ABSTRACT
Ocean wave loading on a gassy soil seabed, results in harmonic changes in stresses, displacements and pore water pressures over depth. For a multi-layered seabed soil with homogeneous properties within each layer, the behaviour of the dependent variables of displacement and pore pressure can be represented by a harmonic function in both horizontal space (x) and time (t). The amplitude of the horizontal & vertical displacement and pore-water pressure will vary over depth, dependent on the particular distribution of the multi-layered properties, together with the wave loading amplitude, wave number and angular velocity, together with the boundary conditions at the seabed, i.e. permeable or impermeable. To simulate the behaviour of the seabed in harmonic wave conditions, this paper presents a series of governing equations based on Biot theory for poro-elastic soil. These equations have been modified to represent the harmonic behaviour using real & imaginary complex number theory. The Finite Element Galerkin formulation combined with Green’s Theorem is applied to these harmonic equations which result in six degrees of freedom per node, i.e. x-displacement, z-displacement and pore-water pressure, in both real (in-phase) & imaginary (out-of-phase) conditions. The harmonic finite element model can be used to match measured pore water pressure amplitude decay at various depths within a seabed, when subject to wave & tide loading.
