Modeling And Rationality Testing Of Clay Samples Based On Particle Aggregates In Discrete Element Method

Discrete element simulation（DEM）has many advantages,such as controllable micro-characteristics,low cost and repeatable results.At present,DEM has increasingly become an important means to study macro-mechanical properties of soils at particle scale.However,due to the irregular shape of clay particles and the complex interaction between particles,the study of clay discrete element method is relatively weak.Based on the framework of clay discrete element simulation program developed earlier in this paper,the application of discrete element method in clay is deeply studied from the aspects of size analysis of clay particles,contact information detection and solution method,sample generation of heterogeneous clay aggregates and program rationality test.Firstly,based on the special microstructure of clay,the complex mechanical effect between particles and the analysis of the actual size of the particle element,a rectangular model element that is more in line with the actual shape of the clay particle is established,and the initial clay sample with multi-particle size is generated successfully.On this basis,a new rough contact detection and information solution method is proposed for the characteristics of element model from two aspects of contact form judgment and contact vector solution,which provides an important basis for ensuring the reliability,accuracy and timeliness of clay discrete element simulation research.Secondly,through two-dimensional processing of the characteristics of the SEM image of clay,statistical information of the particle size ratio of the clay micro-sample is obtained.Combined with the study of the electric double layer,van der Waals non-contact force and Born contact force,the law of the stiffness coefficient changing with the particle size is obtained.Based on the above two conclusions,the non-uniform size aggregate specimens which are more suitable for the actual microstructure of clay are generated.By comparing with Hertz theory,the rationality of the solution method and the reliability of aggregate formation are demonstratedThen,based on establishing the initial sample of heterogeneous clay aggregates and obtaining the contact information detection and solution method suitable for special rectangular geometry shape:1)By analyzing the characteristics of gravity and repulsion interval and peak value of the resultant force curve between particles,a contact repulsion force model,which is similar to Hertzian contact model and continuous with Born force,is added to make the peak bearing capacity of samples.The micro-mechanical effect of clay is greatly improved and more suitable to the actual situation.2)The velocity threshold v₀ is obtained by dichotomy method through the study of collision between different contact forms of samples.The maximum velocity at the end of particles is reasonably limited without changing the movement law of the element.3)The effectiveness of the method of reducing system energy used by Anandarajah and commercial discrete element program is verified by setting up several groups of velocity clearing comparative experiments.It greatly improves the efficiency of simulation loading and avoids the occurrence of error anomalies such as cross-penetration of particle elements in contact response moduleFinally,this paper referring to the standard test method for rationality of balls falling and sloping rolling in the circular discrete element model,the rationality and scientificity of the development program are tested from the point of conversion between the potential energy of clay micro-mechanics and the kinetic energy of unit.By assigning different initial kinetic energy to the test models of particles and particles,particles and aggregates,particles and boundaries,the energy changes of the system before and after collision to final equilibrium are analyzed,and the rationality and scientificity of the development program are checked.Ultimately,the one-dimensional compression simulation of heterogeneous aggregates is realized by controlling the displacement of the frame,which verifies the validity of the program.In summary,this study not only ensures the reliability,accuracy and timeliness of clay discrete element simulation research,but also expands the application scope and depth of discrete element in clay,laying a methodological foundation for establishing macro-micro relationship of clay mechanical properties,which has clear and universal academic significance.