United States Capitol Visitor’s Center
The US Capitol Visitor Center (CVC) was the largest addition ever made to the Capitol Building in Washington, D.C. The CVC building, 50 feet underground, fronts the entire east side of the Capitol. The Capitol itself encompasses 775,000 SF, while the completed CVC contains 580,000 SF on three levels. Initial construction of the Capitol Building began in 1793. The new CVC preserves and maximizes public access to the Capitol while greatly enhancing the experience for the millions who walk its historic corridors and experience its monumental spaces every year.
The United States Capitol Visitors Center involved underground construction of offices, a visitor’s center, and additional space on the east side of the existing capitol building. Construction of the CVC required installation of a slurry diaphragm wall within two feet of the existing spread footings for the building and excavating to average depths of about 50 feet with maximum local excavation depths of up to 75 feet with no movement of the Capitol.
Key Challenges
The construction of the Visitor Center required excavation to a depth of 65 feet, which was 35 feet below the existing capitol foundations and within two feet of the plan area of the foundation elements. Slurry walls with tiebacks were used for the excavation support. GEI’s design included a revised construction sequence to provide cost and schedule savings (of approximately $6 million) while complying with strict settlement and distortion criteria for the adjacent U.S. Capitol Building.
GEI’s design included strength and stability evaluation of the excavation support system to resist the imposed loads due to soil, water, and the surcharges of the Capitol Building. In addition, deformation analyses were performed using finite element models to confirm compliance with movement criteria. GEI’s analyses included evaluation of excavation system deformation performance and the impact of the predicted ground movements on the Capitol Building’s historic fabric and evaluation of the innovative tieback schemes to reduce construction complexity.