Sustainable reuse of coal mine overburden stabilised with microbially induced calcite precipitation

This study was carried out to evaluate the effectiveness of bioaugmentation method of microbially induced calcite precipitation treatment for strengthening coal mine overburdens (OB). Cohesive soil samples were collected from Gondegaon open cast mines in Maharashtra, India. The samples were characterised for their physical properties before exposing them to microbial treatment. Bacillus pasteurii was added to the OB samples along with cementation solutions of varying concentration (0.25–1.0 M), and the samples were evaluated for their unconfined compressive strength (UCS), California Bearing Ratio (CBR), swelling pressure, shear strength parameters, and modulus of resilience (MR). The degree of calcite precipitation for different soil mixes was also evaluated using gravimetric analysis. Finally, microstructural examinations were carried out to understand the effect of microbial treatment on the OB samples. The results indicate that addition of B. pasteurii leads to an increase in the UCS, CBR, and MR values. Simultaneously, the swelling pressure was observed to be reduced for treated samples. The highest increase in CBR from 2.85% to 8.49% suggests that the above technique can be sustainably used to treat OB dump soils for possible end-use as building materials in mine haul roads.