Dissertations / Theses on the topic 'Mine backfill'

The extraction of a significant amount coal in the United Kingdom has over the last four or so decades been made using opencast mining methods. This method involves large-scale excavation to reach the coal seams (with depths often exceeding 100m). Following extraction various forms of restoration have been employed, including backfilling the mine void with material excavated in order to extract the coal. This backfilling was frequently undertaken in an uncontrolled fashion. In recent years it has been more usual to engineer the restoration such that further development of the site can take place. However, settlement remains the major obstacle to development. One mode of settlement commonly encountered on restored sites is creep settlement. Further, on older sites whose restoration was, most probably, undertaken in an uncontrolled way, the potential for creep settlement. is the major obstacle. Creep settlement is understood to be that component of total settlement which, in a coarse granular soil, takes place under conditions of constant stress. It is generally accepted to occur linearly with the decadic logarithm of time. This study investigates the phenomenon from the visualisation of the granular particle mechanics. The technique used for the visualisations is computed tomography (CT), a technique which is common in medical diagnostics but has rarely been exploited in soil mechanics and never at the scale employed in the study. The use of CT supplements a programme of high quality, large scale laboratory testing, which models typical opencast coal mine backfill. The testing programme has revealed that compaction and the diagenesis of the source materials have a significant effect on the creep rate. Further, that the creep rate is defined in the most part by the aggregation of small or minor movements rather being dominated by large or major movements.

This thesis presents the results of an investigation of factors which influence the geotechnical properties of frozen mine backfill (FMB). FMB has extensive application potential for mining in permafrost areas. The uniaxial compressive strength (UCS) of hardened backfill is often used to evaluate mine backfill stability. However, the deformation behaviour and stiffness of the FMB are also key design properties of interest. In this thesis, uniaxial compressive tests were conducted on FTB and FCPB samples. Information about the geotechnical properties of FMB is obtained. The effects of FMB mix components and vertical compression pressure on the geotechnical properties of FMB are discussed and summarized. An optimum total water content of 25%-35% is found in which the strength and the modulus of elasticity of the FTB are 1.4-3.2 MPa and 35-58 MPa, respectively. It is observed that a small amount (3-6%) of cement can significantly change the geotechnical properties of FTB.

Stable mine backfill is necessary for safe working conditions, maximum ore recovery and underground and surface stability. Due to the fact that cement costs can be a significant part of the operating costs in large underground mines, the consumption of cement (or binder) should be minimized. Therefore, developing a safe and economical backfilling method for the large underground mining operations is very significant.
In this thesis, first laboratory tests and in-situ tests are implemented to determine backfill material properties and backfill stress distribution. The laboratory tests include high sulphide paste fill property tests and layered backfill tests. Second, a backfill finite element model is presented and it is validated by the results of laboratory tests and in-situ tests. Finally, by using this model, the following subjects are studied, (1) backfill stress distribution; (2) influences of backfill material properties and dimensions on backfill stability; (3) stress distribution of layered backfill; (4) optimum layered backfill. The results show that: (a) The variation of backfill material properties is quite large, the compressive strength of the layered backfill model is much higher than that of the non-layered backfill model, and the backfill vertical stress is much less than that anticipated by the formula, rhogH; (b) During the process of adjacent pillar recovery, the minor principal stress inside a backfill is tensile, and this tensile principal stress causes backfill failure and spalling near the exposed surfaces. The spalling size progressively increases with the height of the exposed surface, and a sliding zone creates and leads to backfill collapse; (c) Optimum backfill material should be high elastic modulus, high Poisson's ratio and low density. Optimum backfill size should be large depth and small width; (d) For layered backfill, no sliding zone occurs during the process of adjacent pillar recovery, so layered backfill can improve backfill stability. The optimum layered backfill should consist of strong layers distributed evenly with thicknesses of 1~2m and weak layers 2~2.5 times the thickness of the strong layers. This can save binder consumption by about 11%.

Mining has been one of the main industries in the course of the development of human civilization and economies of various nations. However, every industry has issues, and one of the problems the mining industry has faced is the management of waste, especially sulphide-bearing tailings, which are considered to be a global environmental problem. This issue puts pressure on the mining industry to seek alternative approaches for tailings management. Among the several different types of methods used, cemented paste backfilling is one of the technologies that offers good management practices for the disposal of tailings in underground mines worldwide. Cemented paste backfill (CPB) is a cementitious composite made from a mixture of mine tailings, water and binder. This technology offers several advantages, such as improving the production and safety conditions of underground mines. Among these advantages, CPB is a promising solution for the management of sulphidic tailings, which are considered to be reactive materials (i.e., not chemically stable in an atmospheric condition) and the main source of acid mine drainage, which constitutes a serious environmental challenge faced by mining companies worldwide. Such tailings, if they come into direct contact with atmospheric elements (mainly oxygen and water), face oxidation of their sulphidic minerals, thus causing the release of acidic drainage (i.e., acid mine drainage) and several types of heavy metals into surrounding water bodies and land. Therefore, the reactivity of sulphidic tailings with and without cement content can be considered as a key indicator of the environmental behavior and durability performance of CPB systems. For a better understanding of the reactivity, it is important to investigate the influencing factors. In this research, several influencing factors are experimentally studied by conducting oxygen consumption tests on different sulphidic CPB mixtures as well as their tailings under different operational and environmental conditions. These factors include time, curing temperature, initial sulphate content, curing stress, mechanical damage, binder type and content, and the addition of mineral admixtures. In addition, several microstructural techniques (e.g., x-ray diffraction and scanning electron microscopy) are applied in order to understand the changes in the CPB matrices and identify newly formed products. The results reveal that the reactivity of CPB is affected by several factors (e.g., curing time, initial sulphate content, ageing, curing and atmospheric temperature, binder type and content, vertical curing stress, filling strategy, hydration and drainage, etc.), either alone or in combination. These factors can affect reactivity either positively or negatively. It is observed that CPB reactivity decreases with increasing curing time, temperature (i.e., curing and atmospheric temperatures), curing stress, binder content, the addition of mineral admixtures, degree of saturation, and the binder hydration process, whereas reactivity increases with increases in sulphide minerals (e.g., pyrite), initial sulphate content, mechanical damage, and with decreased degrees of saturation and binder content. The effect of sulphate on the reactivity of CPB is based on the initial sulphate content as well as curing time and temperature. It is concluded that the reactivity of CPB systems is time- and temperature-dependent with respect to other factors. Also, binders play a significant role in lowering CPB reactivity due to their respective hydration processes.

This work develops a backfill design procedure aimed to facilitate the optimization of an available mine material in order to meet target objectives in a particular mining role. This required the compilation and analysis of data on fill usage, established design procedures, physical and geomechanical properties, testing techniques and procedures, as well as behavioural modelling methods.
A backfill classification system is proposed based upon size distribution. A series of design equations are presented which relate to this system. These equations represent the means by which backfill geomechanical behaviour can be related to physical properties. This is considered to be fundamental to an effective backfill design procedure. Derivation of the equations has been based upon analysis of data from a program of laboratory and in situ testing conducted in ten operating Canadian mines by the author, together with other published work.
The in situ testing required the development of a pressuremeter testing procedure novel to underground mining. The theoretical basis for the employment of pressuremeter data has been examined and behavioral equations have been developed to describe the deformation and stress history during a backfill material test. In addition two new equations have been developed for the analysis of pressuremeter data. The in situ data collected has been correlated with laboratory derived geomechanical data for the same backfill materials.
The geomechanical properties associated with the proposed backfill classifications have also been related to their influence on backfill behaviour in three mine backfill roles: free standing stability during pillar recovery in bulk mining methods; dynamic interaction with stope walls in rockburst prone ground; and ability to reduce stresses in highly stressed rock masses. This work has been based on new and established modelling methods and aims to provide insight into the effectiveness of the backfill classes in these roles of growing practical significance.

