Pile-to-pile interaction in the time domain – non-linear axial group response under harmonic loading

An approximate, physically motivated procedure to compute the non-linear axial response of single piles and pile groups under harmonic loading is presented. The method utilizes a nonlinear shaft model in conjunction with a time domain formulation for the propagation of waves emitted from the periphery of each pile, to account for pile-to-pile interaction. The shaft model involves standard geotechnical parameters. Yielding of the soil surrounding the pile and slippage along the pile–soil interface are modelled separately. The model is calibrated using data from well-instrumented full-scale experiments. Hysteretic damping is modelled through non-linear distributed springs governed by the Bouc–Wen model, whereas radiation damping is approximated with frequency-dependent distributed dashpots. It is assumed that non-linear behaviour is confined to the near vicinity of the pile–soil interface and that the soil in between piles remains linearly viscoelastic. Plane-strain theory of wave propagation is utilized and an attenuation function in the time domain is derived to approximate the influence of motion of one pile on another. A qualitative study of non-linear effects on pile-group response is presented. It is observed that nonlinear behaviour suppresses pile-to-pile interaction, while reducing the equivalent stiffness and increasing equivalent damping..