Geotechnical Engineering for Realignment of Flatbush Avenue Connector
Weston & Sampson provided geotechnical engineering investigation and design services as well as on-call consulting services during construction for realignment of the Flatbush Avenue Connector between Flatbush Avenue and Interstate I-84 in Hartford, Connecticut. The project involved removing an elevated viaduct carrying eastbound on-ramp traffic and replacing the structure with an embankment supported roadway. The viaduct and adjoining elevated highway is supported on deep end bearing piles driven to refusal more than 80 feet below grade below the bottom of soft compressible Connecticut Valley Varved Clay (CVVC). Replacing the elevated viaduct required designing and constructing an embankment over the soft compressible CVVC. The embankment height ranges from zero to approximately 22 feet above grade where it meets the elevated highway. Portions of the proposed new embankment fills were in proximity to existing utilities, existing embankments, and the deep foundations supporting an I-84 overpass structure. Design and construction of the new embankment needed to consider potential adverse impacts to all existing features.
Weston & Sampson designed and monitored a subsurface investigation program to identify geotechnical constraints and considerations associated with the proposed embankment alignment, evaluated engineering soil parameters, completed geotechnical engineering analyses, and provided geotechnical recommendations for design and construction of the new embankment. Geotechnical analyses concluded that raising grades in proximity to existing utilities and structures using conventional earth fill materials would result in settlement that would adversely impact these features.
Weston & Sampson recommended use of very lightweight expanded polystyrene foam (Geofoam) to achieve a “zero-net-stress-increase” design approach for the new roadway embankment. This approach reduces the risk that the new embankment would cause consolidation settlement of the compressible soil as well as the potential for adding downdrag loading to the adjacent piles supporting the elevated highway.
Weston & Sampson designed an approximately 525-foot long, (up to) 22-foot tall vertical sided Geofoam embankment, the largest Geofoam embankment in the state of Connecticut at the time of construction. The lightweight and modular construction of the Geofoam blocks offered a unique advantage to construction phasing as the new embankment could be constructed beneath the existing viaduct structure while the structure remained in service. Geofoam was also used to control settlement in another area of the site where an existing drainage culvert prevented preload surcharging the new embankment fill.