ON GENERATION OF VIBRATION FAILURES OF SLIDING PLANES OF ROCK SLIDES IN A MEIZOSEISMAL AREA AND ASSESSMENT OF SLOPE STABILITY

Wenchuan Earthquake of Ms8.0 showed that the most severe geological hazards occurred in the meisoseismal area,demonstrated by higher density,larger scales and greater distribution of rock slides than those adjacent areas.Therefore,characteristics of seismic waves,geological structures of rock masses,and mechanical strength over the plane of weakness should be considered in stability assessment of rock slopes and prediction of rock slides in a meisoseismal area.The author assessed existing methods and concluded that these methods may not produce realistic predictions because they only took into account of effects of the horizontal acceleration of seismic waves.Based on structural mechanics of rock masses and analysis of rock strength,the author hypothesized that the slides in a meisoseismal area can be caused by tensile,shear failures,or a combination of them along a plane of weakness.In consideration of a large angle of incidence hitting land surface in a meisoseismal area,one should apply combined effects of seismic force vectors in assessment of slope stability as well as effects of P and S waves.In this paper,two common types of simple geological models were used,namely a single plane of weakness and dual planes of weakness.Five types of failure patterns were defined under the specified critical failure acceleration based on limited equilibrium principles.The critical failure acceleration can be obtained by inputting the angle of incidence of the earthquake wave,geometry for the plane of weakness and its mechanical properties.It can then be compared with the directional acceleration rate converted from the real earthquake acceleration vector to determine failure types for generation of sliding planes and assessment of slope stability.It should be emphasized that detail engineering geological investigation is fundamental for this presented method to achieve better results.