Studying Post-Wildfire Soils to Better Understand Landslides

Yifei Ma, assistant professor of civil and architectural engineering

In a world of changing climate, wildfires are increasingly common.

And because of their heat and destruction of plants, trees, and their roots, those wildfires change the characteristics of soil and rock.

But how, and how much? Those processes—which can lead to landslides and mudslides, fatalities and economic loss—are still poorly understood.

They will be a bit better understood soon, thanks to a two-year, $174,924 grant from the National Science Foundation to Yifei Ma, assistant professor of civil and architectural engineering in Lawrence Technological University’s College of Engineering.

“The research will study the behavior of hill slopes in post-wildfire environments,” said Ma, who joined the LTU faculty in fall 2019 after a postdoctoral research position at Oregon State University. “We can't go there to test materials during a wildfire. And afterward, the physical and environmental conditions are no longer the same. So the best way to study them is to simulate very complicated environmental situations with advanced numerical models on high-performance computers.”

Ma pointed to a huge landslide that closed down a major section of the Pacific Coast Highway in California's Big Sur area as an example of what can happen after a wildfire.

“After a fire, the anchoring effect that roots contribute to are missing, and the combustion of organic material creates a waxy material that makes the soil hydrophobic--it sheds water--which increases surface runoff,” Ma said. “Heating and cooling also affect materials, reducing the strength of rocks. And right now, there’s no experimental data to determine how soils are affected in these complicated environmental conditions. But we can use fundamental physics to characterize the behavior of these materials at microscale, and use that data and numerical models to predict the behavior of materials at the macro scale.”

Ma won't be braving the elements after a wildfire to conduct the research. Instead, he’ll use high-performance computer servers to run extremely complicated three-dimensional mathematical simulations of the materials.

The end result of the grant will be a peer-reviewed paper that will be presented in February 2024.

Preliminary results so far have yielded some surprises, Ma said. “With sandstone, the behavior is not what we expected,” he said. “When heating reaches a certain value, the sample loses strength very rapidly.”

Ma was assisted in his research by Fahd Mohammed Naimatullah Mujahid, a graduate student in the Department of Civil and Architectural Engineering.

Ma’s research career has focused on geomechanics, using measures to study the behavior of granular material, from powders to soils to rocks, under varying conditions. Books on his shelves have titles like “Soil Mechanics and Foundations” and “Soils and Waves.” At LTU in the fall 2023 semester, besides his research, he also taught a soil mechanics class to upper-level undergraduate students.

And with this grant, Ma said, “hopefully in the future, we can be better prepared for landslides,” by learning the fundamental physics that govern the behavior of soils and water on post-wildfire slopes, giving engineers the information they need to analyze--and, hopefully, alleviate--the risk of post-wildfire landslides through stabilization.