Study On The Dynamic Characteristics Of Offshore Silt Under Wave Loadings

The pore water pressure can be generated in the seabed when subjected to wave loading. If the pore water pressure accumulated to a certain value, the liquefaction and failure of the seabed soil will occur. In order to better development and utilization of marine resources, it is necessary to study the dynamic response of seabed under wave loading, so as to provide the basis for the analysis of dynamic characteristics and liquefaction possibility of offshore soil and foundation stability of seabed and offshore structure, which has important theoretical and practical significance.Based on the previous studies, this dissertation used the combination methods of theoretical and numerical simulation method and carried out a serious of work on the dynamic response, the accumulation of pore water pressure and its development law, seabed liquefaction characteristics and its influence factors of the seabed soil, etc., subjected to wave loading. The main results are as follows:(1) A brief overview is made on the domestic and foreign research results and methods related to the dynamic response of seabed soil under wave loading. The definition and properties of silty soil, the formation of soil liquefaction and its evaluation criteria, etc., are understood;(2) Firstly, it is briefly introduced the potential wave theory and its solution, the characteristics of linear wave and the interaction of wave and seabed. Then, the concept and characteristics of waves in soil medium is briefly introduced, and the pore water pressure causes the possibility liquefaction of seabed is analyzed.(3) The Biot’s dynamic wave equation under plane strain condition is solved using analytical method. Combined with the boundary conditions, the stress, displacement and pore water pressure of the seabed soil under harmonic wave loading are deduced. The effect of wave-seabed parameters on the dynamic response of seabed is studied using numerical examples.(4) Using the finite difference software F1ac3D, the dynamic characteristics of seabed under wave loading is numerical simulated and analyzed. The change law of dynamic stress-strain characteristics, total stress, pore water pressure and effective stress of seabed under wave loading is analyzed, and the liquefaction of seabed soil is discussed. The effect of water depth, time and wave height on the ability of anti liquefaction of offshore silt is discussed. The results showed:(ⅰ) The pore water pressure accumulation phenomenon of silt seabed under wave loads is more obvious. Pore water pressure increases caused by pore pressure accumulation and the effective stress decreases. When the effective stress decreases to zero, soil appears to liquefied. (ⅱ) Under the same condition, the cumulative pore pressure is greater with longer wave height. Therefore, the liquefaction depth is larger. The wavelength, wave pressure and wave velocity are larger with longer time, and the depth of liquefaction is greater. (ⅲ) The depth of water affect the seabed pore pressure accumulation and the liquefaction depth. With the increase of water depth, the liquefaction depth first increases, then begin to decrease in the same conditions.