Macro-micro Quantitative Analysis Of The Grain Size Distribution On The Behaviour Of Strength Of Sand

Granular materials are widely used in the field of civil engineering,with large discrete internal structures and complex physical and mechanical characteristics.Particle size distribution is one of the basic characteristics of granular materials,and it is of great significance to study its influence on the physical and mechanical properties of granular materials.This study is focus on sand materials,based on the selected gradation function,the discrete element method is used to study the influence of particle size span and gradation curve shape parameters on the packing characteristics and mechanical characteristics of the representative volume element.At the same time,combined with the macro-micro analysis method,the macroscopic mechanical behavior of the specimen is related to the microstructure change.The main research contents and conclusions of this article are as follows:(1)An isotropic compression test model was established,and it is found that the packing density of the sample increases with the increase of the particle size span,and shows a trend of first increasing and then decreasing with the increase of the shape parameter,reaching the peak when the shape parameter was 0.7.At the same time,the particle connectivity of the sample under this shape parameter is better,and the optimal packing is achieved.(2)A conventional triaxial test model was established,and it is found that the shear strength and dilatancy of the sample decreases with the increase of the particle size span,and increases with the increase of the shape parameter,and the gradation dose not affect the critical stress ratio of the sample,but affects the position of the critical state line on the e-p’plane.The critical state line of the sample with a small particle size span or a large shape parameter has a higher position and a larger slope.(3)After micro analysis,it is found that the increase of the particle size span increases the content of floating particles in the system,and the mechanical coordination number decreases,while the shape parameter has almost no effect on it.The shearing process has a greater impact on the probability distribution of the coordination number of the sample with a smaller particle size span or a larger shape parameter.In the contact force network,the weak contact accounts for the majority,which supports the strong contact carried by the large particles.The contact force distribution range of the sample with a larger particle size span or a smaller shape parameter is wider.(4)The joint invariant of the fabric tensor and the stress tensor in the critical state has a unique corresponding relationship with the average principal stress,and is gradation-related,and moves downward with the increase of the particle size span or the decrease of the shape parameter.Based on the stress-force-fabric relationship,it is found that the anisotropy parameters of the sample in the critical state have no relation with the gradation,and tend to the same value.The phenomenon of the same critical state stress ratio is explained from the micro-scale.(5)The applicability of the state-dependent constitutive model is verified,the gradation correlation of some model parameters is analyzed,and the critical state line prediction model considering the particle size span and the shape parameters of the gradation curve is proposed and verified.