The Stability Evaluation of Tunnel Based On Geotechnical Modelling and And Pull Out Test Methods At Site Kencana PT Nusa Halmahera Minerals, North Halmahera District, North Moluccas Province

Abstract

Site Kencana PT Nusa Halmahera Minerals (NHM) is one of the underground gold mining companies in Indonesia with underhand cut and fill method. To overcome the instability of the tunnel, it is required a support system which is optimum in terms of geotechnical aspects. The location of K1-Sub8A-UC3-LA01 is in the depth of 260 m with a type of andesite lava and has an average with width 5.6 m and a height of 6.4 m. The geotechnical mapping shows that the quality of the rock mass is in classification RMR rocks mass class IV (poor rock), while the Q-System rock mass class is very poor rock. Based on the finite element method, the installation of support system is able to raise the value of strength reduction factor (SRF), the value of SRF before propped for each section is 1.5 and the value of SRF after support at section A-A 'is 2, section B-B' is 3.5 and section C-C is 2.75. Based on data from the pull out test, the installation of a support (splitsets) is appropriate and able to withstand the load and displacement caused by the instability of the rock mass with an average safety factor of 1,98. The use of Splitsets with a diameter of 47 mm length of 2,4 m in the walls and 3 m on the roof with a spacing of 1 x 1 m, shotcrete with a fiber thickness of 100 mm and wire mesh research location is considered effective in areas of research.