Theoretical Study On The Effect Of Void Ratio On Plastic Deformation Of Saturated Sand Under Different Stress Paths

Sand is the most representative of the common particle medium,many scholars havestudied its physical and mechanical properties and engineering significance,at the same time,it is also the focus of geotechnical engineering research.The deformation of sand material is affected by the stress path to a certain extent.The deformation of sand material under different stress paths is significantly different.At present,the effect of void ratio under different stress paths on the plastic strain of saturated sand has not been fully clarified.The main reason for the influence of stress path on the plastic strain of sand is the change of stress ratio.Based on the research results of the meso-mechanism of sand deformation,it is concluded that the change of the void ratio of fine-grained sand units is the main reason for the change of sand stress ratio on the macro level.In this paper,based on the existing research results on the micro-particle of sand material,carries out stress analysis on the simplified fine-particle unit,obtains the relationship between the stress ratio and the internal angleθof the fine-particle unit,and further obtains the corresponding relationship between the stress ratio and the void ratio.For the double hardening elastoplastic constitutive model,the initial void ratio e₀is replaced by the void ratio e_saffected by the stress ratio,the improved model can reflect the plastic strain of saturated sand under different stress paths affected by porosity ratio.At the same time,based on the existing strength criteria of anisotropic sand,the characteristic state stress ratioM_d and peak state stress ratioM_b that can reflect the anisotropic sand are introduced into the improved model in this paper,and a theoretical model that can reflect the strength and plastic deformation of anisotropic sand is obtained.The main conclusions are as follows:（1）In this paper,the corresponding formula between the macro stress ratio and the void ratio is obtained by simplifying the fine-grained sand units.This method is simpler and more direct than using the compression-rebound curve to calculate the void ratio and conducting tests to obtain the void ratio.When the friction coefficient of particle surface is constant,the void ratio of sand gradually decreases with the increase of stress ratio.When the friction coefficient of particle surface is different,the change trend of sand stress ratio with the change of void ratio is approximately the same.However,when the stress ratio is the same,the smaller the void ratio,the greater the corresponding friction coefficient,conversely,the larger the void ratio,the smaller the friction coefficient.（2）The theoretical model of plastic deformation of saturated sand with different stress paths affected by void ratio is numerically simulated,it is found that with the increase of the direction angle of the stress increment,the shear dilatancy characteristics of the sand material are gradually obvious,the plastic strain of the sand rotates counterclockwise,and the plastic flow direction of the sand also rotates counterclockwise,while the different stress increment directions have no effect on the strength characteristics of the sand.（3）For anisotropic saturated sand,the angle between the grain deposition direction and the test loading direction and the initial void ratio of sand have a certain influence on the deformation and strength characteristics of anisotropic sand.The peak stress of sand decreases with the increase of the angle between particle deposition direction and test loading direction,the dilatancy deformation decreases with the increase of the angle between the deposition direction and the loading direction.With the increase of initial void ratio,the dilatancy characteristic of anisotropic sand gradually increases and the peak stress gradually decreases.