Slope collapse along railways sometimes occurs under heavy rainfall caused by typhoons etc. and influences operation of the trains. The practical damage estimation method, which accurately predicts the hazard of slope collapse and can be used easily by railway workers, is a desirable development goal. Therefore, slope risk estimation methods in terms of critical rainfall have been proposed by authors. This paper deals with applicable range of the proposed method, citing various embankment collapse. Furthermore, the significance of critical rainfall is made clear theoretically from a statistical point of view.