Scattering of Plane P1 Wave by an Inclusion in a Three-Dimension Poroelastic Half-Space

Local inclusion topography has significant influence on seismic wave propagation, and the propagation characteristics of seismic waves in poroelastic soils are obviously different from those in single-phase media. Based on Biot’s theory, the scattering of plane P1 wave by inclusion in a three-dimensional poroelastic half-space is studied by using the indirect boundary element method (IBEM). The scattering field is constructed by introducing a virtual wave near the interface between inclusion and half-space and the surface of half-space, and the virtual wave density is obtained by establishing boundary integral equation based on the boundary conditions. The effects of the depth, geometric characteristics, boundary permeability, porosity, incident frequency, and incident angle of the inclusion on elastic wave scattering are systematically analyzed. The results show that due to the soil skeleton-pore water coupling effect, when the porosity is n = 0.3, the surface displacement amplitude of dry soil is larger than that of poroelastic soil. When the porosity is n = 0.36, the surface displacement amplitude of poroelastic soil is larger than that of dry soil. The surface displacement amplitude of poroelastic-drained condition is slightly larger than that of undrained condition. With the increase of inclusion depth, the scattering of elastic wave by inclusion decreases gradually. When P1 wave is incident, the surface displacement amplitude at the depth of H = 0.5 can be increased up to three times as much as that at the depth of H = 1.5. As the inclusion becomes narrower and flatter, the scattering of elastic waves by inclusion decreases gradually. When the ratio between height and length is S = 2/5, the surface displacement magnitude can reach up to 9.5.

Numerical Analysis of Steep Wave-Induced Seabed Response and Liquefaction Around Gravity-Based Offshore Foundations

Gravity-based offshore foundations generally consist of a bottom slab and one or more cylindrical shafts on top of it. The geometry of the structure can strongly affect the flow pattern, dynamic wave pressure and further soil response and the liquefaction risk in the vicinity of the foundation. In this work, gravity-based foundations with bottom slabs of cylindrical shape and hexagonal prismatic shape are investigated. An integrated wave-structure-seabed interaction model applied in this work is developed in Open-FOAM, incorporating a nonlinear wave solver, a linear elastic structure solver and an anisotropic Biot’s poroelastic soil solver consisting of consolidation and liquefaction modules. Soil consolidation behavior in the presence of the foundations is investigated. It is found that the corners of the hexagonal foundation cause stress concentration in the soil. Therefore the initial effective stress around the hexagon corners is relatively high. Then, fully nonlinear waves modelled by fifth-order stream functions are simulated. Wave-induced pressure distributions and momentary liquefaction depths around the foundations are predicted.