Experimental Study On Microbial Induced Calcium Carbonate Precipitation Combined With Bentonite To Solidify Coarse Sand

Microbial induced calcium carbonate precipitation(MICP)technology mainly uses urea in a urease-producing microorganism hydrolysis solution to generate carbonate and hydroxide ions,and combines with free calcium ions to generate calcium carbonate precipitation.Precipitation has a cementation effect,which can make loose sand particles cement and significantly improve the properties of loose sand.It is a more promising green feasible technology.This article mainly uses sodium-based bentonite and MICP technology to improve the characteristics of coarse sand.Different sodium-based bentonite contents(0.0%,0.5%,1.0%,2.0%,3.0%)were used to test the calcium carbonate precipitation content of MCP solidified sand And its microstructure was characterized,and its permeability and strength characteristics were evaluated.The test results verified the feasibility of combining bentonite and MICP technology to improve the coarse sand,which can be effectively applied to the local soil improvement of MICP technology..The main content and research results of the paper are as follows:(1)It is feasible to use bentonite and MICP together to improve the properties of coarse sand.The addition of bentonite does not affect or inhibit the urease activity of bacteria,but is conducive to the formation of calcium carbonate precipitation.Bentonite provides a more suitable material carrier for it,so that the bacteria fixation rate and calcium carbonate content increase with the increase of bentonite content.The content of calcium carbonate increased exponentially with the increase of bacteria fixation rate.With the increase of bentonite content,the water absorption of the solidified coarse sand decreases nonlinearly.The softening coefficient of coarse sand sample increases nonlinearly with the increase of bentonite content.The addition of bentonite can improve the water resistance of the solidified coarse sand.The coarse sand samples solidified by adding bentonite are classified as softened rocks.(2)It is found that the permeability of coarse sand can be reduced by adding bentonite or only using MICP(0.0% bentonite).However,the permeability of bentonite can be further reduced by combining with MICP technology,and the permeability coefficient has been successfully reduced by four orders of magnitude.The unconfined compressive strength and splitting tensile strength in the dry and saturated states increase non-linearly with the increase of bentonite content,and the increase effect is more significant.The unconfined compressive strength of dry samples with different bentonite contents was higher than that of saturated samples.Through regression analysis,it is found that the permeability coefficient of sand column decreased as a power function with the increase of calcium carbonate content,and the unconfined compressive strength increased as a power function with the increase of calcium carbonate content.(3)Through SEM and XRD analysis of the solidified coarse sand samples,the bentonite particles increased the retention capacity of bacteria,promoted the precipitation of calcium carbonate in the pores,and finally wrapped in calcium carbonate,without affecting the crystal type of calcium carbonate.It is confirmed that biocatalysis enhances the combination of sand particles and makes the treated sand particles have more dense structure and higher strength.(4)When the amount of bentonite is 3.0%,the permeability coefficient of the coarse sand sample decreases with the increase of the amount of nutrient injection,and the relationship between them is exponential function;while the unconfined compressive strength and splitting tensile strength of the coarse sand sample increase with the increase of the nutrient injection amount,and the unconfined compressive strength and splitting tensile strength have a linear relationship with the nutrient injection amount.The above research results have confirmed that adding bentonite with different dosage is feasible for MICP curing coarse sand,which effectively improves the physical and mechanical properties of the coarse sand,deepens the understanding of MICP curing mechanism,and provides certain reference value and guiding significance for practical engineering applications.