Experimental Investigation Of Microbial Solidification Of Aeolian Sand

Aeolian sand is mainly distributed in arid and rainless desert areas.It is a kind of special soil with loose structure,fine and uniform particles,poor self-stabilization ability and not easy to compact.It should be reinforced when it is used as building foundation.Therefore,the reinforcement technology of aeolian sand is an important research topic.Microbial induced calcite precipitation?MICP?is a novel microbial soil-strengthening technique.In this paper,microbial-induced calcium carbonate precipitation technology and Bacillus pasteurium are used to reinforce aeolian sand,which can provide technical support for the engineering application of aeolian sand.?1?Using Sporosarcina pasteurii and cementing solution?mixed solution of urea and calcium chloride?by microbial induced calcium carbonate deposition?MICP?technology,calcium carbonate crystals with cementation effect can be formed between aeolian sand particles,effectively solidifying aeolian sand,improving the strength of aeolian sand,and improving the engineering performance of aeolian sand.?2?The injection rate of the cementing solution had a significant effect on the uniformity of the solidified aeolian sand.When the injection rate of the cementing solution was 0.278mol·L^-1·h^-1,the solidified aeolian sand sample was relatively uniform,and the calcium carbonate generated in the sample was evenly distributed,and the solidified aeolian sands have moderate unconfined compressive strength between 4.58⁵.03MPa.The texture of solidified aeolian sand samples is relatively uniform.?3?The more calcium carbonate crystals are formed on the surface and pore of aeolian sand particles by MICP technology,the greater the density of solidified aeolian sand,the smaller the permeability coefficient and the greater the unconfined compressive strength.The permeability coefficient of the solidified aeolian sand gradually decreased from1.08×10^-3cm/s of the original sand to 1.67×10^-5 cm/s.The maximum unconfined compressive strength reached 14.01MPa.Unconfined compressive strength increases with the increase of calcium carbonate content,and the two are positively correlated.?4?Layered consolidation can effectively increase the volume of cemented aeolian sand.The unsaturated infiltration method is less affected by the higher sand column layer,while the saturated grouting method is more affected by the higher layer.The smaller the layer height,the higher the unconfined compressive strength.When the layer height is the same,the average strength of unsaturated infiltration method is higher than that of saturated grouting method.The effective depth of solidifying aeolian sand by saturated grouting is0.2-0.7m,and the unconfined compressive strength reaches its peak at about 0.4m.?5?The distribution of bacteria in the saturated sand column is not uniform.With the increase of depth,the concentration of bacteria decreases gradually.The optimum static time of bacteria in sand column is 4 hours,and the optimum static time of cementing fluid in sand column is 24 hours.?6?X-ray diffraction analysis shows that the calcium carbonate crystals generated by MICP in solidified aeolian sand are calcite.The results of optical microscopy and SEM analysis show that white calcite is formed in the solidified aeolian sand,and the crystal is hexahedron with a size of 5¹0?m.The different filling rates of cementing solution have no significant effect on the morphology and size of calcium carbonate induced by microorganisms.