Drilling in: IDOT, Georgia Tech to bring cone penetration testing to Illinois
7/11/2024
Determining subsurface properties quickly and accurately is key to designing more cost-effective, reliable transportation infrastructure such as bridges, levees and dams, among others.
Illinois Center for Transportation and Illinois Department of Transportation aim to introduce a method to Illinois that quickly tests subsurface properties in a joint project, R27-210: Cone Penetration Testing for Illinois Subsurface Characterization and Geotechnical Design.
Jorge Macedo, Paul Mayne, and Sheng Dai, Georgia Tech professors, led the project with Brian Laningham and Brad Hessing, IDOT’s District 6 Project Engineer and Foundations and Geotechnical Unit Chief, respectively.
The team turned to cone penetration testing — an in-place drilling method that provides real-time information about the properties and strength parameters of subsurface conditions.
Cone penetration testing, a process Macedo compares to “subsurface radiography,” involves vertically pushing an electronic steel probe equipped with sensors into the ground to collect continuous measurements of soil properties and groundwater.
“Cone penetration testing is a modern alternative and supplement to the conventional means of geotechnical site investigation that uses rotary drilling, boreholes, augering, sampling or standard penetration testing,” Mayne said. “CPT is not only faster, more economical, safer and has higher reliability, but it also provides multiple continuous readings (often every 0.79 inches) with depth.”
The team assisted IDOT with developing CPT policies and procedures for Illinois, which currently uses the standard penetration test — a technique that brings significantly more uncertainty and collects only one data point in 5-foot intervals, resulting in considerably less data compared to CPT.
The Georgia Tech team, along with ConeTec personnel, visited sites in all nine IDOT districts and conducted cone penetration testing, retrieving samples for laboratory testing to inform guidelines.
Their findings showed that most soils in Illinois are fine grained, such as clays, silts and loams, which is ideal for cone penetration testing compared to areas that contain coarse or compacted soils.
The Georgia Tech team also provided IDOT with recommendations for using historical borehole and standard penetration testing data to establish a correlation between the cone and standard penetration tests for Illinois.
“This research project provides a roadmap for implementing a CPT practice in the state of Illinois and all the benefits that this entails,” Macedo said. “In this manner, the geotechnical practice at IDOT is expected to be advanced, consistent with the practices at other DOTs in the U.S. that have already implemented a CPT practice.”
The traveling public can expect to see further benefits from improved subsurface testing time: fewer lane closures and safer highways.
“For highway development and reconstruction projects, the current practice involves a time-consuming process of conducting soil borings and running supplemental lab testing to get any results, make decisions and complete the design,” Mayne said.
“The CPT rig only needs one hour to complete a sounding, thus minimizing lane closures,” he added. “Also, CPT data are immediately available for design use. There is no 3- to 5-week waiting period for the laboratory to provide results.”
The project has also contributed to training the next generation of geotechnical engineers with CPT expertise.
The students involved in the different project stages include Cody Arnold, Paola Torres, Luis Vergaray, Yumeng Zhao, Lina Pua and Christopher Abdeen. Arnold and Torres led the project data collection and interpretation components.