Open stope stability using 3D joint networks

The most popular exploitation method used in Canadian hard rock mines is open stope mining. Geomechanical design of open stopes relies on a range of analytical, numerical, and empirical tools. This paper presents an engineering approach for the analysis and the design of reinforcement for open stopes in jointed rock. The proposed methodology, illustrated by three case studies, relies on developing 3D joint network models from field data. The 3D joint networks have been successfully linked to a 3D limit equilibrium software package. The models account for the finite length of joints as well as the influence of random joints. The integrated approach facilitates comparative analyse

A design methodology for rock slopes susceptible to wedge failure using fracture system modelling

This paper demonstrates how the use of fracture system modelling can be linked to limit equilibrium analysis of rock slopes susceptible to wedge failure. The use of fracture systems highlights some of the limitations inherent in traditional structural data analysis and representation. Consequently it allows for more comprehensive input data that can be used for stability analysis of rock slopes. In particular the developed methodology addresses important issues such as spatial variability and wedge size distributions. The paper introduces a series of guidelines for interpretation of the results of rock slopes. The proposed techniques arguably result in an improved level of confidence in the design of rock slopes susceptible to wedge failur

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

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

Integrated structural stability analysis for preliminary open pit design

A design module has been developed for integrating slope stability analysis into the data management, ore reserve and pit optimisation processes of an open pit mine. The developed slope stability analysis tools were successfully implemented along the full projected pit model of a surface mine in Canada. Undertaken stability analyses included both kinematic and limit equilibrium stability analysis for bench and interramp design. The developed stability analysis modules employed geographical information systems (GIS) techniques to provide visualization tools and establish stability susceptibility zones along the pit. This approach facilitated the selection of acceptable slope design criteria for the pit. A case study was used to illustrate the developed methodology and tools. This approach led to an improved design for the optimised 3D pit configuration and can facilitate communication between the mine planning and geotechnical groups. This can contribute to a better understanding of the economic impact of the different slope and pit design scenarios. Given that open pit design is an iterative process, the opportunity of having design tools that can readily accommodate the use of updated data and explore different options provide tangible economic benefits

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

Inter-ramp and bench design of open-pit mines : the Portage pit case study

Cet article présente une méthodologie intégrée pour évaluer la stabilité structurale d’une pente aux niveaux de l’inter-rampe et du gradin, et ce, à partir d’une étude de cas. Des algorithmes robustes ont été développés et implantés afin de calculer, aux niveaux inter-rampe et gradin, les orientations et la stabilité des pentes à l’aide de données compatibles avec la structure de la base de données d’un logiciel commercial pour la conception de mines. Des analyses de stabilité multicritères ont été réalisées à partir des différents critères de conception. Des cartes de susceptibilité, qui permettent d’identifier les zones potentiellement problématiques dans la fosse, ont été produites. Les résultats obtenus suggèrent que les angles inter-rampe ne présentent pas de problèmes d’instabilité sur toute la surface de la fosse. Au niveau des gradins, des zones d’instabilité potentielles ont été identifiées à l’intérieur de deux domaines structuraux totalisant 6 % de la surface de la fosse.Using a case study, this paper presents an integrated methodology for assessing structural slope stability at the inter-ramp and bench levels. Robust algorithms have been developed and implemented to compute, at inter-ramp and bench levels, slope orientations and slope stability using input data compatible with a commercially available mine-design software tool database structure. Multi-criteria stability analyses were performed based on various design criteria. Susceptibility maps were produced enabling the identification of zones of concern in the designed pit. The obtained results suggest that inter-ramp angles do not present instability concerns over the entire pit surface. At bench levels, potential instability zones were identified within two structural domains totaling 6% of the total pit surface

Conception géomécanique de talus de mines à ciel ouvert

20 pagesInternational audienceRÉSUMÉ. Cet article présente les principes de base du dimensionnement des talus miniers relatifs à la création d'un modèle géotechnique, aux calculs de la stabilité, aux méthodes de confortement et de surveillance. L'article souligne les principales difficultés du dimensionnement des talus de mines à ciel ouvert, et finalement présente les principaux défis auxquels devront s'attaquer les géomécaniciens miniers pour optimiser le processus de conceptions de ces pentes. ABSTRACT. This paper presents mine slope design principles for geotechnical modeling, slope stability assessment, slope stabilization and monitoring. The paper also addresses the most common challenges associated with mine slope design and finally suggests issues that should be tackled by the mining geomechanicians to optimize the mine slope design process

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

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 project's 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 mine's block sizes and pit geometry

Capturing the complete stress–strain behaviour of jointed rock using a numerical approach

This paper presents the results of a series of numerical experiments using the synthetic rock mass (SRM) approach to quantify the behaviour of jointed rock masses. Field data from a massive sulphide rock mass, at the Brunswick mine, were used to develop a discrete fracture network (DFN). The constructed DFN model was subsequently subjected to random sampling whereby 40 cubic samples, of height to width ratio of two, and of varying widths (0.05 to 10 m) were isolated. The discrete fracture samples were linked to 3D bonded particle models to generate representative SRM models for each sample size. This approach simulated the jointed rock mass as an assembly of fractures embedded into the rock matrix. The SRM samples were submitted to uniaxial loading, and the complete stress–strain behaviour of each specimen was recorded. This approach provided a way to determine the complex constitutive behaviour of large-scale rock mass samples. This is often difficult or not possible to achieve in the laboratory. The numerical experiments suggested that higher post-peak modulus values were obtained for smaller samples and lower values for larger sample sizes. Furthermore, the observed deviation of the recorded post-peak modulus values decreased with sample size. The ratio of residual strength of rock mass samples per uniaxial compressive strength intact increases moderately with sample size. Consequently, for the investigated massive sulphide rock mass, the pre-peak and post-peak representative elemental volume size was found to be the same (7 × 7 × 14 m)