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

PPT Presentation

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The Wharf Phase 2 development in Washington, DC, required deep garages and multistory buildings on challenging ground near the Washington Channel, WMATA Green Line tunnels, and a 108-inch storm sewer. Variable fill, alluvial and terrace deposits, and Potomac clay complicated excavation, groundwater control, and foundation design.<br /><br />The project combined several measures to control movement and protect nearby infrastructure. A stiff excavation support wall near the Metro tunnels used closely spaced drilled displacement piles (DDPs), which densify soil without removing it, paired with continuous-flight-auger piles. Field tests helped establish an effective DDP coverage ratio. Grouting between piles created a groundwater cutoff, while staged excavation, dewatering, and temporary support managed tunnel uplift and excavation stability.<br /><br />Where building and garage loads overlapped the Metro tunnel zone of influence, 196 load-sharing support elements transferred excess loads to suitable ground. Field load tests informed their bond lengths. Rigid inclusions improved support beneath garage foundations, with verification testing across two soil zones. Jet grouting also temporarily supported the large storm sewer during nearby construction.<br /><br />Construction demanded careful sequencing and monitoring. High-pressure jet grouting caused tunnel movement, so the team switched to lower-pressure, smaller-diameter grout columns. Drilling between the tunnels also led to pressure buildup in the Potomac clay; slower drilling, pre-drilling, relief holes, and revised tooling helped address the issue. Tight staging areas and coordination among excavation, bracing, and foundation crews added further complexity.<br /><br />The project’s success depended on combining established techniques in a tailored sequence, supported by testing and close monitoring. Collaboration among the owner, engineers, construction manager, and specialty geotechnical contractor enabled construction while controlling ground movement and protecting adjacent infrastructure.

Keywords

Wharf Phase 2

Washington DC

deep excavation

drilled displacement piles

groundwater control

load-sharing elements

rigid inclusions

jet grouting

Metro tunnel protection

geotechnical construction