This thesis deals with the flow mechanics of hydraulic and high density mine backfill slurries in pipelines. Various empirical, rheological and mechanistic approaches are presented and analysed along with some aspects pertinent to experimental testing of backfill slurries.
The main contribution of this work is, particularly, in the development of an analytical model to describe the flow and predict the pressure gradient of a class of high density backfill whose motion in pipelines follows the Plug Flow Model (PFM). The development of the model called for investigating the conditions required for establishing Plug Flow. It was found that mix proportioning procedures, similar to those found in the concrete industry, are key factors in obtaining Plug Flow.
Pressure drop was found to be a function of the thickness of the Bingham plastic annular layer surrounding the cylindrical core of aggregates. Analytical equations were proposed to solve for the thickness of this layer by considering the rheology of the mixture. Alternatively, the thickness of the annular layer may be estimated by considering the relative proportions of the mixture with respect to aggregates void content. The model offered pressure drop predictions in good agreement with published data. The proposed model may also serve as an alternative to Mooney's method, when dealing with the annular lubricating layer effect characterising mixtures in Plug Flow.

Over the last three decades, mine backfilling has progressively integrated into underground mining operations. The high stresses associated with mining at depth in the Canadian Shield, also requires innovative approaches to mine backfilling to withstand the loading both during and after mining operations. Not only new or modified minefill systems are required, but also new techniques are needed to increase the speed of the mining cycle for optimizing the mining operation. Three major purposes of mine backfill are known as (1) providing safe working condition, (2) maximizing ore recovery and (3) improving underground stability. Therefore, mine backfill has contributed greatly to the economics and environmental aspects of mining industry.
In order to improve the mechanical behaviour of fill, cementitious materials are used. These cementitious materials are expensive. As a result the consumption of these cementitious materials has to be optimized and minimized in a way that the required strength is met. The objective of this research is to investigate a new type of backfill, which is known as gelfill. Gelfill binders usually consist of alkali activators such as sodium silicate and the other cementitious materials. Sodium silicate has been used in waste treatment and activation of artificial pozzolans such as blast furnace slag and fly ash.
The work presented in this thesis is to evaluate the use of sodium silicate in gelfill. Consequently, the influence of mixing time, mixing sequence and curing time are studied on gelfill and silica sand hydraulic backfill. Various tests including unconfined and confined compressive strength were conducted in order to investigate the mechanical behaviour of samples. By conducting mercury intrusion porosimetery (MIP) and scanning electron microscopy (SEM), microstructure and mineralogical properties of specimens were studied.
The result of this thesis demonstrates that gelfill compared with silica sand hydraulic backfill has better mechanical properties. In addition, other variables, including: mixing time and sequence, have a significant effect on gelfill.

Opencast mining has been and continues to be a favoured method for the extraction of the vast coal reserves in the Highveld of South Africa. Previously backfilled and restored open cast areas are generally zoned for agricultural uses, but with growing pressures on land use, such areas are increasingly being considered for the expansion of infrastructure and regional development. Understanding the backfill permeability and hydraulic behaviour is therefore an important component in defining the land use restrictions placed on a previously backfilled area. Centrifuge modelling provides a means of better understanding the hydraulic behaviour and measuring the permeability of opencast backfill under controlled laboratory conditions. Based on a preselected backfill prototype, an appropriate centrifuge model was developed. Using miniature pore pressure transducers, the pore pressures were measured at discrete locations in the model during falling head tests in a geotechnical centrifuge. Using the measured volumetric discharge, spacing between the transducers and the measured pore pressures, the permeability of the backfill was calculated. Due to polarized opinions on the scaling of permeability in a centrifugal field, a control model was tested at 1g and 23g to validate this scaling law. It was demonstrated that the respective permeabilities calculated at 1g and 23g were effectively the same and that it is in fact the hydraulic gradient that is scaled N times in the centrifuge. Knowing this allowed the calculated centrifuge permeabilities to be directly related to the prototype represented by the model. To determine the accuracy of the centrifuge model, the results of field percolation tests were compared to the results of an analogous centrifuge model. There was no correlation between the results and it was not considered meaningful to compare the results, as the model and percolation test site (prototype) conditions differed significantly. To simulate the preselected prototype backfill sequence, a model configuration that represented the geometry and material properties of the prototype was tested at 35g (half scale) and 70g (full scale) in the centrifuge. The results of the centrifuge model were used to make reasonable predictions on the long term permeability and hydraulic behaviour of the backfill prototype. It was found that the permeability of the backfill is likely to decrease over time due to consolidation settlement. The bottom of the backfill sequence is expected to have the lowest permeability and the top is likely to maintain a higher permeability. It was further demonstrated that the horizon interfaces acted as flow restrictors and resulted in poor vertical permeability between the horizons in the backfill sequence. Overall the centrifuge methodology provided a unique and efficient means of modelling the long term permeability and hydraulic behaviour of the backfill sequence.
Dissertation (MSc)--University of Pretoria, 2015.
tm2016
Geology
MSc
Unrestricted

Advancements in technology in mining have allowed previously unfeasible ore bodies to be developed. Paste backfill is one technological advancement that has allowed for the development of high-grade, low tonne production when employing the cut and fill mining method. Goldcorp Inc.'s Red Lake Mine currently utilizes this method and is the site for the study of this thesis. Paste backfill (paste) is defined as a mine backfill material that consists of eighty-five percent solids by weight and does not bleed water when placed often consisting of between two and fifteen percent Portland cement by weight. A paste barricade or paste fill fence is a constructed barricade whose purpose is to retain backfill within a mined out stope. The construction of the barricade varies with different operations, for Red Lake Mine the barricade consists of an anchored rebar skeleton covered with an adequate thickness of shotcrete. The majority of the applicable barricade research focuses on hydraulic fill barricades in open stope mining. The barricade pressures in these instances are much larger than those experienced in paste backfill barricades. As such, the current paste loading theory is based on material with a different loading mechanism. Although some research is currently underway, the majority of the barricade research is based on brick barricades and not the shotcrete, rebar skeleton as used at Red Lake. Catastrophic failures of barricades can occur without an understanding of the loading mechanisms. Based on the catastrophic risk, this thesis provides an investigation into the behaviour of the paste backfill and paste barricades at Red Lake Mine in order to provide a safe, cost effective design of paste barricades. This thesis develops an understanding of paste loading mechanisms and barricade capacity derived from a field study of nine instrumented fill fences at Red Lake Mine. Eight of thefences were instrumented to monitor the reaction strain in the fence and the applied pressures during standard production paste pours, the ninth fence was a controlled destructive test that determined the ultimate capacity of the fence. The data for these tests were gathered in real time and was subsequently reduced to assist in analysis. Yield Line Theory, Rankine Theory, strain induced stress, stress vs. strain analysis and numerical modeling were used to develop an understanding of the paste loading mechanisms and the capacity of the paste fill barricades. The analysis determined that the paste backfill behaves as a Rankine-like soil in the initial stages of loading with an average coefficient of lateral earth pressure, Ka, of 0.56. The destructive test determined that the yielding stress of a paste barricade is approximately 100 kPa. Further findings from the research determined that the rate of placement of paste does effect the loads applied to the fence and that the largest pressures exerted on the fill fence occur when paste lines were flushed with water at the end of the pour. This thesis provides an understanding of the paste loading and fill fence interaction with respect to failure. Based on this research the Red Lake Mine should be able to increase production without increasing risk to mine personnel by quantifying the overall loading and strengths of the fill barricade.

