County Materials manufactured ArchCast precast concrete bridge sections for Joliet Union Station.
Credit: County Materials County Materials manufactured ArchCast precast concrete bridge sections for Joliet Union Station.

Located southwest of Chicago, Joliet, Ill., is the end of the line for two routes of Metra, Chicago’s commuter train system. Between them, the Heritage Corridor and the Rock Island District lines transport 1,400 passengers each day to and from Joliet Union Station. The City of Joliet is upgrading the area around its downtown train station into a multimodal regional transportation center to reduce conflicts between passenger and freight train traffic, and improve pedestrian traffic flow, safety, and aesthetics in the area.

The largest parking area is across the tracks from the station. A railway underpass provides road access to and from the station. Until recently, pedestrians had to share this space with vehicular traffic. The 104-year-old structure supporting the tracks was also deteriorating to the point of being unsafe. To address these issues and to accommodate upgrades to the train tracks and platforms, planners decided to replace the existing bridge and transform the underpass to a pedestrian-only tunnel. Ideally, construction would not interfere with the twice-daily rush of pedestrian traffic.

County Materials manufactured ArchCast structures at its Salem, Ill., plant for the project. The arched, precast concrete bridge sections allow construction of the new passageway without disturbing the existing bridge.

Bridge reconstruction began in October 2014. To create the 96-foot tunnel, 12 8-foot-long ArchCast structures weighing 48,000 pounds a piece — each with a 16-foot span and 11-foot rise — were pulled under the existing passageway with the aid of Hillman rollers and a winch. C-shaped channels built on the concrete footing guided the rollers for smooth placement of the sections.

In addition to designing and manufacturing the structures, County Materials provided support during this first phase of the project. “We weren’t directly responsible for the installation,” says County Materials project manager Rich Cooper, “but we’ve pulled pieces in before so we worked with the contractor (Ragnar Benson Construction) to help make sure it all went smoothly.”

Once the tunnel was in place, precast head and wing walls were installed to finish the ends. A formliner gave the surfaces the elegant look of a stone wall. The surface of the units will be stained a warm tone when the concrete cures. The stone wall’s appearance adds an architectural element that helps it integrate visually with other aspects of the project.

The third phase involves pumping controlled low-strength fill into the space between the existing abutment walls and the new arch walls. The mix is largely sand bound with a small amount of cement. It flows well, doesn’t require compaction, and reaches around 500 psi within 28 days. It is very hard for structural strength, but can be excavated. The final phase will involve tearing out the existing bridge, filling with ballast, and reinstalling the tracks.

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