The purpose of this paper is to investigate the stability of an unburied offshore pipeline under severe storm condition. Pore pressure accumulation and pipeline movement during cyclic loading due to waves and currents on pipeline are numerically investigated from the view points of the stiffness of seabed and the fine grained soil content in seabed. Both drag and lift forces are numerically obtained for 100 years return period storm condition using the Fourier decomposition method. Pipeline movement strongly depends on the seabed characteristics as well as the cyclic loadings estimated from storm condition. When the stiffness of seabed and the fine grained soil content are large, not only the pipeline movement but also the pore pressure response in seabed beneath the pipeline increases with the number of cycles.
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