Influence of Bacteria on Physical Properties of Black Cotton Soil

Microbial-induced calcite precipitation (MICP) is a sustainable biological ground improvement technique, which is capable of altering and improving physical properties of black cotton soil. In order to evaluate MICP as a soil ground improvement technique for black cotton soil, four types of microbes were used in this study. These were Bacillus pasteurii, Bacillus subtilis, Bacillus megaterium, and Pseudomonas. These microbes in liquid medium were mixed with the soil sample for different percentages (4%, 8%, 12%, 16%, and 20%) by weight of sample. The soil samples were kept for different reaction periods (3 days, 7 days, and 14 days). The physical properties of MICP-treated soil such as liquid limit, plastic limit, shrinkage limit, and swelling pressure were examined. The results show that the plasticity index decreases when upto 20% of microbes were mixed and when microbes were more than 20%, plasticity index increases. The reaction period shows the influence on plasticity index. The shrinkage limit test was performed for soil with 20% bacteria for 3, 7, and 14 days reaction period. The MICP-treated soil shows reduction in shrinkage limit values. Swelling pressure tests were performed for soil with 20% microbes for 7 days reaction period, and swelling pressure was also reduced to 80%. Thus, the use of microbes helps in controlling the swelling and shrinkage characteristics of black cotton soil.