One of the most novel technologies developed in the past few decades is to convert mine wastes into cemented construction materials, otherwise known as cemented tailings backfill (CTB). CTB is an engineered mixture of tailings (waste aggregates), water and hydraulic binders. It is extensively used worldwide to stabilize underground cavities created by mining operations and maximize the recovery of ore from pillars. Moreover, the application of CTB is also an environmentally friendly means of disposing potential acid generating tailings underground. During and after its placement into underground mine excavations or stopes, complex multiphysics processes (including thermal, T, hydraulic, H, mechanical, M, and chemical, C, processes) take place in the CTB mass and thus control its behavior and performance. With the interaction of the multiphysics processes, the field variables (temperature, pore water pressure, stress and strain) and geotechnical properties of CTB undergo substantial changes. Therefore, the prediction of the field performance of CTB structures during their life time, which has great practical importance, must incorporate these THMC processes. Moreover, the self-weight effect, water drainage through barricades, thermal expansion and chemical shrinkage can contribute to the volumetric deformation of CTB. Consequently, CTB exhibits unique consolidation behavior compared to conventional geomaterials (e.g., soil). Furthermore, the consolidation processes can result in relative displacement between the rock mass and CTB. The resultant rock mass/CTB interface resistance can reduce the effects of the overburden pressure or the vertical stress (i.e., arching effect). Hence, a full understanding, through multiphysics modeling and simulation of CTB behaviors, is crucial to reliably assess and predict the performance of CTB structures. Yet, there are currently no models or tools to predict the fully coupled multiphysics behavior of CTB. In this Ph.D. study, a series of mathematical models which include an evolutive elastoplastic model, a fully coupled THMC model, a multiphysics model of consolidation behavior and a multiphysics model of the interaction between the rock mass/CTB interface are developed and validated. There is excellent agreement between the modeled results and experimental and/or in-situ monitored data, which proves the accuracy and predictive ability of the developed models. Furthermore, the validated multiphysics models are applied to a series of engineering issues, which are relevant for the field design of CTB structures, to investigate the self-desiccation process, consolidation behavior of CTB structures as well as to assess the pressure on barricades and the strength development in CTB structures. The obtained results show that CTB has different behaviors and performances under different backfilling conditions and design strategies, and the developed multiphysics models can accurately model CTB field behavior. Therefore, the research conducted in this Ph.D. study provides useful tools and technical information for the optimal design of CTB structures.

Research and experience using various types of mine backfill - hydraulic, rock, paste, and blended - has indicated several benefits to the mining industry. Backfill is a general term that refers to any waste material that is placed into underground mine workings. Paste backfill in particular has shown environmental and economic benefits. Paste fill is generally produced from total mine tailings, meaning that it can include waste rock, sands, and clay-sized particles. It also contains no free water, meaning that water will not flow freely through it after placement causing post filling shrinkage. These characteristics make it the most environmentally "friendly" backfill option currently available. In addition, paste backfill is non-segregating and stackable, containing about 80% solids by weight, and having the consistency of medium-slump concrete, containing a cementitious content. These characteristics make paste backfill the best option for post-mining ground control in room and pillar coal mines. There are two main bodies of research regarding paste backfill. The first studies its composition, application, and performance in past and present mining environments; the second studies its theoretical application for both mine support and waste disposal. While this research has provided much for the burgeoning technology of paste backfill, little has been done to investigate its economic application to the industry in room and pillar coal mines. At present, surface disposal of waste is generally cheaper than underground disposal. The goal of this thesis is to initiate discourse investigating the hypothesis that paste backfill may be used in such a way as to allow for increased coal extraction, which may then not only cover the additional costs of underground waste disposal, but potentially increase overall mine profitability. Inherent to this discourse will be a consideration of the following issues: * The potential for increased extraction. * The preservation of long-term pillar stability. * Improved floor stability. * Diminished environmental impact at surface. * The cost benefits associated with all of the above. Data from three Illinois Basin room and pillar coal mines were collected and used for this thesis. Theoretical computer modeling using LaModel and Phase2, empirical analysis of mine stability, physical testing using simulated paste backfill models, and comparative cost analyses considering current and hypothetical mining scenarios were conducted to identify these potential benefits and their consequences, both theoretical and practical.

The main result of underground mining extraction is creating of large underground voids (mine stopes). These empty openings are typically backfilled with an engineering cementitious material called cemented paste backfill (CPB). The main purpose of CPB application in underground mining is to provide stability and ensure the safety of underground openings, maximize ore recovery, and also provide an environmental-friendly means of underground disposal of potential acid generating tailings. CPB is a mixture of mine tailings, cement binder and water. CPB has a complex geotechnical behaviour when poured into mine voids. This is because of the different thermal (T), hydraulic (H), mechanical (M) and chemical coupled processes and interactions that take place in CPB soon after placement. In addition to these THMC behaviours, various external factors, such as stope geometry, drainage condition and arching effects add more complexity to its behaviour. In order to acquire a full understanding of CPB behaviour, there is a need to consider all of these THMC factors and processes together. So far, there has not been any study that addresses this research need. Indeed, fundamental knowledge of the THMC behaviour of CPB provides a key means for designing safe and cost-effective backfill structures, as well as optimizing mining cycles and productivity of mines. Innovative experimental tools and CPB testing methods have been developed and adopted in this research to fulfill the objectives of this research. In the first phase of the study, experiments with high columns are developed to study the THMC behaviour of CPB from early to advanced ages with respect to height of the column and curing time. The column experiments simulate the mine stope and filling sequence and provide an opportunity to study external factors, such as evaporation, on the THMC behaviour of CPB. However, an important factor is the overburden pressure from the stress due to self-weight that cannot be simulated through column experiments. Therefore, in the second phase of this study, a novel THMC curing under stress apparatus is developed to study the THMC behaviour of CPB under various pressures due to the self-weight of the CPB, drainage conditions, and filling rate and sequence. Comprehensive instrumentation and geotechnical testing are carried out to obtain fundamental knowledge on the THMC behaviour of CPB in different curing conditions from early to advanced ages. The results of these studies show that the THMC properties of CPB are coupled. Important parameters, such as curing stress, self-desiccation due to cement hydration, temperature, pore water chemistry, and mineralogical and chemical properties of the tailings, have significant influence on the shear strength and compressive strength development of CPB. Factors such as evaporation and drying iii shrinkage can also affect the hydro-mechanical properties of CPB. The curing conditions (such as curing stress, drainage and filling rate) also has significant impact on CPB behaviour and performance. The THMC interactions and the degree of influence of each factor should be included in designing backfill structures and planning mining cycles. This innovative curing under stress technique can be replaced the conventional curing of CPB (curing under zero stress and no THMC loadings), in order to optimize CPB mechanical strength assessment, increase mine safety and enhance the productivity.

