A Research On The Seismic Response Behavior Of The Xigeda Strata In Xichang

Earthquakes are a common burst geological phenomenon. Strong ground motion which earthquake induced, in particular the Xichang region with a number of major active faults, is capable of causing damages to buildings. By the influence of active faults, coupling with the Xigeda stratum in this region has different physical-mechanical characteristics from other quaternary strata, leading to stability of crust is poor in this region, Therefore, it is extremely important to study dynamic response of the Xigeda stratum at region of Xichang.Researches on site amplification of earthquake mainly includes platform elevation, slope step-slope grade and restraint effect of acceleration amplification by cut-fill, because structures located in mountainous area often put the base on the platforms with variable elevations. This thesis which backing on physical-mechanical characteristics in Xigeda stratum, studied site dynamic characteristics of the Xigeda stratum by stress wave propagation theory in solid medium, MTS shaking table test, and finite element numerical simulation. The tasks done are follows:(1) Seismic wave reflected and Superposed when propagating to the two medium interface and inducing ground motion amplification, it is obtained based on analyzing spatial distributing characteristics of site acceleration response by stress wave propagation theory in solid medium and restriction mechanism. The bigger difference of Poisson ratio between two medium, the greater amplification effect. Energy conversion was related to incident angle and poisson's ratio while incident wave was P or SV. Particle displacement in free-interface is twice as much as inner at normal incidence. But whatever incident angle is, particle displacement in free-interface is twice the incident wave while it was SH wave.(2) Using MTS shaking table test, seismic response difference between different step-slope strutures, different spectrum characteristics and two input standard strength (0.25g and 0.5g) was simulated. And restriction mechanism of dynamic response in the Xigeda stratum was studied by finite element numerical simulation. The results show that as two platforms with specific height difference, the more slope units, the decreaser acceleration amplification level in the top platform, the greater input earthquake intensity, the increaser ground peak acceleration, but the smaller the magnification factor, as the same input eathquake intensity and spectrum characteristics, the greater the elevation platform, the more strongly surface ground motion on the top platform, seismic response in embankment section is larger than excavation section.Therefore, slope with multi-platforms should adopt structure of slope unit form accord- ing to platforms'height and try to avoid using vertical retaining-wall. The rules to be followed is "more excavation and less embankment".