Publication Date

12-2016

Date of Final Oral Examination (Defense)

5-25-2016

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Civil Engineering

Department

Civil Engineering

Supervisory Committee Chair

Bhaskar Chittoori, Ph.D.

Supervisory Committee Member

Debakanta Mishra, Ph.D.

Supervisory Committee Member

Juliette Tinker, Ph.D.

Abstract

Expansive soils, also known as swell-shrink soils have been a problem for civil infrastructures including roads and foundations from ancient times. The use of chemical additives such as cement and lime to stabilize expansive soils is a common practice among geotechnical engineers especially for lightly loaded structures. However, several occurrences of subgrade failures were observed after stabilizing with chemical additives hence engineers are in search of sustainable stabilization alternatives. Microbial Induced Calcite Precipitation (MICP) is gaining attention as an environmental friendly soil improvement technique. Several researchers have successfully tested its feasibility in mitigating liquefaction induced problems in sandy soils. This research focuses on evaluating its effectiveness in stabilizing expansive soils. For this purpose, three natural expansive soils with high and low plasticity properties were subjected to MICP treatments. Two methods of MICP treatments were followed in this research. The first method was bio-augmentation. In this method the soil samples were first augmented with bacterium Sporosarcina pasteurii and then treated with calcium chloride and urea (substrates) and cured for seven days. In the second method bio-augmentation was followed by stimulation using a nutrient delivery system which was developed to treat microbes with substrates. Variables such as soil types, microbial concentrations and number of pore volumes of substrate injected were studied in this research. Geotechnical testing including Atterberg limits, unconfined compressive strength (UCS) and one-Dimensional (1-D) swell test along with specific surface area were performed to evaluate the efficacy of MICP treatments.

The results indicated that MICP treatments could be a viable alternative for expansive soils treatments. Although the improvement in UCS values after both types of MICP treatments were notable, the strength gain was considerably lower than lime treated soils. However, 1-D strain reduction was on par with lime stabilized soils. It was also observed that MICP treatments do not result in significant clay mineralogy changes.

Download

Share

COinS