The Renström mine, Boliden Mineral AB, uses, among other methods, the Transverse long hole stoping method with backfill. The mine uses a cement-stabilized hydraulic fill (CHF), which is a mixture of enrichment sand, cement and water. The most important factor in relation to strength is the water cement ratio. Today, only tests have been performed on the surface and in laboratory tests. The purpose of this work is thus to study the possibility of using other types of methods that can give a better understanding of the strength of the entire filling volume. Studies on backfill containing Portland cement and sulphur have shown that the UCS strength decreases with time, which can cause problems for the mine. A leaching method (MRM leaching test) used to evaluate potential sulphide soils has been used in this study on the backfill to investigate the sulphurs impact on the cement mixture. Electrical conductivity, pH, and redox potential were investigated and gave similar results, where the higher cement levels (8%, 10%, and 12%) were indistinguishable while the lower cement content (4%) differed significantly from the other levels. This probably indicates that the higher cement levels have a greater resistance to the influence of the sulphur. The most promising results were given when the method was used on enrichment sand alone. The linear lowering of the pH value of the enrichment sand, from pH 4.9 to about pH 3, point to that the enrichment sand contains large amounts of sulphur, as previously chemical analysis has shown. This suggests that the method can best be used in an early stage before the sand is mixed with cement. The strength results on the samples showed a strength after 7 days that was in line with the 90-day strength. However, all 90 day samples had decreased in strength during the time sequence, which may be an effect of the sulphur content, but should be further investigated to be determined. The smaller size of the samples was also experienced as a challenge during the temperature measurements due to small temperature variations and environmental effects. A maturity method for predicting the strength of concrete called "The maturity method" has been investigated in this study. To determine the strength maturity relationship, both the temperature related to time and the equivalent age must be evaluated. The study showed that the method cannot be used on the mine's backfill without first making adjustments related to the lower cement content used in the backfill compared with concrete constructions, since it is not possible to determine the strength growth in the early stage as the method requires.

Com a crescente diminuição de recursos minerais e o alto custo envolvido na construção da estrutura de uma mina, a recuperação máxima possível de uma jazida vem se tornando fundamental. Para isso além da escolha do método de lavra ter a necessidade de ser feito cautelosamente, é possível lançar mão de métodos adicionais de recuperação, como por exemplo, a recuperação de pilares. Essa pesquisa foi baseada na determinação da caracterização do enchimento (backfill cimentado) utilizado nas câmaras vazias que possibilita a posterior recuperação dos pilares. A caracterização do enchimento é composta da determinação da resistência simples do backfill necessária para que o enchimento cumpra com seu objetivo, desenvolvimento da classificação granulométrica ótima para os agregados e dosagem de cimento e água para alcançar a resistência proposta. A metodologia desenvolvida para obter a nova caracterização é composta de várias etapas que incluem pesquisas em campo e trabalhos em laboratório. Primeiramente, foram obtidos através de análise em campo os parâmetros de dosagem de cimento e classificação granulométrica dos agregados já utilizados na planta de fabricação do enchimento, bem como sua resistência correspondente. Em seguida definições teóricas da dosagem de cimento ideal e classificação granulométrica ótima foram realizadas com base na resistência à compressão simples que foi identificada como necessária para cumprir com as solicitações geomecânicas do maciço rochoso, então posteriormente, a nova caracterização definida teoricamente foi posta à prova através da confecção de corpos de prova de backfill, seguido de execuções de ensaios de compressão. Durante a primeira etapa da metodologia, já se pôde identificar que os agregados possuíam um alto índice de partículas tamanho argila que estavam afetando os resultados de resistência obtidos com a caracterização empregada inicialmente. A partir disso se optou por construir a curva granulométrica ótima sem essa fração. A resistência à compressão simples calculada de 2,69 MPa, foi obtida com base no planejamento de longo prazo que prevê a total recuperação dos pilares existentes na mina. Dessa maneira toda a área que será minerada foi considerada como um único bloco. Finalmente, foi identificada a dosagem de cimento sendo de 4% em peso, que juntamente com a granulometria ótima é capaz de alcançar os valores esperados de resistência. Para que o planejamento da produção da mina durante os próximos anos de vida útil seja efetivamente cumprido, o enchimento deverá prover à mina estabilidade geomecânica local a nível de câmaras abertas com paredes verticais de backfill estáveis e também estabilidade global a nível de contato entre níveis e galerias de acesso. Isso somente será alcançado se a nova caracterização for corretamente aplicada.
As a consequence of the ongoing reduction of mineral resources and the high cost involved in the construction of a mine, the maximum recovery of a mineral deposit becomes a fundamental issue. Therefore, besides the need of caution on the choice of the mining method, it is possible to make use of additional recovery methods, such as the recovery of pillars. This research was based on the determination of the characterization of the fill (cemented backfill) used in avoid stopes that allows the subsequent recovery of adjacent pillars. The characterization of the fill consists of determining the uniaxial compressive strength of the backfill required for an efficient filling, developing an optimal particle-size distribution for the aggregates and finding the cement-water ratio necessary to reach the desired resistance. The methodology developed to obtain the new characterization is comprised of several steps which include field work and laboratory tests. First, cement dosing parameters and particle size of the aggregates (already used at the filling manufacturing plant), as well as their corresponding strength, were obtained through analyses in the field work. Then, theoretical definitions of the ideal cement dosing and optimal particle-size analysis were carried out based on the uniaxial compressive strength that has been identified as necessary to comply with the geomechanical requests from the rock mass, and then later, the new theoretical characterization was tested by making backfill samples, followed by execution of compression tests. During the first stage of this methodology, it has been identified a high proportion of clay particle size for the aggregates, that have affected the strength results obtained from the characterization used initially. From this point, we decided to build the optimal particle-size curve without this fraction. Uniaxial compressive strength, calculated as 2.69 MPa, was obtained from the long-term planning that determines the full recovery of the existing pillars in the mine. In this way, the entire area to be mined was considered as a single block. Finally, the cement dosing has been identified as 4% by weight, which together with the optimal particle size, is able to achieve the expected strength values. In order to effectively fulfill the mine production planning over the next years of lifespan, the filling should provide the mine local geomechanical stability at open stopes level, with vertical walls of stable backfill, and also global stability at the contacts between levels and access galleries. This will only be achieved if the new characterization is correctly applied.

The research outlined in this thesis is concerned with the environmental aspects of groundwater re-establishment as a consequence of surface mining. No principal effects which have been identified as being detrimental to the restored land area are as follows; i). The vertical and horizontal displacements of backfill materials following restoration, and ii). The pollution of groundwater from contact with weathered rockfill materials. The research into settlement has attempted to classify the types of movement which may occur within a backfill mass, in particular the differential movements which are of great importance to the stability of proposed structures or surface drainage. The field results from 10 opencast mine sites are presented, 3 of which were instrumented for detailed field investigations. It has been shown that backfill movements do not necessarily show similar trends under similar conditions, and reasons for this are proposed. A variety of instrumentation schemes have been devised to examine backfill displacements, both vertically and horizontally. Permeability testing has been conducted at different horizons the backfill mass in order to locate the zones of collapse settlement due to groundwater recovery. A critical review of the instrumentation utilised in the investigations is presented, with suggestions for improvement. Investigations into groundwater pollution have been devoted to examining the qualities of groundwater flowing into British surface mines and evaluating its likely reactions with fill materials. An insight into general groundwater pollution and treatment techniques is presented together with a critical analysis of their applicability, to British conditions. An investigation into water qualities in each of the six geographical regions of the opencast mining industry of Great Britain is detailed. Finally some suggestions for future research areas are indicated.

