Empirical Method for Engineering Geological Evaluation of Pelosika Dam Diversion Tunnel Design, Southeast Sulawesi, Indonesia

This paper explains a Pelosika Dam Diversion Tunnel in metamorphic rocks (quartz muscovite phyllite) and aims to find out excavation methods, stand-up time, and support systems for tunnel construction. The purpose of this research is that the development of science in tunnel construction with the characteristic of metamorphic rock will increase. Tunnel location in poort rock mass quality based on previous geology investigations. Based on current geology and engineering geological mapping results, diversion tunnel through poor rock mass of metamorphic rocks (phyllite) which have slightly-highly weathered. We classified rock mass quality by GSI, RMR, and Q-System methods which produce the almost same results (poor rock mass quality). The GSI Chart and Pettifer-Fookes Chart which excavation method has the results of the digging and ripping. RMR value determines the stand-up time last 42-240 minutes after excavation. RMR and Q-System values generate the support system which used rock bolts (length= 1.8 m), shotcrete (thick=10-15 cm), and steel sets (spacing=1,5m) if required. A purpose of combination from the different excavation methods and support systems to complement each other and improve the safety of the tunnel without compromising the cost-effectiveness of construction.