UB DIGS DEEP AND BUILDS OVER ADJACENT SUBWAY FOR NEW MEDICAL BUILDING HUB-Paper

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The University at Buffalo’s new eight-story School of Medicine and Biomedical Sciences was built over and beside the active NFTA Allen Street subway station. Its two-level basement required excavation up to 43 feet deep in variable soils, close to station structures and utilities. Construction also had to accommodate the station entrance within the new building and support large, concentrated column loads.<br /><br />The site contained loose fill over layered sands, silts, and stiff clays, with both perched and regional groundwater. These sensitive soils were vulnerable to softening and ground loss when exposed to water. The design combined drilled soldier piles and lagging with a secant pile wall near the station entrance. Excavation walls were supported by tiebacks, internal bracing, and rakers, selected to avoid subway structures, utilities, and neighboring properties. Three-dimensional modeling helped coordinate overlapping tiebacks. Foundations included spread footings, a structural slab designed for hydrostatic uplift, and 107 rock-socketed micropiles, some installed in low-headroom conditions.<br /><br />Construction challenges included micropile core bars becoming stuck during installation, obstructions from possible remnants of earlier subway shoring, and an underperforming vacuum wickpoint dewatering system. The team adapted installation procedures, rerouted tiebacks, and relied on staged excavation, trenches, and sumps to manage groundwater. Groundwater inflow softened some subgrades, requiring over-excavation; sheet piling was added locally. Severe winter conditions also demanded protection of exposed soils from freezing.<br /><br />A monitoring program used automated instruments, surveys, and laser scans to track movement of the excavation support and nearby buildings and subway structures. Data identified soldier-pile and sidewalk movement associated with sheet-pile installation, prompting the team to leave the sheet piles in place. The project demonstrated the value of thorough site investigation, ongoing monitoring, field observation, quality assurance, and close collaboration among designers, inspectors, and contractors.

Keywords

University at Buffalo

School of Medicine

biomedical sciences

NFTA Allen Street subway

deep excavation

micropiles

secant pile wall

groundwater dewatering

excavation support

construction monitoring