Geotechnical analysis below the surface of hydropower plant is one way to determine the stability of the opening holes in determining the supporting system. A discussion about supporting systems cannot be separated from the analysis of the construction of recommended supporting system based on the weighting value of the geomechanical classification of the RMR and Q-System. The aims of this study are: 1) understanding the quality and class types of rock, 2) determining the supporting of RMR and Q-system, 3) understanding the safety factor of opening hole using Phase2. This study was carried out by recording data directly in the field, which later were used to determine the number of rock bolt needed in the installation of the supporting. Based on geomechanical classification, the rock mass in headrace tunnel adit 1 up stream has an average RMR value of 58 (moderate rock quality) and Q-system value of 4.06 (moderate rock quality), while adit 2 up stream has an average RMR value of 47 (moderate rock quality) and Q-system value of 2.30 (poor rock quality). Based on these geomechanical classification data, each type of supporting types is obtained. Supporting headrace tunnel adit 1 and 2 type, RMR value of type 1 can be applied to the RMR (60-80). RMR value of type 2 can be applied to the RMR (40-60). Supporting headrace tunnel adit 1 and 2 type, Q-system value of type 1 can be applied to Q-value (4-10). Q-system value can be applied to Q-value (1-4). Based on the modeling results using phase2, the total displacement of headrace tunnel adit 1 up stream is 0.92 cm with safety factor value of 1.20 and the total displacement of headrace tunnel adit 2 up stream is 1.17 cm with safety factor value of 1.04.
Rock masses in hydroelectric projects: a proposal of geomechanical classification