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By Wedam Nyaaba, Samuel Frimpong, Bruno Ayaga Kansake, Irene Akalanyaba Ateng

Haul truck capacities have increased due to their economies of scale in large-scale surface mines. These high-capacity trucks impose dynamic loads on haul roads. A previous study estimated the dynamic forces imposed by ultra-large trucks on haul roads to be more than three times the static load. These dynamic forces exacerbate haul road stresses and deformation. Current haul road response models are 2D and use static truckloads for low-capacity trucks. No models capture the ultra-large truck dynamic effects on haul road structural response. This study uses 3D finite element (FE) modeling to compute the haul road response to ultra-large truck dynamic loading. The dynamic forces were modeled using multibody dynamics (MBD) in MSC.ADAMS. These forces were used in an FE model developed, verified, and validated in ABAQUS, to simulate the response of the haul road to the dynamic truck forces. The road was modeled using an elastoplastic Mohr-Coulomb model. The results showed that road deformation decreases with increasing layer modulus and increases with increasing payload. Increasing the base modulus from 100 MPa to 450 MPa reduced the maximum deformation from 258 mm to 62 mm. When the subbase elastic modulus increased from 100 MPa to 500 MPa, the maximum deformation decreased from 160 mm to 84 mm. Increasing the payload from 0 to 120% of the rated load increased the maximum wearing surface deformation from 131 mm to 216 mm. This study forms a basis for designing structurally competent haul roads for improving haulage efficiency and truck and operator health.

Jan 7, 2023

Owing to improvements in computer capacity, it is now possible to undertake fully coupled or partially coupled, three-dimensional (3D) hydromechanical Finite Element (FE) simulation of mines, including explicit representations of large numbers of discontinuities. The analysis requires fewer assumptions than uncoupled analysis or two-dimensional (2D) analysis, but may require a change in how hydrological data is collected. The way hydrological data is incorporated in stability assessment and the approach to uncertainty in hydrological information also requires discussion. The current procedures for this type of analysis are discussed, along with some practical difficulties and teachings from early applications. A work flow for integration of 3D hydromechanical modelling with pit planning and some considerations for the management of uncertain data are also proposed.

May 1, 2010

By C A. Foss, D A. Clark, D Hillan

While magnetic surveys are the most common geophysical method used in mineral exploration, magnetics and geology remain to be fully integrated quantitatively in iron ore provinces. Although high-resolution aeromagnetic data has been collected over prospective areas of the Hamersley Province, much of the information in the data sets has hitherto not been fully exploited due to a lack of suitable interpretation methods. Recent advances in the processing and modelling of magnetics in highly magnetic terrains, constrained inversion and 3D visualisation and understanding the magnetic properties of banded iron formations and iron ores potentially create the capability to generate realistic 3D mapping of magnetite and hematite concentrations over large areas. Initial processing of conventional total magnetic intensity data produces true potential field maps that are unaffected by local perturbations of the regional geomagnetic field direction by intense local anomalies. The true potential field can be converted into vector and tensor components, each of which emphasises different structural features of the geology. Scalar quantities derived from these components simplify interpretation, using new methods, developed by CSIRO and elsewhere, that are less sensitive to magnetisation direction. Preliminary interpretations allow interpolation between mapped units and structures and evaluation of remanence and anisotropy effects. Accurate modelling requires rigourous treatment of self-demagnetisation and magnetic interaction effects. Semi-automated constrained inversion, combining magnetics with available geological information and other geophysical data, can be utilised to generate models of disposition of major magnetic units and the 3D magnetisation distribution within them. The final stage of interpretation is to exploit the understanding of magnetic properties (susceptibility, anisotropy and remanence) developed over many studies by CSIRO, the University of Western Australia and others to convert the interpreted magnetisation distributions into 3D maps of magnetite and hematite contents, which are the quantities of direct exploration interest.CITATION:Clark, D A, Foss, C A, Austin, J and Hillan, D, 2015. Three-dimensional mapping of magnetite and hematite concentrations from reprocessing of detailed aeromagnetic data, in Proceedings Iron Ore 2015, pp 229–240 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 13, 2015

