Abstract:

Firstly, influence of only horizontal or vertical earthquake loading on slope seismic safety factor is examined using stress integration along sliding surface and the dynamic FEM time-history analysis method. It is shown that under most conditions the vertical ground motion has the same significant effect on slope stability as the horizontal earthquake motion. Then, the effects of the time combination pattern of horizontal and vertical accelerograms on the dynamic safety factor are considered. It is concluded from the analysis results that the pattern with peak acceleration values meeting in time domain and the random time combination pattern may lead to over estimation of safety factors because of not giving the most significant superimposing effect for the vertical earthquake loading and the pattern with maximum action effects meeting in time domain is the severest pattern which allows for the minimum value of safety factor to be obtained. Due to the largely unknown behavior and random nature of earthquakes, the possibility for the pattern with maximum action effects meeting in time domain should be considered for slope under multiple-dimensional earthquake action to get the more conservative safety factor for the engineering design.

Key words: earthquake, slope stability, vertical ground motion, time combination pattern, stress integration method, time-history analysis, dynamic safety factor