Combined wave-current induced excess pore-pressure in a sandy seabed: Flume observations and comparisons with theoretical models

Abstract

Waves are coexisting with currents in coastal zones; nevertheless, previous experimental studies for excess pore-pressure responses in a porous seabed were predominantly limited to the wave-only condition. In this study, the combined wave-current induced excess porepressures in a sandy seabed were experimentally simulated with a specially-designed flume, which can concurrently generate periodic waves and a following/opposing co-directional current. The effect of a current on the wave profile is firstly examined. The wave steepness is decreased by a following current, but enhanced by an opposing current. Flume observations indicate that, under combined wave-current loading, the wave-induced pore-pressure is increased for the following-current case, but reduced for the opposing-current case. Such wave-current combination effect becomes more significant for shorter wave periods. The variation trend of the excess pore-pressure distribution in the present flume observations is consistent with that of the existing analytical solutions. Nevertheless, due to the existence of wave and/or current boundary layer and non-lineartiy of wave-current interactions as indicated by the flume observations, certain deviations exist between the flume results for excess pore-pressure and the analytical solutions, which can not be ignored especially for the opposing-current case. The effects of the boundary layer on the combined wave-current induced pore-pressures in the seabed are further highlighted by supplementary numerical simulations. A favorable prediction by the analytical solution would be expected for following-current cases and smaller pore-pressure amplitudes would be obtained for opposing-current cases.

Local Scour around a Monopile Foundation for Offshore Wind Turbines and Scour Effects on Structural Responses

“…An alternative hybrid foundation system comprising a monopile and a bearing plate (or skirted footing) has been demonstrated to enhance the lateral bearing capacity compared with a monopile [96][97][98][99]. Nevertheless, the enhanced capacity of the hybrid foundation largely relies on the proper interaction between the bearing plate and the soils at the shallow zone of the seabed, where local scour and wave-induced pore pressure could occur [100][101][102][103][104][105][106][107][108]. The extent of local scour and scour effects on both the bearing capacity and natural frequency of a hybrid monopile need to be further investigated.…”

Effects of Principal Stress Rotation on the Fluid-Induced Soil Response in a Porous Seabed

“…Recently, Liao et al [32] proposed coupling models for residual seabed liquefaction subject to combined wave and current loading. Although numerous theoretical studies have been carried out since 2012, only two experimental studies for the wave (current)-induced oscillatory soil response are available in the literature [33,34]. These studies were used for the validation of the present model.…”

Effects of the Soil Property Distribution Gradient on the Wave-Induced Response of a Non-Homogeneous Seabed

“…When excess pore pressure exceeds the overburden pressure, the effective stresses of the soil skeleton vanish, and the soil behaves like a liquid. This phenomenon is referred to as liquefaction, and it can lead to the collapse of the marine structure [5,6]. Smith and Gordon [7] reported that the failure of marine structures was predominantly caused by wave-induced seabed instability rather than structural deficiencies.…”