THE ANALYSIS OF RAINFALL EFFECT ON SLOPE STABILITY SPILLWAY OF TUGU DAM, TRENGGALEK REGENCY, EAST JAVA

• Main Author: Dewi Mulyani, Kurnia
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/53741
• Institution: Institut Teknologi Bandung

Landslides accompanied by rainfall and occurred during rainy season are common phenomenon in Indonesia. At the area where Tugu Dam was built, there was shallow landslides during rainy season. Rainfall is considered as a factor that can raise pore water pressure and increase ground water level. Understanding rainfall as a triggering factor for landslide is important for disaster mitigation in the future. Two-dimensional modeling with the finite element methods and limit equilibrium was carried out to know landslides mechanism which is triggered by rainfall and to know how the role of other factors such as earthquakes and tension crack in landslides. Drilling data, physical properties, mechanical properties, daily rainfall data, hydrogeological conditions, and earthquake data were used for analysis. The landslides that occurred at the research location has a rotational shape of slip surface. Landslide material consists of soil and rock mixture originating from volcanic rock weathering. The research area is located in the Mandalika Formation which is composed of volcanic breccias, lahars, tuffs, sandstone, and claystones of the late Oligocene-early Miocene age. The subsurface condition results show that there is highly weathered tuff breccias act as slip surface. The results of geological subsurface at spillway are andesite-basaltic lava, medium weathered of tuff breccia and highly weathered of tuff breccia. Shallow landslides occur after rainy days which cause the increase of pore water pressure. The process of landslides began by taking into account tensile fractures. The results of the analysis show that rainfall drastically affected decreased matric suction and caused tensile fractures. Modeling with two simulations are the effect of preliminary rain with a duration of 47 days and the effect of rain with a duration of 10 days with the same initial conditions. The result of preliminary rainfall for 47 days has significant affect the landslide event if compared to the preliminary rainfall for 10 days. Landslide in study area were influenced by pore water pressure and earthquake, therefore resulting safety factor of 0.986. Rainfall threshold for weather forecast that can cause landslides is determined using the cumulative rainfall of 3 days before landslides and 15 days before 3 days 120.4 mm / day and 40 mm / day.