Abstract:
For a new residential tower in Philadelphia’ s historic Society Hill neighborhood, the developers looked for a high capacity alternative to the foundations more commonly used in the area: drilled shafts, driven piles, and occasionally micro piles. The project team opted for an augured cast-in-place piles drilled into the chemically weathered Mica Schist that underlies most of the city. Compression and lateral load tests were performed to verify the foundation selection, with capacities measured exceeding expected values. Additionally, support of excavation to facilitate construction of basement levels and a deep mat foundation was included in the foundation contractors package as well as underpinning of the adjacent hotel. Challenges to the underpinning were encountered when the hotel’ s as-built plans varied significantly from the field conditions. The presentation will discuss the designs, bi-directional testing, and construction processes for this small site situated between cobblestone streets Details of the foundation drilling, support of excavation, and underpinning will all be discussed.