In order to reveal the relationship between failure modes and slope structures, the field investigation aftershock in Wenchuan area was conducted, especially for the dynamic instability of steep slopes. This study takes two typical slope failure sites, namely, Dazhuping landslide at Gaochuan county and Ganmofang landslide at an county in Sichuan province as the example, by considering the landslide related engineering geological condition and dynamic deformation characteristic, a three-dimensional discrete element numerical simulation on instability mechanism of the two slopes was conducted. The results showed that the mode of hard rock steep bedding slope destruction was a slippage type, while the failure of interbedded steep bedding slope was by a sliding bending. Under the same earthquake,PGAamplification coefficient and the slope height was positively correlated, andPGAamplification coefficient turned a first increasing and then decreasing phenomenon with the increase of elevation. ThePGAamplification coefficient of steep bedding hard rock slope was smaller than that of steep bedding interbed slopes. While the amplification coefficient in hard rock slopePGAranges from 2 to 3, the maximum was in 3/4 of slope surface. ThePGAamplification coefficient of interbedded slope ranges from 2.5 to 4.0, with the maximum value located at the top of the slope. In addition, the damage mechanism of hard rock bedding slope could be divided into four stages:the first stage was a slip partly through the locking section; the second stage was shock relaxation; the third stage was the ejection phase; and the fourth stage was a overall instability. For the interbed slope, the first stage was a layer dislocation, the second stage was local lower ejection, the third stage was a continuous crack spreading in the high location, and the fourth stage was a bottom bending failure. The research results can provide technical support for the instability evaluation and mechanism analysis of high steep bedding rock slope in Southwest China.
