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2011, Geotechnical and Geological Engineering
Hydraulic fills are one of the most common backfills used by mining industries to backfill the stopes (voids) created after extracting the ore. It is important to estimate the stresses within to the stope to design the drainage and barricades. Most of the existing analytical models for the estimation of stresses within the stopes consider flat rectangular elements to include the effects of arching, although a continuous compression catenary arch of principal stresses using intersections of shear lines is the reality in field situations. In this paper, a circular compression arch of principal stresses has therefore been used to derive a general expression for stress within the inclined stopes. The results have been compared with the existing analytical and numerical models for vertical stopes as well as inclined stopes. A methodology has been presented to determine the vertical stress variation along the width of stope at different depths. The variation of stresses along the width of stope is also presented graphically.
Geotechnical and Geological Engineering, 2017
There are several good reasons for using backfill in underground stopes, including a reduction of mine wastes on the surface and the improvement of ground stability. Backfilling is now commonly used in underground operations worldwide, so practical methods are required to assess the stress state in stopes, on the surrounding rock mass and on support structures. The majority of existing analytical solutions for the stresses have been developed for vertical openings. In practice, stopes often have inclined walls, and this affects the stress state. Recent numerical studies have shown how the stresses distribution in inclined backfilled stopes is influenced by stope geometry and backfill strength. It has also been shown that existing analytical solutions do not capture the essential tendencies regarding these influence factors. In this paper, a new solution is proposed for the vertical and horizontal stresses in backfilled stopes with inclined walls. This solution takes into account the variation of the stresses along the opening height and width, including the difference between the hanging wall and footwall, for various inclination angles of the walls. Key results are presented and validated using recently performed numerical simulations. Keywords Mine backfill Á Earth pressure coefficient Á Analytical solutions Á Inclined stopes Á Numerical modeling Á Vertical and horizontal stresses
Geotechnical and Geological Engineering, 2014
Arching is a phenomenon that occurs in many situations in geotechnical engineering. When underground mine stopes are backfilled, a significant fraction of the self-weight of the backfill is carried by the side walls. As a result, the vertical stress at the bottom of the stope is significantly less than its overburden pressure. Few analytical expressions published in the literature can be used to determine the vertical stresses of stope with parallel walls. The objective of this paper is to extend the analytical solution previously developed by the authors to long plane-strain stopes with non-parallel walls with both slopes leaning to the same side. Different combinations of wall inclination are examined using the new analytical expression developed. To validate the analysis, the proposed results are compared with numerical model results. The results show that the proposed analytical expression is capable of estimating the vertical stress within mine stopes when the inclination of the hangingwall to the horizontal (a) is less than that of footwall (b). An important behavioural trend for the stress distribution is observed, where with the same overburden pressure and base width, the stress magnitude experienced by fill material significantly varies depending on the wall inclination.
International Journal of Geomechanics, 2009
Evaluating the stresses in backfilled stopes constitutes a critical step for insuring underground mine safety and for analyzing backfill response. In recent years, the writers have presented several methods for conducting numerical and analytical investigations to assess the stress state in backfilled stopes. The results have shown significant stress transfer to the rock mass along stope walls which induces an arching effect. To date, most solutions have been developed for ͑sub-͒ vertical openings. In this paper, the results of an extensive numerical investigation on inclined stopes are presented. Emphasis is placed on the influence of stope geometry, backfill properties, and filling sequence on the stress distribution in the backfill. Results indicate that for a given stope geometry, the most influential factors are the backfill shear strength parameters ͑cohesion cЈ and friction angle Ј͒, Poisson's ratio , and dilatation angle Ј. Some of these parameters not only affect the stress magnitude, but also the distribution pattern which is shown to also depend on the filling sequence. One of the main outcomes from this study indicates that increasing the value of cЈ tends to change the mechanical response of backfill from that of a particulate material to that of a consolidated medium, with each layer responding somewhat like a bending beam under vertical loads. The numerical results are compared to others obtained in previous investigations and also to analytical solutions and experimental test results obtained on a physical model. These are discussed in relation to the effect of the influence factors and their implications for the analysis of backfilled stopes.
Minerals
Evaluation of stress states in backfilled mine stopes (or similar openings), using arching theory, can be largely impacted by the value selected for the earth pressure coefficient, K = σ h /σ v. Recently, the current study's authors addressed the debate about the value of K near the opening center, based on Rankine's active coefficient (K a) and at-rest coefficient (K 0). Here, stress ratios in vertical backfilled stopes are numerically assessed (in two dimension, 2D), considering both the independent and related backfill internal friction angle (ϕ) and Poisson's ratio (ν). Emphasis is placed on the backfill state near stope walls, where local rotation of stresses occurs, so the coefficient (K) and principal stress ratio, K ps (= σ 3 /σ 1), should be distinguished. Parametric analyses indicate that values of K and K ps depend on the position and the relationship between ϕ and ν. Near the opening center, K (= K ps) is close to K a when ν or ϕ is below a critical value; otherwise the value approaches K 0 , defined from ν. Near both walls, K ps is always close to K a , while K is near K 0 for related ν − ϕ cases and depends on their respective values for independent ν and ϕ. Additional simulations conducted with interface elements indicate that the stress ratios near the opening center line are insensitive to interface roughness and are almost identical to values obtained without interfaces, but the stress ratios near walls may change for less rough or smooth interfaces.
