Evaluation of Wave-Induced Pore Pressure in Sand Layer by Wave Steepness

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Abstract
The attenuation of wave-induced pore water pressures inside sand beds is investigated experimentally in a wave tank. It is found that the pore water pressure depends on the wave steepness. The attenuation equation of the pore pressure from the surface to the bottom of the sand layer is presented as a function of the wave steepness and includes two parameters determined experimentally. The parameters depend on the permeability of the bed. The empirical equation consists of both the characteristics of the water wave and the drainage conditions of the sand bed. The proposed empirical equation is examined with individual experimental results and various theories. It is found that the empirical equation is in good agreement with experimental results, and that the attenuation of the pore pressure downward to the bottom of the bed is considerably rapid than those predicted by various theories. The ratio of permeabilities in Sleath's equation, which is defined as the ratio of the horizontal permeability to the vertical permeability can be determined to fit Sleath's solution to our experimental results. By substituting these values of the ratio of permeabilities into Sleath's equation, Sleath's solution is fitted to the empirical solution. Therefore, the ratio of permeabilities in Sleath's equation is explained in terms of the wave steepness in our empirical equation. The ratio of permeabilities is examined with both the characteristics of water wave and the drainage condition of the bed. It is found that the ratio of permeabilities depends on both the wave length and the density of the sand bed. Consequently, the theory for prediction of pore pressure inside the seabed under wave loading must take into account both the characteristics of the water wave and the drainage conditions in the seabed.

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