EARTHQUAKE-INDUCED TOPPLING FAILURE MECHANISM AND ITS EVALUATION METHOD OF SLOPE IN DISCONTINUOUS ROCK MASS

Abstract

The seismic behavior of rock slopes accompanied with discontinuity is heavily governed by the geometrical distribution and mechanical properties of discontinuity. Especially, high and steep rock slopes, which are dominated by sub-vertical discontinuity, are likely to collapse due to toppling failure and it causes serious damage to structures surrounding the slopes. Ten thousands of landslides, collapses and other geological disasters occurred in the Wenchuan Ms 8.0 great earthquake on May 12, 2008 in Sichuan province of central China. The field survey during the disaster investigations indicated that it shows the tensile failure close to the top of slop and the shear failure below it. However, it is difficult to assess quantitatively toppling failure potential. In order to clarify mechanism of toppling failure in rock slopes and evaluation on seismic stability, 2D joint elements around each rock column is proposed to simulate the discontinuity of rock slope, which is different from Goodman joint and composed with normal spring Knand shear spring Kswithout volume. By a nonlinear numerical FEM analysis, the dynamic response of the rock slopes could demonstrate the landslide mechanism. Coupled with the effect of amplification on the toppling, the seismic horizontal acceleration at the top of slopes is often large, and then coursed inertia force would far exceed the tensile strength of rock mass. Eventually, the opening and sliding of joint elements occurs on the slope are identified based on the nonlinear characteristics of the joint elements. The result shows that a toppling failure could have occurred on the slope and the sliding plane also could be observed, which shows agreement with the existing investigation flexural toppling failure during the Wenchuan great earthquake.