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Concerns regarding the uncertainty of stope dilution at MMG Limited's Dugald River Underground Mine led to a trial stoping program to acquire full-scale comprehensive geotechnical information and to test the validity of the proposed geotechnical and mining parameters. As part of the trial, a geotechnical instrumentation program was designed to improve the understanding of the rock mass response to the mining of the trial stopes. This included an array of instruments installed from dedicated hanging wall drives, hanging walls that included 66 multipoint borehole extensometers (MPBX), 23 time domain reflectometers, 24 geophones, six accelerometers and 15 observation holes. Trial mining consisted of 19 sublevel open stopes with cemented rockfill (CRF) that extracted 335 kt of ore, with a panel height of 130 m and strike of 100 m. All stopes were monitored with a minimum of two MPBXs at the open span with a MPBX average density in the panel hanging wall of 180 m 2. The MPBXs were 19 m in length and consisted of six nodes. Instrument displacement information was recorded every 30 minutes by dataloggers to a resolution of 0.12 mm. This provided a high quality, detailed and extensive rock mass response to stope extraction. The displacements were interpreted as hanging wall relaxation and shear on structure from specific stope firing and expansion of the mining front. Rock mass creep was also recorded in the hanging wall. The mechanism of displacement consisted mainly of strike-slip movement on high angle bedding and faults that are orientated sub-parallel to the dip of the orebody. Overall hanging wall behaviour was assessed by investigating the near (stope hanging wall boundary to 6 m) and far (>6 m from stope boundary) displacements as the sequence progressed. The primary rock mass response stage was the extraction of the crown pillar. The secondary responses were associated with the cable bolt arrays mitigating some of the deformation of the hanging walls with more movement mid-span compared to the cable bolt horizon. Finally, the displacement results post-filling showed the backfill mass was being slightly compacted by ground movement.

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Concerns regarding the uncertainty of stope dilution at the MMG Limited's Dugald River underground mine led to a trial stoping program to acquire full-scale comprehensive geotechnical information and to test the validity of the geotechnical and mining parameters. A total of 19 stopes were mined by sublevel open stoping with cemented rockfill (CRF). Specific studies were completed on the rock mass response to mining, rock stress and property measurements, stope blast vibration monitoring, production drilling deviation, CRF optimisation, re-logging of diamond core for structural and geotechnical information. Based on the trial stoping results, key geotechnical inputs into mine design and scheduling were provided. These included:  Stope drill and blast parameters such as borehole orientation, explosive type and stope boundary stand-off distances.  Oredrive and crosscut drive locations to achieve required stope drilling parameters.  Stope strike length and overbreak predictions.  CRF optimisation.  Development through CRF.  The location and sizing of capital development in relation to orebody and major lithological units.  Ground support standards based on expected damage from stress.  Stope sequencing to minimise stress concentrations and location of regional pillars. The considerable volume of data and the practical experience gained during the trial mining greatly increased the geotechnical knowledge of the rock mass and its response to mining. This allowed for a wide range of geotechnical design considerations to be applied to the project feasibility study at a higher confidence level.

The Argyle Diamond Mine (ADM) was an underground block caving operation located in the East Kimberley region of Western Australia. The underground mine was operated from 2012 to December 2020. The mine is located in a tropical climate with very high monsoonal rainfalls, ranging from 600 mm to 1,800 mm during the annual wet season (December to March).A combination of high monsoonal rainfall, significant groundwater inflows, cave connection to the pit surface, and a high proportion of fines in the cave column contributed to a high number of mudrush events over the production life of the Argyle underground mine. The term 'uncontrolled flow of material' (UFM) was used at ADM instead of mudrush. UFM events was one of the critical risks to personnel safety at the ADM block caving mine during its operation.Over the life of the underground mine, more than 1,200 UFM events occurred, approximately 2 to 3 events every week during production of the cave. The UFM events typically ranged in size from 5 m³ to 4,000 m³. However, an extreme UFM event occurred in February 2020 that rapidly discharged 18,000 m³ material from the drawpoints, covering large sections of the extraction level and engulfing one of the underground crushers.Despite the risk to personnel that UFM events posed at ADM, there were no recorded injuries over the mine life. The effective management of these events was critical to ensure the safety of underground personnel and to achieve production targets. This paper details the risk management controls that were put in place to manage the risk of UFM events at ADM.