Second Avenue Subway Project: Deep Excavation Support of a Cut-and-Cover Station

The Second Avenue Subway is currently under construction in Manhattan, New York. Spanning seven city blocks, the cut-and-cover station at 96th Street is the largest station in Phase 1. The station excavation is up to 68 feet deep and is typically within 20 feet of adjacent buildings. The station straddles areas of rock and deep soil at its invert and requires various forms of ground support, including both temporary and permanent secant pile and slurry walls. Construction was undertaken in a dense urban environment, adjacent to fragile buildings, with significant underground utility and traffic maintenance restrictions. Excavation and construction of the permanent earth support was recently successfully completed. This paper reviews the design and construction methodology for the ground support systems adopted and discusses the interfacing and construction challenges faced in a highly constrained environment from the perspectives of both the designer and contractor.