Despite the challenges of working on the Potomac River adjacent to historic buildings and the discovery of an old ship's hull, Keller constructed a watertight TRD earth retention system on time and with minimal movement.
The project
Robinson Landing is a $185 million, mixed-use development that covers a full city block on the Potomac River waterfront in Alexandria, VA. Soils across the site consisted of interbedded layers of silty sand and gravels, soft lean clay, and stiff fat clay. The site is adjacent to the Potomac River and accordingly, the natural groundwater table is very near the surface.
The challenge
The project involved excavating two levels of below-grade parking for the construction of a riverside, five-story above-grade condominium building. A “bathtub” cut-off structure was needed to ensure no impact to surrounding properties through dewatering-induced settlement or migration of contaminated groundwater. Keller had already mobilized to the site when a historic ship’s hull was detected that lay partially within the 50,000 sq. ft. footprint at 25-ft below working grade.
The solution
Keller installed an internally-braced, vertical, soil-cement TRD perimeter cut-off extending to a depth of approximately 80 ft and keyed into the underlying marine clay. The TRD wall was designed to function as both a permanent cut-off and temporary ERS and eliminated the need to design for uplift pressure or for external perimeter dewatering. Following detection of the ship’s hull, Keller worked with the client to redesign the shoring to facilitate inspection and safe removal of the hull without impacting the project schedule.
