Research On Nonlinear Seismic Response Of Two-Dimensional Basins With Soft Soil Layer And Sub-basins

Sedimentary basins have significant amplifying effect on ground motions.Many cities in China,such as Beijing,Chengdu,and Xi'an,are located in sedimentary basins or on the edge of the basin.Therefore,studying the basin effect under earthquake is of great significance to the urban planning,earthquake prevention and disaster reduction of these cities.The geological conditions of real basins are complex,often containing soft soil layers,sub-basins and other geological structures.In this paper,a two-dimensional finite element model of a sedimentary basin with soft soil layer and sub-basin is established by numerical simulation,and the amplification effect of the model under earthquake is studied.The main research contents and conclusions are as follows:(1)The influence of soil nonlinearity on the seismic response of the basin was studied.Considering the non-linearity increases the hysteretic energy consumption of soil,the seismic response obtained is smaller than the linear elastic response,and the gap between them increases with the increase of input ground motion intensity.(2)The influence of the thickness and burial depth of the soft soil layer on the basin amplification effect was studied.With the increase of the thickness of the soft soil layer,the propagation velocity of secondary surface wave decreases and the duration increases.In general,the soft superficial soils enhanced the amplification effect of the basin.When the thickness of the soft superficial soils is 12 m,the PGA at the edge of the basin reached the maximum value.As the thickness of the soft interlayer increases,the PGA of the edge and central region of the basin first increases and then decreases.When the thickness of the soft interlayer is 10 m,the PGA of the central region reaches the maximum,and the thickness of the edge region is 8m.As the burial depth of the soft interlayer increases,the PGA of the basin edge and central region generally decreases.The existence of weak interlayer in sedimentary basin weakens the larger seismic response and amplifies the smaller seismic response.The marginal area of sedimentary basin is sensitive to high frequency components.(3)The effects of the size,location,medium wave velocity of the sub-basin and dip angle of the sedimentary basin on the seismic response of the basin were analyzed.The sub-basin has obvious focusing effect,the size of the sub-basin increases,the amplitude of fluctuation in the sub-basin becomes larger and the duration of fluctuation extends.The closer the sub-basin is to the center of the basin,the larger the PGA amplitude in it,and it reaches the maximum when it reaches the center of the basin.The larger the difference of wave velocity between the subbasin and the surrounding soil,the more obvious the focusing effect of the subbasin.As the dip angle of the basin increases,the amplitude of wave field fluctuation in the sub-basin decreases,and the PGA amplitude in the central region of the sedimentary basin also decreases.(4)The seismic responses of two-dimensional sedimentary basins under non-uniform input and uniform input were compared and analyzed.In general,the acceleration time-history waveforms of non-consistent input and consistent input are very similar,and there is no obvious difference,only a slight difference at the peak value.In terms of Fourier amplitude spectrum,there is a significant difference between the two at the fundamental frequency,and the corresponding amplitude of the high frequency component is almost the same.