Study On Discrete Element Method Program Development Considering The Characteristic Of Clay

Mechanical properties of clay depends on its microstructure properties. Compared to the granular materials, the clay particles exist physical and chemical interaction. At the macroscopic level, mechanical experiment does not adequately reflect the mechanical properties of clay particles. With the development of numerical methods, as discontinuity medium, the mechanical behavior of clay is simulated by discrete element method. Currently, the discrete element software does not truly reflect the characteristics of the clay, such as ignoring linear shape of clay particles and physical and chemical interaction of inter-particle. In addition, there are some restrictions about computing electric double layer repulsive force between clay particles in scope and accuracy. Therefore, it makes further application and development of discrete element method difficult in the clay field.Firstly, the basic theory of the discrete element method is elaborated in this thesis and compared to open-source software Physics2 D. It is more convenient to have a full knowledge of operation about the software, providing the basis for the development of the follow-up program development.Electric double layer repulsive force between clay particles consists of osmotic pressure and Maxwell stress. It is more accurate to solve the electrical double layer repulsive force of clay particles through the improvement of existing academic research. The finite element software Free Fem++ is used to get approximate accurate solution of electric repulsive force between particles. To make it convenient to obtain electrical repulsive force between the particles, two formulas fitted is used to solve the electrical double layer repulsion between two infinite parallel particles. Meanwhile, on the basis of considering the parameters of actual clay and using the numerical solution of electrical repulsion, a better fitting formula for solving electrical double layer repulsion between symmetry particles whose minimum distance is not zero is obtained, making it more applicable and more accuracy. Moreover, the van der Waals forces between the particles is considered. Ultimately, the relationship of force-displacement between two parallel particles is obtained, providing the theoretical basis of the selection of mechanical parameters of program development.In terms of the obtained methods and fitting formula, various mechanical model, such as electrical repulsion moedel, van der Waals model and Born repulsion model, and linear element are established. Compared to the existed study anout ectrical repulsive force, it is more exact to slove repulsive force between particles, for example, selection of arm of force about repulsion and temporary centroid. Through the example analysis and comparison, a more realistic computational methods are selected to compute the damping between elements. Meanwhile, the random generating method is used to obtain the system of the particles.In order to verify the validity of the program developed, a specimens containg 500 particles are generated. Due to the difficulty to immediately generation these particles in a limited rectangle, firstly a specimens with more large void ratio is achieved and sencondly is applied with loading by stages, making its volume smaller. Thus the void ratio the same to laboratory test is obtained.To sum up, a DEM program is developed on the basis of the Physics2 D software and lastest research methods and formula about electrical repulsive force. Through numerical analysis of particles generations of one-dimensional compression, it is shown that it is practicable to study on discrete element method program development considering the characteristic of clay and have significance in application of the clay in DEM.