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The response of saturated porous medium is of significant interest in many fields ranging from geomechanics to biomechanics. Biot was the first to formulate the basic equations governing the process of coupled flow and deformation in porous media. Depending on the nature of loading vis-à-vis the characteristics of the media, different formulations (fully dynamic, partly dynamic, quasi-static) are possible. In this study, analytical solutions are developed for the response of saturated and nearly saturated porous media under plane strain condition. The solutions for different formulations are developed in terms of non-dimensional parameters. The response is studied for various conditions and the regions of validity for various formulations are identified in a parametric space. An assessment of the needed formulation for few important problems is also presented. the rate of loading is much smaller than the rate of pore fluid flow, the pore fluid pressure remains constant and the response is said to be fully drained. For static problems, the steady-state pore fluid pressures depend only on the hydraulic conditions and are independent of porous skeleton response leading to an uncoupled flow and deformation problem. Therefore, a single phase description of a porous medium is adequate. However, for dynamic problems, uncoupling does not occur as long as the fluid density is non-zero. On the other extreme, if the rate of loading is much faster than the rate of flow, then no flow of fluid can take place and the fluid follows the motion of the solid skeleton. This is an undrained condition and here again a single-phase description is adequate. In intermediate cases, the flow (motion) of fluid (in porous media) and the deformation of solid skeleton are significantly coupled and the response of saturated porous media is affected by this interaction.The equations governing the response of saturated porous media incorporating the fluid-solid skeleton interaction was first established for the QS case in 1941 by Biot [1] who then extended them to include dynamics [2, 3]. Later, Truesdell [4, 5] introduced 'mixture theory' to formulate this problem, which provided a new basis for such coupled equations. Such formulations have been subsequently extended to consider the nonlinearity of deformation [6][7][8].In QS analysis usual assumptions of drained or undrained behavior are made depending on the rate of loading vis-à-vis the rate of drainage. For intermediate cases, full consolidating behavior needs to be considered. In dynamic analysis, the formulation is further complicated by the presence of inertial terms associated with both the motion of solid skeleton and that of the pore fluid. Depending on the rate of loading and the characteristics of flow and deformation, for the response of saturated porous media, the following three idealizations are possible:Fully dynamic (FD): In this case, the coupled equations of flow and deformation are formulated including the acceleration of both solid skeleton and fluid.Partly dynamic (PD): I...

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SUMMARYBreaking-wave-induced dynamic response and instability of seabed around a caisson breakwater are investigated. A seabed-rubble-breakwater system is modeled using finite elements. The impact response of the porous seabed and rubble foundation is assumed to be governed by the coupled Biot equations, and three possible formulations are considered with respect to the inclusion of inertial terms. The response is presented in terms of shear stress and pore pressure distributions at three locations underneath the breakwater. The effect of seabed and wave parameters and the inertial terms on the impact response is investigated through parametric studies. Analyses show that usually partly dynamic formulation yields the largest response amplitudes as compared to the fully dynamic formulation, which is the most complete form. The instability of seabed and rubble mound as a result of instantaneous liquefaction is also studied. Breaking wave-induced pressures in some cases are found to cause liquefaction in the rubble and the seabed. The effect of some parameters on the instability is found to be significant.