Effects Of Microorganisms On Physical And Mechanical Properties And Microstructure Of Red Clay In Guiyang

Microorganisms are ubiquitous in the earth’s environment.As a part of the ecosystem,soil has a large number of microorganisms.The activities of these microorganisms will directly affect rock weathering,mineralization,soil formation and structure,as well as the surface properties of soil particles.In the process of their metabolism,some mucilage and gels will be produced to cement soil particles and fill pores to change the deformation and strength characteristics of soil,thus affecting the engineering mechanical properties of soil.According to mineralogy of study at the same time,some special microbial strains（e.g.,pap bacillus）,in the right environment can be realized in the laboratory manual,can let the system to generate calcium ion precipitation in similar to natural stone material ingredient calcium carbonate,the precipitation can be used as a binder,in laboratory to the success of the cylinders or block of loose sand consolidation into a hard body.This reaction process has become the most important research direction of microbial geotechnical engineering,namely MICP technology.In this paper,the effects of protobacterial flora and bacillus pasteurii on the physical and mechanical properties and microstructure of guiyang red clay were studied.Firstly,two kinds of bacterial solutions were obtained in the expanded culture.The growth curves of the two kinds of bacteria were measured by ultraviolet spectrophotometer.The bacterial solutions at a stable period were selected to be added to the remolded red clay sample（a certain amount of CaCl₂ solution was added to the bacillus pasteurii sample as the adhesive）.Based on these samples,a series of physical and mechanical tests were carried out and the changes of their microstructures were observed.The main research contents and achievements are as follows:（1）After 22h of culture,the soil native bacterial flora entered the logarithmic proliferation phase,and after 38h of culture,it entered the stable phase.Bacillus pasteurii entered the logarithmic proliferation phase after 14h of culture,and reached a stable phase after 38h of culture.（2）After constant temperature curing,saturated wet density increased,saturated moisture content and porosity decreased,clay content decreased,and powder content increased,indicating that with the addition of bacterial solution,pores in red clay samples were filled,and small particles of soil were cemented into large particle aggregates.（3）The shear strength of the red clay with different water content increased with the decrease of water content after constant temperature curing with the addition of two kinds of bacterial liquid.Under the same water content,the shear strength of three groups of samples was higher than that of Bacillus pasteurium group.,while the bacillus pasteurii group was the most sensitive to the change of water content.With the decrease of soil moisture content,the shear strength index and peak failure strength of the samples increased most obviously.（4）There was a certain relationship between the reinforcement effect of the two bacterial solutions on the red clay and the time.The mechanical properties of the red clay samples were strengthened with the increase of time in the early stage,and reached a peak at 6d,and then decreased.The mechanical properties of the red clay mixed with bacillus pasteurii and the adhesive increased with time and remained stable after 10days.The shear strength index,triaxial specimen failure peak value and compression modulus of the soil increased with the addition of the two bacterial solutions.The strengthening effect of bacillus pasteurii on red clay was better than that of native soil bacteria.（5）Scanning electron microscopy（SEM）and particle size tests showed that extracellular polysaccharides generated by soil protobacteria and calcium carbonate generated by bacillus pasteurii were filled in soil pores to strengthen the connection between soil particles.The clay content of the most effective sample decreased by 24%and that of the most effective sample increased by 19%.This change resulted in a more stable structure of the soil and a corresponding change in the physical and mechanical properties of the samples.（6）Use of IPP（Image-pro plus）software for mixed with pap bacillus sample analysis of the SEM images processing,micro pore and micro particle parameters with increasing calculation threshold value between 0 and 255,will change:in the early,micro pore number and grain number and clay content increases with the increase of calculation threshold,the peak,with the small pore and intergranular merger between quantity,at the same time,through the analysis and calculation under different threshold of soil micro three-dimensional particle surface area and porosity,accord with the actual situation of soil microstructure.（7）According to the changes in the microscopic pore and particle parameters of the samples,under the action of bacillus pasteurii,the microscopic pore number,three-dimensional porosity and microscopic clay content decreased,the microscopic particle number and surface area increased,and the soil microstructure developed towards a more stable state.