Publications of Research Center for Geotechnology, Indonesian Institute of Sciences
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Deterministic Modeling of Pasir Panjang Debris Flow Using Smoothed Particle Hydrodynamics (SPH)
Full text linkThe debris flow can be modeled as non-Newtonian flow using physical and mathematical modeling methods based on rheological property measurements and movement parameters. The numerical simulation in this research used smoothed particle hydrodynamics (SPH) to solve the momentum and energy equations. The debris flow modeled in this research is located in the Bentarsari Basin, which is surrounded by hills composed of volcanic breccia from the Kumbang Formation (Tpk) and tends to be more susceptible to landslides and may become debris flows. The results of the numerical simulation begin with the collapse of the natural dam and become debris flow with 8.8 m maximum thickness. The debris flow destroyed the bridge in the 40s with 100 kPa pressure. A speed of 6 m/s was reached at 120 s. A small hill in the deposition area was hit by debris flow at 130 s causing 18 casualties. The debris flow enters the deposition area at the 150 s. The debris flow average velocity shows relatively transverse pattern (1-126 s), constant pattern (126-289 s), and random pattern (after 289 s). The debris flow average pressure shows steep negative gradient pattern (1-47 s) and relatively flat pattern (after 47 s). The average debris flow thickness shows a steep negative gradient pattern (1-13 s) and a gentle negative gradient pattern (after 13 s). The results of debris flow modeling using SPH can simulate the debris flow segregation process, which usually cannot be captured by conventional debris flow modeling software
Study of Subsurface Structures for the Sungai Lilin, Coal Prospect Area, South Sumatra using Active Seismic Multichannel Analysis of Surface Waves
Full text linkIndonesia’s dependency on coal, which powered ~47% of its electricity in 2018, highlights the need to optimize exploration amid rising energy demands and volatile fuel prices. This study aims to characterize subsurface structures in the Sungai Lilin coal prospect area, South Sumatra, within the coal-bearing Muara Enim Formation employing the Multichannel Analysis of Surface Waves (MASW) method. We carried out field seismic data collection using a PASI 16S24-P seismograph equipped with 24 geophones, spacing of 4 m. After having dispersion processes, which result in phase velocities (or group velocity) against frequency, we inverted phase velocities to extract subsurface structures through shear wave velocity (Vs) and density. By analyzing Vs variations, we mapped coal deposits at depths of 5–40 m with Vs values of 250–450 m/s, alongside soil, sand, claystone, and siltstone layers. Our subsurface structures derived MASW approach, integrated with borehole data, provided high-resolution 2-D models of young, shallow coal seams varying in thickness and depth. These findings highlight MASW’s efficacy for cost-effective, non-invasive coal exploration, offering insights into resource delineation that support energy security for Indonesia and sustainable coal exploration in similar geological settings
Evaluation of Liquefaction Potential According to Resistivity and CPT Data
Full text linkThis study investigates the liquefaction potential in Tambak Wedi Subdistrict, Surabaya, employing the electrical resistivity geophysical method with a dipole-dipole configuration and the Cone Penetration Test (CPT). The electrical resistivity method is utilized to acceess the resistivity values of soil layers and to generate a 2D subsurface profile. The CPT method is applied to confirm the soil layer types and to compute the safety factor (SF). The soil data from both methods are subsequently analyzed to evaluate the liquefaction potential based on the soil resistivity and SF values. The analysis incorporates a Peak Ground Acceleration (PGA) of 0.3g and considers an earthquake magnitude of 7.5 Mw. The findings from this study reveal that the soil layers ranging from sandy to organic soil, with dominant silt-sandy and clay-silt layers present up to a depth of 10 meters, and clay-silt and clay layers from 11 to 20 meters. Except in the first 2 meters depth, the calculated SF is less than 0.6, indicating a high liquefaction potential in the region. The assessment of liquefaction potential in this study involved the calculation of N-SPT, Liquefaction Potential Index (LPI), and Liquefaction Severity Index (LSI). These findings underscore the importance of incorporating sitespecific geotechnical evaluations into disaster risk reduction strategies, as they provide critical input for the development of effective mitigation plans aimed at minimizing potential loss of life and economic impact
Earthquake Hazard Evaluation Study on the Central Area of Selebar District, Bengkulu City, based on Seismic Response Analysis
Full text linkThe Selebar District, a developing area in Bengkulu City, has been the site of at least two significant earthquakes with a magnitude of Mw 7.0 in the past two decades. This study, which presents a seismic hazard assessment for the central area of the Selebar District, is of paramount importance. The study commences with field investigations at three strategically chosen points in the central area of Selebar District, Bengkulu City, including the airport, educational center, and toll road. The analysis, which involves the propagation of seismic waves, aims to comprehend the seismic behavior during an earthquake. The potential impact of seismic waves on structures and the environment is a serious concern. Seismic response analyses, a critical component of this study, were constructed based on a one-dimensional wave propagation model using a non-linear method. These analyses offer valuable insights into the potential impact of seismic waves on structures and the environment, a matter of serious concern. The results of the field investigations were also examined for seismic response analysis. The PGA, spectral response acceleration, and amplification factors are presented in this study and analyzed to determine the seismic hazard. Based on the PGA values, two earthquake sources can cause very high damage to buildings, and one earthquake source has a high potential. The generated spectral acceleration has exceeded the design spectral acceleration, especially at short periods. Therefore, using local spectra in building structure design can be a recommendation for local engineers to consider the impact of earthquakes on the central area of Selebar District, Bengkulu City
