| Wenchuan Ms 8.0 great earthquake, which occurred in Sichuan Province on May 12, 2008 was the most destructive, widespread and serious geological hazards induced since the founding of People’s Republic of China. The earthquake shocked the whole nation and attracted the attention of the whole world. In Hanyuan County which is about 250 km away from epicenter and located on the front of Beihoushan landslide, two degrees higher intensity anomaly appeared. Such high intensity anomaly attracts great attentions of scholars and the government. In order to reasonably explain whether Hanyuan county’s abnormal intensity associated with Beihoushan landslide and further explore the problems about the stability of slope and dynamic response, this thesis carried out a series of researches related to earthquakes. The researches in this thesis are of great theoretical significance and engineering application value in promoting the research work in this field.In this thesis, the research progress of slope stability have been summarized and commented. Moreover, the engineering geological conditions of Beihoushan landslide have been surveyed detailedly and scientific investigation data during Wenchuan earthquake have been sorted out and analyzed. Based on these, finite element method is applied to calculate and analyze resonance characteristics, static and dynamic stability and dynamic response of Beihoushan landslide and some valuable conclusions are obtained. The main research results are as follows.(1) Damage investigation and scientific investigation have been carried out. After Wenchuan great earthquake, under the united command, Institute of Disaster Prevention has undertaken the scientific investigation work in Hanyuan and Beichuan county and the field investigation has been carried out into Beihoushan landslide in Hanyuan County. In the meantime the detailed data of topography, stratum and geological structure has been obtained, the presence of ancient landslide on Beihoushan has been revealed, the boundary of ancient landslide has been delineated and its activity period, characteristics and current stability have been ascertained. The results showed that Hanyuan old county is situated on the front of Beihoushan ancient landslide and there is not a sign of the ancient landslide revived discovered, just some tension cracks appeared on the back of the slope.(2)The geological model, the mechanical model and the finite element calculation model of Beihoushan landslide have been established. The typical geological section is selected, the geological model, the mechanical model and the calculation model of the landslide are established and the calculational scheme is drawn up. Furthermore, four calculational methods of factor of safety are proposed and the static stability of Beihoushan landslide is calculated and analyzed with the value of static safety factor 4.09. From the results of the static analysis with only gravity, Beihoushan landslide is stable, besides, the static results provide the initial static stress field for the seicmic stability analysis.(3)The resonance characteristics of Beihoushan landslide are analyzed. Through the modal analysis and harmonic response analysis of ANSYS finite element method, the landslide natural frequency and mode of vibration, and the relationship between displacement and frequency(resonance curve) are obtained. Compared with the seismic predominant periods recorded by the strong motion station near Hanyuan Counnty, it is found that the natural frequencies almost agree with it. According to the field investigation it is known that Hanyuan old county is located on the front of Beihoushan landslide. Therefore, it is considered that probably the resonance of the landslide results in the high intensity anomaly in Hanyuan old county during Wenchuan earthquake.(4)The seismic stability of Beihoushan landslide is calculated and analyzed. The quasi static method and the finite element dynamic time history method are both used to calculate the landslide factor of safety under earthquake, and the focus is the latter method which is used to calculate, analyze and evaluate in detail. Through the latter one, the factor of safety time history curve of Beihoushan landslide under earthquake is obtained and the minimum dynamic factor of safety value is 1.1. On this basis, it is judged that the landslide is stable as a whole. For the slope stability evaluation, this paper suggested that some respects can be considered to analyze the slope stability, which include whether the minimum factor of safety value is greater than 1, the end of velocity time history on key points is tending to zero and the displacement vector field and stress vector field at the end of the earthquake are tending to zero. In addition, if the slope is judged stable as a whole, the key parts like the slope shoulder and the slope toe were set to analyze the stress and vibration velocity effect for the local stability analysis. Besides, the safety factor values on key points were calculated. The results show that in Wenchuan earthquake Beihoushan ancient landslide hadn’t slid integrally and the intensity anomaly has nothing to do with the landslide failure, while there were some tensile cracks near the slope shoulder and the upper part, which is basically consistent with the actual survey phenomenon.(5)The dynamic response of Beihoushan landslide and the influence of three parameters of earthquake on the slope dynamic response are analyzed and discussed. In the specific calculation and analysis, 32 monitoring points are set on different parts of Beihoushan landslide in this thesis. The results of calculations show that the peak ground acceleration of dynamic response reaches more than 3 times compared to the input peak acceleration, namely the PGA amplification coefficient is above 3. Besides, the PGA amplification coefficients on the slope increase with the increase of slope altitude; the PGA amplification coefficients increased first and then decreased from left to right horizontally. The horizontal displacements of the slope increase with the increase of slope altitude; the horizontal displacements decrease gradually from left to right horizontally. Through the analysis of the influence of three parameters of earthquake on the slope dynamic response, it can be seen that the absolute values of dynamic responses on the acceleration and displacement linearly increase obviously with the increase of amplitude, while their amplification coefficients remain unchanged which are not affected by the amplitude, depending on geotechnical materials and spectrum characteristics. With the increase of the input seismic wave frequency, the PGA amplification coefficients of the slope decrease, and the peak displacements decrease with the increase of the input seismic wave frequency. The effect of duration on the peak acceleration response of the slope is not evident.In conclusion, in this thesis based on the investigation of the engineering geological conditions of Beihoushan ancient landslide, the geological model, the mechanical model and the calculation model have been established. And the research is feasible and effective which is on the static and dynamic stability analysis, the resonance characteristics analysis and the dynamic response analysis of Beihoushan landslide by using the finite element method. The results of this thesis indicate that Beihoushan landslide haven’t slid integrally in Wenchuan great earthquake, just there were some tensile cracks near the slope shoulder. The two degrees higher intensity anomaly in Hanyuan old county has nothing to do with the landslide overall stability, but associated with the resonance of the landslide. Moreover, the acceleration amplification effect on the slope surface is very obvious. In addition, it is suggested in this thesis that the variation trend of slope response, the position of the response maximum and the frequency segment of resonance response can be analyzed and used to avoid the problem of slope failure under earthquakes, the corresponding aseismatic measures are given meanwhile. |
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