Publication Date

8-2018

Date of Final Oral Examination (Defense)

7-30-2018

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Civil Engineering

Department

Civil Engineering

Supervisory Committee Chair

Bhaskar Chittoori, Ph.D., P.E.

Supervisory Committee Member

Malcolm Burbank, Ph.D.

Supervisory Committee Member

Debakanta Mishra, Ph.D., P.E.

Supervisory Committee Member

Arvin Farid, Ph.D., P.E.

Abstract

Of the four types of soils, clays are often associated with issues related to low bearing capacity, high compressibility, swelling and shrinking nature. For example, expansive soils swell and shrink with moisture ingress and digress and are prevalent in several parts of the world causing billions of dollars in damages annually to various civil infrastructures. Several ground improvement techniques such as chemical stabilization, deep soil mixing, moisture barriers, and others were employed to counteract these soils. However, these methods are impractical in certain situations and unsustainable in others due to their economic and environmental impacts. Microbiological treatment of soils could provide a more sustainable alternative. Microbial Induced Calcite Precipitation (MICP) is one such process where urease-producing bacteria can precipitate insoluble calcite in the presence of urea and calcium chloride. Researchers have successfully used MICP to alter specific geotechnical properties of the sands and silts and improve the overall behavior of soils. In this research an attempt is made to use this technique on clays and improve their engineering behavior. There are two ways to apply this technology to soils, and those are bioaugmentation and biostimulation. Bioaugmentation is a process where urease-producing bacteria are injected into the soil, whereas biostimulation takes advantage of the indigenous bacteria already present in the soil and stimulates them to precipitate calcite. Past studies showed that biostimulation is a superior alternative as the bacteria are already accustomed to the soil environment compared to augmented bacteria. Hence, this research investigates the applicability of biostimulation to clayey soils in minimizing their swelling potential and improving the strength. For this purpose, eight soils were selected out of which four soils were artificially made from a natural soil to have similar microbial communities with varying clay content, while the remaining four soils are naturally occurring soils from different locations and had dissimilar microbial communities. Both macro and micro scale studies were conducted on untreated and biostimulated soils to observe changes in plasticity, strength, swelling and mineralogical characteristics. A considerable amount of strength gain, swelling reduction, and calcium carbonate precipitation was observed in this study. It was noted that calcite precipitation via biostimulation could be applied to clayey soils and alter their engineering behavior. It was also observed that the soils were able to precipitate calcite regardless of the origin of microbial communities.

DOI

10.18122/td/1433/boisestate

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