Abstract
Research on the classification of rock mass quality in the intake tunnel Jlantah dam has not been carried out in detail because the research focuses on the location of the main dam so that empirical excavation methods and support systems have not been carried out. The rock mass quality will be used as a parameter in determining the excavation method and tunnel support system that will be used in the Jlantah Dam intake tunnel. The investigation was carried out through engineering geological mapping, core drill evaluation, and supported by laboratory test data based on the Rock Mass Rating (RMR) and Q-system rock mass classification. The rock mass at the research location based on the RMR classification is in class IV (poor rock). Based on the Q-system method, a very poor rock class is obtained. Based on the analysis of the RMR and Q-system methods, the suitable support system for engineering geological conditions such as the intake tunnel of the Jlantah Dam is shotcrete 10 cm thick, steel set with a distance of 1.5 m and rockbolt length of 1.6 m with a distance of 1.5 m. The proper excavation method for the tunnel intake is top heading and bench.
Highlights
The research location is at the Jlantah Dam construction site
Rock Mass Rating is obtained from the sum of all the rock mass parameter weights obtained from the research location
The Rock Mass Rating (RMR) value obtained from the rock test results, field observations carried out the rock mass classification
Summary
The research location is at the Jlantah Dam construction site. This dam is located in Tlobo Village, Jatiyoso District, Karanganyar Regency, Central Java Province (fig 1). Based on the Geological Map of the Ponorogo Sheet compiled by Samodra & Sampurno [7], the rock formations at the tunnel location and its surroundings consist of Lava Lawu (Ella) Jobolarang Lava (Qvjl), and. Lava Sidoramping (Qvsl) formations Observations of rock outcrops indicate that the research area consists of 4 rock units from old to young, namely: Volcanic Breccia Unit, Slightly and Moderately weathered Lapilli Tuff Unit, and Silt Sand Soil Unit. The map of the distribution of rock units and the geological cross-section of the research location can be seen in Figures 2 and 3. The rock mass classification in the study area has rock discontinuity with high to slightly weathering rates
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