Bed failure induced by internal solitary waves

Abstract

The pressure field inside a porous bed induced by the passage of an Internal Solitary Wave (ISW) of depression is examined using high‐accuracy numerical simulations. The velocity and density fields are obtained by solving the Dubreil‐Jacotin‐Long Equation, for a two‐layer, continuously stratified water column. The total wave‐induced pressure across the surface of the bed is computed by vertically integrating for the hydrostatic and nonhydrostatic contributions. The bed is assumed to be a continuum composed of either sand or silt, with a small amount of trapped gas. Results show variations in pore‐water pressure penetrating deeper into more conductive materials and remaining for a prolonged period after the wave has passed. In order to quantify the potential for failure, the vertical pressure gradient is compared against the buoyant weight of the bed. The pressure gradient exceeds this weight for weakly conductive materials. Failure is further enhanced by a decrease in bed saturation, consistent with studies in surface‐wave induced failure. In deeper water, the ISW‐induced pressure is stronger, causing failure only for weakly conductive materials. The pressure associated with the free‐surface displacement that accompanies ISWs is significant, when the water depth is less than 100 m, but has little influence when it is greater than 100 m, where the hydrostatic pressure due to the pycnocline displacement is much larger. Since the pore‐pressure gradient reduces the specific weight of the bed, results show that particles are easier for the flow to suspend, suggesting that pressure contributes to the powerful resuspension events observed in the field.

Interaction between internal solitary waves and the seafloor in the deep sea

“…Early research on the influence of ISW on seabed stability mainly combined with the two‐dimensional Biot consolidation theory to analyze how internal waves cause excessive pore water pressure on the seabed, and discussed the effects of different seabed and internal wave parameters on dynamic response (Williams & Jeng, 2007a, 2007b). Rivera Rosario et al (2017) found in their study on the permeability horizontal seabed model that the range of seabed damage is 2% of the depth of the low permeability seabed, and the gas‐bearing muddy seabed may experience instability within typical depths of the continental shelf. However, these studies are limited to quasi‐static Biot theory elastic models, thus failing to reflect accurately the accumulation of excess pore pressure caused by dynamic loads.…”

An automatic identification algorithm of internal solitary wave for mooring data based on geometric characteristics of the flow field

“…On the one hand, the resuspension and transport of seafloor sediment induced by the shoaling ISWs can change the seafloor topography (McPhee-Shaw, 2006;Masunaga et al, 2016;Tian et al, 2021a). On the other hand, the strong shearing stress of the shoaling ISWs can lead to sand wave and even seabed failure (Ma et al, 2016;Rivera-Rosario et al, 2017;Tian et al, 2021b;Tian et al, 2022). Moreover, the propagation of the ISWs can lead to strong convergence and divergence of the sea surface or sudden strong currents in local seawater.…”

Transient wave-induced pore-water-pressure and soil responses in a shallow unsaturated poroelastic seabed

“…However, transient waves such as solitary waves and bores can be observed in coastal and ocean regions (Chanson 2009;Chan & Liu 2012;Pujara, Liu & Yeh 2015) and they can cause seabed failure (Packwood & Peregrine 1980;Liu, Park & Lara 2007;Young, Xiao & Maddux 2010;Sumer et al 2011;Jia et al 2019;Tehranirad, Kirby & Shi 2020), suggesting that transient wave-induced pore pressure and effective stresses, and their effects on instability within a deformable seabed, require attention as well. According to our literature survey, only a few studies have been carried out on this topic (Young et al 2009;Merxhani & Liang 2012;Rivera-Rosario, Diamessis & Jenkins 2017;Rivera-Rosario et al 2020) and they are typically numerical approaches. Moreover, the assumptions employed in the governing equations used in the numerical studies are not clearly stated, which demands further attention.…”