Tese (doutorado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Civil e Ambiental, 2013.
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Este trabalho apresenta uma análise tridimensional de mina subterrânea com ênfase na interação entre maciço rochoso e preenchimento (backfill), considerando o comportamento mecânico do maciço enquanto ocorre o progresso das escavações e da disposição com aumento da tensão confinante e endurecimento do módulo de deformabilidade. Foi realizado o monitoramento do caso de estudo da Mina Cuiabá e comparados os resultados com as modelagens tridimensionais. O tipo específico de lavra estudada foi o cut and fill com orientação sub vertical. Nas modelagens foi analisado o processo de endurecimento do modulo de deformabilidade do backfill, de acordo com a etapa do ciclo de lavra. Os resultados do monitoramento e das modelagens mostraram que a adoção pelo backfill contribui de modo ativo para a estabilidade e segurança da mina. O aumento da tensão confinante devido ao endurecimento do backfill aumentou a interação mecânica com o maciço. Um aspecto sócio ambiental importante relaciona-se ao preenchimento das escavações com rejeito que tendem a mitigar os impactos ambientais, principalmente pela considerável redução dos volumes de rejeitos dispostos em superfície. _______________________________________________________________________________________ ABSTRACT
This study presents a numerical and experimental three-dimensional analysis of the interaction rock mass / backfill, considering the mechanic behavior of rock mass, during the process of excavation and backfill disposal, with increase of the confining stress and the module deformability hardening. The study case of Mine Cuiabá was monitored and the results were compared with the three-dimensional models. The specific type of mine studied was the cut and fill with sub vertical orientation. In the simulations was considered the module of backfill deformability that varies according to the stage of the exploration cycle. The disposal via backfill technology was simulated and monitored, which the results showed a positive contribution with the stability and safety of mine. The increase of the confining stress due to the hardening of backfill deformability module improved the interaction rock mass and backfill. This study showed that the backfill disposal linked to underground exploration mine tends to mitigate the environmental impacts in the mine.

The use of backfill in underground mining is increasing due to need for systematic backfilling of mine openings and workings to avoid surface damage, increase safety and contribution to sustainable mining. This study is to investigate backfill materials and new methods suited for systematic selection and application of backfill in underground mines. Laboratory tests were carried out on physical, chemical and mechanical properties of different backfill materials and mixtures thereof. Special attention was paid to materials generated as by-products and other cheaply available materials e.g. fly ash and FGD-gypsum from power plants, natural and synthetic anhydrite. The different material mixtures investigated can be used as a technically and economically viable backfill for underground mines. In summary, the systematic selection of backfill materials from by-products, mine waste and tailings from the mineral processing of mining industry and other industries were suited as a backfill material for test field in China coal fires and recommended for underground potash mines in Thailand.

>Magister Scientiae - MSc
Coal-fired power stations produce large volumes of coal combustion residues (CCRs), which are disposed of in hold ponds or landfill sites. These ash storage facilities are limited in space and are approaching the end of their capacities, thus additional land is required for extensions. If new land is not sourced, power plants will be forced to cease operations, resulting in increased expenditure costs and environmental liability. A proposed disposal solution is to backfill opencast coal mines with CCR monoliths. However, there is limited knowledge on the hydraulic behaviour of CCRs in an opencast coal mine environment. This leads to an inability to assess this applications feasibility and determine whether this activity will have a positive, negligible or negative effect on groundwater quality. This study aims to address this gap in knowledge by assessing the flow and transport properties of CCRs under numerous theoretical backfilling conditions.

Les métaux précieux (tels que l'or et l'argent), et les métaux de base (tels que le cuivre et d'autres) sont extraits du sous-sol par excavation, en créant des vides de différentes tailles appelés (chantiers d’abattage) qui sont reliés entre eux par des galeries (de circulation et de soutirage). Dans le cas de l’exploitation par chambres-remblayées, ces vides ou chambres sont généralement remplis avec du remblai en pâte cimenté (RPC) qui est un mélange fait des rejets de concentrateur (appelés résidus), d’un agent liant (ex. ciment) et de l’eau de malaxage. Vu que le RPC est déposé à l’état liquide (mélange solide-liquide) dans les chantiers d’abattage, il est nécessaire d’utiliser un ouvrage de retenue afin de le contenir pendant le remblayage. Cet ouvrage de retenue est appelé barricade et peut être construit en bois, en béton, en briques, en béton projeté ou à partir des roches stériles disponibles sous terre et qui sont issues du développement des galeries. Les barricades construites à partir des roches stériles sont les plus courantes au Québec et au Canada car elles sont économiques, disponibles (sous terre) et favorisent le drainage de l'eau lors du remblayage; ce qui favorise la consolidation gravitaire du RPC, et donc, la réduction de la pression interstitielle. À ce jour, peu d'informations existes sur les caractéristiques réelles in situ de ces barricades (telles que leur granulométrie, leur résistance à la rupture, le mécanisme probable de leur rupture et les dimensions standards utilisées) afin d’appuyer leur conception de manière à assurer la sécurité des travailleurs et des équipements miniers; ce qui contribuerait à la diminution du cycle de minage, et par conséquent, à l'augmentation de la productivité minière. Les travaux de cette thèse se sont appuyés sur les modélisations physiques et numériques afin de mieux comprendre le comportement géomécanique complexe des barricades de roches stériles. Un modèle physique à l'échelle réduite d’un chantier d’abattage a été développé et construit à partir de plaques en plexiglass translucides, afin de simuler le remblayage dans les mines souterraines. Une méthodologie spécifique a été développée pour l’exécution des essais : instrumentation du modèle réduit à l’aide de capteurs de pression (totale et interstitielle), calibrage des capteurs, remplissage du modèle réduit avec du RPC, suivi en continu des essais avec des caméras haute définition. Les essais réalisés ont permis de mettre en évidence le principal mécanisme probable de rupture des barricades de roches stériles, ainsi que l’estimation de la pression maximale au moment de leur rupture. L'effet de la distribution de la taille des particules de roches stériles sur la stabilité et l’intégrité des barricades de roches stériles à la suite de la poussée exercée par le RPC a également été analysé. Une partie des essais réalisés sur le modèle réduit a été modélisée à l’aide du code de calculs numériques Geostudio 2018 (GeoSlope Intl.) par calibrage avec les résultats expérimentaux. Les résultats des simulations réalisées reproduisaient correctement le comportement général observé lors des essais sur le modèle réduit, avec une différence significative au niveau des valeurs des pressions. Des solutions analytiques simplifiées basées sur l’équilibre limite ont également été proposées sur la base des observations expérimentales pour l’analyse de stabilité (par rapport au glissement et au frottement) des barricades de roches stériles. Des recommandations ont été proposées afin de pousser cette étude plus loin en incluant l’effet de différents facteurs (ex. la position de la barricade dans la galerie de soutirage, la viscosité et le seuil d’écoulement du remblai ou son pourcentage de solides, les paramètres de cisaillement des barricades de roches stériles, l’effet d'arche, etc.)
Precious metals (such as gold and silver), and base metals (such as copper and others) are mined from the underground by excavation, creating voids of various sizes called (stope) which are interconnected by galleries or drifts (for circulation and draw point). In the case of cut-and-fill mining, these voids are usually filled with cemented paste backfill (CPB) which is a mixture made of concentrator mill tailings, of a binding agent (e.g., cement) and mixing water. Since the CPB is placed in the liquid state (solid-liquid suspension) in the underground stopes, it is necessary to use a retaining structure to contain it during backfilling. This retaining structure is called a barricade and can be constructed from wood, concrete, bricks, shotcrete or from waste rock available underground and which come from the drift’s development. Barricades built from waste rock are the most common in Quebec and Canada because they are economical, readily available (underground) and promote water drainage during backfilling, which promotes self-weight consolidation of the CPB, and therefore, reduction of pore water pressure. To date, little information exists on the real in situ characteristics of these barricades (such as their grain size distributions, their failure strength, the probable mechanism of their rupture and the standard dimensions used) to support their design in a meaningful way to ensure the safety of workers and mining equipment, which would contribute to the reduction of the mining cycle, and consequently, to the increase of mining productivity. The work of this thesis project was based on physical and numerical modeling to better understand the complex geomechanical behavior of waste rock barricades. A reduced-scale physical model of a mine stope was developed and constructed from translucent plexiglass plates to simulate backfilling in underground mines. A specific methodology was developed for the execution of the tests: instrumentation of the reduced-scale model using pressure sensors (total and pore water), calibration of the sensors, filling of the reduced-scale model with CPB, continuous monitoring of the tests using high-definition cameras. The tests carried out have made it possible to highlight the main probable mechanism of rupture of the waste rock barricades, as well as the estimation of the maximum pressure at the time of their rupture. The effect of waste rock particle size distribution on the stability and integrity of waste rock barricades due to the CPB pressure was also analyzed. Part of the tests carried out on the reduced-scale model were modeled using the Geostudio 2018 numerical code (GeoSlope Intl.) through calibration with the experimental results. The results of the simulations performed reproduced well the general behavior observed during the tests on the reduced-scale model, but with a significant difference in the pressure values. Simplified analytical solutions based on limit equilibrium have also been proposed based on experimental observations for the stability analysis (with respect to sliding and friction) of waste rock barricades. Some recommendations were proposed to take this study further by including the effect of various factors (e.g., the position of the barricade in the drift or draw point, the viscosity, and the shear yield stress of the backfill or its solids mass concentration, the shear parameters of the waste rock barricades, the arching effect, etc.)

