The historic Howard Theatre, located in northwest Washington, DC, was originally constructed in 1910 and closed its doors in 1970. After a brief revival of the theatre in 1974, the large masonry structure was closed again in 1980 and sat abandoned for 30 years. In 2010, Howard Theatre Restoration, Inc., Ellis Development Group, and The Whiting-Turner Contracting Company began a $17.1 million rehabilitation and revitalization project of the Howard Theatre. The development included a basement addition 15 to 25 feet below the existing stage, on-grade stadium seating area, and elevated balcony. Wet, loose silty sands at the new subgrade introduced unique design and construction challenges for supporting walls along the perimeter and within the interior of the structure. Steele Foundation LLC teamed with designer Schnabel Engineering LLC to develop designs and construction methods to combine traditional, pit-type underpinning, hollow bar micropiles, and structural steel shoring to provide temporary and permanent support of the existing 40 to 60 foot tall structure.
Two performance tests were performed on sacrificial micropiles to verify capacity and settlement requirements of the project. Traditional underpinning pits were excavated and two hollow bar micropiles were installed within each pit prior to concrete placement. The unreinforced concrete underpinning piers were spaced around the perimeter to provide permanent vertical support of the perimeter walls while maintaining architectural space requirements for the new basement. The underpinning piers were laterally braced during the basement excavation to provide temporary earth retention. Structural steel shoring frames connected to partially-cased hollow bar micropiles were installed along interior masonry walls and balcony steel columns to provide temporary and permanent support. The hollow bar micropiles, used as temporary and permanent elements, provided an economical and stiff foundation system for dealing with the poor soil conditions at and below the new subgrade.
The underpinning and shoring operations were successfully completed in early 2011 allowing the new concrete basement structure to be constructed. Combining traditional and modern underpinning/shoring methods proved to be a cost-effective and time-savings solution for the revitalization of the historic Howard Theatre. This case history provides an excellent example where the union of old and new construction techniques was used to address unique foundation rehabilitation challenges of a historic structure.