Wave boundary layer flows and pore pressures in permeable beds

The boundary layer flows and wave-induced pore pressures inside porous beds are both investigated in wave tank. Two kinds of porous beds are composed of two different grades of quartz sands which the porosities are 0.437 and 0.472 respectively. According to the experimental results, it is found that the larger pore pressure in permeable bed is induced by the longer wave period, and the pore pressure has an exponential attenuation with the wave steepness increasing. From the elaborate measurements in the boundary layer, the overshooting induced by wave motion is effected by bed porosity and it becomes smooth. In the experimental cases, the maximum horizontal overshooting occurs at Z/δ≈1.2, which is lower than the impermeable case of Z/δ≈2.7 obtained by Hwung and Lin (1989). Furthermore, the vertical overshooting has also been found in our experiments.