Study On Disarrangement And Renewal Of The Substratum By Pitching And Pulling Out The Piles In The Yellow River Subaqueous Delta Area

The structures of the substratum in the Yellow River Sub aqueous Delta Area can be divided to three categories, the first one is made of a thick layer of slit and a layer of soft silty clay under the thick one, the second one is a thin layer of silt and a layer of soft silty clay which is under the thin one, the third one is made of a layer of soft silty clay and a layer of silt or silty clay which is under the soft one. When the platforms which have pile shoes are pitched and pulled out of the research area, the substratum will be disturbed and damaged, and then shoe pits are formed. The degree of shoe pits'renewal and the characters of new shoal materials will directly affect the following marine engineering.On the base of systematically generalizing the regular patterns of sedimentation, principles of dynamic force, surface features of the ocean floor, the thesis analyses the subsoil in and out of the shoe pits using the data coming from side scan sonar,dual frequency echo—sounder, subbottom profiler, borehole surveying, soil mechanics. We find that the substratum of the three categories is changed in the structure and mechanical characters more or less.After being pitched and pulled out the piles, the surface of the first category of the substratum will not be changed in the structure, but the thickness of the slit will be smaller and the hardness of the slit will be lower. The hardness of the silty clay is not changed obviously and the layer of the silty clay is not disturbed obviously either.After being pitched and pulled out the piles, the surface of the second category of the substratum will not be changed in the structure and the physical features will not be changed ether, but the thickness of the slit will be larger and the under layer of soft silty clay will be changed a lot in hardness and mesh size.After being pitched and pulled out the piles, the surface of the third category of the substratum will express two formats. One is that the shoe pits are mostly filled with slit above which is a layer of soft slity clay, the index of its physical mechanics are obviously improved; the other one is that the soft silty clay filled the shoe pits, but the thickness comes to be smaller, and the type of the soft silty clay is fluxionally plastic.From the analysis on the change of the three categories of the substratum, we find that the elements effect the substratum in and out of the shoe pits are inserting and pulling out the piles, ocean dynamic force, subsoil granulation etc.The research tells us that the substratum will be disturbed by inserting and pulling out the piles. And the soil filled up will be bigger in size and the layer in the shoe pits will be harder, excepting in the area whose surface is thick fluxionally plastic slity clay.