Probabilistic density of safety factor is basic for calculating slope reliability index and failure probability. Some studies of variability and probabilistic density of parameters

for instance

cohesion

coefficient of friction

unit weight

have been done; these parameters have great influence upon stability of slope; but the present studies of variability and probabilistic density of safety factor have not been done. As an example

safety of Shizibao slope in Badong County of the Three Gorges Reservoir Areas was assessed. In this example

we suppose that parameters c and ? obey normal distribution; the results computed by Monte Carlo simulative method show that safety factor obey normal distribution

probabilistic density of safety factor was quantificationally tested by Q-Q plotting analysis further. Based on normal distribution

average safety factor and risk of Shizibao slope were obtained.