Case History: One Chicago Square Top-Down Construction Adjacent to Chicago Red Line Tunnel and Station

One Chicago Square (OCS) is a billion-dollar private development encompassing an entire city block in the River North area of Chicago, Illinois. The project consisted of two high rise towers (55 and 65 stories), along with a four-story below grade parking structure directly adjacent to the existing Chicago Transportation Authority (CTA) Red Line tunnel and station. JDL and Power Construction, the owner/developer and general contractor, respectively, recognized the demands of the proposed excavation and the overall project schedule, which required completion within three years. Additionally, the historic Holy Name Cathedral, directly to the east of the project site, used the existing parking lot on the subject property. In accordance with certain requirements of the proposed development agreement, equivalent parking capacity had to be provided in the proposed below-grade garage within 24 months. These demands, along with cost efficiency, led the project team to choose a top-down construction method for the below-grade work. A design-build approach for the top-down method of the earth retention system and the partnership between the project stakeholders resulted in the overall accomplishment of the project goals. Measured deflections of the earth retention system around the site were controlled and agreed well with the underground construction team’s estimates (often less than our estimates), and instrumentation monitoring in the tunnel indicated negligible movements and no reported damage. The project was completed within the required schedule.