Three-dimensional Seismic Response Analysis Of Coral Islands And Reefs

With the continuous development and construction in the South China Sea,the safety of the construction of the engineering structure on islands and reefs in the South China Sea has become one of the important issues that need to be solved urgently.The South China Sea is an area where earthquakes are relatively active.It is of great significance to study the seismic response characteristics of islands and reefs under the action of earthquakes.Existing studies mainly focus on the physical and mechanical characteristics of coral calcareous sand and reef limestone.For seismic response analysis,onedimensional or two-dimensional simplified models are mostly used,which cannot truly reflect the complex topography of islands and reefs and the conclusions are not perfect.In this paper,the FLAC3 D software is used to establish a three-dimensional calculation model of a coral island in the South China Sea.Based on the existing coral island geological zoning and stratigraphic characteristics,the model is given reasonable calculation parameters.By selecting the measured sea area seismic records recorded by the subsea station of the Japanese K-NET network as the input ground motion at the bottom of the bedrock,the influence of factors such as the topography of the island,the ground motion characteristics of the sea area,the input of multi-directional ground motion,seawater-reef interaction and other factors on the seismic response of the coral island site are studied.The main work and conclusions of the paper are summarized as follows:1.On the basis of summarizing the existing research results,based on the engineering geological survey data,the FLAC3 D software was used to establish a threedimensional numerical simulation model of a coral island.Key parameters such as constitutive model,boundary condition,fluid-solid coupling and sea ground motion are discussed,and the reliability of the calculation model is verified.2.The influence of the topography of the coral island on the seismic response is studied.The research results show that the ground motion amplification effect on the lime-sand island is significant,and the ground motion at the harbor pool is relatively small.Topography has a significant effect on earthquake response.The island ground motion amplification effect is closely related to the input ground motion waveform,and overall decreased with the increase of the input ground motion peak value.3.Analyzed the dynamic effect of the seawater fluid-solid coupling and the seawater outside the island on the seismic amplification effect of the coral island.The seismic response of the island site shows a decreasing trend compared with no consideration of the seawater effect,especially the seawater has a greater impact on the seismic response of the island when the frequency of input ground motion is high.The horizontal acceleration amplification factor of the island tends to decrease with increasing seawater level.4.Comparing the difference of the seismic response of the island between multidirectional input and single horizontal input,the horizontal seismic response of the island under three-directional seismic input is significantly greater than horizontal onedirectional input,the seismic response of the island is not much different between threedirectional ground motion input and dual horizontal input.The vertical acceleration amplification factor is significantly greater than the horizontal amplification factor,and the vertical peak acceleration amplification factor increases with the increase of bedrock input ground motion amplitude,and the trend is decreasing with the increase of seawater level.