Study On The Dynamic Response And The Sliding Failure Of The Seabed In Yellow River Estuary

Yellow River estuary is an area with so much offshore engineering. The siltyseabed is widely distributed around Yellow River estuary. Wave loading is a majordynamic effect for the seabed, and pore pressure or soil strength in seabed changeunder cyclic loading. However, studying on the dynamic response of silt isinsufficient, for which deep analysis is required in order to evaluate the stability ofsilty seabed accurately. So there is a need to analyze the response of pore waterpressure in seabed and its influence on the strength under wave loading，in order toevaluate seabed stability and study on wave induced seabed sliding failure in YellowRiver estuary. This thesis was funded by National Natural Science Foundation Project“The control of erosion and seabed liquefaction induced by the storm in theSubaqueous Yellow River Delta No41072215" and “A Study on internal supply ofsuspended matter and control factors of erosion in the Yellow River Delta No41272316”.Through analyzing the response of pore water pressure and the strength changein seabed under wave loading，this paper studies on wave induced seabed sliding failure inYellow River estuary from three aspects:(1) Study on wave induced response of porewater pressure in seabed. The pore pressure in seabed changes under wave action.There are different responses of pore pressure at different depths of seabed underwave action. By the field experiment of simulating wave loading、the flumeexperiment and the dynamic triaxial test, some studies on the response of cyclic porewater pressure are done in Yellow River estuary.(2) Study on the influence of waveinduced response of pore water pressure on the strength in seabed. Wave inducedaccumulation of pore water pressure in silty seabed reduces the strength of soil. Bythe field experiment of simulating wave loadingandthe flume experiment, somestudies on the influence of wave induced response of pore water pressure on thestrength are done in Yellow River estuary.(3) Study on wave induced seabed slidingfailure in Yellow River estuary. The decrease of the strength caused by accumulationof pore water pressure makes the seabed failure possible. By theoretical computationand laboratory tests, the mechanism and process characteristics of seabed slidingfailure are studied. Through detailed study on the aspects above, several conclusions are drawn：(1) The response processes of pore pressure in seabed include rapidaccumulation of pore pressure、the dissipation of pore pressure、the stability of porepressure and the fluctuation of pore pressure in Yellow River delta. The formerprocesses include rapid accumulation of pore pressure、the dissipation of porepressure and the stability of pore pressure may come up repeatedly. When the seabedis liquefied fully, the fluctuation of pore pressure occurs after the accumulation ofpore pressure again. Pore pressure can increase suddenly in the response process, somany holes appear at the surface of the seabed in Yellow River estuary, and fineparticles come from these holes are piled in little lump. The amplitude of fluctuationof pore pressure have relations with clay content、initial cumulant of pore pressure andliquefaction degree in the seabed.(2) Hyperbolic equation is sufficient to describe the relation between dynamicpore pressure ratio and cycle number ratio or between pore pressure ratio andprincipal strain. Based on the change of pore pressure, principal strain could becalculated under cyclic loading. Clay content decides its accuracy.(3) The distributions of seabed strength with the depth are non-uniform underwave action in the Yellow River delta. The higher the wave height, the larger thepenetration strength and undrained shear strength of the seabed. Different degrees ofsoil liquefaction occur with accumulated pore pressure in the response process of porepressure, and penetration strength and undrained shear strength decreases significantly,when the excess pore pressure to overlying effective stress ratio increases above0.5.(4) Accumulated pore pressure and shear stresses act on the seabed constantlyunder wave action, and the range of plastic zone or the range of liquefied zonechanges to a condition at some point. In this condition, seabed sliding failure appears.Its failure process includes expansion process and recovery process. The relationshipamong dimension parameters of failure soil could be described as a power function.Reactivated landslide from field observations may be the failure of reforming seabed.Based on the limit equilibrium theory, the formula of safety factor between shearstrength and shear stress is established, and this formula could make a preliminaryprediction for the ranges of failure soil depth in seabed.