Replacing a bridge that is part of an already-congested interstate is challenging; add in the restrictions of constructing the replacement span over an environmentally waterway and forest, task may seem to be impossible. Learn how a team engineered innovative solutions to overcome these obstacles.
As part of its $15 billion capital investment in improving mobility, the directors of the Illinois Tollway announced one the projects included in its Move Illinois program would be to contract for the widening and or replacement of the Fox River Bridge. The work on this span, which at 1315 ft is the longest and largest twin bridge along this 62 mile section of I-90, was part of an effort to transform the highway into a 21st-century transportation corridor. Additionally, this section of the Jane Addams Memorial Tollway serves as a major traffic throughway for 101,000 vehicles per day, linking Wisconsin as well as 16 northwestern Illinois counties and 32 towns, cities, and villages to Chicago’s O’Hare International Airport. With a $95 million budget, the project was certainly lucrative, it also posed significant challenges according to an article written by the two principal engineers, Scott Eshleman, P.E., S.E., and Rob Koss, P.E., who worked on the project for the award-winning Chicago-based firm Stanley Consultants.
A Multitude of Challenges Requiring New Approaches to Bridge Engineering
Examples of some of the issues faced by the engineering team that begged for innovative solutions include the following:
- The project required maintaining the existing three lanes of traffic going each way during the construction without the use of contraflow measures.
- Once completed, the bridge needed to accommodate a total of eight lanes of traffic plus a full-sized shoulder to facilitate snow removal.
- To avoid harming the sensitive river and fen ecosystems that lie under the bridge, the engineers needed to design a means of diverting stormwater to an area where any solids could separate prior to the water flowing off the bridge. Additionally, the number of piers had to be reduced to enhance the free flow of the river.
- When designing the bridge plans, the engineers needed to devise a means for the construction crews to avoid overhead high-voltage transmissions lines positioned along the bridge.
- The allocated 28 months for the project did not allow for the use of traditional bridge construction techniques.
- During construction, the highway needed to be safe and free of traffic jams that would hinder the travel of 86 million vehicles using the tollway and bridge during the life of the project.
- Assessment of the original piers and deck, placed when the bridge was built in 1958, indicated that they had reached the end of their safe usable life so they had to be replaced.
- Since the banks of the river were so steep, the engineering team considered the typical means of crane placement unfeasible.
- The construction would not damage the oaks and white cedars under the bridge nor disrupt the free flowing springs underneath the bridge.
Successful Implementation of New Methods of Bridge Engineering and Construction
To meet the technical specifications and the environmental constraints of the project, the engineering team and their contractors developed and successfully used the following innovative approaches to interstate highway bridge construction:
- By constructing the substructure underneath the bridge, this phase of the project had zero traffic impact.
- By specifying the use of beams that were longer and deeper than those typical employed, the engineering team reduced the number of piers needed to support the bridge and decreased the number of expansion joints required. As a result, the engineering built in the benefits of reduced long-term maintenance time, labor, and costs.
- Since the engineering team decreased the number of spans from 15 to 8, they halved the number of piers needed to support the bridge, which facilitated the river flow.
- By providing a monetary incentive, the engineering firm found a subcontractor willing to employ new methods of pier placement, which eliminated the need for construction substages.
- The engineering team maximized deck space by eliminating parapets and reconstructing sacrificed deck sections to connect with the new parts of the deck.
Learn more about the new bridge design and construction techniques developed by the engineering team by reading Built from Below.
See this innovative work in action by watching this time lapse video:
What other solutions can you engineer to overcome the obstacles for completing this project?