Supporting Community Health: Foundations and Excavation Support for Brooklyn Methodist Hospital’s Center for Community Healthcare

The Center for Community Health (CCH) is the latest addition to New York Presbyterian Hospital’s campus at Brooklyn Methodist Hospital in the Park Slope neighborhood of Brooklyn, New York. The CCH will be housed in a new 7-story concrete and steel-framed building with two deep cellars that occupies a 56,000-square-foot (SF) [5,200-square-meter] U-shaped site across the street from a historic landmark district. Below-grade lot-line construction required excavation up to 50 feet (15 meters [m]) below adjacent sidewalk grade, up to 40 feet (12 m) below adjacent 100-year-old row homes, and up to 25 feet (7.5 m) below the hospital’s adjacent medical office building that remained open throughout construction. Excavation support was provided by a combination of secant pile walls (along adjacent buildings) and soldier piles and lagging (along public sidewalks). Secant piles were drilled using the cased continuous flight auger (cased CFA) and Kelly-Bar drilling techniques. This is only the second time the foundation drilling contractor (Hayward Baker) had used the cased CFA technique in the New York City area. Up to four tiers of lateral bracing were provided using a combination of drilled-in hollow bar tieback anchors and rakers. Strict movement tolerances were implemented to avoid damage to the neighboring buildings during excavation. Monitoring of the adjacent buildings was conducted to verify that building movement was kept within tolerance during excavation and foundation construction. The secant piles installed for excavation support were also used as permanent foundation support for the building. Elsewhere, the building was supported on a mat foundation (for the building core) and spread footings (for individual columns) bearing in the glacial till underlying the site. The secant piles were treated as drilled piles, gaining their support by friction in the glacial till beneath the lowest-level cellar slab. Load testing of the production secant piles was impractical. Axial capacity was verified by 450-ton (4,480 kN) load tests on sacrificial piles in the middle of the site that were drilled in the same manner as the secant piles. Piles were instrumented during load testing to determine the capacity for the portion of the pile below the future basement level. Support of excavation construction was completed within the overall project schedule. No soldier piles needed to be re-drilled, and less than 1.5% of the anchors and secant piles needed to be re-drilled because of installation problems or field conditions. Below-grade construction caused minimal disturbance to the neighboring properties. Lateral movement of the secant walls was less than ¼-inch (6.4 mm), which agreed with the FEM models.