Experimental Study Of Response Pattern Of Pore Water Pressure On Sandy Seabed Under Breaking Wave Action

The breaking wave will occur when the wave propagates to the area of near-shore and shallow water. It has a close relationship between the seabed destruction and the distribution of pore water pressure under the action of breaking wave. The relationship between the breaking waves, seabed deformation and pore water pressure distribution are presented combined with theoretical analysis, model test method, and this may provide assistance for coastal engineering design.Based on the wave flume experiments, response pattern of pore water pressure is studied on a 1:30 slope sandy seabed under breaking wave action. The topographic change is observed and its causes are analyzed. It used the image processing technique, and the actual situation of movable seabed change could be calculated. It sets braces near surf zone, obtain the change of the pore pressure under the movable bed and analysis the relationship between moved sand and pore pressure.The results show that the pore pressure changes significantly differently before and after the wave breaking. The pore pressure reaches the maximum on the area away from the nearest bed surface of the breaking point in the whole process, and the vertical decay rate of pore pressure is larger than the before and after wave breaking in the breaking section. The pore water pressure increases significantly at the breaking point. The topographic change is greatly on the wave breaking section. Pore water pressure changing at the top is significantly higher than it is at the bottom. The changing of the pore water pressure has no relationship with the wave breaking pattern. The pore water pressure attenuates slowly before the wave breaking and attenuates rapidly after the wave breaking. The different patterns of the breaking wave have different performance on the sand. It mainly presented the substantial undercutting and accumulation on the sand when the breaking wave is plunging breaker, and it mainly presented that it has a certain degree of leveling effect on the destructed sand.When the sand scours, the amplitude of the pore water pressure increases; and when the sand accumulates, the amplitude of the pore water pressure decreases. When the amplitude of the initial pore water pressure is greater than static earth pressure theory, the wave has a greater impact on bed depth and sand mobility.When the pressure gauges are all in the sand, the upper and lower gauges have a low pressure gradient. And when the gauge in the sand continued to start loosening up and down under the wave action, the two gauges have the greatest pressure gradient. With the continuing action of the wave, the casing on the two pressure gauge is to be disturbed, the two gauges have the low pressure gradient. If the wave action continues eroding the bed, this phenomenon will occur in the deeper sand.