Experimental Study On Movement Characteristics Of Liquefied Silty Seabed Under Waves

Silty seabed is prone to be liquefied under waves. And as a result, micro-landforms such as collapse depressions developed on the gentle seabed and big destroyed disasters are imposed to various platforms, marine cables, pipes etc. Based on these engineering geological facts, series of researches are carried through this paper.Silty soil from the Yellow River Subaqueous delta was studied through in-lab flume experiments by making silty seabed. Through experimental and analytical research, the initial wave-induced liquefaction state of silty seabed, movement characteristics of soil particles, and the liquefaction-induced re-stratification of silty seabed were studied.A seabed of uniform strength and another seabed of local soft area were made, and experimental phenomena and data of water pore pressure were recorded in the experiment. The seabed of uniform strength was liquefied layer by layer form upward down due to the attenuation of the effective strength of seabed due to wave action. The seabed of local soft strength was sheared to slide from the soft area by the horizontal shearing stress. The oscillated soil developed downward with waves.When the seabed was liquefied under waves, mass of fine soil particles suspended into upper water leading the water turbid. Three water layers existed along vertical direction, which were the upper turbid water, the boundary layer, the liquefied soil layer. In the upper turbid water and the liquefied soil, soil particles moved along ellipse path in a wave period. In the boundary layer, soil particles moved along a semi-ellipse path during a wave period. The moving amplitude differed along vertical direction. Attenuation function was calculated and the barrier property of boundary was proposed in this paper. In the upper water, the attenuation rate increased when it was deeper, however, in the liquefied soil layer, the attenuation rate decreased when it was deeper.In laboratory, it is discovered that the initial uniform seabed underwent re-stratification without horizontal mass transport ascribed to wave-induced seabed liquefaction, of sedimentary structure that the finer the shallower. The disturbed stratum at the subaqueous Yellow river delta has the same structure characteristics based on field investigation data. In this paper's opinion, the liquefied seabed induced by storm waves moves like water waves, the finer soil particles move upward with pore water while the coarser particles move downward by self-gravity. It is discovered that the new formed stratum are with normal graded bedding, oscillatory wave marks, horizontal bedding, and convolution bedding etc, and contact with mud layer abruptly at seabed tip.