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The orebody at Eleonore Mine (Eleonore) consists of multiple lenses of narrow thickness. Owing to ground stability issues, the capacity of the support was increased and the mine sequence was changed successfully in 2016. In 2018, mine-scale geomechanical numerical analyses were conducted in the continuum code FLAC3D to better understand the conditions leading to these improvements and further optimise the sequence. Locations of falls of ground and damage, blast hole performance and a micro-seismic database were used to calibrate the model, and different future mining sequences were analysed. The models helped demonstrate that persistent shallow dipping joints subject to high horizontal stress put a lot of demand on bolts in the back of excavation; they are likely to be the main source of energy release as they are sheared peripheral to the top and bottom of the stopes. The narrow-mined width and good rock strength involve limited stope interaction, resulting in highly stressed remnant stopes and limited impact of the sequence.

Operations at Westwood mine in Quebec, Canada, were temporary halted in May 2015 after three large-magnitude seismic events occurred over two days. The mechanisms leading to these events, which caused severe damage to several accesses, were not well understood at first. This was partly due to the complex geology at the site, where massive, unaltered, strong, brittle, and seismically active rock can alternate with highly altered, weak, foliated, and buckling-prone rock at the meter scale. Other ground behaviours such as the significant discrepancy in blasthole performance between secondary and primary stopes and the propagation of damage from stopes to haulage drives in some locations were also not well understood. In 2017, further geotechnical characterization of the rock mass was carried out and numerical back-analyses of several locations were completed using the continuum code FLAC3D. The objectives of the back analyses were to better understand the mechanisms controlling rock mass performance and to obtain a calibrated model for predictive stoping simulations. This paper presents the key aspects of the modelling, which include: (1) An anisotropic rock mass strength model with properties derived from field and lab strength testing, and (2) a scheme to account implicitly for the deconfinement that accompanies buckling around excavations.

The ability to understand and predict the effectiveness and evolving capacity of ground support in mine accesses is paramount to the success of an operation. This paper describes the results of numerical modelling studies of ground support performance in access drifts at Eleonore Mine. These drifts are located in competent rock with undulating sub-horizontal and vertical jointing present and are subjected to mining-induced stress. The studies employ Bonded Block Models (BBM) with explicit ground support represented by the newly developed hybrid bolts in 3DEC (Itasca Consulting Group, Inc. 2016a). These models are used to back-analyse and understand past falls of ground as well as to evaluate the adequacy of the current designs to handle future conditions as mining advances. The shallow dip and undulation of the sub-horizontal joints strongly impact the back behaviour in accesses, with joints susceptible to shearing and opening under high horizontal stresses. The results of the study elucidated that the falls of ground experienced at the mine are due to the bolts in the back (#6 rebar) being heavily strained locally through sub-horizontal joint shearing as nearby stoping took place, causing them to rupture. As foreseen by the mine in 2016, the model results confirm the need for bolts with higher shearing capacity to support the on-ore drifts. Both D-bolts and #7 rebar were analysed as alternatives with the model and shown to provide superior deformation compatibility, which agrees with experience on the mine. D-bolts offer a less stiff response (which increases survivability under highly localised deformations), while #7 rebar offers a higher yield strength. This paper describes how numerical models that allow for realistic fracturing and bulking of the rock mass along with explicit representation of pre-existing discontinuities can be used to more realistically model ground support performance in competent rock.

Validation and calibration of numerical models is vitally important, particularly in the field of cave mining where our ability to monitor the caving rock mass is limited. As part of a project investigating caving mechanics, physical models of caving were tested in a geotechnical centrifuge (Cumming-Potvin et al. 2016b). This paper describes numerical simulations of one of the centrifuge tests. Two approaches were used, so the relative strengths and weaknesses could be compared. The Itasca caving algorithm approach was implemented in FLAC3D and a bonded block model (BBM) approach implemented in 3DEC. The results showed that there was a good match with the physical model in some respects. Both numerical approaches were able to capture the discontinuity in the damage profile seen in the physical model, and the shape of the failed zones also matched the physical model well. The match appeared to be better for the BBM approach. There is some uncertainty as to whether the mechanism of failure seen in the physical model was exhibited in the numerical models. The match between the numerical and physical models could have been improved via further calibration. However, this was outside the scope of this study. Overall, the results show that the numerical approaches used are suitable for practical use in the modelling of caving, particularly if they are suitably calibrated and/or validated using in situ monitoring data.

The design of effective ground support is critical to the success of the next generation of large cave mines. Typically, the behaviour of rock in this setting is controlled by shear and opening movements along fractures induced by the excavation and cycles of loading and unloading during mine development and operation. Support of highly stressed fractured rock shows two important aspects: (i) in blocky or fractured rock the majority of the support deformation is localised at fractures or joints and (ii) the resistance to fracture shear displacement offered by support is important. These observations have led to the use of the discrete element method based three-dimensional bonded block model (BBM) to represent the rock and the hybrid bolt model to represent the bolt support. The hybrid bolt model is an improvement on the classical cable bolt model, which features a more realistic resistance to fracture shear displacement and allows bolt installation in a fractured rock mass exhibiting open joints. This paper presents the application of the BBM and hybrid bolt numerical model to study the performance of tunnelling at depth under a caving-induced stress path. The effect of support pressure, bolts presence, and partial debonding of bolts, is explored. The influence of rock mass quality and support installation timing on the support efficiency is also investigated. It has been found that a small surface pressure is critical for tunnel performance. When a rock mass experiences large deformation and joint opening, local axial and shearing straining of bolts at joints intersection become important and can lead to rupture. Intense axial straining can be mitigated through debonding and intense shearing can be reduced through the use of bolts with higher shear resistance, such as rebars. Keywords: tunnel support bolt, numerical simulation, bulking, 3DEC