place during construction. The entrance structure had to be designed and constructed to adapt future development of the property owner. And, the crossover cavern construction had to be commenced from the The Regional Connector tunnel includes some “firsts” for LA Metro. Most notably, it was the LA Metro’s first cavern excavated in weak rock for a rail crossover using the sequential excavation method (SEM) of tunneling. “The location has a very narrow public right-of-way with a historic ad - jacent structure,” Hansmire said. “Cavern construction avoided many costly constructability problems if done as cut-and-cover construction. The crossover was essential to efficient rail operations. To not construct the crossover would have resulted in unacceptably long single tracking times when one line is shut down for maintenance or other reasons.” One challenge during design was prediction of ground movements and behavior to protect existing adjacent buildings and utilities in one of the world’s most active areas for seismic activity. station excavation.” Firsts for LA Metro A cutting-edge construction schedule orchestrated three major activi- ties at one place: twin bore tunneling by a single TBM, deep station excavation, and SEM excavation. During excavation, the project

• Little Tokyo/Arts District Station – 1st Street/Central Avenue • Historic Broadway Station – 2nd Street/Broadway

• Grand Av Arts/Bunker Hill Station – 2nd Place/Hope Street • Underground crossover cavern at Historic Broadway Station • Flower Street box tunnel connecting to the A Line • Alameda and 1st Street box and U-structure lags connecting to the L (Gold) Line “Most of the stations, crossover cavern, and cut-and-cover structures have been fully excavated and concreting is complete or well ad - vanced,” said Jason Choi, WSP project manager. “The Alameda lag is currently being excavated.” The excavation of Little Tokyo/Arts District Station reached final grade before the TBM launching in January 2017 and the 1st Street cur-and-cover excavation was completed in parallel with bore tunnels in 2018. The Historic Broadway station reached its full depth of about 90 feet in June 2018, and the crossover cavern excavation, which



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