By Chan. C. L., Zehr. R., M. M. Chen, J. Mazumder

"Two three-dimensional models of a surface tension gradient driven flow during laser surface heating are developed. The first model is based on a perturbation solution. The basic solution corresponds to the stationary axisynwnetric case and perturbation is based on a small scanning velocity. The advantage of seeking a perturbation solution, as it turns out, is that the three-dimensional flow is modeled by two sets of two-dimensional equations which are presumably much more tractable than the original three-dimensional equations. Numerical solutions are obtained and discussed. The second model is a full three-dimensional numerical solution of the Navier-Stokes equations, using a point-by-point partially vectorized iteration scheme. Surface shape is also determined in a self-consistent manner. The effect of the presence of convection on pool geometry, cooling rate and solute redistribution is presented and discussed.IntroductionThe existence of fluid flow and convection and their effects were first reported in the fifties (1,2). The role of convection in controlling pool geometry such as pool shape, undercut and ripples, and defects such as variable penetration, porosity and lack of fusion and weld properties such as weld homogeneity and bead formation is studied by a number of researchers and is reviewed by the authors in a recent paper (3).Recently, surface tension gradient driven flow has been identified as one of the forces responsible for convection within the molten pool (4,5). It is postulated that surface tension gradient driven flow is responsible for the surface ripple formation in the weld pool (6-8). Oreper, et al. (9) developed a two-dimensional convection model. Buoyancy, electromagnetic and surface tension gradient forces were considered. The formulation was based on a specified pool profile. It was found that the surface tension gradient is the dominant force in most cases. However, the solid-liquid interface is not known a priori. In fact, the solid-liquid interface, i.e. the pool shape, is a piece of information that the model should be able to predict. A two-dimensional transient self-consistent (i.e. the solid-liquid interface is solved as part of the solution] model for laser surface melted pool was first developed by Chan, Mazumder, and Chen (3)). This model predicted a non-uniform cooling rate, hence non-uniform microstructure. Depending on the Prandtl number (i.e. material) and surface tension number, the shape of the molten region as well as the cooling rate changes. It was also predicted that the recirculating velocity is of one or two order of magnitude higher than that of the scanning velocity. This model provides the detail of the flow field and heat transfer on a plane perpendicular to the scanning direction. However, the front-to-back motion and its effect on heat transfer also play important roles in the physical process, especially for the fact that the recirculating velocity is so much higher than the scanning velocity. Such a motion cannot be obtained from two-dimensional models."

Jan 1, 1986

By K. V. Raj, T. Bhowmick

"Control of fugitive dust in high latitude open-pit mines is challenging due to unique atmospheric phenomenon resulting in complicated flow regimes, and atmospheric inversion due to lack of adequate solar insolation during prolonged winter seasons. In this study, two idealized (One conical and one trapezoidal) three-dimensional open-pit mine geometries are simulated for differing seasonal conditions using the CRADLE-CFD package. The airflow is modeled using Standard Kappa-Epsilon Turbulence Model solved by RANS equations. The concept of particle tracking is used to predict the flow pattern of dust particles. For various climatic conditions, and two different pit geometries, fugitive dust particles varying in size (PM0.1 to PM10) and concentration are generated at various locations of a mine and dispersed by the airflow pattern inside the open-pit mine. The amount and location of dust particles inside the pit is reported at various time intervals. The development of atmospheric inversion during the winter season significantly affected the amount of dust retention inside the open-pit domain. While during the summer, airborne dust particles were transported outside the open-pit domain in a short time. INTRODUCTIONComputational fluid dynamics (CFD) modeling of open-pit mines is challenging. In a recent paper, Bhowmick et. al. [1] presented different constraints and challenges in developing a 3-Dimensional CFD model. In order to obtain realistic results from a simulation, however, appropriate values of various inputs are required. Simulation results of a 3D non-hydrostatic model by Shi et al. [2] showed that both the mechanical and thermal forcing are important mechanisms, controlling the development of the atmosphere inside an open-pit. Alvarez et al [3] used a CFD model for predicting dust dispersions in a medium sized limestone quarry, and presented several iso-surfaces of varying dust concentrations using ANSYS CFX. A similar study by Torno et al [4] introduced a more sophisticated parameterization of the dust sources. Flores et al. [5] used an OpenFOAM CFD simulation package to simulate and predict pollutant dispersion in an idealized and an actual open-pit mine in Chile with an intense insolation condition. The model was simulated for three different conditions: (i) air advection (10 m/s) driven mechanical turbulence; (ii) surface heat flux (240 W/m2) driven thermal buoyancy; and (iii) both air advection and surface heat flux driven conditions. The results of the simulations showed that the buoyant currents contribute to the removal of a large percentage of the dust particles. The buoyant currents modify the purely mechanical-turbulence induced flow pattern and reduce the particle residence time, commonly observed in a purely mechanical turbulent flow (non-buoyant case)"

