Focus on new faculty: Bill Likos and the mechanics of unsaturated soils
In the semi-arid regions of Colorado, clay soils, which swell when they get wet and shrink as they dry, pose any number of challenges for engineers attempting to design everything from paved surfaces to building footings. "From a fundamental research standpoint, I want to know the mechanisms for the volume changes when clay gets wet," says Associate Professor Bill Likos.
A geotechnical engineer who joined the UW-Madison faculty fall 2012, Likos studies unsaturated soil mechanics—an area he says historically has not received much attention. Unsaturated soils like clay contain both liquid and gasses in their pores, and the quantity of liquid in such soils influences their mechanical behavior.
Think, for example, about building a sand castle. A handful of dry sand flows grain by grain through your fingers, while really wet sand turns into a mushy slurry. Likewise, prolonged or intense rainfall weakens soil on hillsides, leading to landslides. "Optimum water content increases strength and stiffness, and identifying this isn't something we have a good handle on," says Likos, who is on the leading edge of this emerging field.
In fact, he is co-author of Unsaturated Soil Mechanics, one of only a handful of textbooks on the subject. He and Ning Lu, a professor of engineering at the Colorado School of Mines, authored the book, which provides a comprehensive introduction to the fundamental principles of unsaturated soil mechanics.
Likos, who holds a bachelor's degree in civil and environmental engineering from Tulane University, earned his PhD in engineering systems from the Colorado School of Mines. Colorado's clay soil piqued his interest in unsaturated soil mechanics, and he continued that research focus first as a postdoctoral researcher there, and for the past 10 years, as a faculty member in civil engineering at the University of Missouri-Columbia.
His research toolbox includes experience as an experimentalist, as well as a background in instrumentation and modeling. At UW-Madison, where his affiliations now include geological engineering and civil and environmental engineering, Likos saw the opportunity to contribute both complementary and unique expertise. "I came out of graduate school with a broad view of geotechnical engineering," he says. "I come from an interdisciplinary background. The geological engineering program here is very much in line with the idea of crossing disciplinary boundaries. The structure here really facilitates the kinds of things I'm interested in."
Already, Likos is collaborating with colleagues in civil and environmental engineering and in geology on a study of the efficacy of a deep insulated single-hole geothermal heat pump system. And with funding from the National Science Foundation, he is continuing his research of unsaturated soils. In one project, he is measuring how water and clay mineral surfaces interact in an attempt to learn more about expansive clay behavior, while in a second project he is using X-ray tomography to image the microstructure of unsaturated soils. In that research, Likos hopes to understand how water affects soil behavior by observing how individual soil pores retain water.
Although he is studying the fundamental mechanisms of unsaturated soils, Likos has not lost sight of the application of that understanding. "There's a lot of uncertainty about how to incorporate unsaturated soil mechanics into practice," he says. "When we understand those mechanisms on a fundamental level, we can do a much better job with making recommendations for how to deal with them."