Historical Landmark, Vaulted Sidewalk

PROBLEM

Once serving as Chicago's City Hall, the architectural gem known as The Rookery was originally completed in 1888 with a design by legendary architects Burnham & Root and a stunning lobby created by Frank Lloyd Wright. After 121 years, the vaulted sidewalk along Adams St. was threatening to collapse. Zera was called in to replace the leaking topping and limestone structural slabs, while taking great care with the unstable rubble wall, keeping high-end storefronts open, and dealing with extenuating circumstances that threatened to delay the project at every turn—not to mention all of the unforeseen challenges lying in wait for over a century below ground.

SOLUTION

• Laterally braced the rubble wall holding back the street and sub-grade with I-beams, C-channels and turnbuckles to prevent its collapse
• Built temporary enclosures separating the work area from the Brooks Brothers tailor shop
• Supported retail storefronts with 4x4 and steal beam shoring
• Replaced structural I-beams supporting the vaulted sidewalk
• Poured a new structural concrete slab
• Installed a new American Hydrotech buried waterproofing system
• Poured a new decorative concrete topping slab with acid-etched finish
• Managed pedestrian traffic with jersey barriers without incident
• Counteracted extenuating circumstances by working around the clock for over a month to complete the project