| China is a country with frequent earthquakes,and its geological environment is complex.It has a long coastline.Many of the basic projects such as underwater tunnels and bridges are located in earthquake-prone areas where land and sea border,but the current local terrain for deep underwater.Or there are few studies on the dynamic response of structures.Based on Biot's two-phase saturated porous medium theory,the seismic dynamic characteristics of underwater submerged sites are studied numerically under the condition of multi-media coupling of water-saturated soil layer and bedrock,which provides seismic design for underwater engineering.Theoretical and technical support.The main research programs and work done in this paper are as follows:1.An input method for free field of underwater ground based on oblique incidence of seismic wavesAccording to Snell's theorem,the one-dimensional seismic response of the existing underwater foundation site is extended to the whole two-dimensional space,and the obtained two-dimensional response is derived as the free-field input file,and the MTF artificial boundary is combined to implement the wavefield separation at different boundaries,the input of the initial displacement field is realized.The finite element program of two-dimensional ground motion analysis of underwater half-space field considering water-saturated soil-bedrock multi-media coupling is developed,and the ground motion response of two-dimensional underwater foundation is calculated.The validity and accuracy of the input method are verified by comparison with the existing literature results.2.The ground motion characteristics of the local depression in the submarine terrain are studied.An underwater submerged site model considering the multi-media coupling of water-saturated soil-bedrock is established,and the finite element analysis method of water-saturated soil-base rock dynamic coupling is used to apply the artificial boundary and the initial displacement field.The input is used to realize the numerical analysis of the ground motion response of the two-dimensional underwater partial depression site.The influences of water depth,wave incident angle,porosity of saturated soil,size of sag and wave type on ground motion of deep sea sag terrain are studied.The calculation results show that:(1)Due to the presence of the concave terrain,the displacement and hydrodynamic pressure time history curves become more and more complicated as the frequency of the incident wave increases.(2)When the P wave is incident,the overlying water layer has a great influence on the vertical displacement and the hydrodynamic pressure.The influence of the SV wave on the whole is small,and the overall trend is firstly increased with the increase of the water depth and the vertical displacement and the hydrodynamic pressure are reduced.(3)The displacement peak and the hydrodynamic pressure peak tend to decrease as the incident angle increases.When the seismic wave is obliquely incident,the amplification factor on the left side of the concave is larger than the right side of the concave.When the vertical incidence occurs,the displacement peak of the concave portion is spatially symmetric.(4)The porosity of saturated soil increases,the peak value of displacement and the peak value of hydrodynamic pressure decrease,and the influence on the peak of vertical displacement is greater than that of horizontal direction,and the influence of P wave is greater than that of SV.(5)The dynamic response of the sag width to the local topography is greatly affected by the frequency of the seismic wave.With the change of the aspect ratio,there is no uniform change of the dynamic response of the sag. |
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