Analysis Of Seismic Effect Of Typical Island Reef Sites In South China Sea Based On OpenSees

Engineering Science and technology problems in the development of offshore areas are one of the important topics in geotechnical engineering and other related fields in recent years.Considering that the earthquake in the northern part of the South China Sea is relatively active,in view of the serious damage to the engineering facilities on the marine islands during the previous earthquakes,this paper first analyzed the calcareous sand characteristics of the calcareous sand in a sea area,and selected the multi-yield plastic constitutive model of the finite element software OpenSees to simulate the saturated calcareous sand.Based on the engineering geological profile of the Fiery Cross reef,a two-dimensional simplified model under the multi condition of the island reef site is established.By selecting the earthquake in the East Japan earthquake in 2011 and the partial bedrock records in the Taiwan ChiChi earthquake in 1999 as the input ground motion,the island reef seismic field under the condition of different reef limestone basin dip and calcareous sand layer thickness is carried out.The study of ground effect is aimed at revealing the mechanism of seismic response of islands and reefs sites,and providing scientific basis for determining the design parameters of the South China Sea Islands and reefs offshore engineering.The main work and achievements of the thesis are as follows:1.This paper shows the typical engineering geological condition of islands and reefs in the South China Sea,through comparison of the techniques for soil layered seismic response analysis around the world,then several critical factors and relevant solving ideas in the process of soil layers seismic response analysis for islands and reefs were put forwarded: The typical terrain of islands and reefs in the South China Sea;The special geo-technical engineering material of islands and reefs in the South China Sea;The seawater –reefs dynamic interaction;Selecting seismic motion record of the South China Sea for the earthquake acceleration input.2.Through the use of the 2-10 Hz dynamic triaxial test system(DYNTTS),a study was conducted on the calcareous sand in a certain area of the South China Sea.Compared to the same type of ordinary quartz sand,the shear of saturated calcareous sand was found.The shear modulus is too small and the critical state features are consistent with the results of ordinary calcareous sand test.The existing elasto-plastic constitutive model of sand can simulate the static and dynamic characteristics of saturated coral sand.3.When the seismic shear wave(SH wave)propagates vertically into the island reef basin,for the same longitudinal section,the horizontal acceleration of the sand layer in the island reef basin is the largest at the edge of the reef limestone,and the transition to the center of the site occurs.The process gradually decreases.The edge of the island reef basin has an abnormal acceleration peak,which is the edge effect of thebasin.For the same lateral profile,the effect of the calcareous sand on the horizontal peak acceleration is the most significant,and with the increase of the amplitude of the ground motion,The zoom factor decreases gradually,and the phenomenon of "weakening" occurs.4.The average response spectrum of the island reef site has obvious effect of amplification,and the order of enlargement of the reef flat area is outer reef flat,inner reef flat,and middle reef flat,and the corresponding magnification is between 1 to 2.4,1 to 1.7,and 1 to 1.4.The peak magnifications are 2.37,1.70,and 1.39,respectively,and the period of magnification is between 0.1 s and 0.3 s.