Dilworth Plaza, City Hall Renovation, Philadelphia, Pennsylvania

Overview: Philadelphia’s City Hall is a National Historic Landmark and the world’s tallest masonry building. Dilworth Plaza’s west side underwent a $50 million renovation to transform this historic civic space into the cultural, social, and commercial center it was intended to be. GeoStructures provided multiple aspects of a design role for the project. 

The project involved reconfiguring the plaza level, as well as adding multiple sitting areas, a programmable and interactive fountain, a cafe, and an outdoor venue that can convert to an outdoor skating rink during the winter months.

GeoStructures’ design role in this project involved a detailed geotechnical investigation, an assessment of existing foundations, foundation design requirements for the planned renovation, and consideration of conflicts between existing and proposed structural supports.

To accomplish the reconstruction, many of the new foundation supports needed to penetrate a labyrinth of two or even three underground subway tunnel levels, as well as pedestrian and utility tunnels. During construction, GeoStructures was also responsible for performing periodic inspections to ensure the foundation conditions were consistent with the subsurface characterization and design assumptions.