Jefferson Memorial
Location
Washington, DC
Client
National Park Service
Services Provided
Data Review
Subsurface Exploration Program
Soil Laboratory Testing
Geotechnical Engineering Study
Instrumentation Installation
Instrumentation Monitoring
Advanced Numerical Analysis
Geostructural Design
Project Overview
Schnabel has completed the emergency repairs to the Jefferson Memorial North Plaza and seawall. Recent settlement and lateral movement of the seawall and Plaza prompted the National Park Service (NPS) to close a portion of the Memorial to the public due to safety concerns. The work at the Memorial was one of the first large projects to take place in DC under the American Recovery and Reinvestment Act 2009.
Since the construction of the Memorial from 1939-1943, the North Plaza and adjacent seawall have been subject to continued settlement. While the Memorial itself is founded on a network of deep foundations and grade beams, the surrounding areas were constructed on-grade. The Ashlar Seawall, which separates the North Plaza from the Tidal Basin at the north of the Memorial, is supported by vertical and battered timber piles. It is believed that the timber piles did not reach rock and, consequently, the wall was also susceptible to settlement.
In September 2006, Schnabel was contracted by the NPS to investigate the area surrounding the Memorial. The investigation included an extensive instrumentation program, consisting of piezometers, inclinometers, extensometers, and an optical survey. The information gathered from the instrumentation on-site allowed Schnabel to design a movement mitigation scheme that included demolition of the Ashlar Seawall and reconstruction of a new seawall supported by 48-inch diameter caissons and inclined pipe piles. The scheme will provide resistance to future vertical and lateral movement of the North Plaza and new seawall. Schnabel monitored the instrumentation throughout construction and will continue on a quarterly basis to confirm the new wall performance.