Scale Effects Of Rockfill Materials Considering Particle Shape

Granular materials are widely used in production and engineering construction,covering agricultural,pharmaceutical,machinery manufacturing,food manufacturing,mining and construction industries.Because of its extensive application prospects,the study on its properties has got the attention of many researchers.Rockfill material is a kind of typical granular material,its mechanical properties are affected by many factors such as grain gradation,particle shape and material properties.Nowadays there are more and more high rockfill dams are under construction or planned to be built,therefore research on the mechanical properties of rockfill and related basic science is necessary to be conducted in all respect and deep level.The discrete element method(DEM)is an effective numerical simulation technique for modeling the behavior of discontinuous media on the particle scale,its basic idea is to devide the discontinuous media into finite simple particle elements and describe the interaction between them.In order to study the mechanical behavior of rockfill from the microscopic scale,many domestic and foreign scholars used the discrete element method(DEM)in their study.Particle shape have obvious effects to the rockfill mechanics performance,however,the software based on discrete element method(DEM)usually use circular particles as basic element,which can not represent the complex shape of rockfill particles.In this paper,with the help of the finite element meshing method,the DEM simulation method of complex particle shape is proposed.Using this method,more types of particle shapes including concave polygon are represented.The influence of particle shape on the strength and deformation of the particle aggregation were studied by biaxial test of different shaped partcles,then the influence is explained at meso-scopic level.During a DEM numerical test,because of the velocity and capacity limits in computer calculating,the quantity of particle is limited,we usually replace some small particles whose size is smaller than a constant value with particles whose size equals the constant value in an equivalent substitution method.The replacement would inevitably cause differences in grading distribution between the numerical and the experimental tests and therefore affects the results of numerical simulations.This paper investigates the effects of minimum particle size on strength and deformation of irregular shape rockfill particles using PFC2D models based on DEM.Five irregular-shaped specimens with different minimum size of particles were analyzed,and two different compactness control standard were considered.The value of the minimum particle size is suggested and the analysis of result can provide efficient references to the chosen of particle size in the equivalent substitution method.Because of the limitation of the exisiting lab equipments size,the mechanical properties of rockfill materials can be studied through scaling the prototype material grading.The scaling would cause differences in particle size,particle shape,and grading distribution of the rockfill,and therefore affects the results of numerical simulations,this kind of affection is called scale effect.Laboratory tests on scale effects of rockfill materials costs many manpower and resources,and can not ensure that the test conditions keep the same,which would affect the results of tests.In this paper,equivalent replacement method,similar grading method and hybrid method are are adopted to create five grading curves for numerical simulations based on the prototype material grading.Fractal characteristic of particle size distribution is analysed.Both circular particles and polygon particles are generated to carry out biaxial compression tests.And the effect of scale method and particle shape on the strength and deformation properties of numerical samples are observed.The relationship between the fractal feature of particle size distribution and the mechanical parameters of numerical sample is determined,and the analysis of result can provide efficient references to predict the effect of scale method on mechanical properties.