ABSTRACT
To create an express train service linking O’Hare International and Midway Airports, the Chicago Transit Authority (CTA) decided to build two short tunnels to connect the Blue and Red transit lines in Chicago. The connection will be at Block 37, located between State and Dearborn Streets, and will link the two subways through a new station (Figure 1).The new Block 37 station structure will be constructed as part of the Block 37 development project using slurry wall construction
and a top down technique. The new connection tunnels will be constructed using mining methods. Mining operations will originate from access shafts to be built within Block 37. The project will also include modifications to the continuous platforms at the existing State Street and Dearborn Street subway tunnels to accommodate the new connections. This project will be accomplished under a complex and tight schedule and must be completed with minimal disruptions to the non-stop subway service. The anticipated subsurface conditions and the stringent project settlement criteria create difficult conditions for the design and construction of the tunnels.
