Experimental Study On Multi-fractal Particle-size Distributions And Plasticity Index In Fine Soils

As a basic index to evaluate the physical properties of fine soil,the liquid index and the plastic index of the soil have been applied to the classification of the soil,but in our country the classification standards have not formed a unified standard,so it is necessary to conduct in-depth study.The particle size distribution of soil has the fractal feature of statistical significance,and it is commonly used to describe the fractal dimension,which provides a new idea for the study of the classification of fine soil.In this paper,30 kinds of fine soil samples were collected from 8 cities in our country for testing,and then do some experiments such as liquid limit,plastic limit test and particle size distribution analysis.By these experiments,the author researched liquid index,plastic index,characteristics classification and multi-fractal distribution,finally revealed the correlation between fractal dimension and physical index.This research is supported by the Fundamental Research Funds for the Central Universities(Grant No.2015-ZY-061).The main results of this paper are as follows:(1)The liquid limit and plastic index of fine soil at 10 mm were less than the corresponding liquid limit and plastic index of 17 mm.There was a significant linear correlation between the same indexes.Comparing the soil name which according to the plastic figure and single plastic index classification,there is a big difference between the two method.(2)The particle size distribution of fine soil shows a more obvious segmentation in the whole grain size range,according to the order of particle size from large to small,each linear segment can be divided into 3 segments,such as fine particle size segment,middle size segment and coarse particle size segment.fine particle size segment is composed of clay particles,middle size segment is mainly silt,coarse particle size segment includes coarse silt and fine sand.In each particle size segment,the soil particle content in the fine and coarse particles size segment are lower,and the content is higher in the middle.(3)In a wide range of particle sizes,fractal characteristics of particle size distribution of fine soil exist 3 different fractal dimensions of particle size,shows the characteristics of multi-fractal.Particle size distribution of fine grained soil shows good fractal characteristics in each particle size segment.The numerical value of the fractal dimension is similar to the corresponding particle size segment,and that is related to size of soil particles in the particle size region.The fractal dimension is the largest in the coarse particle size segment,the second in the middle size segment,and the fine particle size segment.The fractal dimension is the largest in the coarse particle size segment,the second in the middle size segment,and the fine particle size segment is the smallest.(4)There is a positive correlation between the plastic index and the clay content,and the significant level of the linear correlation is higher in the statistical significance of the two.(5)there is a positive correlation between the fractal dimension of fine soil and clay content,plasticity index,and there is a negative correlation between the fractal dimension and the degree of clay activity.However,there is a large difference in the sensitivity of the multi-fractal parameters to these indexes.In the whole,the correlation between fractal dimension and each index of middle size segment is better,correlation between fractal dimension of coarse particle size segment and each index is less better,the correlation between the fractal dimension of fine particle size segment and each index is the worst.Multi-fractal parameters accurately describe the multi-fractal characteristics of particle size distribution of fine soil,but there are significant differences between the multi-fractal parameters and the indexs,such as plastic index,clay content,clay activity degree,etc.The fractal dimension of the middle particle size segment has potential application value in the engineering classification of fine soil.