Improving “Shrinkage-Swelling” Response of Expansive Soil Using Bio-calcite and Exopolysaccharide Produced by Bacillus sp.

Biological phenomena standout as a key towards green method for improving the properties of engineering construction material. The present study investigates the effect of Microbial Induced Calcite Precipitation (MICP) and Extracellular Polymeric Substance (EPS) produced by Bacillus cereus (B. cereus) SG4 on “shrinkage-swelling” behavior of expansive soil. The soil used for the study was commercially available Bentonite cohesive soil. The critical soil parameters such as Liquid Limit (LL), Plastic Limit (PL), and Differential Free Swell Index (DFSI) were found to be very high (LL = 608%, PL = 50%, and DFSI = 661%) due to the presence of Montmorillonite mineral. The results showed that treatment of Bentonite expansive soil with bio-calcite and EPS containing B. cereus SG4 culture media worked effectively. Bentonite soil was treated with bacteria along with culture medium for 5 and 10 days. It was observed that there was no significant reduction in geotechnical properties after 10th day of treatment. Maximum effect was observed at the end of 5th day exhibiting the efficiency and strong capability of proposed soil treatment method. After 5th day, LL, PL, and DFSI values were observed to be decreased; 177%, 39%, and 371% for EPS, respectively. The similar response was observed for Bio-calcite technique, which exhibited a significant reduction in LL, PL, and DFSI values (158%, 39%, and 271%), respectively. Both the treatment techniques worked successfully in improving the shrinkage-swelling response of Bentonite soil, but bio-calcite treatment was observed to be more effective than EPS treatment to control the shrinkage-swelling response.