Effect of Microbially Induced Calcite Precipitation on Clayey Soil

Fine grained soils, in particular, compressible clays are known for their plastic behavior which causes severe damages to infrastructures such as roads and foundations of buildings. Owing to the growing environmental concerns, and demand to meet land for infrastructural needs, environmentally friendly methods which effectively improve the engineering properties (strength and plasticity characteristics) of clayey soils are the need of the hour. Keeping this in view, the present study utilizes bio-cementation by non-pathogenic, urease-producing bacteria, Sporosarcina pasteurii to improve the unconfined compressive strength of clayey soils. The laboratory tests performed included the UCS, acid leaching test, organic content determination, and XRD analysis. The tests were performed on untreated specimens and 7 and 14 days cured MICP treated soil specimens. The changes in plasticity characteristics of soil after treatment were assessed by determining the Atterberg limits of treated samples. The results show that MICP via bioaugmentation can improve the unconfined compressive strength of clayey soils and maximum improvement of 3.48 times was achieved at a lower chemical concentration of 0.25 M. This may be attributed to slow uniform CaCO3 precipitation at lower concentrations and the reaction inhibition property of CaCl2 at higher concentrations. The liquid limits and plastic limits of soil increased significantly after the treatment.