Dynamic Response Analysis Of Multilayer Silt Seabed To Waves On The Yellow River Delta

The seabed sediments of Yellow River Delta, where the hydrodynamicconditions are extremely complex, have spatial non-uniformity. In the verticaldirection, different types of soil superimposes on each other, and in the horizontaldirection, the seabed soil of different areas are different in thickness, sequence,particle size distribution, and the physical and mechanical properties. Previous studieshave shown that the developmental type and size of Yellow River Delta seabedgeological disasters is closely related to its location and soil structure. Previousstudies only give a qualitative description of the morphology, ocean dynamicconditions and soil physical and mechanical properties of the Yellow River Delta.The research of silt seabed dynamic response to waves mainly based on thehomogeneous model, very little research for non-homogeneous model. In this paper,according to the statistical field survey data of the Yellow River Delta, five typicallayered soil models were established. Based on the Biot theory, the dynamic responseof the non-homogeneous silt seabed to wave was simulated by finite differencemethod. The dynamic response mechanisms of seabed and the role played by "weaklayer" in the stability of the seabed were discussed. The main research work andachievements are as follows:(1) Based on a large number of field survey data, classified summary of thesedimentary sequence of seabed was done, and the distribution characteristics ofsedimentary sequences corresponding to different seabed were obtained; The soilphysical and mechanical parameters of sedimentary sequence were got by drillingsampling and indoor soil test. According to the difference in thickness, sequence andphysical and mechanical properties of soil, five typical seabed model of the YellowRiver Delta were established.(2) Taking typical layered model as calculated models to Biot theory, numericalsimulations of stress field, displacement and excess pore water pressure field were done by using the finite difference method. The response characteristics of the soiltypes were compared and key factors which control the seabed stability werediscussed. In order to verify the correctness of numerical simulation, situ porepressure monitoring dates, which were in the distribution area of D soil, werecompared with the numerical simulation data, and the results showed that thenumerical simulation results are very consistent with the actual situation.(3) Taking5typical sequence of silt seabed in Cheng Dao Sea as a model to Biottheory, numerical simulation in the10m deep range was done in the stress field,displacement field and the excess pore water pressure of sea-bed, and the actualobserved results were compared. Research reveals that under the wave loads, the porewater pressure, the stress and displacement of the multi-layer seabed appear the firstextreme value in surface silty layer, then come the second extreme value in next“weak” layer, and stress will be reduced sharply in the interface position. The firstextreme value is dynamics factor for small geological disaster in surface layer, and thesecond extreme value directly leads to large-scale geological disasters. Thesedimentation sequences play a key role in the stability of the seabed, and" Hard-softupper lower" structure is most unstable, where large-scale geological disasters willhappen after the strong wave action.