Engineering Geological Characteristics Based on Rock Mass Rating (RMR) and Geological Strength Index (GSI) in Jlantah Dam Intake Tunnel, Karanganyar District, Central Java Province

Geological Engineering Departement, Engineering Faculty, Gadjah Mada University, Sleman, Yogyakarta, Indonesia

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).