Hayward Baker's design-build hybrid earth retention system provided a value-engineered solution that reduced the project schedule, minimized movement of the adjacent soil, and mitigated impact to the MBTA subway.

The project

Millennium Tower is a 685-ft, 60-story residential skyscraper located in Boston’s Downtown Crossing immediately adjacent to the historic Burnham Building which once housed Filene’s flagship department store. Excavation to accommodate the Millennium Tower’s underground parking levels and mat foundation system extended beyond the footing depths of the adjacent Burnham Building, which was concurrently undergoing extensive interior renovation as part of the overall parcel development.

The challenge

Several engineering and logistics challenges had to be overcome. Subsurface conditions are typical of Boston’s early infilling practices and consist of miscellaneous fill with obstructions, organic silt and marine clay overlying glacial till. During the excavation for the Millennium Tower basement, which reached depths of 50 ft, the exposed basement wall of the sensitive Burnham Building would function as one side of the required earth retention. Any additional loading imposed on the Burnham Building wall during excavation for Millennium Tower was strictly prohibited. The excavation was also bounded on the northwest side by an active, 100-year-old MBTA subway tunnel. Excavation would extend 16 ft below track level. Minimizing the deformation responses of these two adjacent structures was critical to the design and construction of the earth retention system. In addition, a portion of the site miscellaneous fill would require mitigation to provide adequate support for the 8-ft-thick tower mat foundation.

Project Facts


Millennium Partners Management

Main Contractor(s)

Suffolk Construction and J. Derenzo Company

Keller Business Unit(s)

Hayward Baker


Haley & Aldrich, Inc

Download Project Sheet

Millennium Tower Project Summary