Cadia Valley Operations (Cadia) embarked on a path of cave mining in the early 2000s with the establishment of the Ridgeway sublevel cave. The success of that mine led to a significant expansion into block caving operations, first at Ridgeway Deeps, and then to the now established Cadia East operations. What makes Cadia unique is the high-stress, hard rock mining conditions combined with the ability to maximise investor returns through the use of very high lift heights at depths of between 1,200 to 1,400 m. Over the last decade, a significant amount of geotechnical and mining operations knowledge has been gained. A strong safety culture, combined with innovative thinking, has allowed Cadia to challenge existing industry paradigms using empirical data, a proof of concept type approach, followed by rapid implementation. Cadia East is now poised to begin another phase of development as it continues on a multi-decade mine life to exploit over one billion safe tonnes of ore. A critical path for ensuring success is the conversion of the geotechnical knowledge into practical planning guidelines that can be easily understood and adopted during cave feasibility, establishment, and full production phases. This paper summarises the key elements of geotechnical knowledge and its input into the mine planning for the future of Cadia Valley Operations.

The management of seismic risks in metalliferous mines operating in developed mining countries such as Australia, Canada, Chile and Sweden has been very successful during the last decade. The occurrence and magnitude of large seismic events in deep mines has continued to increase with mining reaching deeper horizons, yet, injuries and fatalities due to rockbursts remain very rare in these countries. Although there are many common practices used to manage seismic risks in mines, there is no recognised process to do so. In 2017, Newcrest Mining Ltd, in collaboration with the Australian Centre for Geomechanics (ACG), undertook a benchmarking campaign to document the different seismic risk management practices currently implemented in mines which are considered leaders in this area. Data was gathered from 16 mines operating in five countries, experiencing different degrees of seismicity. Analysis of the data from the benchmarking study led to a better understanding of seismic risk management practices applied in the industry. One of the important outcomes of this project was the development of a flowchart describing in detail a generic seismic risk management process. The process is broken into four different layers of activities: data collection, seismic response to mining, control measures, and seismic risk assessment. Within each layer of activity, there are a number of components, and within each component, there are a number of practices, which have been benchmarked and are discussed in this paper. In addition to providing a road map for managing seismicity in underground metalliferous mines, this work enables users to assess their own practices against standard and advanced practices in the management of seismic risks. A full description of the seismic risk management process is available to the mining industry at https:

Numerous tunnels of the extraction and undercut levels of the Pilar Norte sector experienced violent damage on 24 December 2011. A seismic event with a moment magnitude of 2.4 was recorded by the mine-wide seismic system at the same time. It is difficult to explain the observed damage with peak particle velocities/peak ground velocities calculated for the basic source parameters of this event (location and magnitude). Seismic data recorded in Pilar Norte in 2011 indicate that failure in the sources is driven by sub-vertical compressional stress. The majority of seismic events located around the undercut level have crush-type source mechanisms (significant implosive component, pancake-shaped deviatoric parts with sub-vertical P-axis) evidencing vertical convergence of the excavations. There are no clear indications of active planar geological structures in the seismic data. The large seismic event that occurred on 24 December 2011 during the blasting sequence and its waveforms are complex. The source mechanism estimated from the low frequency part of the waveforms is of a crush-type. It was hypothesised that the source of this event represents a cascading damage of tunnels. The hypothesis was tested by means of comparing the modelled waveforms of spatially distributed episodes of tunnel damage with the recorded waveforms. A reasonable match was obtained for the scenario including an initial 20 mm convergence of the extraction and undercut drives around the southern Pilar Norte undercut front at a rate of 0.6-0.8 m/s and subsequent spread of smaller (3-6 mm) convergence along the eastern Pilar Norte undercut front and eastern Sub 6 cave abutment at a rate of 0.2-0.4 m/s. There was also significant shearing (ride) deformation along the southern and eastern Pilar Norte cave front. The hypothesis of cascading damage of tunnels also agrees with the underground observations (more than 90% of damage was attributed to the side walls of tunnels) and predictions of sub-vertical orientation of maximum principal stress around the tunnels of the extraction level according to a numerical stress model.

Cadia Valley operations is a gold-copper deposit located in Orange, New South Wales, Australia. Currently, two macroblocks are in production-PC1-S1 and PC2-S1 of Cadia East at undercut levels 4670 and 4475, respectively. The production rate during 2016 reached approximately 43 ktonne/day for PC1 and 19 ktonne/day for PC2. These macroblocks have implemented different variants of the block caving method and have different rock mass characteristics and depth. The PC1-S1 block was subjected to intensive preconditioning, hydraulic fracturing (from Gallery 5050) and DDE (blasting), for a column height of 400 m from the production level (4650 mRL). Finally, to propagate the caving effectively to surface, hydraulic fracturing was performed at 500 m below surface (maximum-depth hole). PC2-S1 was preconditioned only by hydraulic fracturing and is located 194 m below PC1. These two macroblocks are at different stages of maturity. PC1, a mature cave, has shown a fine fragmentation, which diminished notably as the cave back reached the surface in 2014. Consequently, there have been few observed hang-ups, resulting in a high production rate when compared to caving standards. On the other hand, PC2 has caving in progress and has shown a coarser fragmentation, and a large number of hang-ups. Therefore, prediction capabilities for hang-ups for PC2 is critical for planning purposes. In order to understand and model hang-ups for PC2, a BCRisk® model was built. BCRisk is a methodology to assess key gravity flow-related risks based on logistic regression. A BCRisk model of hang-ups delivers the probability (P) that the hang-up rate (HUR) would exceed 1 event/1,000 tonnes, that is P(HUR > 1). A univariate statistical analysis indicated that the key variables to be considered were the accumulated draw height (m), the uniformity draw index and the rock mass rating (RMR). The same analysis indicated that the different lithologies observed at PC2 were not a key variable. Each of the key variables has a significant and relative impact on P(HUR > 1). An increase of 10 m on the draw height decreases the probability of hang-ups by 26%, an increase of the RMR in 10 units increases the probability by 30%, while an improvement of draw uniformity index (by 30%) decreases the probability by 13%. The P(HUR > 1) was compared to the hang-ups database of PC2 (which consider hang-up events measured during 2016). The model showed a good fit to the data with an 81% accuracy at predicting events in terms of the number of drawpoints and the percentage of active area that could present hang-up issues.

Ground support systems must provide safe and effective designs for underground excavations under high stress conditions. These systems must be capable to resist dynamic impacts and yielding during the loading process. In this context dynamic testing of the reinforcement and retaining elements that compose the ground support system are required to study and improve the behaviour of these elements under dynamic load events. During the last years, Geobrugg has been working on the improvement of retaining products by testing them in a large-scale impact test facility located at Walenstadt, Switzerland. The test facility is composed of a double level platform with a square-shaped pyramidal trunk geometry, the upper level houses a loading mass that drops from a height up to 5 m. The loading mass is guided by one central steel pipe, and the impact occurs in the sample to be tested, which is located at the lower level in a slab with an area of 3.6 m × 3.6 m. This is where the ground support system is installed. During the last few years, this innovative facility has been used to test several configurations of ground support systems. The results of these tests have enabled the authors to improve the understating of the behaviour of ground support systems under dynamic loads. In this manuscript, the arrangement, measurement, results, and the preliminary analysis of large-scale dynamic tests of two ground support systems performed in 2019 and 2021, supported by the Advanced Mining Technology Center (AMTC -University of Chile), are presented.