15 MARCH 2023 WorldWide Drilling Resource® A Foundation Built for the Future Adapted from Information by Keller North America Since 2018, the Maine Medical Center (MMC) in Portland, Maine, has been working on the largest modernization project in its 150-year history. Known as northern New England’s largest hospital, the new MMC buildings will create additional patient rooms and state-of-the-art surgical suites. The final part of the $588 million development will see the construction of the new six-story Malone Family Tower, designed primarily for improved cardiovascular care and surgery. The tower, scheduled for completion later this year, will replace a 45-year-old, 11-story parking garage. It’s a complex transformation requiring careful demolition and a large excavation with a significant permanent earth retention system and other foundational and ground improvement elements. Keller North America has been involved in the project from an early stage. According to David Finocchio, business development executive for Keller, “A critical element of the hospital’s construction phasing and logistics plan required the existing parking garage structure be kept in use for as long as possible before its demolition. A portion of the proposed structure was to be located within the entire existing garage footprint and nearly 30 feet below the level of the existing spread footing foundations. These constraints required solutions to a significant, unbalanced earth-loading problem and an extremely challenging excavation sequence.” Further complicating matters was a utility corridor located between the garage and another building, which contained the hospital’s fiber-optic cables. This meant any movement or damage during the tieback installation and excavation would have significant consequences. Much of the work happened during the height of the pandemic when MMC was under significant pressure. Additional utility surveys, subsurface exploration, and 3D modeling were carried out to map out the area, making sure none of the proposed work would affect critical utilities. After considerable study, the design-build team’s solution included incorporating a portion of the existing garage foundation wall into the temporary and final earth retention systems. This extended the in-service life of the garage for nearly a year, minimizing patient and hospital worker disruption and removing the need for construction of a new foundation retaining wall. Working within the busy garage, the Keller team drilled permanent anchors 100-200 feet long through the existing garage basement wall in just eight feet of headroom, a painstaking process which took about a year to complete. Once the permanent tiebacks were installed and locked off, the garage was demolished and the site excavated, carefully avoiding disruption of the utility corridor and/or damage to the previously installed, permanent tieback elements. Once the cut reached ground level of the former garage, an additional 30-foot cut was required to reach subgrade for the proposed construction. To facilitate this additional excavation and to add stiffness for lateral movement control, the company constructed a permanently tied-back secant pile wall in front of the previously tied-back garage foundation wall. The secant piles were installed to depths of about 5060 feet. On the other sides of the excavation, temporary earth retention consisted of a more economical drilled soldier pile with lagging support, along with conventional concrete pit underpinning. Although most of the ground was composed of relatively dense glacial deposits, there were pockets of compressible clay materials which were not suited to mat foundation support. So, for a portion of the site, the team incorporated rigid inclusion ground improvement to improve bearing capacity for the new structure. “Given the overall complexity of the job, the long schedule, and demanding conditions, this has been a tremendous commercial and technical success,” said David. “We’ve worked hand in glove with the contractor and excavator, and it has been an extremely safe and well-managed project. I’d like to recognize the excellent work of the whole team . . . They should all be proud of their efforts.” C&G
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