Experimental study on the dynamic response of a silty seabed under waves

Abstract

Scouring and liquefaction of silty seabeds under waves have been recognized as two major modes of the seabed instability around marine structures. A series of wave experiments were conducted to investigate the wave-induced dynamic response in a silty seabed. The seabed was composed of light sand with and without geotextile covering under various wave conditions. When the seabed was not covered with geotextile, the seabed was liquefied under the action of waves, accompanied by sediment incipience and suspension. The results show that with increasing wave height, the seabed develops a series of processes such as sand ripples, ripple attenuation, sheet flow and seabed liquefaction. After seabed liquefaction occurs, an upward force gradient of the accumulated pore pressure is generated, which increases the suspended sediment concentration near the bottom and further enhances the scour of the seabed. When it is scoured, the sediment particles are continuously removed, and the stress in the soil is released, which intensifies seabed liquefaction. When the seabed is covered with geotextile, the concentration of suspended sediment near the bottom is zero. The maximum liquefaction depth of the seabed decreases along with the development rate of the liquefaction depth. The amplitude of the pore water pressure in the seabed decreases by approximately 5%–20% and seabed liquefaction is reduced. Experimental results clarify that liquefaction and scour promote each other.