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Nagaratnam Sivakugan - One of the best experts on this subject based on the ideXlab platform.
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Vertical stress isobars for silos and square backfilled Mine Stopes
International Journal of Geomechanics, 2016Co-Authors: Sankha Widisinghe, Nagaratnam SivakuganAbstract:AbstractOften granular materials are stored in vertical containers with circular or square cross sections. The storage material can be food grains, pharmaceutical powders, chemical pellets, or geomaterials such as Mine fills. The design and analysis of these containers require adequate knowledge of the stresses developed within the filled material. The stress isobars developed herein enable the designers to estimate the vertical stress at any point within the fill contained in a silo. The same isobars can also be used for square cross sections, as in the case of backfilled underground Mine Stopes, without sacrificing the accuracy much. The same method was previously followed by the authors in developing isobars for plane-strain situations. On the basis of the two sets of isobars for trenches and square Stopes, it is possible to interpolate the stresses for other rectangular Mine Stopes, which can serve as good first estimates in the designs.
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Geotechnical Aspects of Hydraulic Filling of Australian Underground Mine Stopes
Ground Improvement Case Histories, 2015Co-Authors: Nagaratnam Sivakugan, Kelda Rankine, Rudd RankineAbstract:Mining for Minerals creates large voids underground that have to be backfilled to provide regional stability for subsequent mining operations. Hydraulic fill is one of the most popular backfill materials used to fill these underground voids, and is generally placed in the form of a slurry at water contents in the range of 30–45%. Porous brick barricades are placed across horizontal access drives to retain the hydraulic fill, allowing free drainage and enabling the hydraulic fill to settle under its self-weight. Several accidents have been reported worldwide, where the porous brick barricades have failed, resulting in an inrush of the hydraulic fill slurry into the drives, claiming lives of Miners and causing heavy economic losses. An example of this is the barricade failure at Bronzewing Mine in Western Australia in 2000, where three Miners were killed. The problems associated with the hydraulic filling of Mine Stopes in Australia, with special references to the numerical modeling and laboratory studies carried out to improve the current state of the art in hydraulic filling of underground Mines, are discussed in this chapter. At James Cook University, extensive laboratory tests were carried out on more than 25 different hydraulic fills obtained from five different Mines, in an attempt to fully understand their behavior and to develop a geotechnical database for the Mines. The data from laboratory tests compare well with the in situ measurements. Tests were also carried out on two types of porous barricade bricks that are commonly used in Australia, to quantify their permeability and load-deformation characteristics. Fast Lagrangian Analysis of Continua (FLAC) and Fast Lagrangian Analysis of Continua in 3 Dimensions (FLAC 3D ) were used to numerically model the drainage through the hydraulic fills and the stress developments within the fill. Due to the arching mechanism, the vertical normal stresses within the Stopes are significantly reduced. Typical parameters for hydraulic fills and porous barricade bricks are given in this chapter and these are very valuable in numerical modeling exercises when no other data are available.
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Analytical Expression for Vertical Stress within an Inclined Mine Stope with Non-parallel Walls
Geotechnical and Geological Engineering, 2014Co-Authors: Ching Hung Ting, Nagaratnam Sivakugan, Wayne Read, Sanjay Kumar ShuklaAbstract: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 ( α ) is less than that of footwall ( β ). 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.
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Vertical stress isobars for trenches and Mine Stopes containing granular backfills
International Journal of Geomechanics, 2014Co-Authors: Sankha Widisinghe, Nagaratnam SivakuganAbstract:AbstractThe vertical stresses within granular fills contained in trenches can be deterMined using Marston’s theory or numerical modeling. Marston’s theory gives only the average value of the vertical stress at a depth. Numerical modeling can be used for determining the vertical stress at any point within the fill. This paper presents vertical stress isobars for trenches filled with granular materials, developed from numerical modeling, and proposed in terms of dimensionless variables. These isobars are similar to the pressure isobars for uniformly loaded circular and strip footings found in literature. These isobars can be used for determining vertical stresses at any point within the granular material contained in trenches and can become a simple and valuable tool. The validity of the isobars was verified through several trenches with randomly selected dimensions and fill properties. It was found that the estimates using the isobars were within 9% of the estimates from the numerical model.
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Vertical Stress Determination within Backfilled Mine Stopes
International Journal of Geomechanics, 2014Co-Authors: Nagaratnam Sivakugan, Sankha Widisinghe, Vincent Z. WangAbstract:AbstractDetermining the vertical stresses within underground Mine Stopes is necessary for designing the barricades that block the drives during filling. This paper discusses two different procedures that can be used for determining the vertical stress profile, which give different values of stresses. The difference is attributed to fixing the bottom of the stope, implying zero displacement in any direction. The reasons are discussed, and it is suggested that the method commonly used in numerical modeling (Method 2) is not necessarily the better of the two. The alternate method (Method 1) models the field situation better when the loadings at the bottom during filling are required, mimics the laboratory model tests, and gives the same stress profile for all Stopes with any aspect ratio. The findings are applicable to backfilled trenches as well.
