Boundary layer theory of waves in a poro-elastic sea bed

Pipelines for transporting petroleum from an offshore terminal to the shore are usually laid directly on top of the sea bed if the water depth is large, or buried in the sea bed if the water depth is small. For sufficiently shallow water or strong waves, the varying wave pressure can exert considerable stress and strain in the sea bed, thereby causing soil failure and breakage of pipe lines. Many offshore platforms are supported on piles which are drilled into the sea bed, while many of the gravity type rest directly on the sea bed. Under persistent attack of sea waves, not only the strength of the structure itself, but also the dynamic stability of the foundation (i.e., the sea bed), is of concern. The latter is of course also a major topic in soil dynamics and has been studied in the context of machine vibrations and earthquake engineering for some time. For foundations on land it is often possible to model the land as a dry solid only. However, it is well known that to model the nonlinear dynamic behavior of a soil realistically is an extremely difficult and yet unfinished task. To provide some reference for design or perhaps only for physical understanding, simplified models (hence not always realistic) have been used in recent theoretical studies. In machine or building foundations a large amount of existing work is based on the assumption that the soil is a singlephased linearly elastic medium.