Development of safe, effective and efficient access to the ore body is an important goal during underground mining. Until today, underground mining possesses a risk of failure even with help of complete data and modeling design, therefore, this uncertainty becomes a challenge that has to be tackled. Failure is a result of incapability of rock mass to cope with the stress, both with the ground support or self-supported rock mass. This failure will initiate tunnel collapse. The collapse that happened at Cibitung decline X/C 4 and X/C 5, Tambang Emas Cibaliung on April 2017 blocked the production access and trapped mine equipments. This decline is located in hanging wall which is classified as an unstable area. Ground consolidation with cement and urea silicate is one of the works carried out during tunnel rehabilitation, along in a cycle with steel set erection, fore poling installation, concrete pouring and shotcrete. Field observation, tunnel deformation data statistical analysis and numerical modeling were conducted to assess the effect of ground consolidation at unstable area. Statistical data analysis and finite element numerical modeling shows an improvement on rock mass quality after ground consolidation work.
Tunnel collapse happened at Cibitung decline X/C 4 and X/C 5 is caused by tunnel instability in that area. The instability in this hanging wall area is significantly initiated by the rock mass surrounding the excavation (Purwanto et al., 2013) based on its modeling results shown in Fig.1.
Ground consolidation objective is to increase strength, to reduce deformability and to decrease permeability of rock masses (Lombardi, 1999). There are various types of materials commonly used to consolidate rock masses, such as cement-with or without additives (ashes, fillers and silica fumes), resin and silica urea.
The selection of the right material and the right specific product for the defined project requirements is one key factor for successful injection, beside its equipment and correct injection method (Sika Services AG, 2015). Materials viscosity, strength and its behavior in contact with water are considered to select the material type. Equipment attainment is affected by pumping ability and accurate dosage, while methods can be arranged to meet objective.
