A New Indirect Boundary Integral Equation Method For Seismic Wave Scattering In Three-dimensional Layered Half Space

Many major projects in our country are located in the high seismic intensity and complex topography area,and the complex site leads to the amplification effect of ground motion.Therefore,it is of great engineering significance to study the source characteristics and complex site effects(river valleys,basins,mountains,coastal soft soil sites,etc.)to provide accurate seismic input for seismic design of structures under complex site conditions.In this paper,the seismic wave scattering in three-dimensional single-phase and saturated layered half space,and seismic wave scattering in layered half space with complex terrain are studied.The main research work and innovative achievements are as follows:(1)A new indirect boundary integral equation method(IBIEM)for seismic wave scattering in three-dimensional single-phase layered half space is established.The free field of three-dimensional single-phase layered half space is solved;A uniform load is applied to the equivalent circular element on the surface of the scatterer to construct the scattered wave field,and the dynamic Green's function of concentrated load is used to solve the far field;After verifying the correctness of the method,the complex scattering characteristics determined by the resonance characteristics of layered media in layered half space are revealed.The results show that,the dynamic characteristics of overburden have great influence on the scattering effect of local topography in layered media.In the first two order resonance model of soft overburden,the displacement can be magnified by nearly one time.(2)A new indirect boundary integral equation method for seismic wave scattering in three-dimensional saturated layered half space is established.The free field in three-dimensional saturated layered half space is solved;Based on Biot theory,the dynamic Green's function of inclined circular load on saturated layered half space is derived,and the dynamic Green's function of saturated concentrated load is used to solve the far field;After verifying the correctness of the method,the law of seismic wave scattering by depression terrain in saturated layered half space is revealed.The results show that with the increase of the porosity of the overlying soil,the displacement amplitude can be enlarged by 1?6 times.The peak horizontal amplitude of the vertical incident SV wave can reach 7.5 at the corner of the depression.(3)A finite element-indirect boundary integral equation coupling method for seismic wave scattering in layered half space with complex sites is developed.Based on the new indirect boundary integral equation method for three-dimensional layered half space,the finite element method is further used to deal with the local complex site,the wave state of near-field complex site and far-field layered infinite domain is accurately simulated.After verifying the correctness of the method,the scattering characteristics of seismic wave in layered half space with local complex terrain are clarified.The results show that,in the complex shape basin,the seismic wave has more focus areas,and the displacement focusing and amplification effect is more obvious in the deeper side of the basin.in the layered site,the position shift of the narrow and long shaped sedimentary basin can be magnified by 1.5 times.