City: San Francisco
State: California
General Contractor: Clark Construction Group & Mortenson Construction Joint Venture

Chase Center Project Background

In 2012, the Golden State Warriors (GSW) of the NBA announced plans for the team to move from Oakland across the Bay to San Francisco. The relocation plans included building a new sports and entertainment center in San Francisco called the Chase Center. The selected site was originally below water in a bay known as Mission Bay. The site was reclaimed beginning in the late 1860’s by placing fill. The filling of the site was completed between 1906 and the 1910s using fill and building rubble from the 1906 San Francisco Earthquake. This new state-of-the-art center, costing $1.4 billion, would have an arena with seating for over 18,000 people, two office buildings, and 100,00 square feet of retail space. The Chase Center would be the new home court and practice facility for the Warriors. Beyond basketball, the arena would also be used to host concerts and other high-profile entertainment events. The Warriors aimed to complete this project in time for the preseason opening game of the 2019-20 NBA season.

Schnabel’s Role

The project’s general contractor, a joint venture of Clark Construction Group and Mortenson Construction, contracted with Schnabel to provide design-build shoring services that included grade separation shoring within the interior of the excavated basement to accommodate steps between different basement levels and shoring for large pile cap excavations throughout the large footprint of the basement. The large pile caps supported the arena and building loads and transferred those loads to the deep foundations (drilled piers). Schnabel’s work commenced in May 2017 and was completed by December 2017. Schnabel’s scope included installing over 7,800 linear feet of driven soldier beams, over 36,500 square feet of driven sheet pile, over 34,000 square feet of timber lagging, over 100 cased tiebacks, 8 internal braces, and over 300 linear feet of deadman anchors.

Challenges

The large variation in soil stratigraphy on site was a major challenge. The top 9 to 32 feet below existing grade was fill that consisted of a mixture of gravel, sand, clay and a mixture of brick and other rubble. Below the fill was a 2 to 42-foot thick layer of a very weak and compressible marine clay deposit, known locally as Bay Mud. The Bay Mud could not be relied upon to support any tieback loads, so tiebacks had to be kept flat enough to stay above the mud or had to be steepened and lengthened to bond into the formation below it.

Another challenge was a very aggressive schedule on a very congested job site. At some locations, our soldier beams and sheetpiles were installed before the structural design of the arena and other buildings was complete. At some of these locations, the design bottom of pile cap elevation at the bottom of the excavation was lowered after we had already installed our soldier beams or sheetpiles. This then required a quick re-design to accommodate the increased retained heights at those locations. In addition to needing to install tiebacks to bond into suitable soil, we also had to locate the tiebacks to clear the significant number of large-diameter drilled piers that were installed behind our shoring walls.

Deadman anchors were used at some locations where tiebacks and braces were not feasible. Using conventional deadman concrete anchor blocks was not feasible due to the cure time that would have been needed for the concrete to reach adequate strength, so deadman rods were anchored to driven sheet piles acting as anchor blocks.

Conclusion

Schnabel successfully completed its work in December 2017 on schedule and to the satisfaction of the client. The new Chase Center Arena had its grand opening on September 6, 2019, hosting a concert by Metallica and the San Francisco Symphony. The Warriors played their first preseason game in the new arena on October 5, 2019. The Chase Center Project received several awards, including the 2021 AGC of California Constructor Award, 2020 ENR Best of the Best Award (Sport/Entmt), 2020 ENR Western Pacific Best Project Award (Sport/Entmt), 2020 San Francisco Excellence in Business Award (Building), and the 2019 AEC of California Excellence Award (Construction).