Study On Contact Element In Geotechnical Simulation And Relative Parameters

There are a lot of noncontinuous problems in civil engineering such as interaction between soil and structure and discontinuities and interfaces inside the material. As a noncontinuous element, the contact element has become one of hot point problems in the research of civil engineering. In this thesis, the two important field of civil engineering, composite foundation and slope, are studied by using computer simulation in which contact element is introduced, and some valuable laws have been obtained. The main works in the thesis are as following: Firstly, the mechanics and calculation method of contact element are studies in FEM. The background of research, element type and constitutive model of contact element are summarized. The arithmetics of contact element, including three aspects of interface condition, Coulomb friction type and the weak formulation of interface condition are investigated in detail. It is pointed out that the key of contact problem is the relation between the contact bodies, which can be divided into the normal and tangential relations before and after touching. In the two aspects, advantage and disadvantage of two methods of penalty function method and Lagrangian method are discussed. The merit of the extended Lagrangian that combines their advantages is also indicated. Secondly, parameters of contact element are investigated in the simulation of composite foundation. The general laws of determining values of parameters are obtained and verified through some practical examples, which prove that a good result can be obtained when the contact element is inserted into between pile and soil and the deformation modulus is chosen as the modulus of soil because of soil structure. Thirdly, influences of the various factors on settlement of composite foundation are completely studies through numerical simulation by using interface element. Conclusions are drawn as follows: 1) Contact element of zero thickness can effectively simulate the sliding between pile and soil for some composite foundation with smooth interface and higher stiffness. 2) Among all the factors influencing the settlement of composite foundation, the influences of compression modulus of soil and the cohesion of soil are great. 3) The effects of the internal friction angle of soil, the elastic modulus,radius and length of pile, and the elastic modulus of cushion on the settlement are also more obvious. 4) The other factors, such as the Poisson's ratio of soil and cushion et al. have only less influences on the settlement. Fourthly, the computation formulas of settlement of composite foundation given by the author are verified through the computation of practical engineering example and simulation. The settlement of a practical engineering is calculated by using the formula and further simulated through selecting proper parameters. The sliding between soil and pile is simulated through inserting the contact elements into between them, which makes the two values of settlement obtained by simulation and calculation to be in good agreement. This result demonstrates the effectiveness of the formula. Fifthly, contact element is introduced into the slope stability analysis, and a strength reduction method of interface parameter is proposed based on partial failure theory. This method is demonstrated by an engineering example and compared with other ones. Conclusions are drawn as follows: 1) The calculation result is larger when circumcircle yield criterion of D-P is used, while the result is perfect when homolographic yield criterion of Mohr-Coulomb is used. 2) The calculation result of strength reduction of contact element is good when weak structure plane is simulated by using contact elements. 3) The safety factor obtained by strength reduction method of contact element is much closed to that by the method in which both soil shear strength parameters and interface ones are reduced. 4) The result obtained by using only the reduction of soil parameters is almost the same as that by the circumcircle yield criterion of FEM, which is larger than that by using both parameter reduction of soil and interface. The above result shows that the new method given by the author is feasible and effective and the strength parameters of weak structuralplane are the key factors controlling the stability of slope. Sixthly, the numerical simulation methods of slope stability analysis have been investigated in detail. The principle and formulas of the strength reduction method and the arc search method of FEM and mathematic programming are discussed. Finally, a search program of failure plane is developed and demonstrated by the practical example based on ANSYS and MATLAB. By comparing the results of the program with strength reduction method of FEM, it is found that two ones are well in agreement, which shows the program is useful.