Jan 1, 2015

By K. V. Raj, T. Bhowmick

"The control of fugitive dust in high-latitude openpit mines is challenging due to unique atmospheric phenomena resulting in complicated flow regimes as well as atmospheric inversion due to the lack of adequate insolation during prolonged winter seasons. In this study, two idealized (one conical and one trapezoidal) three-dimensional openpit mine geometries were simulated for different seasonal conditions using a computational-fluid-dynamics package from Software Cradle. The airflow was solved by Reynolds-averaged Navier-Stokes equations using the standard kappa-epsilon turbulence model. The concept of particle tracking was used to predict the flow patterns of dust particles. For various climatic conditions and two different pit geometries, fugitive dust particles varying in size, from PM0.1 to PM10, and concentration were generated at various locations and dispersed by the airflows inside the openpit mine. The amount and location of dust particles inside the pit were reported at various time intervals. In the summer season, airborne dust particles were quickly transported outside the openpit domain. In the winter season, however, the development of atmospheric inversion significantly affected the amount of dust retention inside the openpit domain. IntroductionThe computational-fluid-dynamics (CFD) modeling of openpit mines is challenging. In a recent paper (2015), we presented different constraints and challenges in developing a three-dimensional CFD model. In order to obtain realistic results from a simulation, however, appropriate values of various inputs are required. The simulation results of a three-dimensional nonhydrostatic model by Shi et al. (2000) showed that both the mechanical and thermal forces are important mechanisms, controlling the development of the atmosphere inside an openpit mine. Alvarez et al. (2007) used a CFD model for predicting dust dispersions in a medium-sized limestone quarry, and presented several iso-surfaces of varying dust concentrations using ANSYS CFX. A similar study by Torno et al. (2010) introduced a more sophisticated parameterization of the dust sources. Flores et al. (2014) used an OpenFOAM CFD simulation package to simulate and predict pollutant dispersion in an idealized and an actual openpit mine in Chile with an intense insolation condition. The model was simulated for three different conditions: (1) air-advection (10 m/s, or 33 ft/ sec)-driven mechanical turbulence, (2) surface-heat-flux (240 W/m2, or 76 Btu/ ft2-h)-driven thermal buoyancy and (3) both air-advection- and surfaceheat- flux-driven conditions. The results of the simulations showed that the buoyant currents contribute to the removal of a large percentage of the dust particles. The buoyant currents modify the purely mechanical-turbulence- induced flow pattern and reduce the particle residence time, commonly observed in a purely mechanical turbulent flow (nonbuoyant case)."

Jan 1, 2015

By R Bertuzzi

This paper presents a three-dimensional analysis of a trapezoidal-shaped segmental tunnel lining for a recent tunnelling project in Sydney. Two- dimensional analyses, hand calculations and equipment selection defined the lining geometry and loads. The analysis, which was undertaken using 3DEC (Itasca), included a complete ring of six segments bolted together to assess the impact of imperfectly built rings. Asymmetry was induced in the analysis by unfavourable positioning of segments within construction tolerances. Model output includes displacement and stress within the entire ring and normal, shear and bending moments at the joints. For the case analysed, the results suggest a 10 mm construction tolerance increases normal and shear stresses along the radial joints by approximately 25 per cent and 15 per cent, respectively and up to a doubling of the induced moments.

