Numerical Simulation On The Liquefaction Triggered By Impact And Vibration Of Yigong Rock Avalanche

The research on the properties of soil liquefaction at home and abroad is mainly focused on the behavior of sand and silt under earthquake; in recent years, especially after Wenchuan earthquake, observation on sand and gravel liquefaction are increased significantly; but for the studies of feature of liquefaction and its mechanism on sand and gravel with wide graded grain formed by the landslide with high speed and long distance are rare.Based on the liquefaction observed at the scene of the Yigong rock avalanche, and the shock vibration may caused by it, We have carried out a qualitative research on the characteristics of avalanche mass under impact and vibration load by applying the FLAC3D. The researches in this paper can be drawn below.(1) This paper has studied the impact of the law of development of pore pressure, strain, and the deformation under shock and vibration load. We found that the gravel soil would liquefy under horizontal and vertical load actually. But it would not liquefy under earthquake of magnitude3.5at the similar energy according to the existing criterion. So, this phenomenon illustrates well that for the the gravel soil, its liquefaction can be caused easily under the shock vibration load than only under the seismic load.(2) By comparing and analyzing the pore pressure criterion and the strain criterion we have found that the strain variation is1%in this article, and it is less than the criterion of2%suggested by Ishhihara. So this result shows that the strain criterion is non-unique and it depends on the particular case.(3) During the dynamic process of12seconds, liquefaction developed from the surface to the depths gradually, the maximum influence depth scope is20m-25m, the development process as follows:the initial liquefaction developed among7.5m at1s, there is little changes of liquefaction depth but the pore pressure accumulated gradually at2s; When the time is3s-4s, the depth of liquefaction is10m～12.5m; And the depth is about12.5m when the time is5s;12.5-15m when6s;15～20m when7s1;20m when8-9s;20-25m when10-11s; So the development of liquefaction depth can reflect the accumulation effect of the pore pressure.(4)Based on the research of the model parameters and find the upper dynamic load is more likely to cause liquefaction of gravel soil, at a certain value range, the greater the modulus, the greater the density, the greater the angle of internal friction, the more of standard penetration number, the less easily liquefied of soil; the reverse is also true. Cohesive force influences the pore pressure notably, and influences on the depth of liquefaction less. Mean the while, parameters change following a rule, namely at the elastic stage, there is a linear similarity and relation between deformation, pore pressure, effective stress and cohesive force; it is relatively more complex at the elastic-plastic stage, because deformation, pore pressure, effective stress changes irregularly at this time.