Estimation of rock mass quality based on engineering geological investigation of a diversion tunnel at Rongkong Dam, South Sulawesi, Indonesia.

This paper analyses rock mass quality based on an engineering geological investigation conducted at the Rongkong diversion tunnel, Luwu Utara Regency, South Sulawesi, Indonesia. The research area's surface and subsurface were mapped geologically, and drill cores were evaluated along the tunnel. In addition, laboratory test data further reinforced these investigations. This study aims to evaluate the characteristics of the rock mass in the tunnel using the Rock Mass Rating (RMR) method. However, in cases involving weak rock and complex geology, another alternative approach is known as the Geological Strength Index (GSI) method. The results indicated that the Rongkong diversion tunnel under investigation primarily comprised lithological, including granodiorite and schist. The rock mass shows varying degrees of weathering, ranging from slight to complete. The study area's RMR rock mass values ranged from 33 – 59 (poor to fair quality), while the GSI values ranged from 15 – 58 (very poor to good quality). The effect of weathering degree can be one of the factors causing poor rock mass quality. Furthermore, this paper also examines the correlation between RMR and GSI. The equation GSI = 1.66RMR – 39.44 (R² = 0.94) was obtained from analysis of the correlation between GSI and RMR in the research area. Therefore, the obtained correlation results may serve as recommendations for other regions exhibiting comparable lithology and rock mass characteristics within the scope of this study. [ABSTRACT FROM AUTHOR]