Investigating The Effects Of Particle Characteristics On The Small-to-medium Strain Dynamic Properties Of Granular Material

The small-to-medium strain shear modulus and damping ratio are important dynamic properties of granular soils.Many researchers have revealed that the two properties are affected by multiple factors in a complicated way,requiring further investigations.Controversial views exist regarding the effects of particle shape and size on the small-to-medium strain dynamic properties,partly due to the difficulties in isolating the two parameters from each other.To address the limitations of previous studies using natural materials,which make it difficult to study and analyse particle shape and size in isolation,polycarbonate particles with well-controlled particle shape and size were used in this paper,such that the effects of the two factors can be investigated separately with a structured testing programme.The Energy Injecting Virtual Mass Resonant Column System was used to measure the small-to-medium strain shear modulus and damping ratio of the specimens.This paper also used Particle Flow Code to precisely control the shape of the particles and structuredly simulated small-strain shear tests with particles of different shape to reveal the mechanism of the effect of particle shape on the small-strain shear modulus of the granular material.The resonant column test results show:1)particle size does not affect the small-strain shear modulus and damping ratio,while the particle shape has significant impacts.The small-strain shear modulus of the specimens of spherical particles is smaller than those of the elliptical particles and the clumped particles under otherwise similar conditions,while the small-strain damping ratio of the specimens of spherical particles is higher than specimens of the other two particles.For the mixtures of spherical and elliptical particles,the dynamic properties are between those of specimens of each type of particles.2)The influence of particle shape on the medium-strain shear modulus is the same as that of the small-strain shear modulus.The medium-strain damping ratio of the ball of 3mm diameter specimens is greater than that of the ellipsoid,clumped particle,and ball of 2mm diameter specimens.3)The effect of particle shape on shear modulus decreases with increasing shear strain while the effect of particle shape on damping ratio increases with increasing shear strain.4)The overall regularity,quantifying the shape of the particles,can be used to characterize the small-to-medium strain properties of the specimens.There is a fairly good correlation between the overall regularity and the fitting parameters of the shear modulus and damping ratio.The Discrete Element Method results show:1)The small strain shear modulus and coordination number decreases as the aspect ratio increases.2)The smaller the void ratio of the specimen,the more significant the effect of particle shape on the small strain shear modulus and coordination number.3)The small strain shear modulus(G_max)increases with effective stress(?')and coordination number(CN),and a good linear correlation between G_max/(?')^1/3 and CN^2/3 is obtained.