Three-dimensional Nonlinear Finite Element Analysis Of Pile-soil Interaction Based On The Secondary Development Of ANSYS

In recent years, the piled raft foundation has been applied widely because of the development of high buildings in our country. But for the reason that the piled raft foundation is a very complicated system, there are many aspects of problems that have not been resolved. Therefore, it is an urgent task to develop effective and reliable theories and numerical analysis methods for the pile-soil interaction, understand the mechanism of the interaction between the piled raft foundation and the soil deeply, make clear about the load-transfer factors of the raft-soil and improve the traditional designing method of the piled raft foundation.In ANSYS, only the Drucker-Prager model is provided for soil simulation. As considering soil as a perfect elastoplastic material, this model can only give an approximate simulation. With a nonlinear constitutive law, the Duncan-Chang model can make a good representation of soil, but it has not been implemented into ANSYS yet, which may limit ANSYS to more geotechnical research fields. Therefore, one purpose of this work is to implement the Duncan-Chang model into ANSYS based on the User Programmable Features (UPFs) of ANSYS. The compatibility between this implemented model and the platform of ANSYS has been verified by some numerical analysis cases, and the efficiency and accuracy of this program have been manifested by validation case studies. It could be expected that this program may be served as a powerful tool for complex geotechnical problems solving.Meanwhile, the problem of the pile-soil interaction is so complex that it is impossible to gain an analytical result. Thus, it is necessary to employ the nonlinear finite element method to analyze this problem. In this paper, a three-dimensional nonlinear numeric model of the coupled finite element-contact interface element is established to simulate the geometrical and mechanical characteristic of piles and the soil. A program named PSIFEM, which is used to analyze the pile-soil interaction, is compiled with the secondary development of ANSYS. Based on this program, the interaction mechanism between soil and single pile or group piles under vertical load was studied. The influence of different parameters on the stress and deformation of piled raft foundation was investigated, which include the number of piles, pile diameter, pile spacing, ratio of pile-length to pile-diameter and the stiffness of cap. Several pieces of improvement advice about the optimization design of piled raft foundations are suggested.Finally, the developed program has been applied to practical engineering problems in Tianjin, and good performance has been achieved.