The Flume Test On The Changes In Seabad Of Abandoned Yellow River Subaqueous Delta

The diversification in seabad of abandoned Yellow River subaqueous delta are investigated by designing the physical model test in the paper. The erosion mechanism of the Yellow River estuary is studied by utilizing the integratement of the little flume experimentation and information measured in the field. The disciplinarian of the sandwave development and movement are studied through big flume experiment, and the relevant circumstances of pore water pressure changes in silt under the wave action is also analysed in the large flume test.The severe erosion has been occurred in the lobe of Diaokou River distributary in the north of the Yellow River delta, since the Yellow River was artificially diverted in the Qingshuigou River distributary flowing into the sea in May 1976, and the little flume experiment was designed on the basis of the in-situ changes. The results show that in the early age of the delta abandoned, the delta front seabad is rapidly eroded because the terrestrial sediment is no longer deposited, and the phenomenon of liquefaction destroy occurs in the subaqueous delta front seabad under the wave action, leading to a lot of disaster of the fauits and subaqueous landslides in the early period. After the erosion-accumulation equilibrium stage, the area changes determined by comparing the final profiles at the end of the experiment with initial profiles, indicate that the amounts of erosion and accretion at either side of the cingulum point are 1143.5 cm2 and 558 cm2, respectively. The soft stratum of the delta deposition deforms greatly with the long time wave action, and the rheological diversification will occur and the phenomenon of diapir is likely to take place under certain conditions, if the soft stratum has enough thickness and acreage, which are destructive to the offshore engineering facilities and engineering stability in the estuary delta. With the flume experiment carried out for a long period, the very obvious sandwave comes into being in the low part of the delta seabad with the sustained wave action. Through the experimental analysis, the seabad sediment is resuspended by waves and then accumulates again, so the sandwave forms in the course of the spread of the wave, in addition, the silty seabed with the broad flat is favorable to the sandwave formation. The sandwave formed on the seabad is enormously destructive to the seabad pipeline and maritime transport. Due to the restrictions of the experimental scale and time of the little flume, the further study on the detail circumstances of the transformation of sandwave and seabad silt are not carried out, the large flume is designed specially to investigated the sandwave and seabad silt.Scaled down according to the average value of observational data in the field for many years, the physical model of large flume test is designed to investigated the development mechanism and mobile disciplinarian of the seabad sandwave. The silt with three different median size is laid in the flume experimental zone, then the different wave and current are brought to bear in proper order, a total of 13 test groups are carried out. The various parameters that influence sandwave development, e.g. wave, current velocity, sediment particle size in the seabad and the seabad characteristic, are investigated and analysed. The investigative outcomes indicate that the oscillatory movement of water body plays an important role during the process of the sandwave development; through the observational study to the experimental phenomenon of 13 test groups and the systematic analysis to the experimental data, the sandwave development is analysed from the role of start-up of sediment, in addition, the further development mechanism is explained taking advantage of the formula of sandwave movement. The shear stress and the friction shear velocity that are in the combined effect of wave-current is applied to replace the corresponding parameters in the formula of the sandwave mobile velocity, and the mobile formula is established by Japanese scholars Shinohara, the experimental data is used to validate feasibility of the replacement. Then, the comparison between the calculated outcomes and the the sandwave mobile velocity of the actual measurement in experimental process, and the results indicate that the anastomose is better, thus, the conclusion could be drawn that such fungible calculation has a certain degree of practical application value when the hydrodynamic circumstances are not very complex.The mechanism of liquefaction damage by waves about the silt is analysed from the role of the changes of the pore water pressure under the wave and current action, making use of the results of the large flume experiment; by means of investigating the changes of the pore water pressure and distribution curve, the cumulative and discutient effect of the excess pore water pressure is taken into account, then, the possibly influencing depth of the liquefaction is analysed. The dynamic response of the seabed soil to seasonal load is analysed in discussing the engineering instability of the seabad. Besides, the liquefaction causation of the silty clay under the wave and current action from the role of the cumulation and abreaction of the pore water pressure as well as the soil structure, and the engineering characteristics and application are further elaborated.