L’objectif de la thèse est de comprendre le comportement géochimique de l’arsenic dans les remblais miniers en pâte cimentés. Cette technique est employée depuis plusieurs années pour remblayer les galeries de mine exploitées à l’aide des rejets de concentrateurs. Pour cette étude, deux types de remblais sont élaborés en laboratoire : des échantillons de remblai minier en pâte synthétiques, fabriqués à partir de silice et enrichis artificiellement en arsenic, et des remblais miniers en pâte élaborés à partir de rejets miniers arséniés. Dans les deux cas, différents liants cimentaires sont testés. Plusieurs types d’investigations sont menés sur les échantillons de remblai en pâte cimentés. Une caractérisation minéralogique est effectuée à l’aide de divers outils. En parallèle, les échantillons de remblais sont soumis à différents tests de lixiviation complémentaires, afin d’évaluer la mobilité/rétention de l’arsenic dans ces matrices. Enfin, une modélisation géochimique est mise en œuvre à partir des résultats issus des deux études précédentes, afin d’affiner les connaissances sur la nature et la stabilité des composés arséniés dans les remblais étudiés. Les résultats obtenus indiquent que l’arsenic est mieux stabilisé dans les matrices à base de ciment Portland et de laitier de haut-fourneau que dans les remblais à base de cendres volantes. Le comportement à la lixiviation variable d’une matrice à l’autre s’explique par des spéciations et des mécanismes de piégeage de l’arsenic variés. L’arsenic peut précipiter sous forme de minéraux arséniés, principalement sous forme d’arséniates de calcium, mais aussi de divers autres composés secondaires variables d’une matrice à l’autre. Un piégeage physique des grains de rejets miniers arséniés par les hydrates cimentaires peut aussi avoir lieu, par formation d’un revêtement limitant l’oxydation des sulfures porteurs d’arsenic. Tous ces mécanismes interviennent dans la stabilisation/solidification de l’arsenic
The objective of this study is to understand the geochemical behaviour of arsenic in cemented paste backfills. This technique consists in transporting the tailings in the mine openings. Two types of backfills are prepared in the laboratory for this study. First, synthetic cemented paste backfills artificially spiked with arsenic are synthesized, using silica in replacement of the tailings. In parallel, other cemented paste backfill specimens are prepared with arsenic-rich tailings. In the two cases, various types of hydraulic binders are tested. Several types of investigations are conducted on the cemented paste backfill specimens. A mineralogical characterization is carried out with the help of specific tools. At the same time, cemented paste backfill samples are submitted to several complementary leaching tests, to assess the mobility/immobilization potential of arsenic in these matrices. Finally, geochemical modeling is implemented, based on the results of the two previous studies, in order to refine the understanding of the nature and stability of the arsenic compounds. The results show that arsenic is better immobilized in Portland cement and slag-based matrices, rather than in fly ash-based matrices. The variable leaching behaviour from a given matrix to another is due to different arsenic trapping mechanisms. Arsenic can precipitate and form several arsenic minerals, mainly calcium arsenates, but also various other secondary compounds, which are different from a matrix to another. Physical entrapment of the tailings grains by the cementitious minerals can also occur, by formation of a coating around the grains, limiting the oxidation and dissolution of arsenic-bearing sulfides (passivation). These mechanisms are involved in the stabilization/solidification of arsenic by cemented paste backfills

Energy conservation is a national strategy for every country. To avoid shortage of energy and high prices, the green sustainable energy resources have become the center of attention. Mining as a prominent industry in Canada consumes a huge amount of energy, so any reduction in energy consumption would result in higher production and profit. In 2005, Hassani of McGill University proposed the use of mine stopes as the heat exchange area for the production of low temperature geothermal energy, since the extraction of ore/ rocks and the backfilling is a part of normal mining operation, then the very low cost associated with the implementation of such system, will make it very viable for mining industry. This work is in collaboration with energy research team of professor Hassani of McGill University (EMERG). This is a part of an overall research program on low temperature geothermal energy from mines. The research was focused primarily on investigating and obtaining a range values for thermal conductivity of different mine backfills, as well as the effect of some of the associated physical parameters. More than 800 samples and 2000 measurements were done on different backfills with different physical properties. This preliminary investigation indicates that pulp density, binder consumption, curing time, and sodium silicate content have negligible to slight influence on the thermal conductivity of backfill. However parameters such as saturation, and to a lesser extent porosity and the thermal conductivity of the inert material, have more significant influence.

In this thesis finite element analyses were performed to investigate the behavior of fill fences installed in underground mines to retain Cemented Paste Backfill (CPB) pressure. For this purpose, two fill fences installed and tested in the Cayeli mine in Turkey were modeled using a 2-D nonlinear finite element analysis program, Augustus-2, and a 3-D nonlinear finite element analysis program VecTor4, and the results were compared with measured field data. Different models were employed representing the material properties, boundary conditions, reinforcement ratio, and geometric properties, and it was found that boundary conditions (stiffness of surrounding rocks) has the highest influence on the pressure capacity of the fence among the other factors. The accuracy of the Augustus-2 program was investigated by modeling and comparing the analytical response with test results of 12 axially restrained beams tested by Su et al. (2009).

A thesis submitted to the Faculty of Engineering, University of the Witwatersrand. Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy
Hydraulically placed cemented backfill is increasingly being used as a means of stope support in South African hard-rock mines. The addition of binder provides backfill with a primary compressive strength. the property for which the material has traditionally been utilised. Binder-induced cohesion, however, is not the only factor determining the quality of cemented backfill and the material's utility can be enhanced significantly by applying all of its attributes to the task of stope support. The main purpose of this thesis is, therefore, to examine those factors which influence the performance of cemented backfill, and to provide relevant and useful information for the design of improved cemented backfill mine support for tabular mining excavations. In an extensive laboratory investigation, a number of relevant factors were tested for their influence on the loading behaviour of cemented backfill. Twenty two cemented backfills. grouped according to aggregate type, water content, binder content and binder type, were analysed to determine the influence of composition on their material properties. This study was augmented by several test series on the effects of curing conditions on cemented backfill quality. In a second major investigation, the effects of geometrical parameters, including sample volume and sample width to height ratios were analysed. A further study dealt with the effect of spatially separating sample backfill ribs under normal compression, as well as at high closure rates. It is concluded, that by co-ordinating the composition design of cemented backfills with the spatial configuration of backfill support elements, it is possible to modify all phases of the cemented backfill loading response. This implies the control of the binder-induced compressive strength at low strains, the large-scale yielding behaviour of backfill support, as well as the stiffness of the backfill body at high stresses. In the light of stope support requirements. particularly under rockburst conditions, the capacity of backfill support to yield and absorb rapid stope closure and then to decelerate the hangingwall by the rapid strain-hardening of the, now, large width to height ratio backfill mass, has the potential of substantially increasing mine safety in tabular stopes,
Andrew Chakane 2020

