Precise Artificial Boundary Conditions And One-dimensional Time Domain Algorithm For Saturated Foundation Site

With the rapid development of China's economy,more and more large-scale large-span structures are constantly being built.In past seismic design,seismic waves are often considered as normal incidence.In fact,seismic waves start from a wave source and go through a complex propagation path.The surface is often obliquely incident.The oblique motion of seismic waves has a great difference between the ground motion response and the vertical incidence of large large-span structures.Simplifying the problem to one-dimensional is obviously a bit rough.In addition,in the current research,the soil of the engineering site is often regarded as a single-phase medium,and many soils in nature are saturated soil,composed of solid-liquid two-phase medium.Studies have shown that the effect of liquid phase on the dynamic response of soil cannot be ignored.Therefore,it is necessary to study the seismic response of saturated ground sites under oblique incidence of seismic waves.In this paper,aiming at establishing a one-dimensional time domain algorithm for layered saturated ground sites,the following work has been carried out:1.Propose an exact artificial boundary condition for a saturated foundation site.The stress-displacement relationship between the scattering soil field and the medium-soil skeleton and the relative displacement term of the transmitted wave field is established respectively.Finally,the stress-displacement relationship of the whole wave field is obtained by superposition,and the incident wave transmission and the scattering wave absorption are realized.2.Based on the Biot wave equation of u-w format,combined with the proposed artificial artificial boundary conditions,a one-dimensional time domain finite element method for layered saturated ground in u-w format is established.The effectiveness of the proposed algorithm is verified by three simple examples.The results of the one-dimensional time domain algorithm proposed in this paper are compared with the analytical results.3.The finite element algorithm proposed in this paper is used to analyze the influence of groundwater level change on the ground motion response,and the variation law of surface displacement time history,acceleration time history and surface displacement amplification coefficient under different groundwater level conditions is analyzed.The following conclusions:i)Under the oblique incident condition of P wave,the influence of groundwater level change on vertical displacement and acceleration is much larger than horizontal direction.As the groundwater level decreases,the vertical displacement of the surface gradually increases,while the vertical acceleration shows a trend of increasing first and then decreasing.ii)The distribution of vertical and horizontal stress peaks at various points below the surface of the groundwater under different buried water depth conditions is basically the same.The peaks of horizontal and vertical normal stress decreased in a certain range below the groundwater level,and the stress peaks in other positions showed an increasing trend,and rapidly increased to the highest value near the incident surface of the P wave.