| The seashore is a zone where waves and tides alternate.It is a direct interaction area between land and sea.This area is vulnerable to erosion by loads such as wind and waves.More than 2400 kilometers of sandy coast in China have been severely eroded.Therefore,under the strategic goal of building a " maritime power " and " double carbon," it is urgent to study the protection of marine land resources in a green and low-carbon way.As a new type of geosynthetic environmental protection material,the geogrid is stable in chemical properties,not affected by microorganisms and the environment,not degraded,not releasing harmful substances to the soil,not polluting groundwater,and the price is low.It has some preliminary engineering applications in soil erosion control,slope reinforcement,beach maintenance and other aspects.Therefore,this thesis proposes three kinds of grille layouts to reinforce the coastal gentle slope,including slope laying,sheet insertion and cage embedding.The effects of strengthening the seabed under different working conditions are studied by numerical calculation and model test.The main research results are as follows :(1)The horizontal seabed model is established by ABAQUS software.Based on the second-order Stokes wave theory,the dynamic response of the seabed under the action of waves is calculated,and the area after the instability of the seabed is displayed.(2)The mild-slope seabed model is established to study the dynamic response of the mild-slope seabed under the action of waves and the failure area after seabed instability,and compared with the analytical solution.By considering the three laying methods of grille,wave load conditions,seabed conditions and grille conditions,the seabed model embedded in grille is established.It is concluded that among the three laying methods,the reduction of wave-induced shear stress is the most significant,but the influence on wave-induced excess pore pressure is relatively small.The influence of wave height,initial water depth and gentle slope angle on the dynamic response of seabed is significant,while the influence of seabed permeability and shear modulus on the dynamic response of seabed is relatively small.The embedded grille has better reinforcement effect in the seabed with poor permeability.The increase of grid strength and laying density can significantly reduce the wave-induced stress.(3)By setting the infinite element boundary in the finite element model of the gentle slope seabed,the seismic response of the gentle slope seabed is studied.Considering the seismic waves of two intensities,the acceleration response and displacement response characteristics of the seabed before and after embedding the grid are compared.It is concluded that when the seismic wave propagates from the source in the direction perpendicular to the free surface of the gentle slope seabed,the acceleration amplification effect of the free surface in the middle of the slope is the most obvious.The three ways of laying the grille can reduce the seismic response of the seabed;when the earthquake is small,the cage embedding has the best ability to absorb seismic waves;during the large earthquake,the reinforcement effects of the three methods are little different.(4)Based on the self-developed flow erosion test device,a gentle slope seabed test model is established to observe the seabed profile shape,surface morphology and sediment loss before and after the grid is embedded.It is concluded that the laying of the grid can reduce the sediment loss in the wave back and forth erosion.The slope flat grid has little effect on the sediment above the laying layer;the plate inserted grid can effectively weaken the impact kinetic energy of the climbing and falling water flow.The cage embedding method will be better than the direct chip insertion method when the arrangement spacing is small enough.If the spacing is too large,the weakening effect of the water flow impact kinetic energy will be greatly reduced. |
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