Foundation Challenges and Innovative Solutions: The Wharf Phase 2, Washington, DC-Paper

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The Wharf Phase 2 in Washington, DC, involved two underground parking garages and five mixed-use buildings on a seven-acre waterfront site. Construction was complicated by soft and variable soils, a large active storm outfall running through the site, and Green Line subway tunnels located only about 10 feet from the northern excavation. Excavation above and beside the tunnels required exceptionally strict movement control.<br /><br />The project used a combination of support-of-excavation systems, including sheet piles, soldier piles, tiebacks, jet grouting, and preloaded internal bracing. Beside the tunnels, alternating drilled displacement piles and conventional auger-cast piles created a “push-pull” wall system. Field testing and continuous tunnel monitoring guided the pile pattern and construction sequence. Controlled dewatering was coordinated with excavation and later building loading to limit tunnel movement.<br /><br />The active outfall was underpinned with jet-grout columns, then protected by sheet piles and connecting tie rods. In areas of weak soil, rigid inclusions improved support for floor slabs and spread footings. A reinforced-concrete mat over the tunnels was designed to restore much of the removed overburden load; where building pressures exceeded that load, grouted hollow-bar rigid anchors transferred excess loads to deeper soils while limiting force on the tunnels.<br /><br />Successful delivery depended on detailed monitoring and close coordination among the owner, engineers, construction manager, specialty contractors, and WMATA. The project demonstrates how multiple geotechnical methods, testing, and adaptive construction controls can address challenging ground conditions while protecting critical infrastructure.

Keywords

Wharf Phase 2

Washington DC

underground parking garages

mixed-use buildings

waterfront excavation

geotechnical engineering

subway tunnel protection

jet grouting

dewatering control

support of excavation