Semester of Graduation

Summer 2021

Degree

Master of Science in Civil Engineering (MSCE)

Department

Department of Civil and Environmental Engineering

Document Type

Thesis

Abstract

The research explored the use of microbially induced carbonate precipitation (MICP) to improve the mechanical properties of fine-grained soil and rapidly repair soil cracks on embankment slopes. Slope failures are often induced by surface cracks on the embankment slopes. To date, most rapid repair methods for slope failures (e.g., geosynthetics, soil nails, plastic pins, and lime treatment, etc.) involve large earthwork, special installation equipment, and unique construction processes, which may require extended construction time, disturb traffic, or increase the total construction cost. This research explored the feasibility of using bio-cement (MICP) to improve soil mechanical properties, seal the soil cracks, and assess the improvement of MICP on slope stability. Most previous studies on MICP treatment have focused on sandy soils. However, limited research on MICP-treated fine-grained soils were reported, which was investigated in this study. The conducted research tasks include (1) direct shear tests to investigate the mechanical behavior and biogeochemical reactions of low-plasticity silt treated by MICP, (2) cyclic wetting-drying tests to assess the feasibility of using MICP to seal and waterproof the soil cracks, and (3) SLOPE/W modeling of a slope treated by MICP. Direct shear tests were used to evaluate the shear responses of the low-plasticity silt under different overburden pressures (12, 25, and 35 kPa) and different bio-cement treatments. A series of cyclic wetting-drying tests were used to assess the effectiveness of MICP treatment on healing soil cracks. Crack lengths, area, width, and area percentage were measured and compared before and after the MICP treatment. SLOPE/W analysis was performed to assess the factor of safety of a slope under MICP treatment. The direct shear tests results show that the peak shear strengths increased by an average of 30% from the untreated to the MICP-treated soil samples. The wetting-drying cycle tests results show that MICP treatment can heal desiccation cracks, reducing crack length, crack width, and crack area. The results of the SLOPE/W modeling show that the MICP treatment had a positive effect on the improvement of slope stability, but more field tests are needed for optimizing the treatment solutions and procedures and assessing the long-term effect and ecological impacts.

Committee Chair

Lin, Hai

DOI

10.31390/gradschool_theses.5338

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