Evaluation of andesite slopes stability using pseudostatic limit equilibrium method in Lembang active fault zone, West Java, Indonesia
Full text linkEarthquakes and rainfall can trigger landslides in many regions of Indonesia. Rock slopes of andesite outcrops in Gunung Batu and Graha Puspa areas coincide with the Lembang active fault zone in West Java. The region is also subjected to high-intensity rainfall. Thus, the rock slopes are prone to failure during earthquake shaking and heavy rainfall. To mitigate the hazards associated with slope failure in residential areas close to the rock slopes, it is necessary to assess the slope failure hazard at the andesite hill slopes. The study presented in this paper aims to analyse the stability of the andesite slopes using the pseudostatic limit equilibrium method and evaluate the effect of variations of regional seismicity and water content on the stability of the slopes. Pseudostatic analysis considered the peak ground acceleration (PGA) and the calculated horizontal seismic coefficient (kh). The limit equilibrium method was focused on toppling and wedge failure cases. Based on the analysis, the andesite slopes in Gunung Batu and Graha Puspa are stable (FoS ≥ 1.1) in factual conditions (dry-static). In contrast, all slopes have the lowest FoS values (less stable-unstable) under the saturated-pseudostatic conditions. The threshold values of kh and %w (percent water fill) for the slopes’ instability were obtained by varying the regional seismicity and water content conditions. It is recommended that numerical slope stability modeling (i.e., finite element method) be conducted to improve the accuracy of the models
Assessing the Water Criticality Index of the Welaran Watershed in Kebumen Geopark, Central Java: Towards Good Water Resource Management
Full text linkThe water criticality index (WCI) is the ratio between water use and availability. The higher the WCI value, the more concerned the water conditions in the area will be. The water crisis can be handled if various parties manage water resources following good management. The Welaran area is a watershed that is part of the Lukulo Watershed, where the population often experiences water shortages. Therefore, by knowing the value of WCI, it is hoped that various parties can know the water conditions in this watershed. Based on research and calculation of the water balance in the Welaran Watershed, it is known that with total water needs in 2019-2020 of 746,937 m3 and total water availability of 1,555,318 m3, the WCI value of the Welaran Watershed is 48.02%. In 2020, Karangsambung was designated as a part of Kebumen Global Geopark, which will certainly increase the number of tourists visiting here. The increase in tourist visits will also increase the need for water, including in the Welaran Watershed. To overcome these conditions, the Kebumen regency’s government and stakeholders are expected to be able to formulate a water management step by effective management
LANDSLIDE SUSCEPTIBILITY ZONATION USING WEIGHT OF EVIDENCE METHOD IN MERTELU AND TEGALREJO, GEDANGSARI, GUNUNGKIDUL, SPECIAL REGION OF YOGYAKARTA, INDONESIA
Full text linkMertelu and Tegalrejo are situated in the Gedangsari Subdistrict, Gunungkidul Regency, Special Region of Yogyakarta, Indonesia. Located in the northern Baturagung Range, Southern Mountains Zone of East Java, with much hilly topography and mountainous areas with steep slopes, Mertelu and Tegalrejo are prone to landslides. The purpose of this research is to produce a landslide susceptibility zone using the weight of evidence (WoE) method. There were 73 landslide data taken from December 2022 to January 2023. As much as 80% of the data were used as a training dataset for weighting and generating the model map, while the remaining 20% were used as a test dataset. Parameters used in this research include slope angle, lithology, distance to faults, distance to rivers, and land use. Each parameter was weighted using the WoE method, and then the map of each parameter was overlaid to produce a map of landslide susceptibility zones. The accuracy of the map was calculated using the area under curve (AUC) method, including the success rate curve (SRC) and prediction rate curve (PRC). Based on the research results, the landslide susceptibility zone in the research area can be categorized: (1) very low, covering 6.34% of the total research area, (2) low, covering 24.15% of the total research area, (3) moderate, covering 44.46% of the total research area, and (4) high, covering 25.05% of the total research area. The landslide susceptibility map shows that the research location is predominantly characterized by areas with medium to high susceptibility to landslides. The medium and high susceptibility zones are close to the rivers that serve as the alignment of the faults. The accuracy calculations result in an SRC value of 0.753 and a PRC value of 0.780, both can be classified as “good” performance
DENSITY DISTRIBUTION OF SHEAR WAVE VELOCITY, CONE RESISTANCE AND CORRECTED SPT IN THE DOMINANT SOILS OF BENGKULU CITY, INDONESIA
Full text linkThis research is of significant importance as it discusses the modelling of a two-dimensional map of soil parameters in Bengkulu City, Bengkulu Province, Indonesia. The two-dimensional modelling was conducted to show the distribution of soil parameter values based on the research points strategically distributed throughout Bengkulu City. These research points were chosen to represent the diverse soil conditions in the city, making the modelled soil parameters particularly helpful for engineers and construction consultants when planning construction in the study area. The parameters to be discussed include shear wave velocity, cone resistance, and corrected standard penetration test. This modelling applies Inverse Distance Weighting as an interpolation method from 215 research points. Inverse Distance Weighting is used because it supports knowing the value of soil parameters around the review point, especially in two-dimensional modelling. The results showed that the distribution of the highest value of shear wave velocity of the clay layer is dominated in the Teluk Segara sub-district. The distribution of the highest value of cone resistance of the clay layer is dominant in the Kampung Melayu Sub-district. The distribution of the highest value of corrected standard penetration test of the clay layer is also dominated in Kampung Melayu Sub-district
