Abstract
This paper presents the results of a geological engineering investigation in the form of rock mass characterization at the Jlantah Dam Intake Tunnel. The study was carried out through technical geological mapping, core drill evaluation and supported by laboratory test data. The determination of rock mass classification at the research site has been carried out using the Rock Mass Rating (RMR) method, but it is necessary to use another method that is more suitable based on rock mass for weak rocks, namely using the Geological Strength Index (GSI) method.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 results showed that the research area consisted of lithology in volcanic breccias and tuff lapilli. GSI rock mass value at the research location ranged from 15 - 65, while the RMR value ranged from 24 - 70. The correlation between RMR and GSI in the study area is different when compared to Hoek and Brown (1997) but has similarities with Zhang et al (2019).
Highlights
The research location is at the Jlantah Dam construction site
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 Geological Strength Index (GSI) value of rock mass in the research area ranges from 15 - 65, while the Rock Mass Rating (RMR) value ranges from 24 - 70
Summary
The research location is at the Jlantah Dam construction site. Administratively, this dam is located in Tlobo Village, Jatiyoso District, Karanganyar Regency, Central Java Province (Figure 1).Several site investigations have been carried out in the design stage of the Jlantah Dam construction [8]. The research location is at the Jlantah Dam construction site. This dam is located in Tlobo Village, Jatiyoso District, Karanganyar Regency, Central Java Province (Figure 1). Several site investigations have been carried out in the design stage of the Jlantah Dam construction [8]. A detailed description of rock mass needs to be carried out for the tunnel's safety because the characteristics of the rock mass influence the stability of the portal slope, the determination of the excavation method, and the tunnel support system. The determination of rock mass classification at the research location has been carried out using the Rock Mass Rating (RMR) method, while the rocks at the study site are lapilli tuff rocks in moderately weathered conditions. Determination of rock mass classification should be made based on rock mass classification for weak rocks, for example by applying the Geological Strength Index (GSI) [7], in order to obtain an appropriate rock support system
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