Abstract:
In early 2020, GZA GeoEnvironmental, Inc., was contracted by the owner of a historic mill complex located in Boston, Massachusetts, to evaluate the structural condition of one of the buildings on their property. The complex was former home to a company that manufactured products such as fishing nets using processed natural fibers.
The buildings of the complex were constructed in multiple phases between the late 1800’s and mid-1900’s, and underwent major renovations in the 1980’s. The foundations consisted of granite block walls and pile caps supported by timber piles. Due to an apparent drop of the local groundwater table below the tops of piles, the pile tops began to decompose, resulting in differential settlement of the structure. Signs of worsening structural deterioration due to the settlement became evident over the years including cracking of the foundations, brick walls/facades, granite windowsills/lintels, windowpanes, interior walls, floor slabs, and timber framing.
The owner had concerns for the stability of the structure and safety of its tenants and requested that GZA assess what measures could be implemented to mitigate future building settlement. Significant challenges were identified early on including ongoing tenant occupation, site logistics in a city environment, equipment access, low headroom, noise ordinances, soil contamination, and COVID-19.
A system of reinforced concrete grade beams sandwiching the foundation walls and ring beams around the interior pile caps, supported on helical Drivecast™ piles was selected to penetrate the upper Organics layer, and derive capacity within the underlying Clay. A state-of-the-art real-time deformation monitoring system was also implemented by GZA to ensure structural integrity during construction. Unforeseen challenges arose during the work. However, thanks to GZA’s innovative, pragmatic, and cost-effective solutions, the Project was successfully completed in October 2021 and remains prime real estate located in the heart of one of the nation’s beloved founding cities.