Large Diameter Auger Cast Piles at Audi Field, DC United's New Soccer Stadium-Paper

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Audi Field, D.C. United’s 20,000-seat stadium in Washington, D.C., was built on a site containing uncontrolled fill, soft alluvial soils, and deeper dense sands. High wind loads, an electrical utility easement, and strict settlement and lateral-deflection limits created demanding foundation requirements.<br /><br />The original design used about 800 driven concrete piles and pile caps, with drilled shafts beneath part of the east stand. A value-engineered alternative replaced these with approximately 300 single-element auger cast piles (ACPs), 1.5 to 4 feet in diameter and up to 85 feet long. Grade beams connected the piles to help resist lateral loads. The alternative reduced excavation and avoided risks associated with driving piles through variable soils.<br /><br />Site-specific cone penetration and dilatometer testing improved estimates of soil strength and provided lateral load-deflection (p-y) curves. These data also supported revised settlement analyses, which eliminated the need to include downdrag loads.<br /><br />Conventional single-pile analysis using LPILE proved inefficient for the many combinations of axial and lateral loading and partial head fixity. GROUP could model pile groups but treated grade beams as rigid. The team therefore used FB-Multipier, which represents grade beams as structural elements with user-defined stiffness, allowing more realistic modeling of load distribution and pile-group behavior. Coordination over how to represent the contract’s partial-fixity limit remained a significant design challenge.<br /><br />O-cell tests on each pile diameter confirmed the geotechnical resistance assumptions, while a lateral test on a 3-foot ACP helped validate and calibrate the p-y curves. The project demonstrates the value of site-specific testing, analytical tools suited to complex loading, early agreement on partial-fixity assumptions, and load testing to verify design parameters.

Keywords

Audi Field

D.C. United

Washington D.C.

augur cast piles

foundation design

pile testing

p-y curves

geotechnical engineering

grade beams

lateral loads