Abstract: Microbial induced calcite precipitation (MICP) is a technique that can be a potential method to solve wetting swelling and drying shrinkage of expansive soils. With the bacteria concentration and urease activity as standards of measurement, the growth properties of Sporosarcina pasteurii in various conditions were studied, and the most favorable temperature, pH and vibration velocity were determined. Two different types of expansive soils were treated with MICP, and the effect of this method was studied by comparing expansive properties, cohesive force, internal friction angle and shear strength before and after the treatment. The mechanism of MICP treated expansive soils was explained through microstructure perspective. The results showed that the optimal culture conditions for the bacterial growth were as follows: the pH of 7, the vibration velocity of 200 r/min, and the temperature of 30 ℃. After treating with MICP, the free swelling ratio and unloaded swelling ratio were decreased significantly, while the cohesive force, internal friction angle and shear strength were increased. The calcium carbonate generated during MICP played the role of pore filling and soil particle cementation, and the replacement of low valence cations by calcium ions and the wrapping effect of calcium carbonate on soil particles improved the properties of expansive soils. The research can provide beneficial references for the technology and engineering applications of MICP treatment of expansive soils.

Key words: microbial induced calcite precipitation(MICP), expansive soil, swelling ratio, strength