Seismic stability analysis of rock slopes using the numerical manifold method

Seismic stability of rock slopes is numerically investigated using the numerical manifold method (NMM). Instability mechanisms of rock slopes under horizontal and vertical ground accelerations are revealed, respectively. A block resting on an inclined slope moves when the total destabilizing force exceeds the total resisting force. Horizontal ground acceleration enlarges the destabilizing force, which makes the originally moving block (i.e., phi < alpha) move faster and produces the originally stable block (i.e., phi > alpha) a finite displacement. When a vertical ground acceleration is introduced, the friction angle along the interface may be significantly reduced or even disappear, which is known as the ultra low friction phenomenon. Because of this phenomenon, the vertical ground acceleration reduces the resisting force, which makes the originally stable block unstable. Its effect depends on the frequency and amplitude of the vertical ground acceleration. The validity of the NMM in predicting the ground acceleration induced permanent displacement has been verified by comparing its results with the analytical solutions and the Newmark-beta numerical integration solutions. Furthermore, the proper values of control parameters for NMM calculations are suggested.