Geotechnical Application of <i>Methylobacterium radiotolerans</i> in Expansive Soil: Bacterial Isolation and Optimization Using Response Surface Method

The present study focuses on enhancing the unconfined compressive strength (UCS) of an expansive soil with the help of microbially induced calcite precipitation (MICP). Here, Methylobacterium radiotolerans (MRT) was isolated, and used for the first time in black cotton soil. Further, the response surface methodology (RSM) utilizing a Box–Behnken design in Minitab version 20.2 has been used to optimize this process. The urea, calcium chloride concentration, and bacterial cell volume were optimized to maximize the UCS value. Statistical parameters with reasonable model fits were obtained, showing the reliability of the analysis conducted in the present study. The optimal values obtained from the analysis were 0.1 M urea, 0.3 M calcium chloride, and 21.36 mL of bacterial cell suspension for a maximum compressive strength of 1,738 kPa. Compared to other bacterial strains reported in the literature, M. radiotolerans yielded better results in MICP-based stabilization of fine-grained soils. This study emphasizes the need and importance of identifying indigenous bacteria for possible application in MICP-based stabilization of local compressible soils with low bearing capacity. The potential application of such bacteria in improving the strength properties of road subgrades in fine-grained soils is expected to be more eco-friendly, sustainable, and cost-effective.