Publications of Research Center for Geotechnology, Indonesian Institute of Sciences
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Site selection for artificial recharge in Cisangkuy sub-watershed, West Java, using combined fuzzy logic and genetic algorithm
Full text linkThe Cisangkuy sub-watershed is part of the Citarum watershed with ±300 km of river length. The total area is in line with the potential of water resources which is quite good, but over time the hydrological condition of the site has decreased. Decreasing the hydrological state is due to changes in land use and land cover from year to year and is indicated by high discharge and flooding in the rainy season. This study aims to find the optimal location of artificial recharge to maintain water balance in the Cisangkuy sub-watershed. Fuzzy logic is used for determining the location of artificial recharge by considering the input variable DRASTIC in the form of depth to groundwater level, net recharge, aquifer media, soil type, slope, vadose zone, and hydraulic conductivity. In addition, subtractive clustering is performed to obtain the class of each DRASTIC parameter. Furthermore, a genetic algorithm is carried out to get the optimal location of the artificial recharge zone. The priority zone is indicated by the high class of each DRASTIC parameter input. Combined fuzzy logic and genetic algorithm show that the optimal location for artificial recharge is in the northern part of the Cisangkuy sub-watershed, precisely in the Banjaran area
Dewatering requirements assessment for the Central Kalimantan NCP open pit gold mine
Full text linkOne of the most critical aspects of open pit mining is the dewatering and mine drainage systems. The NCP Open Pit Gold Mine is located in Central Kalimantan. This study area has a range of rainfall intensities and durations from moderate to heavy. Good dewatering is required to manage runoff water and reduce runoff from entering the pit and mine front loading. The study used daily rainfall intensity data from 1994 to 2018. Using the Mononobe Method, the hydrological data for this area were evaluated by determining the value of the rainfall intensity plan. According to the evaluation of rainfall data from 1994 to 2018, the research area saw a rainfall intensity of 86.23 mm/day over a two-year return period. The majority of water extracted from mines is from precipitation and runoff rather than groundwater. An open channel was made around the open pit, flowing water naturally into the sump to reduce water entering the mining area. The water was pumped into the settling pond with 520 m3/hour and 780 m3/hour capacity pumps
Geothermal Reservoir Identification based on Gravity Data Analysis in Rajabasa Area- Lampung
Full text linkGravity research in the Rajabasa geothermal prospect area was conducted to determine geothermalreservoirs and faults as reservoir boundaries. The research includes spectrum analysis and separation of the Bouguer anomaly to obtain a residual Bouguer anomaly, gradient analysis using the second vertical derivative (SVD) technique to identify fault structures or lithological contact, and 3D inversion modeling of the residual Bouguer anomaly to obtain a 3D density distribution subsurface model. Analysis was performed based on all results with supplementary data from geology, geochemistry, micro-earthquake (MEQ) epicenter distribution map, and magnetotelluric (MT) inversion profiles. The study found 3 (three) geothermal reservoirs in Mount Balirang, west of Mount Rajabasa, and south of Pangkul Hot Spring, with a depth of around 1,000-1,500 m from the ground level. Fault structures and lithologies separate the three reservoirs. The location of the reservoir in the Balirang mountain area corresponds to the model data from MEQ, temperature, and magnetotelluric resistivity data. The heat source of the geothermal system is under Mount Rajabasa, which is indicated by the presence of high-density values (might be frozen residual magma), high-temperature values, and the high number of micro-earthquakes epicenters below the peak of Mount Rajabasa
HYDROGEOLOGICAL IDENTIFICATION OF THE WELARAN WATERSHED KARANGSAMBUNG BASED ON DESCRIPTIVE-QUALITATIVE METHOD
Full text linkThe Welaran watershed in the Karangsambung area is hydrogeologically interesting because of its morphology, “U” shaped morphology like an amphitheater with the lithology consisting of tertiary to quarternary rocks. The character of Welaran river is an intermittent river that watery during the rainy season and dry during the dry season. This study intended to identify and determine the general hydrogeological condition of the Welaran watershed on a scale of 1:20.000. This study applies a descriptive-qualitative research method. The steps used are hydrogeological analysis and water balance. The results obtained indicate that the hydrogeological conditions of the area affect the character of the rivers in t
Depositional Environmental Evolution of Nyalindung Formation based on Paleontology Molluscan Study, Ciodeng Area, Sukabumi, West Java, Indonesia
Full text linkThis research was conducted to understand and identify changes in the depositional environment of the Nyalindung Formation in the Ciodeng area, Sukabumi, based on mollusk paleontology and lithological associations. Paleontological study of mollusks to interpret the depositional environment becomes important due to the scarcity or absence of foraminifera in mollusk bearing rocks. Foraminifera is commonly used to determine depositional environment. The results of this mollusk paleontology study and lithological associations show at least sixteen changes in depositional environment. The environmental changes range from rivers, mangroves, beaches, tidal areas, shallow marine nearby the coast, shallow open marine, and relatively deeper marine. The depositional environmental changes shown by thissection might be related to tectonic activity and global sea level fall that occurred since the early Late Mioceneto Pleistocene. The sedimentary units in this section are also characterized by predominant fluvial, mangroves, beach, and tidal in the upper layers.