Jan 1, 2008

By L. T. Isaacs, W. H. Traves

A numerical model for analysing the drainage of fill in mine stopes has been described. The model can be used to analyse the process of fill drainage in existing and proposed mine stopes. The validity and potential value of the model have been established by experience with a simpler, 2-dimensional numerical model and by testing the new model against the earlier model. The new model is more useful than the 2-dimensional model because it allows for heterogeneity of fill material within the stope - a factor that has been demonstrated to affect drainage characteristics significantly. The 3-dimensional model is also capable of predicting pore pressures and drainage rates at specific locations in the stope without the need to resort to 2-dimensional generalisations. Such information, integrated with relevant field data as they become available, will provide valuable mine planning information for the scheduling of filling operations and design of fill mixes

May 1, 1991

This paper describes the application of a three-dimensional finite element modelling tool to help assess the stability of a highwall at a Central Queensland mine following the weakening of its base due to highwall mining. With traditional stability assessment techniques, likely failure modes are identified on the basis of previous experience and structural, sedimentological and geomechanical data and a mechanistic analysis of these individual modes is performed. The value of the full three-dimensional model over these traditional techniques is that it provides a coherent approach to assessing highwall stability without the necessity of initially deciding upon the dominant failure mechanism and gives a useful adjunct to the traditional tools. The three-dimensional model assumes the rock mass is made of elasto-plastic blocks, incorporating possible planes of weakness, separated by near horizontal joints. The model includes the relaxation of stresses due to the excavation of the highwall and incorporates estimates of blast damage near the highwall surface

Jan 1, 1995

By Onur Kacar

A numerical approach has been implemented to assess the settlements of pile groups bearing in clay. A three-dimensional finite element program has been utilized to model a vertically loaded spread footing, a single pile and a pile group. The soil-pile interaction was modeled with elastoplastic soil and interface elements. The model has been calibrated using a full scale load test results of the spread footing. The load transfer between the pile cap and the piles was assessed and compared with the measured load transfer. The predicted settlements for the pile group were compared with the settlements measured in the load test. Two analytical methods were adopted to predict the pile group settlements and they were compared with the measured values. The group effect determined from the analysis and load tests was compared with the interaction factor approach. It was shown that three-dimensional finite element approach can be successfully utilized to assess the soil-structure interaction and hence the load transfer between the piles and pile cap. Also, it was shown that the interaction factors method and equivalent footing method work well in the working stress range, however they underpredict the settlements at larger loads. INTRODUCTION The settlement and stress distribution of pile groups have been traditionally estimated based on load test results of single piles and accounting for the group effect using various approaches. The most widely used approaches are group interaction factor method, equivalent footing method and equivalent pier method. These approximate solutions are used very commonly in practice as full-scale load tests on pile groups are very expensive and time consuming. These approximate solutions are also adopted in design guidelines such as AASHTO LRFD Bridge Design Guidelines (2014) and FHWA Design and Construction of Driven Pile Foundations (2016). In this paper, a full-scale foundation load tests performed by Nagai et al. (1961) and reported by Koizumi and Ito (1967) is modelled using a three-dimensional numerical method. The settlements and the stress distribution on foundations were then compared with the traditional equivalent footing method and interaction factor methods.

Jan 1, 2018

By L H. Chapman, I J. Kelso, N H. S Oliver

Utilisation of modern 3D visualisation tools, can improve our ability to correlate between different datasets, and thus to produce more accurate geological models. Here, we present an application of such techniques to the Century Zinc Deposit, northwestern Queensland, Australia. This stratiform orebody is the second largest Zn resource in the world (167.5 Mt at 8.2 per cent Zn, 1.2 per cent Pb, and 33 g/t Ag). It is hosted in the Page Creek Syncline affecting Mesoproterozoic shales and siltstones of the Wide Supersequence of the Isa Superbasin. As in other deposits, (eg McArthur River, Lady Loretta, George Fisher and Dugald River), the mineralised sequence is bound by an important regional structure, the Termite Range Fault, which partly intersects the deposit along its Eastern side. This fault is thought have been active during sedimentation and probably also during mineralisation of the lowest part of the Wide Supersequence. The anastomosing geometry of this fault system and crosscutting relationships with other NE trending structures indicate that it was reactivated several times from Mesoproterozoic to at least late Devonian times (>1000 million years in total); as a result, the ore sequence is subdivided into several fault blocks.Using two different computer modeling packages (GOCAD and 3ds max), we have reconstructed and restored the stratigraphic horizon with the highest Zn content, realised a series of isopach maps for each mine scale stratigraphic unit, plotted the three-dimensional distribution of Zn, Pb, Ag, Fe and SiO2, and have begun to evaluate the degree of correlation between thickness changes and sulphide zoning. With this approach it is possible to better understand the timing of mineralisation from a genetic perspective, because the origins of the orebody are controversial. Three-dimensional reconstruction is a vital tool for identification of syn-sedimentary and post-sedimentary fault activity. In conjunction with sulphide precipitation, these are factors that greatly influence the stratigraphic thickness distribution. Post-sedimentary deformation can be recognised directly by core logging and pit mapping, but the effect of tectonic movements during sedimentation (growth faults in particular), that represents a substantial variable when we attempt to reconstruct basin evolution, is difficult to evaluate without this methodology. The 3D models improve our understanding of the local basin architecture, identifying similar grade characteristics at different structural levels and thus suggesting that much faulting and folding are post-mineralisation events. In addition, we identified several growth faults adjacent to thickened layers, representing two possible sedimentary depocentres. These thicker domains apparently relate to the highest Pb content. If further analysis of rocks, thickness and grade distributions support this preliminary correlation, then a syn-sedimentary model for mineralisation might be applied, and would contrast with the sub-surface model for mineralisation of Broadbent et al (1998).

