Spatial Analysis of Safety Factors due to Rain Infiltration in the Buyan-Beratan Ancient Mountains

Abstract

Sukasada and Sawan Subdistricts are areas in Buleleng Regency that are often hit by landslides due to their geological conditions, since they are composed of weathered volcanic rocks, consisting of intersections with faults and rock joints. A rainfall model analysis is carried out in order to determine the probability of precipitation, while WindRose is used to analyze the duration of the dominant rainfall. Furthermore, SoilVision is used to determine the grain size distribution. Meanwhile, the equations proposed by van Genuchten and Fredlund and Xing are used to estimate the Soil-Water Characteristic Curve (SWCC). The Green-Ampt model is also used to calculate infiltration capacity. Slope stability is analyzed using an infinite slope model in order to produce a spatial-temporal prediction map of slope stability in the form of safety factor (SF). The results of the hydrology analysis reveal that rain with an intensity of 87.32-92.27 mm/day, a duration of 6-7 days, and types of soil in each study location in Sukasada and Sawan Subdistricts affects the amount of infiltration and it, in turn, affects slope stability. Extrapolation results for the spatial-temporal map of landslide hazard reveal the classification of safety factor as follows, SF > 2.13 (low/stable), 1.40 < SF < 2.12 (moderate/critical) and SF < 1.39 (high/landslide).