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Project Aims to Stabilize Expansive Soils Beneath U.S. Roadways

By: Kathleen Tuck   Published 4:17 pm / September 9, 2016

Stoplight marking starting point of construction on rural roadway.

Every year, the United States spends billions of dollars repairing and maintaining roadways built on expansive soils, including transportation corridors in northern and parts of southwest Idaho. Civil engineers have devised several methods to deal with the problem over the years, including pre-wetting, moisture barriers, mechanical compaction, chemical stabilization and innovative pavement design.

Portrait of Bhaskar Chittoori.

Bhaskar Chittoori

Bhaskar Chittoori, assistant professor of civil engineering, is working on an innovative — and more sustainable — approach to the problem called microbial-induced calcite precipitation, or MICP. The technique stimulates bacteria in the soil to produce calcite, which then strengthens the soil. While the technique has been used in the past, mostly in sandy soils by introducing bacteria into the soil, Chittoori’s approach is unique.

Instead of introducing new bacteria into the environment, he and his co-PI Malcolm Burbank with CDM Smith propose stimulating already present bacteria, using clay soil as a natural incubator. “Feeding” nutrients to the bacteria, thus encouraging them to reproduce, will prompt them to precipitate calcite, which then changes the physiochemical behavior of the soil.

The work is being funded by a grant from the National Academies of Science’s NCHRP-IDEA program. The study is titled “Application of Microbial Facilitated Stabilization for Sustainable Improvement of Expansive Pavement Subgrades.”

“If successful, this technique would be both environmentally friendly and economical, which essentially means sustainable,” Chittoori said. “In the past, I have used various chemical methods to mitigate the swelling nature of these soils, but they have the downside of environmental concerns. This is an environmentally friendly alternative that can use the existing microorganisms in the soil. The project has a great potential to revolutionize the way pavement rehabilitation is done in areas with expansive subgrades.”