Experimental Study On The Microcosmic Fractal Property Of Soil Subjected To Repeated Freezing And Thawing

The effect of temperature on seasonal frozen soil area often makes the soil appears the phenomenon of freezing and thawing.After repeated freezing and thawing,most of the mechanical characteristics of soil develop to an unfavorable direction.The change of the microscopic structure is the nature of the macroscopic mechanical properties change,so the study on the evolution process of frozen soil microstructure is conducive to get the failure mechanism and.Accordingly,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 effects of water content and freeze-thaw cycles on microstructure and strength characteristics of soil were deeply analyzed.In order to explore the relationship between microstructure and mechanical properties of frozen soil,the approximate equations between fractal dimension and strength were established.The main research achievements are as follows:(1)With the increase in the number of freeze-thaw cycle,the soil particle structure broken and rearrange and the porosity distribution change.Three-dimensional particle fractal dimension of soil is estimated by combining SEM image with the method of box counting in fractal theory.(2)The soil pore volume and specific surface area are both increase after freeze-thaw cycling.The distribution of pore in the range from 0.3?m to 20?m is relatively centralized.Soil water contents have a large impact on medium and small pores.Three-dimensional pore fractal dimension of soil is received by the mode of thermodynamic relation.(3)The change characteristics of soil microstructure after freezing and thawing are quantitatively described by the particle and pore fractal dimensions.The larger the fractal dimension is,the more complex the soil microstructure is.The decrease of fractal dimension after repeated freezing and thawing shows the microstructure distribution is more uniform.(4)When the number of freezing and thawing is few,the microstructure and strength of the soil change distinctly.With the increase of cycling times,the effect of freezing-and-thawing action on soil gradually weaken.The higher the water content is,the more complex the microstructure of cement-treated soil is,and the effect of freezing thawing is also larger.(5)The connection between macro mechanical properties and microstructure of soil after freezing thawing is well revealed by the relationship between fractal dimension and soil strength.This provides an effective research method to analyze the mechanism of soil strength change from a microeconomic view.