Experimental Study On Microbially Improved Red Clay Soil And Slope Stability Analysis

With the rapid development of highway construction in China,it is inevitable to encounter the red clay distribution area during the process of highway construction,and the special nature of red clay softening in water often brings great loss to highway construction,so it is necessary to find an effective and environmentally friendly red clay improvement method to deal with red clay to ensure the stability of the highway.Therefore,this paper relies on the Hunan Provincial Transportation Science and Technology Program Project "Key Technology Research on Ecological Landscape Restoration of Highway Slopes in Ecologically Fragile Areas"(No.2018.03)to improve the red clay soil along Longlang Expressway Loudi City,Hunan Province based on microbial induced calcium carbonate precipitation technology,and carried out the physical The physical properties and microscopic mechanism of microbially improved red clay were investigated.The relevant calculation parameters of microbially improved red clay soil were obtained through indoor tests,and then numerical simulation analysis of microbially improved red clay soil slope stability was carried out based on ABAQUS finite element software,and the main conclusions were obtained as follows:(1)The physical and mechanical properties of the red clay before and after microbial improvement were compared and analyzed by physical and mechanical tests.The liquid-plastic limit and plasticity index of the modified red clay were found to be reduced by the limiting water content test,indicating that the water-holding capacity of the red clay was weakened and the compactness was improved.The effective shear strength of the modified red clay was found to be increased by triaxial consolidation undrained shear test,indicating that the ability of the red clay to resist external load and deformation was enhanced.The permeability coefficient of the modified red clay was found to be reduced by the variable head infiltration test,indicating that the ability of the red clay to resist infiltration of rainwater was improved.(2)Through comparative tests,it was found that the strength of microbially modified red clay increased with the increase of cement concentration and decreased with the increase of cement concentration when the peak strength was reached,so as to find an optimal cement concentration.(3)The changes of mineral composition of red clay before and after microbial improvement were analyzed by X-ray diffraction test,and it was found that calcite,magnesite and feldspar were added to the mineral composition of the improved red clay,indicating that the calcium carbonate precipitation generated during the improvement of red clay was in the form of calcite in the red clay.It was also found that the presence of large amount of iron ions in the red clay would affect the generation of calcium carbonate and increase the amount of cementing solution.(4)The microstructure of the modified red clay soil was observed by scanning electron microscopy tests to understand the distribution of microorganisms and calcium carbonate.The microorganisms were found to fill the pores in the soil and adhere to the surface of soil particles,and calcium carbonate was distributed around the microorganisms,indicating that there are two mechanisms for microorganisms to improve the red clay soil:first,the generated calcium carbonate fills the soil pores and improves the strength of the soil,and second,the calcium carbonate gathers with the microorganisms as the core and eventually forms agglomerates with cementation,which enhances the association between soil particles and improves the deformation resistance of the soil.capacity.(5)Using the calculated parameters of the red clay soil before and after improvement obtained from the indoor test,the red clay slope models under different improvement conditions were constructed,and the stability analysis of the microbially improved red clay slope under the action of rainfall was carried out.The calculation results show that the displacement and plastic strain of the microbially improved red clay slope are well limited,and the safety factor of the slope is greatly improved.When the improved area crosses the sliding surface of the slope,the maximum displacement of the improved red clay slope is reduced by 93.7%,the plastic strain is reduced by 98.5%and the safety factor is increased by 26.7%compared with the unimproved red clay slope,which indicates that the red clay slope is improved well.