Chase Center, San Francisco DFI 2020 Outstanding Project Award Winner For 23 years, DFI has recognized superior work performed by its members on projects related to their geotechnical, deep excavation and deep foundation aspects. This year’s Outstanding Project Award is being given for Chase Center in San Francisco to the team of Langan Engineering and Environmental Services (geotechnical and environmental services), Malcom Drilling Company (foundation contractor) and Condon-Johnson & Associates (shoring contractor). Special Recognition Awards will also be given to two other entries: Schnabel Engineering, which submitted a project at West Virginia’s Yeager Airport, where a team stabilized and restored the safety area for Runway 5; and Mueser Rutledge Consulting Engineers for rehabilitating New York City’s Canarsie Tunnel for the L Line subway due to Superstorm Sandy damage, including tunnel feature upgrades. The winning team addressed the deep foundation aspects of Chase Center, a new sports and entertainment center for the owner, the Golden State Warriors. The space covers four city blocks and will provide seating for 18,000 fans, as well as 58,000 sq ft (5,388 sq m) of office/lab, event space, retail, restaurants and underground parking. The Chase Center is being completed in the poor ground conditions of the Mission Bay area. A tidal cove thousands of years ago, the area was built up in the early 1900s from thousands of cubic yards of sand, rocks, dirt and debris that came from the 1906 earthquake. Besides the engineering and construction challenges that entailed, the team had to excavate as deep as 30 ft (9.1 m) to fit all the facility programming on site. The unprecedented depth and size of the excavation presented challenges with dewatering, maintaining a stable subgrade and supporting the excavation. In addition, the foundation conditions varied significantly across the site, with bedrock as shallow as 30 ft (9.1 m) and as deep as 130 ft (39.6 m). Langan engineers provided geotechnical, environmental, dewatering and civil excavation consulting services to address site issues. That included offering novel ideas for foundations, cutoff wall design, soil treatment and dewatering system design. For instance, foundations needed to provide adequate compression and tension support, especially where Bay area bedrock is shallow and the arena core loads would be high. A combination of large-diameter drilled shafts and augered cast-in- place piles were used for foundation support. Due to extreme variation in subsurface conditions, the total length of piles and/or embedment in bedrock needed to be identified on a case-by-case basis during construction. DEEP FOUNDATIONS • JULY/AUG 2020 • 29
