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.