Illinois Tollway Central Tri-State Corridor (I-294)
Project Name: Illinois Tollway Central Tri-State Corridor (I-294)
Project Date: 11/18/2015 to 12/07/2015
Location: Chicago, IL
Partners: GSG Consultants, Inc., Wang Engineers, Inc., Illinois Tollway Authority, Applied Research Associates (ARA)
Public Agencies (Pavement System Owners): FHWA, State DOTs, Tollway Authorities
Pavement Engineering Consultants
Ingios Engineers Involved: David White, Pavana Vennapusa, E. Tom Cackler, Brendan Fitz Patrick, Heath Gieselman
Challenge: The Illinois Tollway required a geotechnical exploration program for one of the most heavily traveled Chicago area expressways, the Central Tri-State Tollway project extending from approximately Balmoral Avenue to 95th Street. The Tollway’s objective was to design and reconstruct this section of expressway in the most cost-efficient manner for the life of the pavement. The pavement design team on the project used the AASHTOWare™ Pavement ME Design method to provide cost-effective designs.
Solution: Ingios assisted the geotechnical exploration teams on this project by deploying APLT to provide a direct measure of the stress-dependent resilient modulus (Mr) values for the existing foundation layers, which is the key pavement foundation design input parameter. Tests were conducted directly beneath the existing pavement through a core hole at 90 test locations along the 22-mile stretch of the roadway, using multi-stress sequence cyclic Mr tests. 1,100 cycle tests were performed at each test location within 15-20 minutes at each test location.
Often Mr values are obtained from generic relationships to simple laboratory tests (e.g. gradation) as the basis for design which leads to use of conservative values because of the lack of reliable “real” design data. This conservatism, driven by uncertainty in existing properties, yields design solutions for more expensive pavement sections. Using the APLT technology, the pavement design team was able to obtain direct measurements of the existing support beneath the pavement, the “Universal” model parameters for Mr, and directly use the values in their design analysis.
Benefits: Results from the project revealed important foundation behavior information such as the “break-point stress” that is key to limiting permanent deformations beneath pavement, differences in the support conditions between the different lanes constructed between 1950s to 1990s. Using the directly measured in situ support information, the pavement design team was able to optimize the foundation design and avoid over-designs.