Abstract: Based on microbial induced carbonate precipitation (MICP), soil modification technology has attracted widespread concern in geotechnical engineering. This technology can not only improve the soil strength, stiffness, the properties of anti-liquefaction, anti-erosion and anti-permeability but also maintain good soil permeability and water permeability and improve the growth environment of the plants simultaneously. As the microbial mineralisation involves a series of complex biochemical and ion chemical reactions in the curing process, soil modification through MICP curing can be affected by many factors. In this paper, the effects of influence factors on the performance of microbial improved geomaterials were summarised, such as bacterial species, bacterial concentration, temperature, pH, the ratio of cement solution and soil properties, and their optimisation methods and future research direction were discussed as well. The conclusions are as follows. The bacteria type, bacteria concentration, temperature, pH, and the nature of the cement can affect the crystal type, crystal appearance, and size of calcium carbonates microscopically, and further affect the cementing effect of geomaterials macroscopically. The optimized conditions for strengthening the geomaterials are under the high bacteria concentration, the temperature from 20℃ to 40℃, the pH from 7 to 9.5, and the concentration of the cementation solution within 1 mol/L. In the optimised range of those factors, the soil permeability is improved by relatively low temperature, high pH value, and low concentration of cementation solution, while the soil strength is enhanced by the relatively high temperature, low pH value and high concentration of cementation solution. The effective grain size ranges from 10 to 1 000 μm, and the relatively large size and good gradation can promote the consolidation effect. The methods of multi-phase grouting, multi-concentration grouting and electroosmosis grouting improve the uniformity of soil solidification. The grouting speed below 0.042 mol/L/h is beneficial to improve the utilization ratio of the cement solution. The grouting pressure of the sand specimen is generally between 10 kPa～30 kPa bar, the grouting pressure of the silt and clay specimen should not exceed 110 kPa, and the high grouting pressure destroys the structure of soil and reduces the curing effect.

Key words: microbial-induced calcite precipitation, factors, bacterium, concentration, temperature, pH, cementation solution, soil properties, grouting method