his paper derives a complex dynamic stiffness function for a poroelastic layer and uses this to examine the range of validity of solutions to Biot's dynamic poroelasticity equations when either inertia or dissipation terms are neglected. It also examines the effects of certain inertia terms and of surface boundary conditions on the solutions to these equations and presents a systematic study of the effect of the dissipation term of Biot's theory on the system storage and loss moduli.
Biot's equations of poroelasticily are first phrased in terms of a single equation which governs both the fluid and solid phase dilatational strains. A general solution to these equations is derived in the Laplace domain and expressions for the displacement and stress Laplace transforms in a poroelastic layer are obtained. The constants of integration occurring in these solutions are next evaluated for the case of an impulsive load applied to one surface of the layer. Cases of both a permeable and an impermeable loaded surface are considered. The resulting solutions for the Laplace transform of the impulsive excitation response are then transformed into frequency domain complex response functions, called dynamic stiffness functions, which characterize the stiffness and damping of the layer. Parametric studies arc then carried out employing these complex frequency response functions.