AQUIFER MAPPING BASED ON STRATIGRAPHIC AND GEOELECTRICAL DATA ANALYSIS IN BEDOYO REGION, GUNUNG KIDUL REGENCY, YOGYAKARTA SPECIAL REGION
Full text linkThe research area is a high karst area composed of carbonate rocks, where drought occurred almost every year. This study aimed to determine water availability in aquifer rocks by analyzing the surface geology and subsurface layers (geophysical method). We used the Schlumberger configuration in the geoelectric method at four locations in the study area to determine the resistivity value of the rocks beneath the surface. The results revealed that the site comprises tuff, crystalline limestone, layered limestone /chalky, and gravel to clay deposits. An aquifer was only found in Asem Lulang Village, which has a wedge layer with a thickness of 59 meters and thinned down to 5 meters towards the village of Ngalas Ombo. The value of the resistivity aquifer ranges from 0.18 to 9.18 ohm.m. The existence of that aquifer could indicate that the aquifer is only found in weakly undulated
TWO-DIMENSIONAL INVERSION MODELING OF MAGNETOTELLURIC (MT) SYNTHETIC DATA OF A GRABEN STRUCTURE USING SimPEG
Full text linkThe magnetotelluric (MT) method is a passive exploration method in geophysics that utilizes natural electromagnetic waves as a signal source. MT operates in the frequency range of 10-5 - 106 Hz, designed to study the structure of the conductivity below the earth's surface with a depth range from several tens of meters to the upper mantle. In this paper, 2-dimensional inversion modeling is performed on MT synthetic data using the SimPEG software. First, forward modeling is done by making a 2-dimensional conductivity model in the form of a valley (graben), which aims to produce MT synthetic data in TE (transverse electric) mode, TM (transverse magnetic) mode, and a combination of TE mode and TM mode. Next, an inversion modeling is performed on the MT synthetic data by adding a 5% Gaussian noise and a 10-5 floor as data uncertainty to obtain a 2-dimensional conductivity inversion model. The final result can be validated by comparing the true model and the inversion model and between observational data (synthetic) and predictive predicted data. The results of this study provide a significant fit of the model and suitability of the data. The inversion quality is validated with an RMS Error for TE mode of 0.349%, TM mode of 0.348%, and a combination of TE and TM mode of 0.249%.
Time Defendability of Ground Resistance Properties and Its Application of Vitric Tuff on the Development of Ground Enhancement Material
Full text linkGround repair material is an essential part of the grounding system as a lightning rod to reduce the risk of lightning activity. Grounding repair materials consist of conductive and superconductive materials, commonly known as Ground Enhancement Materials (GEM). GEM has a low resistivity, very effectively supporting lightning shock energy to earth. Vitric tuff, a pyroclastic rock, is composed of an aluminosilicate (phyllosilicate) mineral group developed as a grounding improvement material. The primary purpose of this study was to determine the decrease in resistivity of vitric tuff in its development as a GEM. The research method consisted of field observations and laboratory experiments (treatment with chemical-physical activation and formulation with additives). The results showed that moisture content, SiO2/Al2O3 ratio (quartz and feldspar mineral/albite), clay mineral, crystal quality (impurities), carbon, and salt were influenced by vitric tuff resistivity. With the vitric tuff formulation and additives, the resistivity reduction is above 99%. Based on experiments, the best formulation of GEM made from tuff is 65% activated vitric tuff, 27% activated charcoal, 6% NaCl, and 2% Cement Material Cellulose. The formula produces a resistivity value of 0.0124 Ω-m, which is stable with time and meets GEM requirements (ρ ≤ 0.20 Ω-m)
Coseismic and postseismic deformation from the 2007 Bengkulu earthquake based on GPS Data
Full text linkOn September 12, 2007, a M8.5 megathrust earthquake occurred along the Sunda trench near Bengkulu, West Sumatra. GPS data in Sumatra have indicated the coseismic and postseismic deformations resulting from this earthquake. Our estimate of coseismic displacements suggests that the earthquake displaced up to ~1.8m at GPS stations located north of the epicenter. Moreover, our principal strain estimation in the region suggests that the maximum coseismic extensional strain is ~40 ppm. Our analysis of GPS data in the region suggests that the postseismic decay of the 2007 Bengkulu earthquake was 46 days, estimated using a logarithmic function