Dynamics of Saturated Porous Media: Wave Induced Response and Instability of Seabed

Abstract

Problems in fields ranging from geomechanics to biomechanics require response of saturated porous media subjected to dynamic loading. An engineering problem requiring the true behavior of saturated porous medium should consider the coupling of both fluid and solid phases yielding the simultaneous analysis of flow of pore fluid and deformation of solid skeleton. Depending on the nature of loading vis-à-vis the characteristics of the media, different formulations; fully-dynamic (FD), partially-dynamic (PD), quasi-static (QS) are possible. In this study, analytical solutions and numerical models are developed for the response of plane strain saturated porous media, and wave-induced response of seabed in free field and around a breakwater under pulsating/breaking waves. For each formulation, the results are presented with pore-pressure, shear and normal stress distributions within porous medium. The response is studied for various conditions and regions of applicability of formulations are identified in non-dimensional and actual parametric spaces. This can be used for a specific case with known loading and medium characteristics and may help engineers identify the necessary formulation to be used in a given problem. Effect of seabed-wave parameters and inertial terms on standing/breaking wave-induced pulsating/impact response of seabed-caisson system were investigated. The selection of the adequate formulation is decided depending upon the response variable and ranges of physical parameters. While FD formulation yields the minimum response in cyclic wave, for impacting wave it yields variable distributions in between the other two formulations. The areas of instantaneous liquefaction were identified inside the domain through contours of mean effective stress for both types of waves. Liquefied regions are concentrated at the front toe of rubble under cyclic wave which can initiate a vertical-horizontal movement and rotation towards the seabed causing structural failure. Liquefied areas in case of breaking waves are much larger compared to cyclic waves. Additional analyses made introducing a constitutive model for the inelastic behavior of soil to evaluate the nonlinear dynamic response of seabed reveal the importance of the inclusion of material nonlinearity effects.