Abstract: Due to the concentrated rainfall and severe hydraulic erosion, the loss of the sandy clayey purple soil in Chongqing region is serious. The microbial-induced calcite precipitation (MICP) has been widely used in the soil improvement owing to its low energy consumption and less pollution. In this paper, the culture medium and culture conditions of Bacillus megaterium (BNCC 336739) were optimized by orthogonal tests, and the number of viable bacteria increased by 126% with good activity. Under a water pressure of 9.8 kPa, the soil solidification tests using Bacillus megaterium were conducted to investigate the change rules of solidification effects with treatment times. The results show that calcium carbonate production and dry density increase progressively with the increase of treatment times, and the unconfined compressive strength positively correlates with the calcium carbonate production. The strength tends to be stable with less effective calcium carbonate precipitation and increases by 77% after nine times of treatment. As the pores filled with calcium carbonate and the formation of upper and lower crusts, the permeability decreases continuously and eventually drops by two orders of magnitude. The sample standard deviation (s) of calcium carbonate production (C) in the upper, middle and lower layers of the soil column was used to reveal the discreteness of calcium carbonate distribution. Besides, it is shown that the secant elastic modulus fluctuates with the increase of C under the influence of s. When C is close or s differs greatly, the smaller the s is, the greater the elastic secant modulus is. This study provides scientific basis and reference for the application of MICP technology in foundation, slope reinforcement and soil and water conservation in the purple soil area.

Key words: microbial-induced calcite precipitation, bacillus megaterium, treatment, unconfined compressive strength, permeability