Macro-and Meso-investigation On The Effect Of Particle Elongation On Mechanical Properties Of Coarse-grained Soil

Granular materials are widely used in geotechnical engineering,such as sand,earth rock dam,ballast,etc.According to previous investigation,their geometric characteristics will have significant effect on the mechanical properties of soil（shear strength,shear dilatancy,degree of compaction,fabric anisotropy,etc.）.However,due to it is difficult to control the particle shape index in experiments,few investigations have quantitatively analyzed the influence of particle shape on strength,volume change and critical state line.In this paper,the stress-strain characteristics,volume deformation characteristics and shear strength of granular soil with three different particle shapes are analyzed by triaxial test.Based on the discrete element numerical simulation,the influence of elongation index on the macro mechanical properties is analyzed,and mechanism of shear behavior is investigated from the meso-parameters（contact force chain,coordination number,sliding rate,particle rotation and fabric anisotropy）.Considering the effect of elongation on the critical state line,an elastic-plastic constitutive model is established which is suitable for granular materials with different particle elongation.Finally,based on micro-mechanics,the evolution of generalized deviatoric stressq_Tduring shear is analyzed,then the shear dilatancy of elastic-plastic constitutive model is modified considering the effect of elongation on fabric anisotropy.The main research results are as follows:（1）The consolidated drained triaxial tests were carried out to analyze the stress-strain relationships and volume strain of coarse-grained materials with spherical,cylindrical and angular shapes,which provides a basis for the calibration of discrete element parameters.The numerical tests of triaxial compression show that there is a threshold value of slenderness ratio,which changes the effect of elongation on peak strength and maximum dilatancy angle from promoting to inhibiting;The influence of residual strength is linear.In the mesoscopic view,the decrease of elongation makes the specimen have a denser initial structure,and limits the rotation of particles in the shear process.At the end of loading,the vertical contact force is significantly greater than the horizontal contact force to resist the external force,and the contact force presents an anisotropic distribution.The elongation mainly affects the shear strength of the specimen by affecting the internal structural fabric.（2）The influence of elongation on the critical state line is analyzed.It is found that the critical state line shows a linear relationship in thee_c-（p’/p_a）^0.7 plane.The quadratic function relationships betweene-_rand elongation,λ_c and elongation are introduced and the linear relationship between critical state stress ratio and established are established.These three critical state parameters are applied to the critical state line and shear dilatancy equation.The modified elastic-plastic constitutive model based on critical state theory can brilliantly reflect the soil mechanical response of granular soil.（3）Considering the significant influence of elongation on fabric anisotropy,based on the theory of shear dilatancy considering fabric anisotropy,q_Tis quantified based on DEM and the effects of elongation onq_Tare analyzed.Then the constitutive model is modified by adding the state function related to fabric.The modified model can effectively reflect the mechanical response of the sample considering the fabric anisotropy.The research conclusions of this investigation have guiding significance for the application of granular materials with different elongation.48 figures,11 tables,and 115 references.