Study On Dynamic Response And Stability Of Large Loess Landslides Under The Action Of Near And Far Earthquakes

The earthquake structure in the Northwest Loess Plateau and its surroundings is well developed,historical strong earthquakes occur frequently,the nature of rock and soil engineering is poor,and the distribution of densely populated areas and facilities is scattered.The disaster effect of the earthquake loess landslide is very serious.According to the national earthquake risk zoning statistics,the area of?and above intensities on the Loess Plateau accounts for about64%;since the new century,many national-level city clusters have been planned in the Loess Plateau.The risk of disaster is also bound to increase,so the study of the formation mechanism of earthquake loess landslide is of great significance to disaster prevention and risk prevention and control.The thesis takes the landslide of Liping Village,Wushan County,Tianshui earthquake area as an example,according to the combination of field mapping and engineering survey,in-situ and indoor testing,dynamic response and stability analysis;the sample is combined with the slope body dynamics research and experiment Combined with numerical simulation,the research work on dynamic response and stability of large loess landslides under the action of near and far earthquakes has been carried out.The following points of preliminary understanding:Based on the geological disaster investigation and the previous data,this paper summarized the regional seismic geological background in tianshui region,the landslide development characteristics in liping village,wushan county,and the geotechnical mass dynamics characteristics,as well as the numerical simulation to study the slope dynamic response and stability evaluation under the near-earthquake and far-earthquake conditions,and finally reached the following conclusions:1)The analysis revealed the morphological structure and seismic deformation characteristics of the Liping Village landslide.The loess-mudstone landslide in Liping Village is located in the fault zone of the northern margin of the West Qinling Mountains,the transition zone between the northern margin of the Qinling Mountains and the loess hilly landforms,and in the secondary branch ditch on the right bank of the Weihe River;The landslide is characterized by the development characteristics of hard and soft under the stratum,multi-level and rotary translational sliding of deep sliding body.The 2008 Wenchuan Earthquake caused the main sliding body to slip,and the sliding form showed a pull-shear slip mode.However,during the 2013 Minxian earthquake,although there was a sense of earthquake,only small cracks appeared on the trailing edge,and a small amount was seen on the front edge of the slope body.Loess slippage phenomenon,the main sliding body has no obvious signs of sliding.2)the basic dynamic characteristics of loess and mudstone were revealed,and the hyperbolic constitutive model of mudstone was verified.Considering the influence of confining pressure,water content and frequency on the model parameters,two mathematical models of power law increase and exponential decay were proposed.The measured mudstone dynamic data conforms to the dynamic constitutive hyperbolic model:~?d=?_d(a+b?_d),and the correlation coefficients are all above 0.9;the confining pressure has a good negative correlation with the parameter a;the frequency has different effects on the parameters a and b,this time The statistical analysis of the test data shows that the value of parameter a decreases first and then increases,and the value of b increases first and then decreases;the effect of moisture content on parameter b is stronger than that on parameter a;the trend of dynamic shear modulus change is consistent with the exponential decay model,damping The ratio change trend conforms to the power law increasing function model,and the correlation coefficients between them and the influencing factors are all greater than 0.9,and the correlation degree is better.3)The simulation reveals the dynamic response characteristics of landslide under the action of near-far earthquake.The near and far seismic action is characterized by the amplitude,frequency and duration of the earthquake,which can be used to analyze the characteristics of its influence on the dynamic response of landslides.GDEM numerical simulation is used to reveal the standard sine wave response characteristics of the landslide under different working conditions,the results showed that under different ground motion element analysis,found that more than 0.75times that of the high slope,monitoring PGA basic decreases with the increase of amplitude magnification coefficient,when less than 0.75 times of the high slope monitoring PGA basic increases with increasing amplitude magnification coefficient;The PGA amplification coefficient of monitoring point decreases with the increase of frequency.Time-holding has significant effect on the maximum displacement of slope.The slope body has the surface effect and high efficiency response to the input vibration wave.Different geotechnical layers can selectively amplify seismic waves in a certain frequency range.Combined with the field pulsation test,the data processing results show that the overburden thickness of the slope reaches 5-50m.The predominant frequency range of the site is about 0.2~2Hz.4)The deformation mechanism of the Liping Village landslide under the two phases of Wenchuan earthquake and Minxian earthquake was discussed,and a dynamic stability analysis was carried out.Under the effect of the weight of the slope body(static conditions),according to the safety factor of the landslide and the site survey results,the landslide body remained basically stable.Comparing the effects of Wenchuan earthquake and Minxian earthquake,the deformation characteristics of the slope body are inseparable from the seismic waves of relatively high amplitude,low frequency,and long duration.The influence of amplitude on slope instability is greater than that of frequency on slope instability The duration of impact on slope stability is relatively minimal.After testing under various working conditions,the critical amplitude of instability of this slope is about 0.05g and the critical frequency is about 5Hz.Comprehensive analysis shows that the current Lipingcun earthquake landslide is basically stable,but in case of strong earthquake conditions,especially in combination with rainfall conditions,it is very easy to cause another slip.