Research On Frost Heave Characteristics Of Coarse Grained Subgrade Filling And Its Evaluation Method

Gradation of soil particle size is a major factor affecting soil frost heave sensitivity.For high-speed railway subgrade filler,this paper combines its grading characteristics and its existing research results of frost heave characteristics.Firstly,compare the results of two different test methods of conventional frost heave test and large-scale frost heave model test to analyze the influence of large-size coarse gravel on the frost heave characteristics of coarse-grained soil.Secondly,pore fractal model of porous media is established by using fractal theory,fractal dimension algorithm of coarse-grained soil is analyzed at the same time.Thirdly,fractal dimension algorithms of coarse-grained soil under different gradation conditions are used to construct comprehensive fractal dimension of pores which can comprehensively describe complex distribution characteristics of coarse-grained soil microstructure.Conclusions of pore distribution fractal theory are introduced into classification of frost heave sensitivity of coarse-grained soils,and rationality of a classification and evaluation method of frost heave based on fractal theory of porous media is discussed.Based on the above research content,the main research conclusions of the paper are as follows:(1)For conventional frost heave test and large-scale frost heave model test,the comparative analysis of the results shows that frost heave characteristics of coarse-grained soil are not only affected by the content of fine particles,but also the content of coarse particles with a particle size greater than 20.0 mm.Content of fine soil(particle size less than 0.25mm)and content of coarse gravel soil(particle size greater than 20.0mm)will have an opposite effect on the development of frost heave in coarse-grained soil.(2)Different fractal dimension algorithms of coarse-grained soil,such as gradation particle size fractal dimension,statistical dimension and box-counting dimension,are compared and analyzed.Based on the accurate self-similar fractal model,the pore distribution fractal model of coarse-grained soil is established and its correctness is tested.(3)Discrete element model of coarse-grained soil is established by using PFC particle flow program.Pore distribution parameters between particles of soil sample model are analyzed.Under different working conditions,pore distribution of coarse-grained soil and variation trend of macroscopic parameters and mesoscopic parameters of soil sample pores are discussed.Comprehensive fractal dimension of pores under different gradation conditions is calculated.And comprehensive fractal dimension of pores is verified and corrected through pore fractal model of porous media and test data.(4)Classification and evaluation methods for frost heave sensitivity of existing soil are summarized.Relationship between gradation change of coarse filler and its fractal dimension is analyzed.A frost heave classification method based on fractal dimension as the evaluation index of frost heave characteristics of coarse-grained fillers is proposed.