Study On The Modification Of Liquefiable Soil By Silicate Weathering Bacteria

The weathering of silicate minerals is an important geochemical process.The influence of microorganisms on p H and the secondary reaction in the process of reproduction promote the evolution of soil,which can transform the non viscous weathering silicate minerals into viscous secondary minerals.As a result,the content of clay particles in soil increases,so as to improve the cohesion of soil and enhance the anti liquefaction ability It is of great significance to study the effect and feasibility of mineral decomposing bacteria on the biological weathering of silicate minerals in improving the anti liquefaction characteristics of soil.In this paper,Bacillus gelatinosus was used as mineral decomposing bacteria,and biotite and potassium feldspar were used as weathering silicate minerals.In the solution test,mineral species and particle size were used as variables to determine the changes of p H value and cation concentration released by minerals in120 d solution,and to study the process and mechanism of mineral weathering by microorganisms.The main research contents and results are as follows:(1)In the experiment of microbial weathering solution,the change of p H in the reaction solution of K-feldspar and biotite with different particle sizes is consistent,and the p H decreases rapidly and then increases gradually.Single factor analysis of variance shows that there is a significant correlation between the particle size of different minerals in the reaction solution of K⁺feldspar and biotite,only for the change of Si²⁺concentration,which indicates that the change of mineral particle size will only have different changes on the concentration of Si²⁺,and the smaller the particle size is,the more Si²⁺is dissolved by bacteria,and the more serious the weathering effect on minerals is.Under the action of the strain,the actual order of the dissolution ability of elements in minerals is:k>Al>Fe>Si,that is,the dissolution order is:interlayer,octahedral wafer,tetrahedral wafer.The weathering rate of biotite is 5.0744×10^-7mol/(L*s),and that of potash feldspar is 5.2704×10^-8mol/(L*s).The weathering rate of biotite is obviously higher than that of potash feldspar.(2)Through the correlation analysis of p H and ion concentration in the reaction solution,it is found that p H in the reaction solution of biotite and K-feldspar has a high positive correlation with Si²⁺,a low positive correlation with K⁺,and no correlation with Al³⁺,but p H in biotite has a medium negative correlation with Fe³⁺;the correlation between Si²⁺and K⁺and Al³⁺in the reaction solution of biotite and K-feldspar is significant There is a moderate positive correlation between Al³⁺and Fe³⁺,linear regression analysis of the relationship between the variables,biotite and K-feldspar reaction solution in the law is similar,p H and Si²⁺have a very significant impact,Si²⁺+and Fe³⁺,Al³⁺and Fe³⁺have a significant impact.(3)With the increase of treatment days,the Cu content of soil samples increased,while the CC content decreased.The proportion of each particle size also showed that the content of fine particles was increasing.After 120 days of microbial treatment,the clay content of soil samples increased to 1.595%.Comparing the activity index of clay particles,it is found that the soil sample after microbial weathering has 4.439 activity,indicating that the clay minerals after microbial weathering have strong activity.(4)Through the analysis of scanning electron microscope,it was observed that the weathering effect of the strain on the mineral made the surface of biotite become uneven and produce cracks.The surface of potash feldspar also disintegrates and thin layers fall off,but the overall structure change is not obvious.The weathering effect of Bacillus gelatinosus on biotite is more obvious.Through the XRD analysis of soil samples treated by microorganisms at different times,it is found that with the increase of microbial treatment time,the effect of microbial weathering on quartz is minimal.After 120d,a new diffraction peak was found at d=4.044nm,which indicated that the bacteria weathered biotite,potash feldspar and other silicate minerals and transformed into secondary minerals.(5)The triaxial shear test results of sand after microbial weathering show that the samples show strain hardening under confining pressures of 100KPA and 200KPa.The liquefaction potential index LPI is used to describe the liquefaction results of sand.It can be seen that the liquefaction degree of soil samples at different stages of microbial weathering is sensitive to confining pressure in the selected stress range,and LPI has the characteristics of decreasing with the increase of confining pressure The liquefaction degree decreases with the increase of temperature.