Canadian Geotechnical Journal, 2009
In current underground mining using ''open stoping'' methods, it is common to backfill mined-out voids (''stopes'') using hydraulically placed backfill, which is commonly composed of tailings, to which cement is often added. Knowledge of the stress state within a backfilled stope is required for safe design of drawpoint barricades and for other operational reasons. This stress state depends, inter alia, on the degree of ''arching'' that occurs, resulting from the development of shear stress between the fill and the stope walls. This paper presents a numerical modelling study of aspects of the arching phenomenon, carried using the computer code Plaxis. The backfill is characterized using the Mohr-Coulomb soil model, and both dry backfill and saturated backfill are considered to completely cover the full spectrum of backfill types that are used in practice. It is shown that even with dry backfill, the behaviour is governed by a complex interaction between the soil parameters. The behaviour is more complex with saturated backfill, with a key parameter being the permeability of the backfill relative to the rate of filling -i.e., whether the backfilling operation can be considered to be ''drained '' or ''undrained'' or somewhere between these two extremes.
Backfilling is being increasingly used in underground mines for ground control and wastes disposal. The behavior of backfill is significantly influenced by its interaction with the surrounding rock mass and support structures such as barricades. Previous work conducted on backfilled stopes, including some recent studies by the authors, indicates that the theory of arching can be used to estimate the earth pressures in narrow, vertical backfilled openings. In this paper, a new 3D analytical solution is proposed to evaluate the state of stress within a backfilled vertical stope. The solution is validated using laboratory experimental results taken from the literature.
2011
Backfill is increasingly used in mines to ensure the stability of underground openings where ore is extracted from the rock mass. Tools to evaluate the total and effective stresses within the backfill are required to assess the mechanical response of the stopes and to optimize fill placement. This paper presents some key results from a numerical study aimed at analyzing the response of backfill after placement in a narrow vertical stope, in the presence of arching effect. Three cases are presented here, namely: simulation of dry (or drained) backfill with different stope widths, a stope backfilled with saturated fill under hydrostatic pore water pressure, and a backfilled stope with progressive drainage and consolidation. The first two cases represent the stress state when the backfill reaches equilibrium, while the results obtained in the third case illustrates how the stress distribution varies with the groundwater conditions in the stope. The influence of other factors is also discussed in the paper. RÉSUMÉ L'utilisation du remblai est en croissance constante dans les mines souterraines afin d'assurer la stabilité mécanique des ouvertures où le minerai est extrait de la masse rocheuse. Il est nécessaire d'avoir des outils appropriés pour évaluer l'état des contraintes effectives et totales dans les chantiers remblayés afin d'évaluer leur réponse mécanique et pour optimiser la mise en place. Dans cet article, on présente quelques résultats d'une étude numérique qui vise à analyser la réponse du remblai après sa mise en place dans un chantier minier vertical étroit où se développe un effet d'arche. On présente ici trois cas, soit : la simulation d'un chantier remblayé en condition sèche (ou drainée), un chantier remblayé submergé soumis à une pression hydrostatique et un chantier remblayé avec évolution de la pression interstitielle suite au drainage et à la consolidation. Les deux premiers cas représentent l'état de contraintes lorsque le remblai atteint un état d'équilibre, alors que le troisième cas illustre l'évolution des contraintes et de la pression d'eau en fonction des conditions d'écoulement dans le chantier. D'autres facteurs d'influence sont aussi discutés dans cet article.
Canadian Geotechnical Journal, 2017
The earth pressure coefficient K, defined as the horizontal to vertical normal (effective) stresses ratio (σh/σv), is a key parameter in analytical solutions for estimating the stresses in backfilled stopes. In the case of vertical stopes, the value of K has sometimes been defined using the at-rest earth pressure coefficient K0, while others have applied Rankine’s active earth pressure coefficient Ka. To help clarify this confusing situation, which can lead to significantly different results, the origin and nature of the at-rest and Rankine’s active coefficients are first briefly recalled. The stress state in backfilled stopes is then investigated using numerical simulations. The results indicate that the value of K can be close to Ka for cohesionless backfills along the vertical central line (CL) of vertical stopes, due to sequential placement and partial yielding of the backfill. For inclined stopes, simulations show that the ratio between the minor and major principal stresses (σ...
