Analysis of Landslide Risk Distribution Pattern under Extreme Precipitation

Abstract

This study analyzed the landslide risk in Ulsan, Korea using infinite slope stability analysis considering rainfall infiltration in the soil layer. The parameters used in the analysis were obtained by geographic information system (GIS) and field survey using the following parameter values: a cohesion of 30.84 kPa, unit weight of 1.46 t/m3, specific gravity of 2.65, effective soil depth of 0.41 m, and internal friction of 27.15°. The rainfall intensity was set to last for 60 min at a 10-year frequency of 57.8 mm/h, 50-year frequency of 78.5 mm/h, 100-year frequency of 87.3 mm/h, and 500-year frequency of 107.5 mm/h. The minimum safety factor for the landslide risk was set at 1.3, according to the slope design criterion of construction slope announced by Korea's Ministry of Land, Infrastructure, and Transport. The safety factors with the values of 0-1.3 have been classified into four grades based on the saturation depth ratio varying with the rainfall intensity. The higher the rainfall intensity, the higher the percentage of the first grade (very dangerous) area. For verification, the landslide risk area proposed in this study was compared with the ‘Landslide Risk Map’ provided by Korea Forest Service. It is expected that high accuracy could be achieved in future by increasing the field survey data. Keywords: Infinite Slope Stability Analysis, Rainfall Infiltration, Landslide, Wetting Front