Filling the Foundation Strategically with Existing Basement Vaults: One Vanderbilt, New York
Session: G: Geotechnical Engineering Award & Systems Award
Principal, Langan Engineering
One of the critical items to support the tower was the design and construction of the 100 ft by 100 ft mat foundation that supported the heavily loaded core. This core foundation element consisted of 10,000 psi concrete and was embedded 9 feet into the bedrock. In addition to the massive core foundation, the project had a complicated excavation of over 50-feet-deep. The deep excavation for the tower foundations was advanced through notoriously hard Manhattan schist bedrock. The design and installation of the perimeter excavation support required innovative earth retention; rock removal and stabilization methods to prevent undermining of nearby buildings; adjacent landmarked structures; Grand Central Terminal (and the associated multiple below grade levels); four extremely busy NYC streets; a vital, old and complex utility system; and several subway and train tunnels.
An effective innovation in the earth retention design included filling in parts of the cellar spaces to essentially form mass “retaining walls” at the site perimeter. Through various field investigations, the vaults were found to be sitting on or near bedrock. The bedrock foundation allowed these old vault spaces to be filled with low-strength concrete to create a large concrete “block.” The “block” retaining walls served dual purposes: (1) to retain the soil outboard of the site and (2) to provide at-grade construction staging areas.
This approach accelerated the excavation schedule, reduced construction costs, and minimized the penetrations in the foundation wall.