PROCESSES AND THE EXTENT OF INFLUENCE OF INTERNAL EROSION UNDER TRANSMITTED WAVES WITH THEIR COUNTERMEASURE USING A TWO-LAYER FILTER

Abstract

 Internal erosion under the action of transmitted waves was reproduced by a large-scale visualization experiment. The effects of hydraulic conditions such as wave period, wave height, and initial water level on the processes of internal erosion and the extent of its influence were investigated. As a result, it was shown that the flow velocity of sand increased when the sea level was lower than the groundwater level because the internal erosion was promoted by the seepage flow toward the sea side. In addition, it was clarified that the scale of expansion of the cavity formed tended to be large and the extent of influence of the internal erosion was widened in the case where internal erosion occurred in a deep point under the groundwater level, regardless of the wave period and wave height. The particle size condition of the filter material for deterrent of internal erosion under the action of transmitted waves was examined by the same series of experiments. As a result, it was verified that the geotechnical two-layer filter kept sufficient deterrent effect against the continuous action of relatively strong waves and backwashes, under conditions where the median particle diameter ratios were less than 25 and the uniformity coefficients of the filter were larger than 3, regardless of the shape of the filter material.