The Telfer Underground Sublevel Cave (SLC) Operation is located approximately 800 m below the West wall of the Main Dome Open Pit. The Telfer SLC initiated in late 2006 and is caving successfully at a global rate of approximately 0.6 m per day. The cave is expected to break into the planned 5384 bench on the West wall of the active Main Dome pit which has a haul ramp running along the wall at approximately 70 m horizontal distance from the edge of the cave. The breakthrough area of the pit was being mined as the cave was propagating, requiring assessment of the potential for rapid propagation and unexpected subsidence. The key trigger points for evacuating and barricading the breakthrough area were based on monitoring of the cave propagation, the calculation of air gap and risk assessment of the interaction. Monitoring of key parameters was critical for informed decision making and safe management of the interaction between the cave and the pit. Part I of this paper discusses the risk management strategy and tactics used for managing the interaction, including implementing a second ramp, preloading the breakthrough area and setting up a major hazard management plan. A trigger, action, and response plan is also used to monitor key parameters, identify predetermined triggers and take the designated action.
The Telfer Underground Sublevel Cave (SLC) Operation is located approximately 800 m below the west wall of the Main Dome Open Pit. The Telfer SLC initiated in late 2006 and is caving successfully at a global rate of approximately 0.6 m per day. The cave is expected to break into the planned 5384 mRL bench on the west wall of the active main dome pit which has a haul ramp running along the wall at approximately 70 m horizontal distance from the edge of the cave. The breakthrough area of the pit was being mined as the cave was propagating, requiring assessment of the potential for rapid propagation and unexpected subsidence. Key trigger points for evacuating and barricading the breakthrough area were based on monitoring of cave propagation, calculation of air gap and risk assessment of the interaction. Monitoring of key parameters was critical for informed decision making and safe management of the interaction. Part II of this paper discusses the monitoring systems used to track the cave and monitor the interaction area of the pit. These include deep hole extensometers, seismic array, open hole surveys with video cameras, prisms and a radar monitoring system. The monitoring systems are used to determine the cave shape, location, rate of propagation, potential for air gaps and ground response in the open pit. The extensometer array was buried under backfill used to preload the breakthrough area. This required protection for the instrument heads and cabling to ensure that the monitoring continued to function as required. The monitoring systems are critical for indentifying approaching hazards and taking proactive mitigation measures.
A planar failure of approximately 600 kT occurred on the north wall of Centre Pit North (CEPN) at West Angelas Mine site in February 2010. The failure impacted a substantial resource of high grade iron ore and left a number of significant geotechnical hazards on and adjacent to the failure surface. These presented a series of challenges which had to be overcome in order to remediate the failure and reclaim the bulk of the buried ore. A number of recovery options were investigated and presented to management. This paper outlines the plan which was adopted, the challenges encountered during its implementation and the risk management and mining procedures used to bring the remediation and recovery to a successful conclusion. A significant fall of ground occurred on the north wall of CEPN at the West Angelas Mine site on the evening of the 3 February 2010. The failure occurred in the Mount Newman Member of the Marra Mamba Iron Formation, which is comprised predominantly of banded iron formation (BIF) with interbedded shale. Bedding dip was roughly parallel to the overall slope angle, except where it flattened towards the pit, on the lower benches. The failure was due to planar sliding on the NS2 shale, which was daylighted in places, towards the toe of the slope. The resultant failure surface is approximately 112 m high, dipping at an average of 42°. The failed rill heap of approximately 600 kT, covered a significant resource of high grade iron ore.
Rio Tinto Iron Ore (RTIO) operates 16 mine operations in the Pilbara region of Western Australia. At each operation, there could be many active pits that pose a challenge for the effective management of geotechnical risks with limited resources. There are many information sources which the geotechnical engineer uses for risk management, including temporal and non-temporal data that may or may not be georeferenced. This information can be in various places, such as proprietary software, network servers or local devices. Consolidating this information can be time-consuming for the engineer and may not include all available data sources. To address this, RTIO developed an in-house tool for aggregating and visualising data, where all geotechnical data can be accessed in a single platform and also included a dashboard to provide visibility of monitoring status and risk profiles across all RTIO Pilbara operations. Sustainability of an in-house developed tool poses business challenges and a decision was made to explore available external options. Although a number of off-the-shelf applications were identified, none met all the RTIO requirements. The best-fit application was ultimately selected with RTIO working with the vendor to incorporate all defined software requirements. This paper discusses RTIO expectations and requirements for the data aggregation and visualisation application, challenges relating to the in-house system development, the evaluation process for a vendor managed option and development of the application functionality with the selected vendor.
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