Study On The Responses Of Silty Seabed Soil In The Yellow River Delta Under Wave Loadings

Based on the project sponsored by the Shandong Science Foundation, Discussions on wave induced seabed deformation in yellow river delta and the effects to stability of submarine pipeline, the present study aims to investigate the evolution, liquefaction and variations of strength of silty seabed soil in the yellow river dalta under wave loadings, and to propose a simple method to fix the sliding surface of the silty seabed soil.To understand the dynamic response of seabed under wave loadings is of significant importance for the design and construct of oceanic engineering. The evolution of shear stress and pore water pressure in sea bed under wave loadings might induce instability of base,which is dangerous for oceanic construction. In the yellow river delta area, sediment of seabed is dominantly consisted of silt, and so the dynamic response of the silt-seabed under wave loadings (which has been proved to be more complex than that of sand seabed) is a crucial and attractive problem for us to study.In this paper, our study of this problem will be exhibited below, the main content including:(1)A flume experiment has been conducted in order to simulate seabed response to wave loadings, in which the evolution of seabed elevation, pore water pressure and seabed consolidation have been studied.(2)A series of dynamic tri-axial test has been done to study the pore water pressure evolutions of different conditions, the relationship between stress and strain has been discussed too.(3)A 2D elasticity numerical modal has been employed to calculate the effective stress, pore water pressure and shear stress of sea bed under shoaling traveling wave loadings.The main conclusions of this paper: (1)Under wave loadings, an oscillatory layer begin to form and expand downward in the surface of seabed due to liquefaction(can be interpreted by the sharply decreasing of pore water pressure in this layer). In the underlying layer,the periodical accumulation and dissipation of residual pore water pressure induce remarkable effective stress variation, which can reduce the inter space between soil particles and favor its consolidation. The above theory is employed to explain the forming of hard layers in silty seabed which can be found in many areas of yellow river delta.(2)By a series of dynamic tri-axial tests, we found that lower wave frequency and larger wave height is more helpful for liquefaction and the relation between stress and strain can be described by a visco-elastic model. Moreover, we obtained the dynamic shear modulus and the dynamic damp ratio by data fitted,witch is important for numerical modal simulations.(3)We employed a elastic model to simulate the dynamic response of silty seabed under wave loadings. The result indicate that the effective stress increasing rapidly firstly in deep layers.therefore the up layers.The maximum shear stress and pore water press can be found below wave nodes and the breakage interface is very similar to that of observations in flume experiments.In this paper, flume model test, triaxial test, numerical simulation method have been used to study the responses of silty seabed in Yellow River Delta under waves loadings, some new discoveries and new conclusions have been discovered. The results of this research is to predict silt seabed under the action of the waves and sea bed evolution in the position of slip surface foundation of engineering practice significance, enriched silt seabed on wave dynamic response of experimental research, put forward many new issues, new speculation on the future role of further study for.