BACK ANALYSIS OF SLOPE EMBANKMENT AT EAST BANKO-1 MINING AREA, MUARA ENIM DISTRICT, SOUTH SUMATERA

• Main Author: Fadhilah, Astrid
• Format: Theses
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/53502
• Institution: Institut Teknologi Bandung

PT. Bukit Asam, Tbk. is a mining company that applies good mining practices and implements a backfilling method of mining. Mining activities in the form of overburden stripping and coal excavation can disrupt the rock mass, one of which is causing slope instability. Slope stability analysis, both at the design stage and at the mining and post-mining stages, is an important part and must be done to prevent disturbances to the smooth running of production. The problem of slope instability of the embankment slope at East Banko-1 mine area has hampered the continuity of mining activities, such as the distance for the hauling of disposal materials to be further away. Slopes that experience failure can provide a useful source of information on the conditions in the slope at the time of the landslide. Slope instability can be due to several reasons, one of the main factors is saturation of the material by rainwater infiltration. Therefore, this study aims to identify the characteristics of rainfall before landslides and to validate the physical and mechanical properties of the slope material that have the most influence on deformation. Antecedent rainfall conditions can be used to identify thresholds associated to critical daily rainfall. It is important to accurately determine the beginning of critical rainfall and the time of triggering landslides, as well as rainfall measurement tools that are relatively close to the study area. Based on the results of cumulative rainfall analysis, the intensity of antecedent rainfall that triggered landslides was 627.9 mm. The critical intensity of cumulative rainfall was obtained at 117.4 mm in 18 days period before the landslide event. This causes the slope to experience a saturated condition due to the increase in slope mass due to rainwater infiltration and causes a decrease in matric suction. Back analysis is an effective approach to provide insight into the mechanism of the underlying slope landslide and increase understanding of the factors that influence slope stability. Back analysis can be used to determine the parameters of shear strength, pore water pressure, and other conditions during an avalanche. Fully coupled analysis is used to model pore pressure formation and dissipation in the soil structure in response to external loads through software incorporation. Rainfall with a critical duration of 56 days can affect changes in pore pressure on slope A of 92 kPa, slope B of 96.62 kPa, and slope C of 3.93 kPa. Based on the stress-strain analysis on the effective stress parameter, the optimum deformation for slope A is 0.34 m, slope B is 1.33 m deformed, and slope C is 1.63 m. The variation of data on physical and mechanical properties of soil based on laboratory tests was carried out in a sensitivity analysis of the data to determine the effect of variations in the value of random variables on the deformation that occurred so that it was known which parameters greatly influenced the deformation conditions due to stress-strain behavior. The results of the sensitivity analysis show that the parameter that has the greatest effect on deformation is the modulus of elasticity. Based on the graph between the standardize and deformation functions on slopes A, B, and C in the study area, it is found that the intervals of the modulus of elasticity in the test samples that have a correlation with the actual deformation are values below average modulus of elasticity and modulus of elasticity in average -0.7 standard deviation.