Internal solitary wave-induced soil responses and its effects on seabed instability in the South China Sea

Internal solitary waves (ISWs) are a frequently observed phenomenon in the ocean and significantly affect sediment soil dynamics and transportation. This study entailed the use of the poroelastic theory to investigate ISW-induced soil responses. To validate this theory, the solution for pore pressure was compared with a set of laboratory measurements. The theoretical results agree well with the experimental data, indicating that the poroelastic solution can be used to study ISW-induced soil dynamics. The Dubriel-Jacotin-Long (DJL) model was used to examine the flows and pressure induced by a large ISW observed in the northern South China Sea, and the wave-driven pressure at the water-seabed interface was obtained. The validated analytical solution was then used to analyze the ISW-induced soil dynamics for sandy silt and clayey silt. The results indicate that the effective stresses are relatively small under the observed ISW, and the stress angle inside the clayey silt is larger than that inside the sandy silt owing to the smaller penetrated depth. According to the Mohr-Coulomb criterion, shear failure is difficult to happen under the observed ISW conditions and seabed properties. Moreover, the effects of the water density profile and shear modulus on the shear failure potential of the soil were analyzed. The results show that the ISW-induced soil dynamics are sensitive to the shear modulus of soil and the density profile of water. In the event of substantial density variations in the pycnocline, shear failure may occur within the seabed in regions with a large shear modulus.