Martin Grenon

Drift reinforcement design based on discontinuity network modelling

The results of structural mapping are used to generate 3-D joint networks. By introducing a virtual excavation in the generated rock mass it is possible to identify all wedges that can potentially be defined at the exposed surfaces of the excavation. The number and size of these wedges are controlled by the geometry and orientation of the excavation, as well as the properties of the generated joint sets and individual random joints. Consequently it is possible to determine the stability of every individual wedge along the span of an excavation. The influence of various reinforcement strategies (type of bolts, reinforcement patterns, mesh, etc.) on the stability of an excavation is quantified. This is a prelude to an economic analysis whereby the costs associated with different stabilization techniques are assessed. This methodology is illustrated by means of three case studies in a polymetallic underground mine in the Canadian Shield.

Stability Analysis of the 19A Ore Pass at Brunswick Mine Using a Two-Stage Numerical Modeling Approach

The longevity of ore pass systems is an important consideration in underground mines. This is controlled to a degree by the structural stability of an ore pass which can be compromised by changes in the stress regime and the degree of fracturing of the rock mass. A failure mechanism specific to ore pass systems is damage on the ore pass wall by impact load or wear by material flow. Structural, stress and material flow-induced failure mechanisms interact with severe repercussions, although in most cases one mechanism is more dominant. This paper aims to provide a better understanding of the interaction of ore pass failure mechanisms in an operating mine. This can provide an aid in the design of ore pass systems. A two-stage numerical approach was used for the back analysis of an ore pass at Brunswick mine in Canada. The first stage in the analysis relied on a 3D boundary element analysis to define the stress regime in the vicinity of the ore pass. The second stage used a synthetic rock mass (SRM) model, constructed from a discrete fracture network, generated from quantitative rock mass field data. The fracture network geometry was introduced into a bonded particle model, in a particle flow code (PFC). Subsequently, the ore pass was excavated within the SRM model. A stability analysis quantified the extent of rock mass failure around the ore pass due to the interaction of pre-existing fractures and the failure of the intact rock bridges between these fractures. The resulting asymmetric failure patterns along the length of the ore pass were controlled to a large degree by the in situ fractures. The influence of particle flow impact was integrated into the model by projecting a discrete rock fragment against the ore pass walls represented by the SRM model. The numerical results illustrated that material impact on ore pass walls resulted in localised damage and accelerated the stress-induced failure.

Applications of fracture system models (FSM) in mining and civil rock engineering design

Engineering design in rock must, implicitly or explicitly, take into consideration the influence of small and large scale geological fractures. The complexity of a jointed rock mass is best captured using 3D fracture system model based on quality field data. In this article, we describe on-going work in developing and implementing fracture system models (FSM) to solve three engineering problems using the developed stochastic fracture modelling tool, Fracture-SG. The first case study uses field data from 53 mine sites to demonstrate the advantages of using FSM, as compared to empirical classification indices to quantify the structural complexity of a rock mass. The second case describes the determination of a structural representative elemental volume (REV) along a rock slope, and the third case study describes the use of FSM as an integral part of the stability analysis of a slope subject to structural failures.

Slope orientation assessment for open-pit mines, using GIS-based algorithms

Abstract Standard stability analysis in geomechanical rock slope engineering for open-pit mines relies on a simplified representation of slope geometry, which does not take full advantage of available topographical data in the early design stages of a mining project; consequently, this may lead to nonoptimal slope design. The primary objective of this paper is to present a methodology that allows for the rigorous determination of interramp and bench face slope orientations on a digital elevation model (DEM) of a designed open pit. Common GIS slope algorithms were tested to assess slope orientations on the DEM of the Meadowbank mining projects Portage pit. Planar regression algorithms based on principal component analysis provided the best results at both the interramp and the bench face levels. The optimal sampling window for interramp was 21×21 cells, while a 9×9-cell window was best at the bench level. Subsequent slope stability analysis relying on those assessed slope orientations would provide a more realistic geometry for potential slope instabilities in the design pit. The presented methodology is flexible, and can be adapted depending on a given mines block sizes and pit geometry.

Analysis of a large rock slope failure on the east wall of the LAB Chrysotile Mine in Canada: back analysis, Impact of water infilling and mining activity

Abstract A major mining slope failure occurred in July 2012 on the East wall of the LAB Chrysotile mine in Canada. The major consequence of this failure was the loss of the local highway (Road 112), the main commercial link between the region and the Northeast USA. LiDAR scanning and subsequent analyses were performed and enabled quantifying the geometry and kinematics of the failure area. Using this information, this paper presents the back analysis of the July 2012 failure. The analyses are performed using deterministic and probabilistic limit equilibrium analysis and finite-element shear strength reduction analysis modelling. The impact of pit water infilling on the slope stability is investigated. The impact of the mining activity in 2011 in the lower part of the slope is also investigated through a parametric analysis.

Rock slope stability analysis using fracture systems

This paper presents a methodology whereby statistically representative fracture patterns can be used for an accurate representation of structural discontinuities in rock. This implies that field data can be used to generate characteristic fracture systems for a rock mass. It is then possible to introduce any range of slope geometry in the generated rock mass. The stability of such excavations can be evaluated using traditional limit equilibrium analysis. The advantage of this approach is that it can consider the influence of both large-scale (major) fractures whose relative location in the rock mass is well defined and minor fractures whose location and orientation is defined by probabilistic algorithms. This is demonstrated in this paper with reference to a rock slope susceptible to wedge-type failures.

Discrete fracture network based drift stability at the Éléonore mine

Photogrammetry tools were used to characterise the rock mass structural regime at selected mining drifts at the Éléonore underground mine in Canada. This information was used to provide the input data for generating a series of discrete fracture networks (DFN) models. The generated DFN models were subsequently used to investigate the creation of rock wedges along the drifts that may impact the stability of the excavations. The impact of the choice of employed DFN model on the analysis was investigated with reference to the stability of excavations. A series of parametric analyses demonstrated the sensitivity of the model to variations in the properties of the structural regime. The benefits of using stochastic modelling to capture the inherent variability are reviewed.

Quantifying in-situ rock block size and resulting fragment size distributions due to blasting

Abstract The structural regime of the rock mass has an important influence on the resulting blast induced fragmentation. This paper presents a case study whereby the in-situ block size distribution is determined based on field data. This is compared to resulting fragmentation after blasting assessed by image analysis of photographs.