A three-dimensional FEM model is proposed and verified with existing experimental data for simulating wave-induced transient and residual pore pressure responses in the soil around pile foundations. The numerical results show that the residual pore pressure tends to be amplified around the pile foundation, especially at the bottom of pile foundation. Parametric study indicates that the residual pore pressure in the vicinity of the pile foundation increases and the amplitude of transient pore pressure decreases with the decrease of soil permeability. The effect of pile diameter on the oscillatory pore pressure is much more obvious than that on the build-up of residual pore pressure.
Pile foundations have been widely used in coastal and ocean engineering, such as oil platforms, long-spanning bridges and offshore wind farm, etc. Under the action of ocean waves, pore water pressure may be induced in the seabed around pile foundations, which is usually accompanied by the reduction of effective stresses. In some severe conditions, i.e. hurricanes or storms, the soil around pile foundations may be liquefied, resulting in large displacements of the pile foundation and eventual collapse of upper structures. Thus, a proper evaluation of wave-induced pore pressure around pile foundations is crucial for the geotechnical design of maritime structures.
Generally, there are two significant mechanisms accounting for wave-induced pore pressure responses, which are also observed in laboratory experiments and field measurements (Nago et al., 1993). The first mechanism, termed as transient or oscillatory pore pressure, is characterized by the attenuation of amplitude and the phase lag within the seabed. The other is residual or build-up of pore pressure caused by the compress of soil skeleton leading to the generation of excess pore pressure. The latter is much similar to the pore pressure responses induced by earthquakes.