Mechanical Properties of Eolian Sand Solidified by Microbially Induced Calcium Carbonate Precipitation (MICP)

Eolian sand is widely distributed in desert areas, and can easily trigger sandstorms under the combined effects of wind and thermal conditions. In this paper, an eolian sand solidification test via microbially induced calcium carbonate (CaCO3) precipitation (MICP) was conducted to explore prospective applications of MICP in the field of dust prevention and sand fixation. A bacterial growth test and a MICP mineralization reaction test were performed based on the response surface method and an orthogonal experiment. Based on eolian sand solidification test, the effects of cementation number and dry density on the permeability and strength characteristics of solidified eolian sand, as well as the content of CaCO3 generated were analyzed. The results showed that the bacteria grew best at a temperature of 35 °C, a pH of 9, and a shaking frequency of 170 rpm. Both urease activity and bacterial concentration increased as the temperature and pH increased but showed a trend of rising before falling as the shaking grew faster. The optimal conditions for MICP mineralization were a bacterial concentration of OD600=1.5, a consolidating fluid concentration of 1 mol/L, a reaction time of 16 h, a pH of 9, and a temperature of 25 °C. The permeability coefficient of solidified eolian sand decreased as the dry density and the number of cementations increased, whereas the CaCO3 content increased with the number of cementations. As the number of cementations increased, the unconfined compressive strength (UCS) of eolian sand initially rose before stabilizing and then increasing again. The CaCO3 content had a positive relationship with UCS, which with the correlation coefficient reached 0.80.