Microcosmic Fractal Characteristics And Gray Correlation Analysis Of Soils Subjected To Repeated Freezing And Thawing

After the soil is repeatedly affected by the freeze-thaw cycle,the permeability of the soil will change,and the mechanical properties of the soil will be weakened,causing great loss to the project.The change of the microstructure is the root cause of mechanical strength failure.Therefore,this paper studies the damage of mechanical strength by microscopic structure and penetration test.With the basis of Hebei Province Nature Found,fractal dimensions of particle and pore were calculated by reasonable fractal models and the quantitative parameters of soil microstructure were received in this paper.The microstructure and fractal dimension were studied by scanning electron microscopy(SEM).The pore structure and pore fractal dimension were analyzed by mercury intrusion test.The infiltration test was carried out to study the variation of permeability coefficient.The effects of water content,freeze-thaw cycles on permeability,soil microstructure and the unconfined compressive strength of the soils were studied.The gray relational analysis between permeability coefficient,fractal dimension,microstructure parameters and strength was established.The relationship between microstructure and mechanical properties of soils after freeze-thaw cycles was deeply studied.The main research results include the following aspects:(1)With the increase of freeze-thaw cycles,the permeability coefficient of soils under different water contents tends to increase,and the larger the water content,the larger the permeability coefficient.(2)The microscopic particle structure of soils under different moisture content after freeze-thaw cycles was studied by scanning electron microscopy,including abundance,circularity and average particle diameter,and the fractal dimension of three-dimensional particles was calculated.(3)The mercury porosimetry test was used to study the regularity of microscopic pore structure of soil under different moisture content and freeze-thaw cycles,and the 3D fractal dimension of the pore was calculated.As the moisture content increases,the fractal dimension is higher.With the increase of freeze-thaw cycles,the fractal dimension is smaller.The smaller the fractal dimension,the smoother the inner wall.(4)The unconfined compressive strength gradually decreases from 0 to 10 times,and it gradually decreases.Under the increase of water content from 12% to 18%,the unconfined compressive strength is also gradually decreasing.(5)The correlation between permeability coefficient,grain structure,pore structure and fractal dimension and soil strength value indicates the gray correlation between macroscopic mechanical properties and microstructure,and the gray correlation analysis explains the unconfined compressive strength of microstructure and soil variety.