The Stability Analysis Of Thick Accumulation Slope In The Three Gorges Reservoir Area Under The Action Of Frequent Microseism

The accumulation slope has loose structures and low safety coefficient. And it is also characterized by its wide distribution, large scale, high unexpectedness and serious perniciousness. The previous studies mainly focused on the landslide which is in the critical instability state and high seismic intensity situation. While, little attention has been paid to the impact of the frequent microseism on the long-term stability of the accumulation slope. In this paper, a thick accumulation landslide in the Three Gorges Reservoir was taken as an example. Through data summary, theoretical analysis and numerical simulation and so on, the deformation mechanisms and the dynamic response feature of accumulation body have been studied after the action of three consecutive Ⅳ and Ⅴ degree earthquake, and the corresponding dynamic safety factor has been calculated. Then these evaluation indexes were used to analysis the long-term stability of thick accumulation body under the action of frequent microseism. The main research contents and results are following:①The dynamic calculation principles and analysis methods of FLAC3 D dynamic analysis have been introduced. What’s more, the setting of the boundary conditions, the input of the dynamic time history and other issues during the establishing of numerical models have been discussed.②By contrasting the distribution law of the thick accumulation’s displacement and velocity amplification factor under different conditions, the impact of seismic wave parameters and slope characteristics on the dynamic response when the accumulation slope is under the action of the frequent microseism were analyzed. The results show that: with the increase of the seismic wave frequency, the maximum value of the accumulation slope shoulder dynamic magnification factor would increase and then decrease; the impact of the slope angle on the dynamic response is closely related to the slope height: the higher the height, the more significant the impact.③By analyzing the deformation mechanisms and dynamic response features of the thick accumulation body under the action of three consecutive Ⅳ and Ⅴ degree earthquake, the paper revealed the frequent microseism’s effects on the accumulation body’s long-term stability. The results show that: the accumulation is relatively stable after the action of three frequency Ⅳ degree earthquake, and it still can keep stability as a whole after three frequency Ⅴ degree earthquake, but the instability damage in the slope shoulder region may have occurred.④With the help of strength reduction method and dynamic time analysis method, the paper got the dynamic safety factor after the action of three frequency Ⅳ and Ⅴ degree earthquake, and then through different dynamic safety factor indicators to evaluate the thick accumulation body’s long-term stability under the action of frequent microseism. The results show that: the Ⅳ degree earthquake’s impact on the stability of the accumulation is smaller, and its dynamic safety factor is greater than 1.1; while the dynamic safety factor had appeared briefly to be less than 1 sometimes during the action of three frequency Ⅴ degree earthquake, but the accumulation is still in a relatively stable state as a whole, which indicates that it does not necessarily lead to an overall damage of the whole slope while the slope is entering the instantaneous instability state, but the instability damage in the partial area of the accumulation may occurred in the process of frequency Ⅴ degree earthquake.