ANALYSIS OF NATURAL UNDERGROUND TUNNEL BASED ON ROCK MASS RATING CLASSIFICATION IN TASANGKA AREA, JAYAPURA CITY

The construction of underground tunnels serves various purposes. In tunnel design, support capacity must be considered to prevent or minimize collapse caused by deformation of the surrounding rock. Rock deformation occurs due to external forces, both vertical forces from heavy equipment activity and horizontal forces caused by geological influences, such as ground movement, groundwater seepage, and rock conditions that are soft or contain numerous fractures and joints. Unstable rock conditions are frequently encountered in underground mine tunnels because they can threaten worker safety. The main objective of this research is to determine the rock mass class so that an appropriate support system can be designed for underground openings. This research is an initial stage in determining the class and quality of the rock mass as a basis for evaluating support requirements, with a focus on rock mass classification. The method used is the Rock Mass Rating (RMR), which classifies rock mass based on parameters that influence rock properties, including intact rock strength, Rock Quality Designation (RQD), discontinuity spacing, discontinuity condition, and groundwater condition. These parameters are then presented as an assessment index based on weighting, and the result determines the rock mass class. Based on the average calculation for each interval, the RMR value obtained is 73, indicating that the tunnel rock mass is classified as Class II (good). With this classification, the support system can be adjusted to the rock mass conditions so that the risk of collapse can be minimized and worker safety is better ensured.