Three-dimensional finite element modelling of dynamic pile-soil-pile interaction in time domain

Dynamic analysis of embedded foundations like pile groups have received considerable attention in the past. Most existing approaches are established in the frequency domain, not allowing the simulation of material and geometric nonlinearities. In this paper, transient analyses are conducted to calculate the impedance of piles and pile groups, using a full three-dimensional numerical model for both the soil and the structure. Based on a combined viscous boundary and infinite elements, defining an efficient non-reflecting boundary, a finite element model is developed. Modelling guidelines, in terms of domain and element size, are presented and appear to be less severe in time domain than in frequency analysis. The proposed three-dimensional model can be processed with no excessive computational resources. Besides boundary efficiency, wave propagation effects are studied through dispersion diagrams in the case of homogeneous and layered soil. In particular, dissipative conditions are described, with the emphasis on the proper representation of wave propagation. These analyses thoroughly validate the proposed modelling approach for transient excitations. Viscoelastic model of soils are therefore developed including piles group considered as concrete material. A decay function is chosen for the excitation defined in the time domain, allowing a large covering of the input force spectral content. The implementation and validation of the numerical model for predicting the dynamic stiffness and damping of pile groups are presented. Vertical and lateral pile and pile group impedance examples are given and compared to a published analytical model. The proposed analysis methodology provides a convincing example of the capability of the finite element method to reproduce foundation response to dynamic loading.