Jan 1, 2003

By J. -C. Tricket, W. A. Düweke, S. Kock

The high-resolution three-dimensional (3-D) seismic reflection data acquired for Impala Platinum between 1998 and 2002 in the western Bushveld Igneous Complex form an integral part of Impala?s mine planning and development programme. These data are of sufficiently high quality to provide unprecedented 3-D models of the geological structure of the Merensky Reef and UG2Chromitite Reef, from which the mine deduces the size, geometry and distribution of mineable blocks. Conversely, the seismic data details zones of un-mineable ground caused by structural disturbances in the form of potholes, fault zones and pegmatoid intrusions. Furthermore, variations in dip and strike are well imaged, allowing the mine planners to optimize the mine design and layout. Current interpretation work is focused on enhancing the accuracy of these geological model seven further through the analysis of ?seismic trace attributes.? Preliminary testing on the Impala Platinum 3-D seismic volume has shown that attribute analysis has the potential to illuminate a number of geological reef disturbances that are otherwise ?invisible? in the original seismic time volume. Potential areas of improvement include inter alia: ?Improved definition of major fault zones ?Improved definition of zones of reef depression (?slumping?) ?Identification of reef terracing and/or reverse dip.. Keywords: 3D reflection seismics; Impala Platinum Ltd; seismic attribute analysis; Seismic Micro Technology (SMT); rock solid attributes; dip-azimuth; instantaneous phase and similarity.

Jan 1, 2004

By J. -C. Trickett

The high-resolution three-dimensional (3-D) seismic reflection data acquired for Impala Platinum between 1998 and 2002 in the western Bushveld Igneous Complex form an integral part of Impala?s mine planning and development programme. These data are of sufficiently high quality to provide unprecedented 3-D models of the geological structure of the Merensky Reef and UG2 Chromitite Reef, from which the mine deduces the size, geometry and distribution of mineable blocks. Conversely, the seismic data details zones of un-mineable ground caused by structural disturbances in the form of potholes, fault zones and pegmatoid intrusions. Furthermore, variations in dip and strike are well imaged, allowing the mine planners to optimize the mine design and layout. Current interpretation work is focused on enhancing the accuracy of these geological models even further through the analysis of ?seismic trace attributes.? Preliminary testing on the Impala Platinum 3-D seismic volume has shown that attribute analysis has the potential to illuminate a number of geological reef disturbances that are otherwise ?invisible? in the original seismic time volume. Potential areas of improvement include inter alia: ?Improved definition of major fault zones ?Improved definition of zones of reef depression (?slumping?) ?Identification of reef terracing and/or reverse dip. Keywords: 3-D reflection seismics; Impala Platinum Ltd; seismic attribute analysis; seismic micro technology (SMT); rock solid attributes; dip-azimuth; instantaneous phase and similarity.