Journal of Rock Mechanics and Geotechnical Engineering, 2017
Backfill is commonly used in underground mines to help to increase the ore recovery rate and reduce the ore dilution. The use of a part of mine waste as underground backfill material also helps to reduce the environmental impact of mining operations. After all, backfill is used to provide a working platform or safer working space. Its primary and most important role is to improve the rock mass stability around mine openings. However, most available solutions to stress analyses were developed for an isolated stope, without taking into account the influence of mine depth, or of adjacent stopes. In this paper, results from a numerical study carried out to evaluate the stresses in backfilled stopes overlying a sill mat are presented. Mine depth and excavation of the underlying stope below the sill mat (horizontal pillar) are both taken into consideration. The influence of stope geometry, backfill, sill mat and rock properties on the stresses is also evaluated. Compared with the case of a single isolated backfilled stope, the numerical results show that the stress magnitudes in the overlying backfill are considerably increased due to the excavation of the underlying stope. In general, the stresses also increase with mine depth and backfill stiffness, while these tend to decrease with an increase in the surrounding rock mass stiffness. These results suggest that existing solutions for backfill design may need to be revised.
Canadian Geotechnical Journal, 2012
Backfilling contributes to the improvement of ground stability and reduction of ore dilution in underground mines. A critical issue for backfilled stope design is the required strength for the fill material. A practical solution to address this question was proposed by Mitchell and co-workers for stopes with an exposed face and a high aspect ratio (height H over width B). However, this solution is not directly applicable to stopes with a relatively low aspect ratio (H/B). Its application is also restricted by additional limitations on the strength along the fill–rock interfaces and the load applied on top of the backfill. In this note, the model proposed by Mitchell and co-workers is modified to provide an estimate of the required strength of backfill for various geometries, material properties, and surface loads. The modified Mitchell (MM) solution is validated against experimental results. Sample calculations with the MM solution are also presented and discussed.
International journal of geosynthetics and ground engineering, 2024
This paper highlights the importance of considering hydraulic backfill consolidation and wet arching when determining the stresses in underground mine stopes and acting on the barricade. The wet arching is introduced here as an arching effect during consolidation. Most studies consider hydraulic backfill consolidation as an instantaneous process and ignore its effects on stress within the stope and acting on the barricade. Mainly the reasons would be the granular behaviour and higher permeability of mine tailings used for hydraulic backfills. Yet, recent laboratory experiments and tests carried out under this study show that the consolidation is slow enough to significantly affect the hydraulic backfill stresses. According to the literature, hydraulic backfills have a considerable amount of fine particles which can slow down the consolidation process as evident in the tests. The paper discusses available stress variation between dry and wet fills while demonstrating its significance and requirements for further studies in consolidation and wet arching. Another important factor ignored in the literature is the hydraulic backfill property variations which were evident in tests carried out in this study. The results suggest segregation occurs within the fill which follows property variations over depth and considerably influences stresses. These effects must be considered when determining the stresses within the fill and developing a hydraulic backfill stress model.
Advances in Civil Engineering, 2019
The pore water pressures (PWPs) and total stresses during the placement of a slurried backfill in underground mine stopes are the key parameters for the design of barricades, built to retain the backfill in the stopes. They can be affected by the drainage and consolidation of the backfill. Over the years, several studies have been reported on the pressure and stresses in backfilled stopes by accounting for the drainage and consolidation. Most of them focused on the pressure and stresses in the stopes, few specifically on the barricades. The effect of the number of draining holes commonly installed through the barricade has never been studied. In this paper, the influence of hydraulic properties and filling rate of the backfill, stope size, barricade location, and number of draining holes is systematically investigated with numerical simulations. The results show that the stresses in the backfilled stope and on the barricade largely depend on the filling rate, hydraulic conductivity,...
2017
Sublevel stoping mining with delayed backfill is a widely employed method in many Canadian underground metal mines (e.g., Bosquet, Doyen, Laronde, and Lapa mines in Quebec and Garson, Creighton, Red lake and David bell mines in Ontario). In this method, the extracted stope(s) must be tightly backfilled before advancing to extract the adjacent secondary stope(s). Thus, backfill is necessary to provide good-confinement to the host rock mass. Therefore, its objective is to maintain the stability of mined out stope(s). Otherwise, the failure of backfill column into adjacent stope(s) leads to higher operation cost (e.g., cost of ore milling/ore processing operation, costs associated with ore dilution when waste/backfill material mixed with unmined block(s)). Consequently, backfill instability could lead to an overall unsafe/interrupt mining operation. This article presents the results of numerical modelling analysis to evaluate the performance stability of vertical and inclined backfille...
