Experimental Study On The Solidification Effect Of Calcium Carbonate Deposited By Urease In Soil

Microbial mineralization technology has attracted more and more attention because of its green and environmentally friendly characteristics.Microbial induced calcite precipitation(MICP)is a technique accelerating carbonate deposition for cemented particles and filled pore by means of the microbial metabolic.Microbial induced calcite precipitation(MICP)has been applied to the reinforcement and improvement of soil in recent years,which is a new breakthrough in the application of microbial mineralization technology in the field of geotechnical engineering.In the process of microbial induction of mineralized soil,the loose sand particles are reinforced by the filling of calcium carbonate crystals.This process requires the participation of microbial cells,but due to the incompatibility between the pore size of soil and the size of microbial cell's size,the microbial induced mineralization process is slowed down,and the microbial induction is limited.Further,the EICP technology is proposed.The EICP technology is a technology that the enzyme is used to catalyze the corresponding substrate,accelerate hydrolyze and induce carbonate deposition.Since the urease from microorganism cell is used in the mineralization process,the microorganism itself does not participate in the reaction process,which overcomes the environmental requirements of microorganism cultivation.At the same time,the enzyme has a smaller volume,it can be applied to fine-grained soil with smaller pore sizes,then the scope of use of microbial solidification technology can be extended in geotechnical field.First,the Bacillus pasteurus was cultured,and two kinds of ureases were extracted from the cultured bacterial liquid,one was the intracellular urease of Bacillus pasteurus and the other was the extracellular urease of Bacillus pasteurus.The influence of various factors on the cell broken effect during the extraction of intracellular urease from Bacillus pastoris was analyzed,and the most suitable combination of cell broken conditions was proposed: cell broken temperature 25 ° C,cell broken time 1h,lysozyme usage 300(mg / m L).Through the indoor test,the mineralization effect of the Bacillus pasteurus liquid,intracellular and extracellular urease liquid was verified.The solidification tests of three fine-grained soils of standard sand(fine sand),Aeolian sand(fine sand)and silt were carried out by using Bacillus pasteurus bacterial solution,intracellular urease solution and extracellular urease solution.The samples after solidification of the urease solution inside and outside the cell have a higher calcium carbonate precipitation level in the central area of the sample than the solidification results of the bacteria;and the uniformity is greatly improved compared with the samples solidified by the bacteria.In particular,in the reinforcement test of the silt sample,the uniaxial compressive strength of the specimen treated with the urease solution is higher than that of the specimen cured by bacteria.Therefore,the silty soil was reinforced based on EICP technologycompared with the traditional MICP technology,it can achieve better reinforcement effect and improve the uniformity and integrity of the solidified soil.In this paper,EICP technology is applied toimprove the dispersible silt for the first time,and the disparity modification method of two soils is compared with MICP technology.After the modification,through the pinhole test,the fragment test and the double hydrometer test,both modification methods have received modification effects on the dispersible silt.Among them,the soil after modification based on MICP technology changed from dispersive to transitional.The dispersity of the soil modified by EICP technology completely disappeared.The soil changed from dispersive to non-dispersive.It has achieved better results that the dispersion of fine-grained soil cab be modified and improved based on EICP technology.The compatibility between the pore space and the size of microorganisms can be satisfied when the fine-grained soil is reinforced by the mineralization behavior,which further expands the application range of microbial mineralization technology.