Mizzou Engineer studies how construction methods impact drilled shaft foundations

December 13, 2023

Crews test a foundation
Erik Loehr’s team tests a drilled shaft foundation.

A Mizzou Engineer has received funding from the Transportation Research Board — a division of the National Academy of Sciences, Engineering and Medicine —to study how construction methods may impact the foundations of bridges and other transportation structures.

Specifically, Erik Loehr, Glen Barton Professor of Mechanical and Aerospace Engineering, will be looking at the design and performance of drilled shaft foundations, which are used to support load-bearing structures. Drilled shaft foundations are made by drilling holes into the ground, then filling the holes with concrete and reinforced steel.

Historically, the performance of these foundations has been measured based on observation. Loehr’s goal is to come up with better techniques to determine how they hold up in varying conditions.

“Empirical measurements don’t work out perfectly because there’s a lot of variability,” he said. “Ground conditions vary. Concrete varies. There are different ways to drill a hole, and depending on where we are and what kind of ground conditions exist, that’s going to influence the choice of construction method. The question here is if we isolate these different construction techniques, can we do a better job of predicting performance so we can be more cost effective while still ensuring safety and reliability.”

Simultaneously, Loehr will be determining how size has impacted the performance of drilled shaft foundations over the past couple of decades. Twenty years ago, he said, drilled shafts were up to five feet in diameter. Now, they can be up to 15 feet in diameter and sometimes reaching 200 feet in length.

“Construction technology has advanced faster than design technology, such that we’re designing big shafts just like we designed the smaller shafts,” he said. “And we don’t fully understand the distinctions between smaller ones and larger ones. So we’ll be considering the size issue in this work, as well.”

During the three-year project, Loehr will collect and evaluate tests previously conducted to assess the performance of drilled shaft foundations — tests conducted by his team and others. A panel made up of representatives from the Federal Highway Administration and state departments of transportation will provide guidance and feedback over the course of the work.

At the end of the study, Loehr will present findings to the Transportation Research Board. Those findings could eventually lead to updates in the American Association of State Highway and Transportation Officials (AASHTO) bridge design specifications.  

“The ultimate goal would be to update the AASHTO code to account for different construction methods,” Loehr said. “States have to vote on any changes, so it’s a high bar, but that would be the ultimate goal.”

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