In 1909, Daniel Burnham and Edward Bennett produced a long-range plan for the development of the city of Chicago, which included the construction of Wacker Drive—a two-level street alongside the Chicago River circling two-thirds of the downtown Loop. But construction didn’t begin until 1924 on the $8 million east-west portion of the street; the north-south section wasn’t constructed until the 1950s.For the initial two-year project completed in 1926, workers installed 598 caissons to a depth of 95 feet below the surface to support the 5700-foot length of the upper deck. More than 1 million pounds of reinforcing steel, and 116,000 cubic yards of concrete were used for the columns and deck with a thickness as great as 3 feet.
Rebuilding Upper and Lower Wacker Drive in Chicago, workers place high-performance concrete on a 2800-sq.-ft. upper deck. The white plastic ducts house PT cables. Specifications call for a 100-year service life.
Keeping Lower Wacker open to traffic was a major challenge. Shown here is a driveway access to a loading dock, exiting to an 11-ft.-wide traffic lane. The forming structure used trusses to carry the forming system.
This worker puts the finishing touches on a beam form. Notice the close truss spacing for the deck spanning a traffic lane below.
The Upper Wacker deck has PT ducts (white plastic) running every 2 ft. in both directions to control cracking and permit a thinner deck. Notice the draped ducts at top right, adding support to midpanels.
Testing and quality control are seen as vital to the project’s success. Flood Testing Laboratories represented McHugh Construction, also making sure that ready-mix trucks met the specs before unloading.
The high-performance concrete used on this project included silica fume. Slight amounts of water loss in silica-fume concrete results in cracking so curing blankets were placed and saturated shortly after the concrete was placed.