SEDIMENT FLOW CHARACTERISTICS AROUND CYLINDRICAL STRUCTURE REGARDING SEABED EFFECTIVE STRESS RESPONSE

Abstract

Stability of onshore and offshore structures subjected to stormy ocean waves is influenced by the
soundness of seabed foundation ground, as well as the intensity of wave pressure acting directly on the structures.
The seabed soundness would be affected by the change of the seabed surface elevation caused by erosion and/or
deposition of sediment. The fluctuating effective stress in the seabed ground, which is induced by sea wave
loading, would cause the reduction in seabed stiffness, and then the sediment flow and related scouring of seabed
must be also affected by the effective stress fluctuation. The present study proposes a calculation method for
sediment traction flow on seabed around cylindrical structures. The calculation method used comprises with
linear wave theory, pore-linear-elasticity theory for seabed medium, and empirical sediment traction flow model
regarding seawater flow velocity. Although the intensity of sediment traction flow is mainly a function of
seawater flow velocity, the sediment traction flow must be also influenced by the soundness of seabed ground.
The sediment flow and associated erosion-deposition around upright cylindrical structures of several types were
calculated. The characteristic behavior of sediment flow was clarified.