Study On Mechanical Behavior Of Sand Incorporating The Real Particle Shape And Fluid-Particle Interactions

Sandy soil,as a typical discrete dielectric material,is widely used as building and foundation materials.The geometry and physical properties of its constituent particles,as well as the complex interactions between particles,result in a variety of unique characteristics of sandy soil at the macro level.Such as its unique stress-strain behavior(including strain softening,anisotropy,strain localization,etc.),complex shear contraction and dilatancy,etc.The discrete nature of the discrete element method determines its natural applicability in the numerical simulation research of discrete granular materials such as sandy soil.At the particle scale,it can obtain the data of particle field in the whole simulation process,thus revealing the connections between the complex interactions of constituent particles and the various unique mechanical properties of sandy soil at the macro level.At the particle scale,particle shape is one of the most important factors that affect the complex interaction between sand particles.Incorporating the real shape effect of sand particles in discrete element simulation is the basis of constructing connections of macro and micro mechanics of sandy soil.Therefore,this paper used a series of CT data processing methods to process the original CT morphological data of quartz sand particles,and performed spherical harmonic analysis and reconstruction of particle shape,reconstruction of numerical samples,clump reconstruction of numerical samples,and finally incorporated the real shape of sand particles into the discrete element simulation.This paper construct a complete method framework for incorporating the real particle shape into DEM simulation,and also discussed the accuracy and computational efficiency problems that may be caused by the clump reconstruction method.Within this framework,a series of direct shear tests based on real-shaped clump samples were carried out,and they were compared with the results from spherical particle samples.The study found that the incorporation of real particle shape can result in stronger anti-shear and dilatancy effects than conventional spherical particles,and also the evolutions of internal fabric are different.Clump samples with real shape exhibit stronger friction and bite effects.In addition,sandy soils in nature are often accompanied by interstitial water and exist as semi-saturated or saturated state,various macro and micro-mechanical behaviors of sandy soils are unavoidably affected by the interaction between sand particles and water bodies.Therefore,this paper takes the simulation of the forming process of a conical sand pile as the main research object.Three kinds of particle samples,including clump particles with real shape,spherical particles incorporated with the anti-rotation moment,and pure spherical particles,were used to conduct this simulation both in the dry state and immersed in water.The particle shape effect and fluid-particle coupling interactions on the pressure dip phenomenon in conical sand piles were studied.The study found that the irregular shape effect increased the pressure dip,and the internal fabric was more inhomogeneous;on the contrary,the presence of water alleviated the pressure dip,and the internal fabric of the submerged conical piles was generally more homogeneous.Finally,in this paper,a simple particle column collapse simulation was conducted.Three types of specimens,clump particles with real shape,pure spherical particles and spherical particles incorporated with additional anti-rotation moment,were used to simulate the collapse process,both in the dry state and immersed in water.The effects of irregular particle shape and water-particle coupling on the velocity field of particle flow,the accumulation morphology of particles,and the energy evolution during the collapse process were investigated.It was found that the particle friction and bite effects induced by the irregular morphology of the clump particles would cause the collapse process to end significantly earlier than the other two types of specimens.In addition,the presence of water-particle coupling effects would lead to a very different development of the accumulation morphology with in the absence of water,and would exert different effects on the final stacking heights of the three types of specimens.Finally,the energy revolutions reveal the different energy dissipation of different specimens in the presence and absence of water,and the energy evolution of the clump particles sample is still obviously different from the other specimens.In conclusion,studying the effects of particle shape effect and fluid-particle interactions on the microscopic particle motions,contacts,fabric,and particle-fluid field interactions is an effective approach to explain the various macro and micro-mechanical behaviors and also external phenomena of sandy soils.