Wave-Induced Sediment Bed Pore Pressure Response to Random Wave Generated by Vessels

Abstract:

In recent years, several researchers have applied experimental and theoretical approaches to study wave-induced sediment instability. However, most of these studies are limited to regular and periodic waves while in the marine environment waves generated by vessels are irregular and random. In estuarine environments, irregular waves can be drivers of accelerated shoreline marsh erosion and bed morphology through wave-induced physical soil stress and strength changes. There is still a lack of understanding on the generation of residual pore pressure due to random waves as most of the research has been based on the oscillatory pore pressure response. In order to advance our understanding of residual pressure generation, field observations were carried out to measure the pore pressure due to random waves. Data collected over 48 hrs in July 2018 along the Intracoastal Waterway near Ponte Vedra Beach, Florida includes time series of wave pressure and pore water pressure in addition to the sediment bed physical characteristics. Analysis of the data showed multiple irregular wave events that induced pore pressures with gradual and highly varying components. Further analysis showed the residual pore pressure to dominate more for low-frequency waves. Using the measured water surface levels, the pore pressure was investigated using a developed numerical model with a modified source term that considers the contribution of each component of the irregular waves. The model results showed a similar trend in pore pressure to those from measurements and matched the field measurements with a slight deviation on the initial pressure peak. Also, the results show that waves generated by vessels can lead to the oscillatory and residual pore pressures and that excess pore water pressure due to random waves may result in more than one residual pressure peak, unlike that due to regular waves. Accounting for the residual pore water pressure in an irregular wave regime can improve model estimates on shoreline erosion and the sediment bed instability.