Recommendation of excavation method and support system based on rock mass classification of the Matenggeng Dam Tunnel, Cilacap, Central Java

The Matenggeng Dam is situated in Matenggeng village, Dayeuhluhur, Cilacap district, Central Java. It features a diversion channel equipped with a tunnel that has a diameter of five meters and is formed like a horseshoe. Therefore required engineering geological analysis for tunnel planning. The purpose of this study is to ascertain the tunneling technique and the corresponding support systems. This study will provide suggestions and input before and during the construction. This research uses rock mass classification and the Point Load Test for several samples. Tunneling method and support systems using empirical method Rock Mass Rating (RMR) and Geological Strength Index (GSI). The study location is composed of sandstone, conglomerate, andesite, and siltstone with alluvium deposits in Cijolang River area. Classification of rock masses is fair to good rock. The GSI and RMR analyses suggest that the excavation technique uses hammer and blasting methodologies and a max stand-up time without support of 20 to 144 hours. The tunneling method uses top heading and bench and support systems using rock bolts, wire mesh, shotcrete, and steel sets.