EVALUASI DISKONTINUITAS BERDASARKAN DATA KARAKTERISASI MASSA BATUAN DAN NILAI LUGEON PADA FONDASI BENDUNGAN UTAMA LADONGI, KABUPATEN KOLAKA TIMUR

• Main Author: Vivian Tri Adhitama, Kukuh
• Format: Theses
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/63129
• Institution: Institut Teknologi Bandung

In the construction of a dam, geological investigations need to be carried out, one of which is on the foundation. The permeability coefficient factor is important to determine the potential for seepage of subsurface water because if it is not controlled it can result in dam failure. Ladongi Dam in East Kolaka Regency is a dam built on metamorphic rock. This study aimed to evaluate the distribution of discontinuities on surface outcrops, to determine the significance of the relationship between the quantification of rock mass parameters from core rock samples and the lugeon values at the same depth interval, and to perform several simulation scenarios of the potential for subsurface seepage based on the distribution of hydraulic conductivity values. The schist rock at the Ladongi Dam foundation is part of the Mekongga Complex (Pzm) geological formation unit. This study applies a non-parametric statistical approach (Spearman's rank) and parametric (multiple regression) adjusted based on the type of data resulting from the quantification of rock mass characteristics from the RMR89 and Q-system classifications to the lugeon value (the dependent variable). In the early stages of the research, field data were collected, such as the lugeon test (in-situ), surface outcrop observations using the scanline method, and observations of core rock samples. The results of field data processing from the pressurized water passing test get the distribution of lugeon values (Lu) and hydraulic conductivity as much as 207 interval data with an accumulated depth of 1,035 from 18 pilot holes points along the axis of the Ladongi Dam. Then get the results of the analysis of the anisotropy level (ARMR) of the research area based on observations of surface outcrop data analysis. Based on the quantification of rock mass characteristics from core rock samples such as UCS, RQD, spacing discontinuity, aperture, velocity, injection pressure, roughness, infilling, weathering, groundwater, Ja, Jr., joint condition, and block friction on the dependent variable lugeon. The simulation of seepage potential modeling applies several scenarios with variations in controlling factors such as the target value of the lugeon value reduction resulting from the grouting method, the anisotropy level of the distribution of hydraulic conductivity values, the orientation of the foliation slope of schist rock, and the design of the embankment representing three parts (left main dam, river bed, and right main dam). The results of the analysis of the frequency distribution of lugeon values in the range 0-5 (low) are dominant with a percentage of 55.10% and the rock mass discontinuity condition is tight. At subsurface depths above 30 m, the distribution of lugeon values is relatively stable with values below 20. Based on statistical analysis, only the aperture variable has the most significant effect than the other independent variables partially. Several independent variables simultaneously affect the value of lugeon with the percentage of the influence factor of 78.40% with a very strong correlation value (0.88). Based on the anisotropy factor from surface observations using the ARMR rock mass classification method, the research area has a slightly to moderately anisotropic range, while based on the vertical distribution of the conductivity coefficient values the Ky/Kx ratio is 0.0630 on the left main dam, 0.1010 on the river bed, and 0.0210 on the right main dam. The evaluation results from several seepage simulation scenarios show that the lower the value of the anisotropy Ky/Kx ratio, the direction of the orientation towards the downstream, and the greater the foliation slope makes the smaller the seepage potential value. Based on some of the results obtained in this study, it can be an additional consideration in planning the construction of a dam at the base of the foundation composed of schist rock formations.