Research On Time-Domain Separation Method Of Seismic Incident Wave Based On Site Response Simulation

At present,when using strong earthquake observation records to evaluate the site amplification effect,it is difficult to eliminate the pseudo resonance phenomenon caused by the destructive interference between incident wave and downgoing wave.The separation of incident waves from bedrock records is of great significance for evaluating the amplification effect of ground motion in near surface sites.Based on the one-dimensional(1D)finite element simulation process of site response,this paper proposes a time-domain separation method for separating the incident wave and downgoing wave in bedrock observation records,and uses this method to carry out the simulation of site response.The main research contents are as follows:(1)The boundary conditions and ground motion excitation forms of numerical simulation of site response are summarized.Based on the relationship between the node reaction force at the bottom of 1D site response finite element model and the equivalent node force corresponding to bedrock wave,the time-domain separation method for incident wave is proposed,and the principle and operation process are described.Based on this method,the separation method of incident wave at any position between the site surface and the bottom of borehole is further proposed.The multi-layer ideal site model is used to verify the effectiveness and accuracy of the proposed method and interlayer separation method.(2)Taking the site of IKRH01 array of KiK-net strong earthquake observation network in Japan as the research object,the incident wave time-domain separation method is applied to the linear site response,and the two parameters of Rayleigh damping are calculated by variable damping ratio α and β in order to simulate the small strain damping characteristics of the site soil,the influence of the randomness of shear wave velocity on the surface response is studied.It is found that the change of shear wave velocity structure will change the surface response to a certain extent,but can not significantly improve the correlation between numerical results and observed values.Based on the interlayer incident wave separation method,the interlayer incident wave field and reflected wave field are calculated.It is found that the downward wave peak decreases gradually with depth,but it is still half of the incident wave peak when it propagates to the bottom of the borehole.(3)Taking the Garner Valley Downhole Array(GVDA)site as the research object,the modified Davidenkov constitutive model is introduced to simulate the site nonlinear response caused by strong earthquakes,and the influence of the randomness of constitutive parameters on the site response is studied.The coseismic variation of GVDA array site response is numerically reproduced and compared with the measured records,which of two are in high consistency,At the same time,the numerical results show that the strongest nonlinear position of the site soil occurs at the depth of 10 ～ 20 m below the near surface rather than the surface.The downward wave interference effect between the surface and GVDA site at different depths is more obvious in the shallow layer,and gradually weakens with the increase of depth,and the destructive interference law of ground motions with different intensities is similar.The nonlinear characteristics of soil lead to significant differences in the spectral ratio of ground motions with different intensities.