Jan 1, 2005

By J. A. Cremeens, D. D. Overton, J. C. Varnier

"Slope failures that occurred in 2008 and 2009 at the Pikeview Quarry in El Paso County, Colorado, USA were investigated using three-dimensional discrete element modeling methods. Large scale block sliding failures occurred along weak bedding planes that dip steeply into an excavation located at the toe of the slope. Several mining sequences at the toe of the slope were simulated to evaluate the effects of various degrees of extraction and backfill on slope stability. Slope stability back analysis was conducted using pre-failure and post-failure conditions to determine the joint shear strength properties. Laboratory testing was also conducted to determine intact rock properties. Three-dimensional discrete element analysis was uniquely applicable to this evaluation because it allowed representation of shear stress of the basal sliding surface and it afforded evaluation of several scenarios of extraction and backfill at the toe of the slope. INTRODUCTION The Pikeview Quarry is an aggregate quarry located approximately five miles northwest of Colorado Springs in El Paso County, Colorado, USA. The quarry has been operated by several owners since the early 1900s. The Pikeview Quarry has been a major source of construction aggregate for the Colorado Springs area for many years (MSHA 1986). In the 1950s, the site was mined by Peter Kiewit and Sons to provide limestone for the construction of the nearby Air Force Academy. A large scale slope failure occurred on December 2, 2008, which stopped mining activity at the Pikeview Quarry. A second, related slope failure occurred on September 13, 2009. The second slope failure was located immediately adjacent to the initial December 2008 failure. The objective of this publication is to discuss the three-dimensional slope stability evaluation. The causal relationships of slope instability are not within the scope of this publication. However, omitting the precursors to slope failure would limit understanding of the nature of the slope stability evaluation. The regional and local geology and the history of slope instability at the Pikeview Quarry aid in understanding these precursors. Two main failure mechanisms were hypothesized during the failure investigation to explain the triggering of the 2008 and 2009 large slope failures at the Pikeview Quarry. Both mechanisms are given equal credence in this publication. Quarry excavation was a key factor in the slope instability for both failure mechanisms. The objective of the three-dimensional model was to evaluate the effects of extraction and backfill at the toe of the slope with respect to slope stability. GEOLOGY Regional and local geology are both important factors in slope instability at the Pikeview Quarry. Geologic structure at the quarry is related to regional mountain building and basin development associated with the Laramide Orogeny and the Rocky Mountains. Lithologies at the Pikeview Quarry are also related to regional trends. Localized geologic features, primarily related to weathering and erosion, have also been major contributing factors to slope instability at the Pikeview Quarry."

Jan 1, 2017

By J. -B. C. Varnier, J. A. Cremeens, D. D. Overton

"Slope failures that occurred in 2008 and 2009 at the Pikeview Quarry in El Paso County in Colorado in the United States were investigated using three-dimensional discrete element modeling methods. Large-scale block sliding failures occurred along weak bedding planes that dip steeply into an excavation located at the toe of the slope. Several mining sequences at the toe of the slope were simulated to evaluate the effects of various degrees of extraction and backfill on slope stability. Slope stability back-analysis was conducted using prefailure and post-failure conditions to determine the joint shear strength properties. Laboratory testing was also conducted to determine intact rock properties. Three-dimensional discrete element analysis was uniquely applicable to this evaluation because it allowed representation of shear stress of the basal sliding surface and afforded evaluation of several scenarios of extraction and backfill at the toe of the slope. IntroductionThe Pikeview Quarry is an aggregate quarry located approximately 8 km (5 miles) northwest of Colorado Springs in El Paso County, CO, USA. The quarry has been operated by several owners since the early 1900s. According to the U.S. Mine Safety and Health Administration (MSHA, 1986), the quarry has been a major source of construction aggregate for the Colorado Springs area for many years. In the 1950s, the site was mined by Peter Kiewit and Sons to provide limestone for the construction of the nearby Air Force Academy.A large-scale slope failure occurred on Dec. 2, 2008, which stopped mining activity at the Pikeview Quarry. A second, related slope failure occurred on Sept. 13, 2009. The second slope failure was located immediately adjacent to the initial December 2008 failure.The objective of this paper is to discuss the three-dimensional slope stability evaluation. The causal relationships of slope instability are not within the scope of this publication. However, omitting the precursors to slope failure would limit understanding of the nature of the slope stability evaluation. The regional and local geology and the history of slope instability at the Pikeview Quarry aid in understanding these precursors. Two main failure mechanisms were hypothesized during the failure investigation to explain the triggering of the 2008 and 2009 large slope failures at the Pikeview Quarry, and both of these mechanisms were given equal credence in the present study. Quarry excavation and backfilling was a key factor in the slope instability for both failure mechanisms. The excavation was backfilled in stages in an effort to provide slope support. The objective of the three-dimensional model was to evaluate the effects of extraction and backfill at the toe of the slope with respect to slope stability."

