Discrete Element Simulation Of The Mechanical Properties Of Granular Materials Under True Triaxial Stress

As a particle material in nature,the soil is widely used in engineering.It is significant to investigate the mechanical properties of soil.Early,researchers studied soil stress and strain changes based on finite element methods by regarding geotechnical materials as continuous media.With the emergence and development of the discrete element method,researchers have found that using the discrete element method to simulate the stress and deformation characteristics of soil and other particle materials has natural advantages.It can not only study the change law of macroscopic quantities such as stress and strain of soil but also study the change rule of meso-quantity such as the contact inside the soil and the particle arrangement.However,the application of the discrete element method is less in the research of geotechnical engineering materials,and the research of particle materials under complex stress states is not thorough enough.In this thesis,the basic principles and applications of the continuum method and the discrete element method in geotechnical engineering are compared.Then,the research status of the discrete element method,the true triaxial test,and the influence of the changes of particle mesoparameters on the macro parameters are summarized.Finally,a simplified discrete element model of unsaturated soil is established,and the true triaxial numerical simulation of wet particles is carried out.The main research contents and results are as follows:(1)Based on the analysis of the loading principle and related research of true triaxial apparatus,the discrete element model of the true triaxial shear test is established by secondary development in the PFC3D particle flow program.By compiling the monitoring function,the changes of stress,strain,and fabric tensor in the whole process of true triaxial shear are recorded,and the discrete element numerical simulation of the true triaxial shear test is realized.Based on the established numerical model,the true triaxial shear numerical simulation of loose sand and dense sand was carried out respectively,and the stress,strain,and internal fabric contact changes of samples were analyzed.(2)Through the stress analysis of the meso-contact of water-bearing particles,the corresponding relationship between the meso-parameter friction coefficient ? and the macro-parameter water content w is obtained through theoretical derivation.Based on the results of the direct shear test,a simplified discrete element model that can reflect the change of water content is established.The discrete element simulation results are compared with the results of the direct shear test and true triaxial shear test.The numerical simulation results are in good agreement with the test results;(3)The proposed method is applied to the true triaxial shear numerical simulation of wet granular materials,the model meso-parameters are determined according to the existing true triaxial test data of loess,and the normally consolidated loess under different moisture contents is analyzed.And the law of strength and deformation of over-consolidated loess.