Date of Final Oral Examination (Defense)
Type of Culminating Activity
Master of Science in Civil Engineering
Bhaskar Chittoori, Ph.D., P.E.
Nick Hudyma, Ph.D., P.E.
Yang Lu, Ph.D., P.E.
Expansive soils undergo vast changes in volume when subject to change in water contents and cause damages to infrastructures across the world. Traditional methods of tackling the problem of expansive soils using cement or lime are environmentally unfriendly and expensive. Microbial Induced Calcite Precipitation (MICP) is a new method which uses bacteria in the soil to precipitate CaCO3 (calcite) and improve the engineering properties of soils. Various laboratory studies have shown that this method can be applied successfully to treat expansive soils, but the field application of the method have barely been studied.
To study the applicability of MICP in field, a protocol was developed to perform in-situ chemical injections through a borehole and tests were conducted in Marsing, Idaho. Multiple rounds of chemical injections were performed, and soil samples were monitored for calcite content and swelling potential changes. Results showed an increase in calcite precipitation and decrease in swelling potential of the soil with each round of chemical treatment.
Additional study to understand the influence distance of chemical injections in the soil were performed by injecting water into the soil and collecting moisture change data around the borehole. A finite element model was created in ABAQUS to establish the influence zone of the injections and verified against field data. The finite element model was then used to study the effects of pressure, permeability and sorption characteristics of soil in influence distance. Results suggest that, in soils with low permeabilities, such as in case of expansive soils, higher matric suction can result in greater influence distances over time. It was also seen that change in pressure of injection had minimal effect in influence distance. This suggests that it may be possible to implement MICP protocols in expansive soils by injecting solutions through boreholes at very low pressures and longer durations.
Pathak, Anish, "In-situ Fluid Injections to Achieve Bio-Stimulated Calcite Precipitation in Expansive Soils" (2020). Boise State University Theses and Dissertations. 1766.