THE EFFECT OF INCREASED RAINFALL ON SLOPE STABILITY USING TRIGRS MODEL IN WEST BANDUNG AND SURROUNDING AREA, WEST JAVA

• Main Author: SUGIANTI, KHORI
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/60993
• Institution: Institut Teknologi Bandung

Landslides are common geological disasters in Indonesia during the rainy season. Rainfall is one of the triggering factors for landslides. Rainfall infiltration can increase soil saturation which will increase pore water pressure. It can disturb slope stability. The problems not only topography but also soil shear strength parameters and rainfall intensity affecting the slope stability on landslides. Knowledge of soil mechanic characteristics and rainfall characteristics triggering landslide are required to decide mitigation efforts and to reduce the landslide hazard risk in the future. West Java Province has the potential for high susceptibility levels of landslides. West Bandung is one of the areas in West Java that has a landslide hazard problem. The research area is in West Bandung and its surroundings, West Java Province. The TRIGRS (Transient Rainfall Infiltration Grid-based Regional Stability) model is a model developed to predict shallow landslides triggered by rainfall infiltration. There are three purpose of this research. First, evaluate the parameters that affect the stability of the slope in the research area using the TRIGRS model. Second, determine the rainfall characteristics that affect the slope stability in the research area in the future using the TRIGRS model. Third, evaluate the modeling results of slope stability for landslides is spatially triggered by the rainfall intensity influence in West Bandung and its surroundings, West Java Province. This study applies a deterministic analysis method using the TRIGRS model to calculate the safety factor in slope stability analysis modeling triggered by rainfall infiltration. Parameters used include Digital Elevation Model (DEM), flow direction, slope, bulk density (?), effective cohesion (c’), effective internal shear angle (?’), permeability (Ks), groundwater level, the soil thickness and rainfall intensity. TRIGRS modeling uses maximum daily rainfall data with a range of 35 years from 1986 until 2020. Statistical analysis of rainfall data use the distribution of Gumbel method to obtain the planned rainfall value as input for model parameters. Modeling uses two scenarios. First is to use a 10-year return period high rainfall intensity of 11,65 mm/s with short duration for 6 hours (situation I) in scenario A and second is to use low rainfall intensity of 7,34 mm/s with long duration for 12 hours (situation II) in scenario B. Based on the modeling results, the increase of rainfall intensity can affect slope stability, where the stable slope changes to an unstable condition and the decrease of the safety factor (SF) value makes the slope more vulnerable to landslides. The stability of slopes in West Bandung and surrounding areas is influenced by the lower soil shear strength parameter characteristics of volcanic rock units and geological structures lineament density in the reseacrh area. Other factors include hilly morphology, steep slopes, weathered volcanic rocks, and lower soil shear strength parameters. The character of rainfall intensity that affects the decrease in slope stability is low (rainfall intensity and long duration (situation II). Types and materials of landslides in the study area are rock or soil slide, debris slide, rock or soil fall, and soil flow. The classification of performance evaluation with the TRIGRS model is quite good in slope stability modeling and landslide occurrence inventory data are factors that influence the model validation.