Study On The Evolution Law Of Microstructure Of Expansive Soil Based On Fractal Theory

Expansive soil is a special soil that shrinks with water loss and expands with water absorption,which is widely distributed in China,and the engineering accidents it caused are countless.At present,the material composition and mechanical properties of expansive soil have been clear,but most of the internal microstructure studies remain in the qualitative research.Microstructure has important influence on macroscopic physical and mechanical properties of soil,and many researchers have realized that the difference in mechanical properties of various soils is mainly due to the differences in the microstructure of the soil.Changes in the microstructure of the soil will also lead to changes in macroscopical mechanical properties.As a member of the nature,the internal structure of the soil is complex and irregular,which makes it difficult for traditional Euclidean geometry to describe it.The burgeoning fractal geometry as a mathematical theory for studying irregular objects provides a method for quantitative research of the microstructure of expansive soil.The expansive soil samples were taken from the Nanyang Expressway.Mercury penetration test and scanning electron microscope test were carried out for expansive soils with different dehumidification environment,compaction degree and initial moisture content.Firstly,the various fractal models and the calculation methods of fractal dimension were summarized.Then,The microstructural analysis model and fractal model were used to study the experimental data quantitatively,and the microscopic structure of expansive soil surface was qualitatively studied by scanning electron microscope images.The experimental data of the mercury pressure test were studied by three parameters of the pore distribution model,the translation,compression,and the degree of dispersion,and the three different fractal dimension calculation methods.The scanning electron microscope images were studied by box counting method.The relationship between dehumidification environment,compaction degree and initial moisture content and fractal dimension was analyzed,and the pore size of Nanyang expansive soil was divided according to fractal theory.Based on the three parameters of pore distribution model and fractal dimension,the change rule of microstructure of expansive soil after dehumidification was studied.According to the changes of the three parameters,it is found that the dehumidification environment has an obvious influence on the micro pore structure in the soil,which makes the pore distribution more uniform and no longer concentrates on the average pore size;The larger the compaction degree,the more concentrated pore size distribution of the expansive soil.The total pore volume of the expansive soil decreases,and the average pore diameter moves towards the micro pore;According to the change of the translation,the process of the micro pore variation with the initial water content was divided into two stages.According to the change of the amount of compression.It was found that there was a value of the initial water content,which made the largest volume of the total pore.According to the degree of dispersion,it was found there was an initial moisture content which had the greatest dispersion effect;Secondly,the particle morphology,arrangement and structure types of expansive soil surface were qualitatively studied by scanning electron microscope;Finally,the fractal theory was used to study the influence of the dehumidification environment,the initial moisture content and the degree of compaction on the fractal dimension and the influence on the internal and surface pore structure,and the range of compaction and initial moisture content which made the transformation of the internal structure of the soil change dramaticly was found.And it was considered that multiple fractal dimension calculation methods were more rigorous and scientific than using single fractal dimension method.