Abstract:
The IL Rt 390 Ramp Q5 project in Bensenville, DuPage County, Illinois, was a successfully value engineered tollway project that used innovative ground improvement solutions. Once a wetland, the site presented challenges that necessitated a strategic redesign for improved efficiency.
The project involved supporting an embankment for a new highway ramp over highly organic peats, covering a ground improvement area of 41,500 sq. ft. The soil layers posed a challenge, comprising of soft silty clay, very soft organic silt loam, and loose to dense sand. Initially conceived as a timber pile and pile cap supported embankment, Menard optimized the project's cost schedule and efficiency by redefining the support system through ground improvement.
The revised geotechnical strategy introduced 461 Controlled Modulus Columns (CMCs) and 1839 Wick Drains, instead of the original timber pile plan. Settlement criteria played a crucial role, with timber piles designed for 1” total settlement. In the absence of CMC specifications, the CMCs were ultimately designed for up to 1” total post-paving settlement, and a maximum of 3” settlement before paving. The installation of wick drains served as a precautionary measure to ensure the anticipated 3” settlement occurred before road paving.
The project encountered various challenges, including persuading the Illinois State Toll Highway Authority about the merits of ground improvement over traditional timber piles. Decision-making complexities involved load transfer and working platform elevations, the choice between a traditional load transfer platform and a fiber slab and determining performance and verification requirements. Addressing the liability associated with unsupported culverts, 3D design challenges, and managing the impact of flooding and working pad collapse added further challenges.
In the presentation we provide a detailed examination of the inefficiencies inherent in timber pile-supported embankments in peat and highlight the benefits of a value-engineered shift to ground improvement strategies, particularly through CMCs. We navigate the process of redesigning a tollway project, shedding light on the complexities of CMC design and modeling, and discussing operational challenges during implementation. Finally, we explain our use of load testing and installation monitoring to verify the design and successful performance of the ground improvement.
The presentation underscores the adaptability and foresight crucial for successful execution in challenging geotechnical settings. It emphasizes the transformative impact of a carefully engineered shift from traditional foundations to cutting-edge ground improvement methodologies.