In design of offshore structures that rest on or are buried in sand bed, an important factor is the calculation of seepage force acting on the structures. The objective of this paper is to set up a model to calculate wave-induced seepage force exerted on structures of arbitrary shapes. The theory used in this paper is based on Biot's theory which takes into account the compressibility of both soil skeliton and the water. The unknown variables in Biot's equations are displacement of soil and pore water pressure. It is difficult to solve the coupled equation with all these variables. The displacement of soil is therefore eliminated from momentum equation of pore-water and the momentum equation of the soil skeliton. Finally, the governing equation for pore-water pressure is obtained. The governing equation is solved in a finite diferential way. To check if the numerical method is correct, a seepage flow field under a two dimensional structure is analyzed, and the results are compared to the authers" analytical results that have been published. Good agreement is found. Then the numerical method is used to calculate pressure around a pipeline of square section that is buried in sand bed. In shallow water, non-linear wave theory is often applied. For structure built in shallow water, non-linearity of waves is taken into account. Results of applying cnoidal wave is compared to that of applying linear wave and the importance of applying cnoidal wave theory is shown.


When wave passes over permeable seabed, pore-pressure will be induced within it. The seepage pressure acting on structures is an important factor in design. A lot of work has been done on this subject.

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