Marine structures are commonly situated near the mildly sloping sandy seabed characterized by the slope angles (alpha) not exceeding 10 degrees. The seabed liquefaction can be triggered due to the generation of the excess pore water pressure (EPWP), posing a threat to the stability of marine structures. This study focuses on the analysis of waveinduced liquefaction in the mildly sloping (MS) sandy seabed. A dynamic poro-elasto-plastic seabed model is developed to simulate the behavior of the MS sandy seabed under wave loading. The results indicates that the loading cycle required to trigger the initial liquefaction decreased as the position moved from the toe towards the crest of the MS sandy seabed. The amplitude of shear stress increases with the loading cycle and tends to increase with growing alpha before liquefaction, resulting in a slower accumulation of EPWP with larger alpha. Both the horizontal and vertical displacements induced by wave action reach the maximum at the crest of the sloping seabed. Notably, the horizontal displacement is much greater than the vertical displacement in the seabed under wave action. The displacement of the MS sandy seabed depends on not only the shear stress amplitude developed in the soils but also the accumulation of EPWP required to trigger the liquefaction in the seabed.

Pipelines are frequently embedded in layered sloping liquefiable seabed. This study proposed a dynamic effective stress numerical model for buried pipelines in the clay-over-sand sloping seabed under wave loading. The u-p formulation of Biot ' s theory was used to describe the porous saturated seabed. The elastoplasticity of clay was determined by Mohr -Coulomb yield criterion. The liquefaction characteristics of sands was modeled by a bounding surface plasticity constitutive model. The proposed model was validated through a wave flume model test and can capture the influence of pipelines on the excess pore water pressure (EPWP) in the liquefiable seabed. The pipeline-soil interaction can significantly increase the EPWP ratio at the bottom of the pipeline under wave action. The rate of increase in the EPWP ratio at the bottom of pipelines increased as the thickness ( h c ) of upper clay layer increased. Increasing h c caused a significant increase in the settlement of pipelines in the flat seabed and the horizontal displacement of pipelines in the sloping seabed. The study also highlights the significance of considering the slope angle, the relative density of sands, and the specific gravity of pipelines.

Sloping seabeds often exist in offshore areas with complex structures. It is difficult to accurately analyze the seismic response characteristics of sloping seabeds based on the assumptions used for horizontal seabeds. The degree of saturation in nearly saturated soil notably affects the seismic response of seabeds. Therefore, we developed an analytical solution for the seismic response of a sloping, nearly saturated multilayer seabed. Using this solution, we analyzed the effects of the slope angle and soil saturation degree on the seismic response of the seabed. The results show that the seafloor inclination may has a minor impact on the seismic motion at a specific point, but it has a very significant effect on the overall site. A weak interlayer refers to a layer of material that has lower strength and/or permeability compared to the surrounding soil or rock. This layer can reduce the natural frequency of the seabed and increase the amplitude of long-period seismic components. In addition, the presence of a weak interlayer can lead to increased pore water pressure, decreased effective stress, and increased susceptibility to shear failure. These factors combine to reduce the stability of submarine slopes, highlighting the importance of understanding and managing the effects of weak interlayers in geotechnical engineering and coastal defense projects.