This paper presents the monitoring and management of a large-scale toppling failure that was first observed in 2005 at the Ok Tedi mine. Ok Tedi is a large open-cut copper gold mine in the Western Province of Papua New Guinea and is one of the wettest mines in the world (>10 m annual rainfall). The management of large-scale failures in open-pit mines expresses geotechnical challenges in terms of balancing economical designs and safe operations. The failure located at the southern end of the West Wall was reactivated in June 2019 due to continuous mining and prolonged rainfall events. Erosion, cracking, and rock toppling associated with lateral displacements, evolved rapidly. Hence, ground control and groundwater management plans, including a Trigger Action Response Plan (TARP) and measurements to monitor movement across the wall, were implemented. This monitoring system, associated with daily visual inspections, enhanced the understanding of the necessary controls to maintain a safe mining operation. Furthermore, the water management plan was crucial in managing this failure. The successful risk-control of this large-scale toppling failure at Ok Tedi ensured continuous mining with a functional balance between economic and safety during operations.
This paper presents the reactivation and successful management of a large-scale toppling failure in 2019 at the Ok Tedi mine in Papua New Guinea (PNG). Ok Tedi is a large open-cut copper and gold porphyry mine in the Western Province of PNG and, due to its reserves, it is considered as one of the largest copper-rich and gold porphyry deposits in the world [1], [2]. The mine is currently operated by Ok Tedi Mining Limited (OTML) [3]. Furthermore, the mine is subject to severe weather conditions with more than 10 m of annual rainfall and hence considered as one of the wettest mines in the world [4], [5].
The pit is about 2,000 m by 1,500 m in plan and approximately 900 m deep. The toppling failure zone presented in this paper is located towards the southern end of the West Wall in an area called Belfast; the West Wall is approximately 2,000 m long, 1,000 m wide and 500 m deep. In the past 4 years, the West Wall experienced numerous instabilities including two large-scale pit wall failures (referred to as ‘chasms’) and additionally several complex failures of varying scales across the entire extent of the West Wall. These instability zones present significant challenges in terms of mine safety and, from an economical perspective, in reaching the life-of-mine design.