Landslides are one of the most disastrous natural hazards that frequently occur in Indonesia. In 2017, Balai Sabo developed an Indonesia Landslide Early Warning System (ILEWS) by utilizing a single rainfall threshold for an entire nation, leading to inaccuracy in landslide predictions. The study aimed to improve the accuracy of the system by updating the rainfall threshold. We analyzed 420 landslide events in Java with the 1-day and 3-day effective antecedent rainfall for each landslide event. Rainfall data were obtained from the Global Precipitation Measurement (GPM), which is also used in the ILEWS. We propose four methods to derive the thresholds: the first is the existing threshold applied in the Balai Sabo ILEWS, the second and third use the average and minimum values of rainfall that trigger landslides, respectively, and the fourth uses the minimum value of rainfall that induces major landslides. We used receiver operating characteristic (ROC) analysis to evaluate the predictability of the rainfall thresholds. The fourth method showed the best results compared with the others, and this method provided a good prediction of landslide events with a low error value. The chosen threshold was then applied in the Balai Sabo-ILEWS.
Abstract:The mapping of soil movement was examined by comparing an extension of the deterministic Soil Stability Index Mapping (SINMAP) method, and an overlay method with trigger parameters of soil movement. The SINMAP model used soil parameters in the form of the cohesion value (c), internal friction angle (φ), and hydraulic conductivity (k s ) for the prediction of soil movement based on the factor of safety (FS), while the indirect method used a literature review and field observations. The weightings of soil movement trigger parameters in assessments were based on natural physical aspects: (1) slope inclination = 30%; (2) rock weathering = 15%; (3) geological structure = 20%; (4) rainfall = 15%; (5) groundwater potential = 7%; (6) seismicity = 3%; and (7) vegetation = 10%. The research area was located in the Buleleng district, in particular in the ancient mountain area of Buyan-Tamblingan, in the Sukasada sub-district. The hazard mapping gave a high and very high hazard scale. The SINMAP model gave a validation accuracy of 14.29%, while the overlay method with seven trigger parameters produced an accuracy of 71.43%. Based on the analysis of the very high and high hazard class and the validation of the landslide occurrence points, the deterministic method using soil parameters and water absorption gave a much lower accuracy than the overlay method with a study of soil motion trigger parameters.
556 INTRODUCTIONThe main characteristics of peat soil are high compressibility, low shear strength, and high moisture content [01]. Such characteristics pose problems if peat soil is used as a subgrade construction. Several methods to improve peat soil include soil replacement, reinforcement to improve soil strength and stiffness, preloading and stage construction, soil improvement, stone columns, piles, and mixing of chemicals such as cement and lime [02]. Sand fi ll on peat soil can improve parametric values of peat soil. Adding the thickness of sand on peat soil will increase the value of subgrade reaction modulus and the modulus of deformation [03]. Deposition of fi ll with better soil types can be performed on peat soil, but its implementation may encounter several problems. Some problems include excessive lateral movement, heave occurring on deposit of soft soil and the formation of mud wave, mixing of fi ll with the very soft soil, and differential settlement, as in [04]. The large deformation took place together with tension cracks and heave when the height of embankment rapidly increased [05]. Secondary settlement can be reduced by surcharging [06]. The effective method to improve peat soil are preloading and surcharging [07]. Preloading consists of applying a load, equivalent to or greater than a total load of a planned structure, over the site prior to constructing the structure which is being partially or fully removed when the required settlement has taken place. Preloading consisting of loading and unloading methods can accelerate peat soil compression [08]. The increase in OCR on loading and unloading methods for high organic soil can reduce the rate of secondary compression [09]. In addition to reducing compression, preloading can also increase the bearing capacity of peat [10]. The Embankment with stage construction and thin layers can be applied to peat soil to allow consolidation and increase shear strength.Reinforcement can contribute to increasing the stability of embankment, that reinforcement and shear strength of peat will resist lateral forces [11]. Reinforcement with slabs without piles only affects the top layer of the surface with a depth of generally not more than the width of the foundation slab [12]. Slabs can be reinforced by piles to support the embankment. Some of the advantages of the piles in supporting embankment include the implementation of embankment construction can be completed in a short time, embankment-supporting piles can reduce total settlement and differential settlement signifi cantly [13]. In addition, the implementation of the piles corresponds to non-uniform geological conditions. Another alternative use of piles on soft soil is the use of nailed-slab system [14], [15], [16]. Piles affect the increase in modulus of subgrade reaction. The height of piles affects the stiffness of nailed-slab system and the reduction of slab defl ection at the load center. The nailed-slab system generated uniform settlement, increased the strength of subgrade support, improved the...
This paper focuses on the potential utilization of volcanic ash and coarse volcanic slag for nofine concrete for drainage structure of Prambanan temple yard. This material produced from volcanic eruption also becomes environmental important issues as waste material if it is not effectively reduced or reused. Coarse volcanic slag is commonly known by local people as Bantak. The experimental study was conducted to determine engineering properties of no-fines concrete materials and discharge capacity of drainage system was calculated to identify the optimal dimensions of the drainage channel. In addition, a numerical analysis was carried out using SAP2000 and Plaxis to control structure stability. Based on numerical and experimental study, the utilization of no-fine concrete from volcanic ash and bantak by using certain mix design can be used as a porous drainage structure. By utilizing the eco-friendly material as structural material, the originality of the building will not be disturbed.
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