ABSTRACT This research evaluated the application of post consumer glass as a cementing agent in underground mine backfills. The underlying theory indicates that glass is pozzolanic and, when used in finely divided form, reacts as an activator to generate binding products, thus contributing to the development of backfill strength. The objective of the research was to evaluate the strength performance of backfills when Normal Portland Cement (NPC) is replaced with various percentages of post consumer glass. The research evaluated the performance of backfills prepared using tailings from three candidate mines, namely Stobie, David Bell and Kidd Creek. Each backfill was prepared using unique recipes, and the strength and other properties were evaluated at cure times of 7, 14, 28, 56, 112 and 224 days. Laboratory work involved visual, physical and chemical material characterization followed by strength evaluations. Results of strength assessment reveal that glass, when incorporated as part of the binder in backfill development is reactive, and can contribute to the strength of backfill. Further analysis of the results also indicated that the reactivity of glass may be affected by the incorporation of slag within the recipe, the availability of lime and the level of hydration of the binders. The research concluded that, at 15 % glass replacement of NPC, backfill prepared with David Bell tailings, NPC and glass can achieve improved or equivalent strength performance compared to backfill prepared with David Bell tailings and NPC. NPC and slag outperformed backfills prepared with NPC, slag and glass at all replacement levels, using tailings from Kidd Creek and Inco-Stobie. However, future work should be designed to maximize the effect of specific pozzolan (for example glass) and material properties (aggregates) on backfill strength performance.
Thesis (Master, Mining Engineering) -- Queen's University, 2008-01-29 15:09:30.281

A dissertation submitted to the Faculty of Engineering, University of Witwatersrand, in fulfillment of the requirements for the degree of Master Science in Engineering
The Electricity Supply Commission of South Africa (Eskom) have identified open cast coal mine backfill areas as potential disposal sites for the large volumes of coal ash produced by their power stations. As Eskom's power stations are mainly situated in agricultural and coal rich areas of the provinces of Mpumalanga and the Free State, the sterilisation of substantial areas of agricultural soil and coal deposits is thus reduced. The construction of a tailings dam or dump on uncompacted open cast mine backfill creates various problems related to the settlement of the backfill. The scale of the operation, the large particle size and heterogeneous nature of the backfill and its method of placement complicates the prediction for settlement of the backfill. Areas in excess of 74 000 ha could be subjected to opencast mining in Mpumalanga and for future development of these areas more information regarding the magnitude and mechanics of mine backfill settlement is required. This dissertation describes two large scale field tests in which the settlement of mine backfiil was studied during the construction of a test section of an ash tailings dam and the construction of a dry ash dump.
Andrew Chakane 2019

Large voids created by underground mining are backfilled to provide regional ground support. This thesis examines using conventional oedometer techniques and electromagnetic (EM) techniques to characterize consolidation and binder hydration in mine backfill so that EM monitoring can be used in the field to provide real-time feedback to operators to optimize the backfilling process. New techniques are given for interpreting the full range of deformation (initial compression, primary and secondary consolidation). Deformation due to initial compression is non-trivial and may have to be accounted for in numerical back-analyses of field case studies. EM parameters are sensitive to binder content, progress of hydration and loss of water caused by consolidation and binder hydration. The integrated interpretation of consolidation and EM behaviours has significant potential impact on real-time monitoring of mine backfill operations, and recommendations are made to advance the technique for this purpose.

This paper details an investigation into the feasibility of using agglomerated tailings in a 'dry' aggregate fill for underground mining. A test program began with the agglomeration of tailings materials from Eskay Creek Mine, British Columbia, using Portland cement as a binding agent. Thereafter, a series of backfill tests were conducted in which agglomerates, river aggregate, and tailing materials were combined in various proportions to develop a high quality fill. The results of the investigation showed that it is technically feasible to utilize agglomerated tailings in an aggregate backfill used for structural support in underground mining operations. Three related factors reveal their importance: grain size distribution, the degree of compaction and the void content of the mixture. These variables, among others, significantly affect the strength and quality of the fill - for example - the lower the void ratio, the greater the strength of the fill. The strengths of the individual constituents and the water to cement ratio also play major roles in determining the fill strength, but only in those cases where the materials are compacted to minimize voids. The effects are an increase in strength with the increasing strength of the constituents and with decreasing water/cement ratio. Where the void content of the aggregate mix is high, the effect of changing the water to cement ratio is minimal. Although the process of agglomeration is technically feasible, it seems that the associated costs are in opposition to its implementation. An economic analysis of the agglomeration process has revealed that other methods of disposal such as using a tailings pipeline are significantly more attractive from a financial viewpoint mainly because such an option allows the removal of the tailings filter from the process (now in use at the mine). However, the presence of mercury, antimony and arsenic in the tailings raises health and environmental concerns; the need to insure that ARD generation and the release of heavy metals after mine closure is unresolved. In mining situations where ARD generation is an issue, the agglomeration concept may be technically feasible, although the agglomerates may require sealing with a reagent such as sodium silicate, however testwork is required to verify the efficacy of this concept. Where ARD generation is not suspected and where surface or submarine disposal are not viable, the use of agglomeration is a technically feasible alternative.

