Rock Mass Classification for Support System Design and Stand-up Time of Asahan 3 Hydroelectric Power Plant Tunnel (STA 7+085 - STA 7+717)

This Engineering geology research on rock mass classification to determine the support system’s design and stand-up time at the Asahan 3 hydroelectric tunnel STA 7+085 – STA 7+717 has not been thoroughly carried out in detail. This study aims to estimate the support requirements. Rock mass classification is determined through core drill observations and then analyzed by Q-system and RMR methods. The results show that the rock mass at the tunnel depth elevation consists of sandstone with good quality based on RMR and Q-system. Based on the Q system classification, good quality sandstone is obtained. Based on RMR, the suggested support system is shotcrete in the crown and rockbolt. Meanwhile, a rock bolt is the appropriate support system based on the Q-system. The use of an RMR based support system is recommended because it provides a higher level of security with the addition of shotcrete. The tunnel stand-up time is 2,200 - 2,700 hours based on RMR. The result of this research is expected to be applied in other tunnel construction having similar engineering geological condition.