The design of backfilled stopes requires that the interaction that develops at the interface between the fill material and surrounding rock mass be evaluated. In this paper, the authors present analytical and numerical results from calculations performed to estimate the mechanical response of backfilled openings, emphasizing the effect of load transfer along the interface between the rock and relatively soft fill. The results indicate that the arching effect that can develop in the backfill may have a significant influence on load distribution along the walls and at the bottom of narrow stopes. The discussion that follows the comparison between sample numerical and analytical calculations, highlights some of the key influence factors. It also emphasizes the limitations of commonly available tools, which do not represent adequately key components of the interaction between fill and stope walls.
2008
on Environment and Mine Wastes Management Toute reproduction de ce document à des fins d'étude personnelle ou de recherche est autorisée à la condition que la citation ci-dessus y soit mentionnée. Tout autre usage doit faire l'objet d'une autorisation écrite des auteurs. Les demandes peuvent être adressées directement aux auteurs (consulter le bottin sur le site http://www.polymtl.ca/) ou par l'entremise de la Bibliothèque :
It is now a common practice in mining to use backfilling as a ground control measure. The design of backfilled stopes requires that the interaction that develops at the interface between the fill material and surrounding rock mass be evaluated. In this paper, the authors present analytical and numerical results from calculations performed to estimate the mechanical response of backfilled openings, emphasizing the effect of load transfer along the interface between the rock and relatively soft fill. The results indicate that the arching effect that can develop in the backfill may have a significant influence on load distribution along the walls and at the bottom of narrow stopes. The discussion that follows the comparison between sample numerical and analytical calculations, highlights some of the key influence factors. It also emphasizes the limitations of commonly available tools, which do not represent adequately key components of the interaction between fill and stope walls.
Annales de Chimie - Science des Matériaux
This research is focused on evaluating the effects of joint orientation on the stability of open stopes. Joints are often seen as the source of failure in an open stope. Joint orientation adversely affects the stability of the open stope by majorly causing non-uniformity in stress and providing a surface for free movement of strata. Effect of joint orientation on stope stability is less discussed with few publications. This study exclusively identifies the effect of joint orientations on stope stability with the help of numerical model designed in finite difference method computer software. In this research, different rock strengths were considered to determine how joint orientations ranging from 0 to 165 degrees affect the stability of open stopes having variable horizontal to vertical stress ratio values and thus the failure behavior is obtained. The application of the results of this research in the metal mining industry should lead to improved understanding of the effects of joint orientation on stope stability for different rock strata at variable depths, and hence useful in devising a suitable design method of mining metal orebody that offers optimum stope span, maximum production and required factor of safety.
International Journal of Geo-Engineering, 2017
Mine backfilling is a technique that has been used for decades in Canada and across the globe [1, 2]. This method has several advantages such as stabilizing the drifts and stopes of a mine and increasing worker safety. Backfilling serves to fill excavations in a mine and allows ore to be extracted more completely because the underground excavations have better support. Environmental benefits result from the use of tailings as backfill material: problems related to the disposal of surface tailings can be reduced as substantial quantities of potentially polluting tailings can be returned underground. This backfill material generally consists of a mixture of tailings, water and cement. The backfilling process has several technical aspects that interact with one another. This includes the hydrogeology, mineralogy and geochemistry of both the host rock and backfill material as well as the mechanical behavior of these two media. Mechanical
International Journal of Mining Science and Technology, 2018
Stress-induced failure is among the most common causes of instability in Canadian deep underground mines. Open stoping is the most widely practiced underground excavation method in these mines, and creates large stopes which are subjected to stress-induced failure. The probability of failure (POF) depends on many factors, of which the geometry of an open stope is especially important. In this study, a methodology is proposed to assess the effect of stope geometrical parameters on the POF, using numerical modelling. Different ranges for each input parameter are defined according to previous surveys on open stope geometry in a number of Canadian underground mines. A Monte-Carlo simulation technique is combined with the finite difference code FLAC3D, to generate model realizations containing stopes with different geometrical features. The probability of failure (POF) for different categories of stope geometry, is calculated by considering two modes of failure; relaxation-related gravity driven (tensile) failure and rock
Back analysis of open stope performance is essential in the dilution control process, as an improved understanding of mechanisms allows one to check the validity of any assumptions and refine geotechnical parameters used in the design process. This paper describe the results of a back analysis of over-break geometries, using non-linear elasto-plastic finite element modelling undertaken at Barrick Gold Australia's Kanowna Belle Gold Mine. The entire sequence of bench and longhole open stopes at the Kanowna Belle mine was modelled. The back analysis study involved analysing hangingwall over-break data from longhole open stopes from a number of key mining blocks. For the numerical modelling exercise, results grids were placed such that various components of velocity and plastic strain could be ascertained into the hangingwall rock mass, with modelling steps calculated at the individual stope's extraction, prior to backfilling. Stochastic analysis of the CMS over-break data, tog...
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