Many slope failures have been taken place in Korea during rainy season. Rainfall as one of the most significant factor related to the landslides which cause a considerable damage to society. The rainfall-induced landslides in Korea are generally shallow and are triggered by decrease in matric suction of slope materials during rainfall. Unsaturated geotechnical properties and other factors(rainfall characteristic, geomorphology, etc) have to be considered in order to evaluate the stability of real slope. Even though antecedent rainfall is also an important factor on the slope stability, Therefore, in this study, the case of slope failure is a major cause of rainfall Pattern were analyzed and Effect of antecedent rainfall was considered in analysis by using initial matric suction, Effects of antecedent rainfall on variation of factor of safety(FS) of slope, failure time and cumulative rainfall were evaluated.
To determine the relationship between rainfall and landslides, we proposed landslide-triggering rainfall threshold consisted of rainfall intensity-duration(I-D). For this study, the landslide database was prepared using data from NDMI(National Disaster Management Institute), various report and newspaper. And most of the required rainfall data were collected from KMA(Korea Meteorological Administration). Some 114 landslides occuring from 1999 to 2011 were studied to analyze rainfall threshold from granite soil. The threshold relationship fitted to the minimum level of the field defined by landslide-triggering rainfall event is I=19.38D-0.45(I=rainfall intensity in mm/hr and D=duration in hours). Also, the rol of antecedent rainfall in causing landlsides was proposed by considering initia matric suction.
The Reliable Slope stability analysis and landslide-triggering rainfall thresholds maybe most appopriately used in landslide early warning systems in Korea.