For evaluation of the effective rainfall considering the slope factors, uni-factor such as hourly rainfall, continuous rainfall or efficient rainfall is examined as the criterion to judge possibility of slope failure in 1975, and combination of two-factors were also used for that same possibility second year 1996, and following results are obtained.
(1) (Slope factor model) By means of applying Logit model to slope failure, resistance potential of slope against failure can be expressed as a criterion containing the slope conditions like angle, existence of countermeasure and constituent soils of slope, etc.
(2) (Rainfall factor model) The probability of slope failure expressed by logit model using the ratio of resistance potential to rainfall factor (each of above three kinds of rainfall) is fairly effective to judge the possibility of slope failure.
(3) The index of judging rainfall factors (combination of hourly rainfall and efficient rainfall) is best way to discriminate whether or not slope fails. To realize this, the graph with the abcissa, hourly rainfall intensity, and the ordinate, efficient rainfall, is drawn, in which we get a boundary line (LM-line) to judge whether or not slope fails.
(4) The characteristics of LM-line (slope and cutting ordinate) represents a magnitude of above resistance potential. It becomes clear that for the slope of very strong resistance, efficient raifall is greater effect on the stability than hourly rainfall, and for the slope of weak one, hourly rainfall have greater effect than efficient rainfall.
Accordingly, the criterion that discreminates between stable slope from dangerous one, is expressed by the slope factor model, rainfall factor model and combination of hourly/efficient rainfall.