| Pile foundation has a long history and is durable. As China's rapid economic development, the cause of modern architecture is flourishing. Various types projects of high-rise building, water conservancy and hydropower facilities, mines, ports, highways, rail and energy projects start one after another. Then, the lower part of the basis is more and more complex and the application of pile groups is increasing. The computational theories of pile foundation are mostly based on the simple theory and empirical formula. These formulas are regional and one-sidedness and the calculation parameters is not perfect. These formulas may not be applicable for the complex geological conditions or large-scale pile group. When the settlement characters and the carrying capacity of foundation pile play the same , the bearing capacity of Single pile and pile groups is different, for soil resistance at the end caps will also have to share part of the load. So it must be integrated into the work characteristics of pile groups in the design of pile groups to determine the carrying capacity of vertical piles. As the caps, piles, soil interaction is different, the side resistance of piles, pile tip resistance and resistance to cap the bottom are different. The total ultimate bearing capacity of pile group does not mean that the ultimate bearing capacity sun of single pile ultimate bearing capacity, so the pile group efficiency factorηmay be greater than 1, equal to 1 or less than 1. The pile group effect efficiency factor is difficult to analysis with the interaction method of cap - pile - soil .To sum up, a pile group effects problem generate as the different pile group and single pile calculational theory and the different work characters of them. The reason for these differences in the final analysis is due to the impact of group factors in the work of many factors such as their own pile length , pile diameter and pile spacing, the impact of external factors such as the impact of soil and the impact of the construction process. The reliable method to determine pile group effect factors is to conduct on-site load test. However, due to test conditions, the vertical bearing capacity of pile group is often calculated by the vertical bearing capacity of single pile and pile group effect factors in the practice pile foundation projects. The vertical load of low cap friction pile group in composite pile acting on the platform is shared by pile and foundation soil. Tests of pile groups based on the enormous cost, longer time-consuming, to carry out large-scale test is very difficult, so at home and abroad in the load of pile groups, particularly the large number of small piles of research materials, not enough to clarify the group pile foundation load in the outer characteristics of the reaction. Pile group is more in the actual project, so the study of the work characters and the failure mechanism is still far from being able to satisfy the requirements in engineering applications. If pile group foundation tests can be simulated with numerical analysis method ,the analysis under load can be more convenient to carry out different forms of group pile foundation in different soil analysis . It has unparalleled advantages which experimental study has not. The results of numerical simulation analysis can guide the design and construction. Therefore, in order to thoroughly understand the behavior of pile group , the analysis of the pile groups based on three-dimensional finite element is very necessary.This paper first introduced the development process of pile foundation and the design theory of pile foundation. In the vertical load, the calculation of the theoretical study of pile foundation began in the fifties and sixties in the last century. So far, the theoretical calculation is divided into four categories: Elastic theory method, shear displacement method, load transfer method and finite element method. Finite element method has been very mature for its part with its highly function. There are a lot of advantages to analysis pile foundation with it. In theory, the continuity, non-uniformity, anisotropy, non-linear, visco-elastic of soil and pile-soil interface properties as well as a variety of complex factors can be considered, so the method has become a calculation and analysis tools that more and more people use.With the continuous development of computer technology, finite element method (FEM) come to the fore in numerical analysis methods. It has become the major method when the scientific research and engineering staff to resolve complex issues. ANSYS software is a large general-purpose finite element analysis software which melt structure, fluid, electric and magnetic fields and the sound field analysis into one. In this paper, a pile group foundation is simulated with ANSYS. ANSYS has three main steps in the pile group analysis: pre-processing (model), solving the calculation and post-processing. The structure of pile and soil works as a non-linear behavior. In a state non-linear analysis, contact is a highly nonlinear behavior, which need greater computing resources .And it is the difficult which affect the results of the analysis of pile groups. In order to carry out effective calculations ,this paper simulate the pile-soil interaction with contact to contact ANSYS method. Drucker-Prager model is a strength criteria which can accurately describe the rock, concrete and soil. The yield strength of compression larger than yield strength in tension of these materials, When these materials is sheared, the particles would grow, which is more in line the actual situation. Therefore, DP criteria for soil is used in this paper, and contact to cntact method is used to analyse pile-soil. The auxiliary pile and soil element is PLANE42 element, the element of piles, pile cap and pier material such as reinforced concrete are SOLID65,soil element is SOLID45, pile - soil, cap - the target surface and the soil surface are CONTA173 element and TARGE170 contact element in this paper.ANSYS10.0 is adopted in this paper. There are three steps ,one is to establish the pile group model in the Pre-treatment and mesh finite element model first . The second is to use the power calculating capacity of ANSYS to solve and analysis pile group foundation with changing factors .The last is to get the graphics and lists of some of the results from the ANSYS general post-processing part. At the last , the changes of the behavior of pile group with the changes of every effect factor are summed up.
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