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The proper understanding of the functioning of ground support under dynamic loading and the current approaches to designing of dynamic support is plagued by a great deal of uncertainty and lack of knowledge. This applies equally to the understanding of the support capacity as well as the demand placed on to the support due to dynamic loading. Stacey (2012) suggests that the lack of understanding currently leads to a case of design indeterminacy. This paper does not aim to solve this problem of design indeterminacy but to explore some of the issues that need considerations to better understand the dynamic demand on ground support systems.

Reservas Norte (RENO) is one of the panel caving sectors of El Teniente mines, owned by Codelco Chile. The sector has experienced mine induced seismicity for many years. The work presented in this paper focuses on seismic activity recorded between the period from January 2004 to July 2008. The interpretation of the seismic data revealed that the sources of elevated seismic hazard (large events) at RENO during this period could be attributed to four major geological structures: Falla G, Falla F, Falla C, Falla N1. In particular, the seismic response of the four structures to undercut blasting activities is examined in detail. The use of numerical modelling has shown that it is possible to simulate this response after calibrating the model against the cumulative seismic moment released by the faults, as mining advances towards them. This calibrated numerical model can then be used to forecast future seismic responses. The main product of this work is a tool that can be used to rank different undercutting rates and geometries in terms of seismic hazard.

Rockburst risk is an increasing problem in underground mining worldwide, as the general trend is for mines to operate in deeper environments. In most mines affected by seismicity, the first line of defence to mitigate the potential consequences of rockburst is to install dynamic resistant ground support systems. The assessment of ground support capacity when submitted to dynamic loading has been the subject of intensive research over the last two decades. In particular, drop tests were developed to investigate the capacity of support elements while the performance of various support systems was examined by simulating rockbursts with carefully designed blasts. The above research has yet to yield an accepted method to determine the dynamic capacity of ground support. In this paper, the published results from many of the above tests are compiled and practical observations are made regarding the dynamic capacity of ground support systems.

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The Duplancic model of caving (Duplancic, 2001) is widely accepted in industry and is the framework within which most monitoring and numerical modelling results in caving mines are interpreted. The Duplancic model was created based primarily on simple microseismic analysis and linear elastic numerical modelling of one case study. At the time, it provided a much-needed interpretation framework and, as a result, has been applied to numerous mines. The model is generally interpreted as indicating that the damage ahead of the cave back in block caving mines continuously decreases with increasing distance from the cave back. From basic seismic analysis and with the assumption that slip along preexisting discontinuities will take place preferentially to intact rock failure, Duplancic found that the most likely failure mechanism in the cave crown was slip along pre-existing discontinuities. As such, the model downplays the role of intact rock failure, including extensional failure. Extensional fracturing occurs parallel to the major principal stress and perpendicular to the maximum extensional strain. This may occur under a compressive macro-stress regime (Stacey, 1981).Physical modelling of cave development in a centrifuge was carried out, and the results of the physical modelling did not correspond with the expectation of the Duplancic model. The main mechanism of cave propagation observed in the physical models was via a series of extensional fractures parallel to the cave back.This discrepancy between the Duplancic model and the physical model raises the question whether the governing mechanism evident in the physical models is also present in the field, and whether the Duplancic conceptual model for caving mechanics should be reviewed.A literature review revealed that several observations that were made in the past support the existence in the field of the mechanism evident in the physical models, although it seems that the importance and the full implication of these observations were not appreciated by the respective authors.In addition to the physical models and literature review, an investigation was performed in order to establish whether any banding formation can be supported by the interpretation of microseismic monitoring data in modern block caving mines. Analysis of microseismicity was conducted at two large copper-gold porphyry block cave operations. The results of the analysis indicated that the mechanism seen in the physical model may have occurred at both mines. This paper discusses the Duplancic model and presents an overview of the results from the physical modelling, literature review, and microseismic event monitoring.Fracture banding in caving mines by D. Cumming-Potvin*, J. Wesseloo*, S.W. Jacobsz † , and E. Kearsley † The Duplancic model of caving is widely accepted in industry and is the framework within which most monitoring and numerical modelling results in caving mines are interpreted. As a result, the damage profile ahead of the cave back is often interpreted as continuously decreasing d...

The Duplancic conceptual model is the industry accepted model of caving and is the framework within which most results from numerical modelling and cave monitoring are interpreted. The Duplancic conceptual model implies that the damage ahead of the cave back decreases continuously with increasing distance from the cave surface. Evidence from a variety of sources indicates that this may not always be the case and that a discontinuous damage profile may be present. Cumming-Potvin et al. (2016b) describes a physical modelling program which was undertaken to investigate the fracturing and propagation of the cave. The results of these centrifuge tests showed that caving could occur via a series of fractures oriented parallel to the cave surface and that the cave back progressed vertically via 'jumps' to the next successive parallel fracture. In Cumming-Potvin et al. (2016a), this caving mechanism was termed 'fracture banding'. Multiple examples of a similar mechanism of failure were observed in literature. In addition, the patterns in microseismic event location indicate that fracture banding could be occurring in currently operating caving mines. This paper examines evidence from a number of sources in the field of caving mechanics and presents an extended conceptual model of caving. The new model is able to account for the mechanism of fracture banding, along with the continuous style of failure from the Duplancic conceptual model. There are still many unknowns about the fracture banding mechanism and propagation of caves. These include the specific conditions under which the caving mechanism changes and whether the mechanisms lie on a continuum, or if there is a sharp, sudden change. Two conceptual models are presented: one which includes only that which is known about the mechanisms of cave propagation and one which speculates upon the factors involved and the underlying origins of the fractures.