Experimental study on the irregular wave-induced pore pressure of a sloping beach with cross-shore profile evolution

Wave-induced seabed response, associated with beach instability, is a great concern to the coastal engineers. Previous studies mostly focused on the flat seabed, neglecting the effects of wave nonlinear transformation ($e.g.$ wave shoaling, breaking) and complex underwater bed morphology that is commonly seen in a natural beach condition. This study performed a series of physical experiments to investigate the temporal and spatial distribution of pore pressure inside a sloping beach that is subjected to irregular waves. Cross-shore beach evolution profiles over a continuous 60-h period were prepared, and 15 h of these were used for the pore pressure recording and analysis. Effects of $e.g.$ non-linear wave loading, bed morphology, and seabed thickness on the pore pressure response were systematically examined. Based on dimensional analysis, one empirical model was proposed for the prediction of wave-induced pore pressure inside the sloping beach. The main findings of this study indicate that (1) low-frequency components of the pore pressure signal are found chiefly below the sandbar and are more sensitive to the sandbar movement, (2) the increasing wave nonlinearity (Ursell number) would decrease the normalized pore pressure which indicates the normalized pore pressure has a gradual decrease with wave shoaling process from offshore to nearshore, and (3) the local slope of the seabed is found with a negative correlation to pore pressure, $i.e.$, an increase in local slope decreases the magnitude of pore pressure.