A Research Of Physical And Mechanical Properties Of Lignin Modified Red Clay

At present,researchers from diverse fields have carried out experiments to explore lignins,utilising various properties of different lignins to modify or improve adverse soil.Guangxi is rich in natural resources,but with few studies on lignin-modified soil.Red clay is widely distributed but with poor engineering properties.Taking Guilin red clay as the research object,this article explores lignins’effect on the properties of red clay and mixes lignins into the red clay to conduct various macro and micro tests.Boundary water content test,specific gravity test,p H test,and shrinkage test were conducted to explore their physical properties’change laws.Direct shear test and unconfined compressive strength test were conducted to explore the change laws of their mechanical properties,and standard consolidation test to explore the change laws of the compression deformation characteristics.The crack test was applied to explore the regularity of crack characteristics,and the X-ray diffraction test and scanning electron microscope test to explore the mechanism of lignin in the red clay.The main research results are as follows:（1）The liquid limit,plastic limit,and plasticity index of lignin-modified red clay increase with the increase of the lignin mixing ratio,while the specific gravity decreases with the increase of the mixing ratio.The p H value increases with the increase of the mixing ratio.The increase of the mixing ratio shows an upward trend,and the shrinkage of the modified red clay shows a trend of first decreasing and then increasing with the increase of the mixing ratio.（2）The incorporation of lignin can effectively increase the strength of the red clay.When the mixing ratio is between 0%and 8%,the unconfined compressive strength of the modified red clay increases with the increase in the mixing ratio and age but decreases with the increase of water content.The failure strain of unconfined compressive strength increases with the increase of mixing ratio,and the curing age has little effect on the failure strain,and does not fluctuate with the increase of age.The failure strain of high moisture content is less than that of low moisture content.The shear strength and cohesion of lignin-modified red clay also increase with the increase of lignin mixing ratio and age.The internal friction angle only increases with the increase of the content,and the increase is apparent.It does not change with age but only fluctuates up and down in a small range.（3）The red clay itself has certain compressibility.The incorporation of lignin changes the compressibility of the red clay within the range of 0.1MPa^-1～0.5MPa^-1,which belongs to the medium compressibility soil.The compressibility increases with the increase of the mixing ratio and decreases with the increase of age.In contrast,the compression modulus decreases with the increase of the mixing ratio and increases with age.（4）The cracks of the red clay are more developed.The smaller the thickness of the lignin-modified red clay,the faster the water evaporation,and the moisture content has a more significant impact on the cracks’development.When the water evaporates to the cracks’development’s moisture content,the cracks crack,the more lignin content does not lower the red clay crack rate.The fractal dimension increases with the thickness’s increase,and the high content of lignin will not alleviate the cracks’final development.（5）Lignin is an inert material and does not react chemically with red clay.Lignin can be more uniformly dispersed in the soil,filling the pores between soil particles or being wrapped by soil particles to form a new framework.After a curing period,it is further cemented with the soil particles so that the pores between the soil particles are reduced,the loose structure becomes tight,and the structural stability better.