Authors: Widijanto, E; Setiawan, I; Afrizal, K; Stawski, M; Warren, P; Utama, B


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Widijanto, E, Setiawan, I, Afrizal, K, Stawski, M, Warren, P & Utama, B 2013, 'Slope stabilisation program at West Gully, PT Freeport Indonesia', in PM Dight (ed.), Proceedings of the 2013 International Symposium on Slope Stability in Open Pit Mining and Civil Engineering, Australian Centre for Geomechanics, Perth, pp. 1077-1088,

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PT Freeport Indonesia operates a copper-gold mine located in the province of Papua, Indonesia, about 3,500 km east of Jakarta. Current ore production from the project is about 220,000 tonnes per day (tpd) of which about 2.5 ktpd from Big Gossan stope mine, 60 ktpd come from the DOZ block cave and the rest is mined from the Grasberg open pit. Two new underground mines under development are the Grasberg block cave and Deep Mill level zone to ultimately replace surface mine operation. One of the critical zones for entire mining operation is the mill-processing area. This area is not only dedicated for the processing plant but also is used as access to one of underground waste dump areas. The mill area is surrounded by steep natural slopes and extreme topography which often results in instabilities (debris flows, rockfalls) related to the geological features. West Gully is one of locations at the mill area which requires extensive work to mitigate rockfall hazard which impacts on the operations at the mill. Historical rockfall incidents, geological information, site observation, rockfall simulation, and road access reliability requirement for the future mining operation drive geotechnical recommendations to provide robust rockfall mitigation option. Scaling and meshing of more than 7,000 m2, constructing two × 8,000 kJ of debris flow barriers, and 8,000 kJ of rock fence for an approximately 700 m high slope was required to reduce rockfall risk to an acceptable level. Those rockfall protections are augmented by 225 m corrugated steel tunnel at the mill level as an additional road protection from potential rockfall events. Complex geological conditions, steep mountainous topography, average annual rainfall of 5,000 mm, foggy conditions, limited working space and the short distance to the critical facilities created a challenging situation for engineering design, construction, geotechnical monitoring and logistics. This paper outlines the slope stabilisation challenges and unique conditions and also the efforts of the team to reduce and mitigate rockfall hazards to ensure the safety of the workers and future safe production continuity.

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