Viability Index Method for Wedge Analysis in Gudang Handak Underground Mine PT. Antam Tbk Fithriyani Fauziyyah 1 , Ryan Pratama 2 and Zufialdi Zakaria 3 1 Magister Program of Hydrogeological Engineering, Institute of Technology Bandung, Indonesia 2 Geotechnical Department, UBPE Pongkor PT. Antam Tbk, Bogor 16650, Indonesia 3 Laboratory of Geology Technic, Geological Engineering, Padjadjaran University, Bandung, Indonesia * fithriyani.uji.fauziyyah@gmail.com Abstract Common problems that are often found in an underground mine is unstable tunnel. Instability of tunnel based on the mechanism is divided into two, caused by structural controll and stress controll. The stability on Gudang Handak underground mine PT. Antam Tbk is more influenced by structural controll. The presence of these structures has potential to form Wedge failure. Wedge analysis both in terms of dimensions and the disaster will became the basis in determining the appropriate type of ground support. Wedge area and its possibility to fall can be predicted more accurately by using the Viability Index approach initiated by Diederich et al. This will be very beneficial, especially from the safety factor which can be improved and the cost can be reduced. Tunnel supporting that is needed, based on this research, is rock bolt with splitset types that has length more than 2,4 m. Because of splitset limitations that owned by UBPE Pongkor, so the supporting design can be added by using the shotcrete and H-Beam which suited with the needs of ground support. Keywords: structural geology, wedge, ground support 1. Introduction There are a lot off parameters that must be accounted for tunnel instability analysis, which are rock mass strength, geology structure, main stress and strain, rock mass classification, discontinuity, etc. These parameters must have same influence in stability and or in different action. Instability of tunnel based on mechanism is divided into two, caused by structural control and stress control (Eberhadrt 2006). According to historical tunnel collapse in UBPE Pongkor especially in underground mine Gudang Handak, mechanism instability tunnel more influenced by structural control. Common problems are often found in excavation tunnel is the fall of rock blocks formed by the intersection of the tunnel face and discontinuities plane in rock mass. This discontinuities can be found as structur likes bedding plane and joint which generally consists of several sets in different direction. The most common failure type is wedge that falling from the roof or sliding from the side walls of tunnel. This research was conducted to determine wedge formation (geometry and rock mass stress) in underground mine Gudang Handak using Wedge Viability Index approch by Diederich et al (2000). The research is located in several front production and development areas. Generally, divided into two block; central and south block. To make the research easier, each block divided into several domain according to distance of sampling areas. Central block consist of 6 domains with 3 primary vein and south block consist of 4 domains. Fig 1. 3D view Gudang Handak Mine L500, PT. ANTAM (PERSERO) Tbk.