Mesoscopic Study On Compaction Characteristics Of Rockfill Considering Gradation And Shape

The construction of high earth rock dam puts forward higher requirements for the compaction quality of rockfill materials.High power compaction machinery improves the rolling quality,but it will also produce a large force on rockfill,and may even cause the crushing of large particle size and special shape aggregate,which will affect the working state of rockfill.In addition,the grading and shape of rockfill are also important factors affecting the compaction characteristics of rockfill.Therefore,considering the grading,shape and fracture of rockfill,a three-dimensional discrete element model of rockfill compaction process under vibration force is established,main work and conclusions regarding the study of compaction characteristics of rock piles and their fine-scale mechanisms are as follow:（1）The three-dimensional model of real rockfill is established to realize particle crushing and calibrate the parameters of discrete element model.Realistic rockfill model is obtained by 3D laser scanning technology.The three-dimensional rockfill model is simplified based on SHAPE architecture method,and the optimal number of simplified surfaces is determined to be 30.The contact parameters of DEM are calibrated through the classical particle column collapse test,and the particle crushing is realized based on the Ab-T10 model.The accuracy of the particle crushing model is proved by the single particle uniaxial compression test,and the crushing parameters of the discrete element model are calibrated.（2）The discrete element model of rockfill rolling process is established to study the influence of rockfill shape and gradation on compaction characteristics.A three-layer unloading method based on density is proposed to simulate the stratification phenomenon of rockfill,and a numerical test is carried out on the influence of rockfill gradation and shape on compaction characteristics.The results show that the final cumulative settlement rate increases with the increase of slenderness ratio and decreases with the increase of median particle size(d₅₀).The first four passes of rolling contribute most of the cumulative settlement rate;The final porosity decreases with the increase of slenderness ratio and increases with the increase of median particle size(d₅₀),and the porosity of surface rockfill decreases more obviously;The crushed rockfill particles during rolling are mainly concentrated in the surface layer,and the content of rockfill with particle size of 80-100mm decreases most obviously.（3）The mechanism of rockfill compaction is revealed from the meso point of view.The compaction characteristics are explained from the perspectives of coordination number,velocity field and force chain.The research shows that the coordination number of rockfill is negatively correlated with porosity,and the coordination number is positively correlated with settlement rate;The velocity of rockfill is mainly concentrated on the surface,and the maximum particle velocity is directly below the roller,and the closer it is to the surface,the greater the velocity of rockfill.Overall,the average particle velocity increases with the decrease of rockfill particle size;In the rolling process,some weak force chains are transformed into strong force chains,and the proportion of strong force chains decreases with the increase of slenderness ratio and the increase of median particle size(d₅₀).