Numerical Study On Particle Crushing Of Coarse-Grained Soil Based On Discrete Element Method

With the deepening of modern theoretical research and the improvement of construction technology,the height of earth rock dam has exceeded 200m and gradually developed to300m level.The high earth rock dam has played a significant role in improving the power structure of our country,ensuring the water for people,industry and agriculture,and reducing the flood disaster in the middle and lower reaches of river.However,there are obvious disadvantages of earth rock dam:large amount of settlement and deformation in the later period of dam body,and the core wall materials are easy to be cracked and leak under the uneven settlement and deformation,once that formed,it is difficult to completely cure,which would endanger the project safety seriously;The integrity of the dam body filled with granular materials is poor,and the safety of operation under high stress state needs to be demonstrated in many ways.The grading range of filling materials for earth rock dam,especially for rockfill dam,is wide.The particle size of filling materials used for ultra-high earth rock dam has reached more than 1 m.Under the limitation of current laboratory instrument size,it is not able to directly study the prototype grading filling materials.It is inevitable to scale down the prototype grading according to a certain scale method,and test the substitute material after scale reduction under the conditions allowed by the laboratory,so as to evaluate the safety and reliability of the actual project by using the laboratory research results.For many years,the research results show that there are differences between the substitute grade and the prototype grade in the aspects of compactness,strength,deformation and other engineering characteristics.However,the parameters of substitute materials based on the indoor scale triaxial test can not reflect the corresponding characteristics of the prototype dam materials,and the deformation and settlement of the dam body is an obvious example.One of the important sources of dam deformation is particle crushing.The particle crushing of rockfill material has an important influence on the deformation,permeability and other characteristics of the dam,so it is more and more important to analyze the particle crushing characteristics.In view of this,based on the particle flow code in 3-dimensions(PFC^3D),this paper studies the size effect and shape effect of single particle crushing strength,analyzes the change rule of single particle crushing strength and explaines it.On this basis,a series of true triaxial numerical tests are carried out on the coarse and same size particles to study the influence of particle size d,intermediate principal stress ratio b,and minor principal stress?₃level on the particle group strength,deformation and crushing characteristics.The following research work in thesis is carried out around the particle crushing:?1?Uniaxial compression tests are carried out on pure round clusters of different sizes.The sizes of clusters are 40 mm,60 mm,80 mm and 100 mm respectively.The basic particles composed of clusters are 4 mm in size.The variation of single particle crushing strength with particle size was studied numerically;?2?In order to study the influence of the initial defect content on the particle crushing strength,the single particle compression under uniaxial test was carried out.The initial shape of the particle cluster is pure circle,the diameter is 60mm,the diameter of small particles is4mm,the initial defect content is 0%,10%,20%,30%,40%,50%,60%,70%,etc;?3?In the particle flow code,different real particle shapes obtained by indoor scanning are introduced to generate different shape clusters,and the influence of particle shape on single particle crushing strength is studied;?4?The numerical true triaxial test of equal intermediate principal stress ratio?b=0.5?is carried out for pure round clusters with different particle size.The size of particle is 40mm,60mm,80mm and 100mm respectively.The basic particle composed of cluster is unified as10 mm in size.The size effect of strength,deformation and crushing characteristics of particle group is studied;?5?In order to study the influence of stress path on particle crushing,strength and deformation,the true triaxial numerical tests are carried out under the condition of different intermediate principal stress ratio b,and different minor principal stress?₃ was set under each intermediate principal stress ratio b.