Long Island Sea Ranching Seafloor Sediment Stability Evaluation Research And Site Selection Engineering Application

With the deepening of the sea ranching construction,the importance of the stability of seafloor sediment on the site selection and construction of sea ranching are also increasing.The stability of seafloor sediment will directly affect the stability performance of sea ranching facilities,which is mainly manifested in the instability problems of the sediment such as transport displacement or shear failure,and leading to the siltation or capsizing of sea ranching facilities.Then in turn affects the economic and environmental benefits of pasture.Therefore,it is of great significance to study the location of Marine pasture based on the stability of seafloor sediment.This paper focuses on the stability of seafloor substrate in the process of selecting Marine pastures,taking the planning area of Marine pastures in the North four Islands of Long Island as the research background.Based on the three-dimensional geological model,geotechnical test and numerical simulation,the evaluation model and prediction model of submarine sediment stability were established respectively according to the fuzzy evaluation theory and BP neural network.The submarine sediment stability of the study area was analyzed and studied,and the site selection suggestions were given.The main research work and conclusions of this paper are as follows:(1)Based on the field survey data of the study area,Surfer modeling software was used to establish three dimensional geological models for the east and west sea areas of the North Four Islands.Thus,the formation data and borehole data are displayed in 3D visualization,which provides a visual 3D topographic model for further research on the stability of the bottom material under different slope conditions in the following chapters.(2)Laboratory soil tests were carried out according to the borehole soil samples from engineering geological drilling in the sea area of the study area.The relevant physical and mechanical parameters and mechanical curves of drilled soil samples were determined.Further,Pearson correlation analysis method was used to carry out multivariate physical and mechanical properties correlation analysis of relevant parameters,which verified the authenticity and validity of the geotechnical tests,and laid a data foundation for the subsequent numerical simulation and evaluation of the stability of Marine pasture bottom.(3)Using PFC3D particle flow 3D discrete element numerical simulation software,the coupling calculation model of submarine sediment(DEM)and hydrodynamic(CFD)are established.At the same time,based on the comparison between the numerical triaxial test and the conventional triaxial test,the sensitivity of the micro parameters of the numerical model to the macro mechanical properties was analyzed.According to the results of sensitivity analysis,the microcosmic values of relevant physical and mechanical parameters of seabed sediment in the coupled model were calibrated.According to Marine meteorological monitoring data,four kinds of wave hydrodynamics with different intensities and four kinds of tidal current hydrodynamics with different velocity are defined respectively.By numerical calculation,the stability of seafloor sediment under different hydrodynamic conditions at 0°,5°,10° and 15°slopes is studied,and the displacement field of seafloor sediment under corresponding conditions is given.The results show that the sediment displacement increases with wave intensity and tidal current velocity at the same slope.With the same wave intensity and tidal current velocity,the sediment displacement increases with slope.(4)Based on the results of geotechnical tests and numerical simulations,seven influencing factors,including water content,natural density,pore ratio,compression modulus,water depth,flow velocity,and formation slope,were selected as evaluation indexes for the stability of the sediment.Combined weights of the indexes were determined by the combination weighting method combining analytic hierarchy process(AHP)and rough set theory.Based on the Fuzzy evaluation theory and BP neural network,the evaluation model and prediction model of the bottom sediment stability of the Marine pasture were established respectively,and the evaluation and prediction results of the bottom sediment stability of the study area were carried out.The evaluation results and prediction results showed good results.Further,the two results are compared and the site selection suggestions are given.