Study On Vibration Compaction Characteristics Of Sand-Gravel Mixed Fillers Based On Discrete Element Simulation

Sand-gravel mixed fillers were often used in subgrade filling of roads and railways.Their compaction effect and compaction characteristics affect the filling quality of subgrade.Many factors affect the compaction characteristics of sand-gravel mixed fillers.The effects of particle composition and shape on the vibration compaction characteristics of sand-gravel mixed fillers need to be further studied.Based on the indoor vibration compaction test and discrete element simulation,this thesis explores the influence of particle composition and shape on the vibration compaction characteristics of sand-gravel mixed fillers,and reveals the change mechanism of macro vibration compaction characteristics on meso-level.The main research contents and conclusions are as follows:（1）The indoor vibration compaction test is carried out with sand-gravel mixed fillers.The model parameters of discrete element simulation are obtained by improving the physical experiment calibration method.The results of vibration compaction test and discrete element simulation are compared from macro and micro perspectives,which verifies the reliability of vibration compaction discrete element simulation and the accuracy of parameter determination.（2）The effects of coarse to fine particle size ratio（SR）and fine particle content（FC）on the compaction characteristics of sand-gravel mixed fillers are explored through discrete element simulation.The meso-mechanism of the change of compaction characteristics under different SR and FC is revealed from the perspective of particle contact and movement.In terms of contact characteristics,the transformation point of particle skeleton system is determined.The indexes for dividing the functions of different contact categories are put forward.It is found that the vibration compaction process of particles is a process of"entropy reduction".In terms of motion characteristics,it is found that when FC≤40%,the motion amounts of fine particles are significantly greater than that of coarse particles.When FC>40%,the motion amounts of fine particles decrease significantly,but there are still slightly greater than that of coarse particles.The difference of SR will lead to the difference of the influence of fine particles on the motion amounts of coarse particles.（3）Based on the real particle shape,the coarse particle models with different roundness are constructed.The influence of roundness on the vibration compaction characteristics of sand-gravel mixed fillers is studied.By analyzing the contact characteristics and motion characteristics,the meso-mechanism of the change of compaction characteristics under different roundness is revealed.In terms of contact characteristics,it is found that the change of particle contact characteristics is positively correlated with the particle compaction process.In the process of vibration compaction,the existence of particle shape makes the coarse-fine average contact number(Z_cf)of samples with different roundness greater than that of spherical particles.The smaller the roundness,the more prominent the edges and corners of the particles,the easier it is to form contact,and the larger the coarse-coarse average contact number(Z_cc).In terms of motion characteristics,it is found that the change of translational amount of particle system is positively correlated with the particle compaction process,while the change of rotational amount is weakly correlated with the particle compaction process.The roundness has little effect on the formation and strengthening of coarse particle skeleton,but changes the shape and fluidity of coarse particle skeleton gap through the change of roundness,thus affecting the process of fine particle filling gap.