Factors Affecting Improvement in Engineering Properties of Residual Soil through Microbial-Induced Calcite Precipitation

Studies of soil improvement by microbial-induced calcite precipitation (MICP) have focused primarily on fine sand. This paper explores the viability of the MICP technique for improving the engineering properties of a typical tropical residual soil. A species of Bacillus, B. megaterium, was used to trigger calcite precipitation. Four variables were considered in this study: the concentration of B. megaterium, the concentration of the cementation reagent, the treatment duration, and the flow pressure of the cementation reagent. The results show that the improvement in the engineering properties of the MICP-treated residual soils is comparable to those of treated fine sands. The preferable treatment conditions for the soil studied are B. megaterium concentration of 1×108 cfu/mL, cementation reagent concentration of 0.5 M, flow pressure of 1.1 bar of the cementation reagent, and treatment duration of 48 h. Using this combination of parameters, the obtained shear strength increase and hydraulic conductivity reduction are 69 and 90%, respectively. A minimum calcite content of 1.0% (15 kg/m3) is required to provide measurable improvement in the engineering properties of the soil.