Three-dimensional nonlinear finite element analysis of pile groups in saturated porous media using a new transmitting boundary

The dynamic behaviour of pile groups subjected to an earthquake base shaking is analysed. An analysis is formulated in the time domain and the effects of material nonlinearity of soil, pile-soil-pile kinematic interaction and the superstructure-foundation inertial interaction on seismic response are investigated. Prediction of response of pile group-soil system during a large earthquake requires consideration of various aspects such as the nonlinear and elasto-plastic behaviour of soil, pore water pressure generation in soil, radiation of energy away from the pile, etc. A fully explicit dynamic finite element scheme is developed for saturated porous media, based on the extension of the original formulation by Biot having solid displacement (u) and relative fluid displacement (w) as primary variables (u-w formulation). All linear relative fluid acceleration terms are included in this formulation. A new three-dimensional transmitting boundary that was developed in cartesian co-ordinate system for dynamic response analysis of fluid-saturated porous media is implemented to avoid wave reflections towards the structure. In contrast to traditional methods, this boundary is able to absorb surface waves as well as body waves. The pile-soil interaction problem is analysed and it is shown that the results from the fully coupled procedure, using the advanced transmitting boundary, compare reasonably well with centrifuge data. Copyright (c) 2007 John Wiley & Sons, Ltd.