Strength enhancement of lateritic soil through mechanical mixing with magnetite nanoparticles, starch solution, and calcite precipitating bacteria

The present study was undertaken to strengthen lateritic soil through a biogeochemical process. The solution curtails the project’s cost by eliminating expansive ground improvement and negating deep foundation construction. The conventional technologies for ground treatment mostly consist of chemical processes that harm the environment through lithospheric pollution due to subsurface migration of the toxic compounds as leachate. The improvement of soil strength through the biogeochemical process was undertaken through calcite precipitation using ureolytic microorganisms. A gram-positive bacterium, Sporosarcina pasteurii, was used, precipitating CaCO3 within the soil and improving strength through chemical bonding. Magnetite nanoparticles (Fe3O4) were added with the microorganisms for growth acceleration and metabolic improvement, which caused enhanced precipitation of CaCO3 in the soil. Starch solutions were also added to prevent agglomeration of the Fe3O4 nanoparticles. Four different sets of experiments were carried out, namely (i) untreated soil, (ii) soil treated with cementation solution, (iii) soil treated with microorganism as well as cementation solution, and (iv) soil treated with the microorganism, Fe3O4/starch solution, and cementation solution. The higher amount of CaCO3 precipitation under this condition perhaps increased the UCS value of the lateritic soil. Soil column was treated with a bacterial cell concentration of 2.30 × 107 (cell/ml) at OD600 value 0.38, the compressive strength of soil increased from 22.60 to 29.62 kPa, that is almost 30%, after increasing cell concentration of 4.09 × 107 (cell/ml) at OD600 value, 0.58 compressive strength of soil becomes 34.18 kPa, which is almost 50% strength increase than natural soil sample. The higher amount of CaCO3 precipitation under this condition perhaps increased the UCS value of the laterite soil. In a further extensive study, an optimal amount of Fe3O4 nanoparticles was added to two different concentrations of bacterial solutions 2.30 × 107 (cell/ml) and 4.09 × 107 (cell/ml), respectively. After treating soil columns, the UCS test result shows a significant improvement of strength (i.e., 77%) in the soil column due to the addition of Fe3O4 nanoparticles. The study’s outcome provides the engineers and contractors with a cost-effective alternative solution for in situ ground improvement.