Jan 3, 2018

By Reza Y. Khaksar

Presented is a rigorous solution for the three-dimensional stability analysis of vertical shafts (excavations) subjected to the self-weight of the soil based on the upper-bound theorem of limit analysis approach. A rigid-block translational collapse mechanism is assumed, with energy dissipation taking place along planar velocity discontinuities. This mechanism is optimized to obtain the critical failure mechanism giving the lowest factor of safety for stability of shafts. Based on comparisons with other solutions, the method is generally found to be accurate in predicting the stability of vertical cuts.

Jan 1, 2006

By Kray Luxbacher, Mario Karfakis, Erik Westman, Peter Swanson

Three-dimensional velocity tomograms were generated to image the stress redistribution around an underground coal longwall panel to produce a better understanding of the mechanisms that lead to ground failure, especially rockbursts. Mining-induced microseismic events provided passive sources for the three-dimensional velocity tomography. Surface-mounted geophones monitored microseismic activity for 18 days. Eighteen tomograms were generated and high-velocity regions correlated with high abutment stresses predicted by numerical modeling. Additionally, the high-velocity regions were observed to redistribute as the longwall face retreated, indicating that velocity tomography may be an appropriate technology for monitoring stress redistribution in underground mines.

By X. Zhang, Z. T. Yuan, C. Zhang, H. M. Zheng, X. M. Wang, L. X. Li, N. Li

In metal mines, comminution is commonly used to liberate minerals for subsequent mineral concentration processes, such as flotation, magnetic separation and gravity separation. However, ores are aggregates of valuable minerals and their disseminated gangue minerals, and these minerals exhibit diverse comminution behaviours. In carbonate-bearing iron ores, hematite, siderite, and quartz are the predominant minerals, of which hematite is the objective recoverable mineral. In this regard, the present study aimed to identify the imperfections in siderite minerals by X-ray computed tomography (XCT), and thus quantitatively characterise their size and shape in terms of Feret diameter and aspect ratio, as well as other parameters. XCT images indicated the protogenetic ubiquity of pores <5 μm in diameter and cracks of 7-8 μm inside siderite particles. In the ground product of artificially mixed siderite and hematite, siderite particles were smaller than hematite particles. Siderite particles had a larger surface area and greater surface roughness than hematite particles of the same volume, which was attributable to the intrinsic holes and cracks in siderite particles. This study provides an insight into the relationship between the inherent imperfections of minerals and their comminution properties. Keywords: Siderite; X-ray computed tomography; particle imperfections; grinding behaviour; sliming

Jan 1, 2020

By H. A. Pearse

NORMALLY, the Britannia ore mixture contains chalcopyrite and pyrite as the chief sulfide minerals, together with minor amounts of gold and silver and a low zinc content. Reduction is accomplished by jaw crushers underground, followed at the concentrating plant by Symons cone crushers, rolls, and ball mills. The standard flotation practice, evolved during several years of experimentation, provided for bulk flotation of the two sulfides, after primary grinding to only approximately 35 mesh, followed by regrinding of the bulk concentrate, with subsequent separation of the chalcopyrite and pyrite to make a marketable concentrate of each mineral. This so-called standard milling practice has previously been described in detail in U. S. Bureau of Mines Information Circular 6619. A modification will he discussed here. In the face of a constantly increasing world surplus of copper and a steadily falling price during 1930 and 1931, it was obviously undesirable to continue unprofitable production of large quantities of this metal. On the other hand, company officials were

Jan 1, 1934

By N. P. Kripakov

Results of a complex three-seam interaction analysis in a western U.S. coal mine are presented. The physical situation simulated by the models represents the development of a set of entries underneath two previously mined seams with all three seams in proximity to each other. The layout and the geometry of the remnant pillars in the upper seams were nonuniform and not always directly superimposed over each other, creating a very challenging modeling problem. The U.S. Bureau of Mines&apos; MULSIM/PC computer code was upgraded and enhanced to perform the required three-seam interaction calculations. Analysis was limited to simple linear-elastic assumptions as only peak stresses were required. Results clearly indicated that stress concentrations in the lower seam increased approximately 100 percent when compared to cases simulating no extraction in the two upper seams. These stress concentrations generally occurred in zones directly below points of highest abutment pressures in the upper seams. Overall, the model results compared favorably with actual documented observed behavior where roof failures were known to have occurred.

Jan 1, 1996