2009 Third Asia International Conference on Modeling & Simulation 978-0-7695-3648-4/09 $25.00 C 2009 IEEE 491 Boundary Element Model Coupled with Finite Element Model for Dynamic Soil-Pile Interaction Paulus Karta Wijaya Parahyangan Catholic University paulusk@home.unpar.ac.id paulusk@bdg.centrin.net.id Abstract The Boundary Element Method coupled with the Finite Element Method is used to model the dynamic interaction of soil – pile. The system considered is a single pile embeded in a viscoelastic half space. The system is subjected to upward propagating harmonic shear wave. The displacement of the pile has to be found. The pile is modelled using the finite elements and the soil is modelled with boundary element. A computer program using FORTRAN is developed for the purpose of this study. A parametric study is made in this study . The parameters are the ratio of modulus of elasticity of the pile to the modulus of elasticity of the soil, length of pile, diameter of pile and frequency of the shear waves. The result of the analysis yields conclusions that give an insight into the dynamic interaction behavior of the soil-pile-structure system. 1. Introduction Dynamic soil-pile interaction has been a subject of research for many researcher. Consider a pile that support a structure and than the system is subjected an upward propagating seismic waves. If the interaction between soil-pile and the structure is not considered, the analysis of structure is made with the assumption that the motion of the support of the structure is the same as the free field motion. Free field motion is the motion of the soil when there is no foundation and structure. But in actual fact, the presence of the foundation and the superstructure will modify the soil motion so that it will not be the same as the free field motion. The interaction effect can be classified as two kinds. The first one is kinematic interaction that is caused by the stiffness of the foundation, and the second one is inertial effect that is caused by inertial forces induced by the mass of the structure [11]. The kinematic and inertial dynamic interaction analysis of soil-foundation and structure is usually made separately and then the final result is the superposition of both of them [10]. The analysis of kinematic interaction is made by considering a system of soil and pile without superstructure. The kinematic seismic response of pile has been studied [5]. The method of analysis for soil-structure interaction can be classified as direct method and indirect method. In the direct method the soil structure system is modeled as one model. In the indirect method the soil- pile-structure system is separated into two substructures and dynamic stiffness of one substructure has to be computed first. Some researchers have studied dynamic interaction of the soil-pile system using the finite element method. Flores et al [6] studied the seismic response of piles using the finite element method. Liam studied the interaction of the soil-pile-structure system by the direct method using reduced 3D finite elements [8]. Han studied seismic behavior of a tall building supported on pile foundations and the indirect method has been used [7]. Mamoon used the boundary element method to analyze the response of a pile (without superstructure) to traveling SH waves [9]. In this study, Mamoon used the analytical solution of beam vibration for the pile. In this paper, a method for analyzing dynamic interaction of soil-pile will be presented. The soil is modeled with boundary elements. The pile is modeled with finite elements. Since a fundamental solution for the half space will be used, only the soil-pile interface needs to be discretized. The fundamental solution that is used in this study is the fundamental solution found by Banerjee and Mamoon [1]. The system is subjected to upward propagating harmonic shear wave. The response of the system will be sought. If the waves are not harmonic, the soil free field motion is decomposed into a sum of harmonic waves by using the discrete Fourier series and the response is the superposition of each harmonic response. 2. The Model of the system The system considered is a floating vertical pile embeded in a viscoelastic halfspace. The system is subjected to a vertically propagating shear wave with unit amplitude at the tip level of the pile. The model is