The WMC Fertilizers operation at Phosphate Hill, north-west Queensland, began production of ammonium phosphate fertilizer in late 1999. In the production process, Cambrian marine phosphorites are crushed and dissolved (acidulated) in sulphuric and phosphoric acid to produce stronger phosphoric acid and, as a by-product, phosphogypsum (PG). The phosphoric acid is used, with ammonia, for fertilizer production while the PG is permanently stored on-site in gypsum stacking facilities. In common with other fertilizer plants, the volume of PG in storage at Phosphate Hill has increased rapidly. Eventually tens of millions of tonnes of the material will need to be maintained in permanent facilities. Above-ground stacks, such as those currently used, will be subject to erosion, potentially forming sources of pollutants for the surrounding pastoral country. An alternative option is to store the PG in the voids left after mining of the phosphorite ore body. This would immediately negate most opportunities for erosion of, and contamination from, the storage facilities. This study was instigated to assess the likely impact of in-pit disposal. Very little work had been done on characterizing the PG produced at Phosphate Hill. A single initial set of analyses taken from samples obtained during the commissioning period identified the major components and subjected the material to rigorous mechanical testing. By contrast, this study has focussed on fully identifying the mineralogy, chemistry, radiochemistry and physical characteristics of the PG in its two main species: the hemihydrate (bassanite - CaSO4.0.5H2O) as it is produced from the phosphoric acid plant and the dihydrate (gypsum - CaSO4.2H2O) that is transported from the re-slurry tank into the gypsum stack for storage. In addition, the liquid component of the PG slurry, derived from acid process water that is recirculated through the stacking system, has also been analysed. The results show that the four species of calcium sulphate can be found in the PG. Bassanite (CaSO4.0.5H2O) is dominant in the hemihydrate filter cake but also remains in the stack material. Dihydrate gypsum (CaSO4.2H2O), including species with extra H2O molecules (identified as *.0.5H2O), dominates the stack gypsum but also occurs at low levels in the hemihydrate filter cake. Anhydrite (CaSO4) is also found at low levels within samples from both areas. Quartz (SiO 2) is the other dominant mineral in the PG assemblage. This is at significant levels (>20%) and causes the PG to be notably different to that produced elsewhere in the world, where quartz makes up <1% of the total. The high volumes of this mineral result from the make-up of the parent phosphorite ore body, which has a comparatively high level of chert and silicified siltstone and shale. P2O5 levels are elevated and relate primarily to the presence of co-precipitated and reprecipitated phosphates and remnant phosphoric acid with very minor amounts of unreacted phosphorite and phosphatised chert and siltstone. Mica (paragonite [NaAl2(Si3Al)O10(OH)2] and probably muscovite [K2Al4[Si6Al2O20](OH,F)4] and glauconite [(K,Ca,Na)~1.6(Fe3+,Al,Mg,Fe2+)4.0Si7.3Al0.7O20(OH)4] sourced from the ore body) was a consistent presence at low levels in the PG mix. An unidentified amphibole was also found, although some doubts exist as to the accuracy of the XRD technique to adequately identify such minerals at the low levels seen here. If correct, the latter is probably from the hornblende group (magnesiohastingsite to hastingsite) that occurs in the basement Kalkadoon Granodiorite, or from the basement Proterozoic metasediments of the Plum Mountain Gneiss and Corella Formation. Various clays, most commonly smectite ((½Ca,Na)0.7(Al,Mg,Fe)4[(Si,Al)8O20](OH)4.nH2O) and clinoptilolite ((Na,K)6[Al6Si30O72].24H2O) were also consistently present. Major element analyses are consistent with the mineralogical interpretation. Elements, apart from Ca, S and Si and including F, were at levels similar to those found in PG manufactured at other sites around the globe. Trace elements showed elevated levels of Ba, Mn and Pb relative to foreign-sourced PG. This appears to reflect the primary and secondary (weathering products) mineralogy of the ore body. Crystal morphology was also shown to be similar to that produced abroad, at sites as diverse as the USA, north Africa and the Middle East. The gypsum component of the Phosphate Hill PG appears to contains fewer acicular crystals and no swallow-tail twins were observed, unlike at other sites. Massive clusters are common. Radiochemical analyses have identified U-238, Po-210, Pb-210, Ra-226 and Rn-222 as being present in the ore and throughout the manufacturing process. All are present to varying degrees in the PG but the U-238 tends to partition more into the fertilizer. None of the radionuclides occur at levels that could be considered a risk. However, the study has identified that recirculation of the fluids through the re-slurry-stacking circuit is concentrating the radionuclides occurring in the process water. This issue will need to be monitored and addressed by the Company in future. The second part of the project has been to study the effects of dissolution on the PG if placed into surface mining voids as backfill. At Phosphate Hill, potential dissolution of mine backfill material can be derived from two sources. The first is the monsoonal "wet season" over summer, where individual rain events can result in over 150mm of rain falling in the space of a few hours, leading to flash flooding and inundation of wide areas around the local watercourses. This has the potential to result in the temporary submergence of any of the backfilled areas located within the flood plain. The second source is from interaction of the PG with the groundwater. The latter will occur because the Beetle Creek Formation, which hosts the ore body, also contains the local aquifer and post-mining recharge will see the SWL return to pre-mining levels, well above the floors of the pits. Dissolution experiments were performed using hemihydrate and two forms of dihydrate PG, simulating approximately two years’ annual rainfall/intermittent full inundation of a PG backfill pile by either groundwater or floodwater. The dihydrate PG was newly deposited material that still contained high levels of fluid and "aged" dihydrate that had been on the stack for 4-6 months and was dry. Analyses of the dissolution and the pre and post-dissolution PG showed that highly contaminated dissolution would occur in the first 2-3 flushing events and that levels of contaminants fall rapidly with further flushing. The major long-term contaminant has been identified as sulphates and acid derived from gypsum dissolution. Ca and total P are also significant. Radionuclide analysis of leachate could not be undertaken in this study but should be considered for any future studies, if the Company plans to utilise in-pit disposal of PG. Gypsum dissolution is also likely to be a long-term problem in that the aquifer is essentially a closed system. This, along with the dominant flow direction, will result in concentration of any contaminants in the southern part of the aquifer. Basic simple modelling of the effects of a sulphate-rich solution mixing with the groundwater at its current quality suggests that the sulphate may reach levels of concern for human consumption (i.e. >500mg/l) with an input of contaminated fluid the equivalent of <25% of the total volume of the aquifer. As the site is covered by active pastoral leases the effect of sulphate contamination of groundwater on cattle was also considered. In this environment problems occur at sulphate levels of ~1000mg/l which the modelling suggests would not occur until a mix of 50% leachate to 50% groundwater was achieved. Although this appears to be a remote possibility for contamination of the whole aquifer, the very high transmissivity of the aquifer will result in a polluted plume being drawn directly into wells that are pumping, which could easily result in the ingestion of poor quality water by cattle drinking from troughs supplied by any such bore. Acidification of the groundwater could also possibly occur with the escape of acid leachate into the aquifer, with the pH of the water rapidly falling below the preferred minimum of pH 6 at relatively low levels of mixing (10% leachate to 90% groundwater). Acidification to this extent can cause acidosis in cattle, a condition that is potentially fatal. Phosphorous is also present in high levels in the PG leachate. There is potential for this to lead to outbreaks of toxic cyanobacteria in water storage tanks and troughs in the warmer months, which can result in fatalities in cattle through liver or respiratory failure. However, this potential may be buffered by the likely acidity of any high-P leachate, as cyanobacteria prefers neutral to alkaline water conditions. Although contaminated leachate can be largely contained by use of liners and capping material, the use of PG as backfill at Phosphate Hill faces challenges that would be extremely difficult to overcome. The mining method leaves walls that are sub-vertical (>70º) and exposes the full ore seam on the down-dip side of the ore body. Pit floors have a dome-and-basin morphology. Although the latter could be flattened and lined, the steep walls, with their exposures of abrasive, sharp-edged phosphorite would preclude the use of most lining materials. The scale of earth- moving and lining required would also be cost-prohibitive. The type of PG used for backfilling operations and the method of delivery also create difficulties. Filter cake hemihydrate PG would require a very large truck fleet and/or the construction of a new overland conveyor. Once deposited, the material’s tendency to form large, loose clumps would allow rapid through- flow of fluids. PG slurry could be piped directly to its deposition point, requiring the construction of an extensive pipe network, but is otherwise completely unsuitable for the task due to the liquid component. Dry dihydrate PG is the best material for backfill. However, it would also require a very large truck fleet and the act of rehandling the material from stack to pit would create dust problems for the term of the rehandling exercise. After deposition the leachate problem would still exist, albeit produced at a slower rate due to the dihydrate’s lower permeability. The leachate problem could be countered by using a layer-cake style of construction where calcareous rocks are interlayered with PG to neutralise any fluids derived from the PG. Despite this, other engineering and environmental issues probably preclude the use of even this method of backfill. This study has produced the base-line information required for any future work involving the PG, such as the recommendation for trials of in-pit dumping to go ahead, observing a range of conditions. As a result, it is recommended that WMCF only use dihydrate PG as backfill in areas that are well above the natural standing water level and that have been adequately lined. The majority of PG will still need to be stored in lined and capped stacks, as are currently used. It is also recommended that the radionuclide content of the recycled stack fluids being regularly monitored and plans drawn up to deal with the contaminated fluids if it proves necessary. Future research should also be conducted on radionuclide transport and behaviour in PG leachate.

An understanding of the performance of uncemented backfills used for support in deep level South African gold mines is essential in evaluating the effectiveness of this support medium. Three main types of uncemented backfill material have been used for underground support in deep level gold mines. They are full plant de-watered tailings, full plant classified tailings and comminuted waste. The purpose of this dissertation is to document the data on the performance of all three of these types of backfill that have been collected at many underground sites, and to present an analysis of their general three dimensional behaviour.