Abstract:
This presentation concerns the design, analysis, construction, and performance of an internally braced slurry wall for temporary support of excavation for the Boston Seaport Parcel P project located at 400 Summer Street in Boston, Massachusetts. The proposed 16-story tower development includes air-rights over the I-90 Tunnel Ramp and is bordered by the Summer Street Bridge (South), Congress Street (North), Boston Wharf Road (West) and the I-90 Ramp/Tunnel (East) which was located about 10-ft away from the excavation. The plan area of the main excavation was about 55, 500 SF with an additional 15, 500 SF located below the Summer Street Bridge.
A support of excavation consisting of 65, 300 SF of 30” reinforced concrete slurry wall and LBE’s was required to construct the 3 basement levels for the proposed development. Two to three levels of internal bracing were required to support the excavation that ranged from 40-ft to 49-ft deep in the main excavation. Additionally, a 19-ft deep support of excavation consisting of sheet piles and micropiles was required to facilitate the excavation in the area under the Summer Street Bridge.
Design and construction challenges faced during the project include the unique and complex site geometry (depth and area), the adjacent existing structures, presence of the abandoned CAT/T Project C01A3 soil mixed wall and tiebacks and working under the Summer Street Bridge.
The excavation was analyzed using both Limit Equilibrium (LEM) and Finite Element (FEM) methods to study the effects of the excavation on the surrounding structures. Instrumentation data gathered from the excavation during construction confirmed the design methodology and provided valuable insight on the slurry wall and internal bracing system. Lessons learned from this project will serve further development projects in the South Boston area.