Abstract:
In 2018, the Maine Medical Center (MMC) began constructing their proposed new cardiovascular medical building addition to their campus in South Portland, Maine. The campus addition would start with demolishing an old 10-story parking garage cut into the side of a hill and constructing an up to 80 ft deep permanent Support of Excavation (SOE) system with existing medical facilities and critical utilities located behind. MMC engaged Simpson Gumpertz & Heger (SGH) to design this complex and critical element of the new construction.
The permanent SOE system consists of an approximately 330 ft long secant pile wall with 421 tiebacks along the site's south side and a 36 ft long line of underpinning pits along the site's east side. The upper portion of the south SOE used the southern concrete wall of the previously existing parking garage as a temporary SOE by phasing tieback installation during the demolition operations. Tieback installation required the specialty contractor to avoid the maze of utilities supporting the medical campus operations and thread through, sometimes within inches, of existing deep foundations.
Our presentation will consist of a general discussion of the design of the permanent SOE system, with emphasis on re-using the existing south wall of the parking garage to act as a temporary SOE until the new secant wall and permanent concrete facing wall were constructed. We will also discuss the risk management approach we undertook to design and install the tiebacks while avoiding the myriad of existing utilities and deep foundations and how the collaboration between the contractors and SGH made this project a success.