An artist’s concept of a redeveloped Suffolk Downs neighborhood, complete with residential units, business space, two retail squares and 40 acres of public open space, all served by two MBTA Subway stations. (Copyright HYM Investment Group, used with permission.)
To support the excavation, the team began designing a permanent shoring system that used steel sheeting and internal bracing to stabilize the excavation and reduce the amount of groundwater entering the excavation during construction.
GeoEngineers’ team used GeoStudio’s SEEP/W software to model groundwater flow and seepage and then made recommendations for temporary dewatering strategies.
The team recommended a continuously waterproofed, fully compensated, pressure mat foundation that would bear on the underlying natural sand and gravel layer and natural silty clay.
Suffolk Downs Redevelopment (Building R10)
Geotechnical services help turn a historic Boston horse track into a unique planned community.
In 2019, The HYM Investment Group, LLC announced plans to redevelop Suffolk Downs, a historic Boston horse track, as a sprawling planned community. HYM would turn 10.5 million square feet of land into a mixed-use neighborhood with residential units, business space, two retail squares and 40 acres of public open space, all served by two MBTA Subway stations. GeoEngineers provided support of excavation, construction dewatering and other geotechnical services for one of the project’s first phases—a 280,000-square-foot, five-story biomanufacturing complex with two levels of below grade parking.
Approach
Seepage Analysis: The GeoEngineers team performed slug tests within on-site groundwater monitoring wells to evaluate the hydraulic conductivity of subsurface material. In addition to in-situ testing, laboratory data were also analyzed using HydrogeoSieveX, an Excel-based tool for estimating hydraulic conductivity from grain-size data results.
Excavation Support: Thanks to the building’s two levels of underground parking, excavation would need to go 29-33 feet deep—well below the local water table. To support the excavation, the team began designing a permanent shoring system that used steel sheeting and internal bracing to stabilize the excavation and reduce the amount of groundwater entering the excavation during construction. (Another teaming partner completed the shoring design.)
Temporary Dewatering: Below-grade construction for the building’s parking levels extended nearly 26 feet below the local water table, requiring significant dewatering during construction, and permeable soil made complete groundwater cut-off impossible. GeoEngineers’ team used GeoStudio’s SEEP/W software to model groundwater flow and seepage and then made recommendations for temporary dewatering strategies.
Earthwork and Subgrade Preparation: GeoEngineers delivered performance criteria for subgrade preparation and structural fill gradation, placement and compaction.
Recommendations for Foundation and Below-Grade Walls: Before a foundation could be constructed, GeoEngineers advised removing a layer of organic material spread across the site. Once removed, the team recommended a continuously waterproofed, fully compensated, pressure mat foundation that would bear on the underlying natural sand and gravel layer and natural silty clay.
Instrumentation and Monitoring: GeoEngineers planned and implemented a monitoring program to validate the geotechnical performance of support systems, fill placement, and other earthworks during construction. The team also monitored vibration during sheeting installation.
Results
GeoEngineers’ interdisciplinary team blended support of excavation and temporary dewatering services with traditional geotechnical consulting for this fast-paced redevelopment project. This unique blend of services and skills improved efficiency by enabling the team to coordinate with the contractor in parallel with the structural engineer and architect. This level of collaboration allowed real-time value engineering during the project’s design phase. By bringing people together, the team could find efficient solutions that balanced risk and constructability for this groundbreaking initial phase of the Suffolk Downs redevelopment.
Community Impact
The Suffolk Downs redevelopment will create a dynamic and walkable neighborhood that will reconnect East Boston with 40 acres of public recreation and greenspace, including access to wetlands like Belle Isle Marsh, and shoreline at Revere Beach and Constitution Beach.
