Drilling down into long-lasting bridges

Drilled shafts help support key infrastructure like bridge foundations — making their construction critical for safe, long-lasting structures.

Illinois Center for Transportation and Illinois Department of Transportation aim to optimize their use in a joint project, “R27-188: Evaluating the Accuracy and Use of Drilled Shaft Integrity Testing Methods in Illinois.”

Timothy Stark, University of Illinois Urbana-Champaign CEE Excellence Faculty Scholar, and Abdolreza Osouli, Southern Illinois University Edwardsville associate professor, lead the project with Michael Short, IDOT’s District 3 program development engineer.

The three are joined by UIUC doctoral candidate Abedalqader Idries.

The team evaluated two integrity tests for drilled shafts, which consist of a circular hole into which concrete is placed.

“The project was developed to quickly and cost effectively test the foundation element of major bridge structures,” Stark said. “Drilled shafts support bridge piers, so if one of those piers do not meet capacity, you have a major problem.”

Determining whether the concrete foundation is constructed correctly is challenging, as it may be deep underground or underwater.

“A lot of times drilled shafts in small bridges might be 10 or 15 feet deep, but on a larger bridge they may be 50, 60, 80, even 100 feet deep,” Short said. “So, they’re really tricky to build, and they’re really difficult for an inspector to actually inspect and see what’s going on while they’re being built.”

Nondestructive tests of a drilled shaft’s concrete can assure the foundation is reliably constructed.

One test — crosshole sonic logging — involves placing steel tubes in the shaft and measuring how fast vibration waves travel. The other — thermal integrity profile — measures temperature continuously in the foundation during concrete curing and can be monitored remotely.

Key to the project were three full-sized test drilled shafts the researchers constructed in Illinois with intentional defects. Consultant experts in the two integrity testing methods performed their tests and reviewed the data to identify defects.

The test shafts allowed the researchers to determine which test method was more effective at identifying typical defects as well as provide guidelines on integrity testing for IDOT.

The two methods each had strengths and weaknesses, with crosshole sonic logging better suited for end-bearing shafts and thermal integrity profile better suited for shafts relying on side resistance.

From their findings, Stark, Osouli and Idries developed an easy-to-use decision flowchart, shown below, to assist IDOT in selecting the appropriate testing method for drilled shafts.

They also provided recommended updates to IDOT’s drilled shaft specifications and inspector’s checklist, which will allow the agency to use the integrity testing methods more effectively.

“I like working with IDOT on ICT projects because the whole goal is implementation,” Stark said. “The research is being used. It’s in practice. That’s what I like to do: do the research and then see it implemented.”

Effective use of integrity-testing methods will lead to better-performing and longer-lasting bridges.

Short cautions that quality construction processes should not be sacrificed when using integrity tests.

“Integrity testing is one part of a good inspection process,” Short said. “It’s a good tool, but it is not a replacement for a good, experienced inspector to be present and paying attention to what’s going on during the construction process.”