Michel Aubertin - One of the best experts on this subject based on the ideXlab platform.
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Theoretical and Numerical Analyses of Earth Pressure Coefficient along the Centerline of Vertical Openings with Granular Fills
Applied Sciences, 2018Co-Authors: Pengyu Yang, Michel AubertinAbstract:Granular filling materials are placed into confining structures for various purposes, including but not limited to silos, trenches, Mine Stopes, and retaining walls for backfill. Stresses in these backfilled openings are commonly estimated using theoretical arching models, with equations that often involve the earth pressure coefficient K (=σ’h/σ’v). Such stress estimation can be dramatically impacted by the magnitude of K, but its value remains debatable. Along the centerline of vertical openings with granular cohesionless fills, the value of K is sometimes obtained by Jaky’s earth pressure coefficient at rest K0, based on the assumption of fixed confining walls, whereas Rankine’s active earth pressure coefficient Ka is regarded more suitable for K as claimed by some others. Recent numerical analyses from the authors have shown that the state of stress close to the center of backfilled openings cannot be solely related to wall movement. It was also shown that the K value can vary between Ka and K0 in backfilled openings with fixed (immobile) walls, depending on the locations and respective values of fill internal friction angle ϕ’ and Poisson’s ratio ν. However, none of the existing works have addressed the mechanisms and answered this fundamental but critical question: which value of coefficient K (K0, Ka, or other) should be used with analytical solutions to assess the stresses in backfilled openings (and why)? After assessing the state of the fill placed in a confined opening, theoretical relationships and specific mechanisms are proposed, for the first time, to evaluate critical values of ν and ϕ’ for defining the at-rest and active states in fills. The approach indicates that when ν or ϕ’ are smaller than or equal to critical values, the value of K near the center line of a backfill opening should be close to Ka; otherwise, K tends to approach K0 defined from ν. The theoretical analysis is complemented and validated (in part) by numerical simulations. The results also demonstrate that Poisson’s ratio can play a major role on the stress distribution within cohesionless fills, and should thus be accurately evaluated.
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Analysis of the Stress Distribution in Inclined Backfilled Stopes Using Closed-form Solutions and Numerical Simulations
Geotechnical and Geological Engineering, 2018Co-Authors: Abtin Jahanbakhshzadeh, Michel AubertinAbstract:Backfilling is often used in underground Mines to ensure stope stability and workers safety. Evaluating the stress state in the fill material and surrounding rock mass is a critical step for the design of backfilled Stopes. The majority of analytical (closed-form) solutions to obtain the stresses have been developed for vertical openings. In reality, most Mine Stopes have inclined walls. Previous studies have shown that in such cases, the stresses developing along the hanging wall and footwall can be quite different. Recent investigations have also indicated that the stress transfer between the relatively soft backfill and stiff rock mass is typically not as well developed in inclined Stopes, compared with vertical openings. In this paper, the authors first recall analytical solutions that have been proposed for evaluating the stresses in backfilled Stopes with vertical and inclined walls. Numerical simulations are then used to assess the interactions between the backfill and rock mass. The influence of backfill properties and stope geometry (in terms of height, width and inclination) is exaMined. The stresses obtained from existing solutions and new simulations are then compared and discussed. This comparison points to significant differences, indicating that an alternate formulation is required to properly assess the stress state in inclined Stopes.
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Three-dimensional stress state in inclined backfilled Stopes obtained from numerical simulations and new closed-form solution
Canadian Geotechnical Journal, 2018Co-Authors: Abtin Jahanbakhshzadeh, Michel AubertinAbstract:Backfill is commonly used world-wide in underground Mines to improve ground stability and reduce solid waste disposal on the surface. Practical solutions are required to assess the stress state in the backfilled Stopes, as the stress state is influenced by the fill settlement that produces a stress transfer to the adjacent rock walls. The majority of existing analytical and numerical solutions for the stresses in backfilled openings were developed for two-dimensional (plane strain) conditions. In reality, Mine Stopes have a limited extension in the horizontal plane so the stresses are influenced by the four walls. This paper presents recent three-dimensional (3D) simulations results and a new 3D closed-form solution for the vertical and horizontal stresses in inclined backfilled Stopes with parallel walls. This solution takes into account the variation of the stresses along the opening width and height, for various inclination angles and fills properties. The numerical results are used to validate the ana...
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Stress Ratios in Entire Mine Stopes with Cohesionless Backfill: A Numerical Study
Minerals, 2017Co-Authors: Pengyu Yang, Michel AubertinAbstract: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 (Ka) and at-rest coefficient (K0). 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, Kps (= σ′3/σ′1), should be distinguished. Parametric analyses indicate that values of K and Kps depend on the position and the relationship between ϕ′ and ν. Near the opening center, K (= Kps) is close to Ka when ν or ϕ′ is below a critical value; otherwise the value approaches K0, defined from ν. Near both walls, Kps is always close to Ka, while K is near K0 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.
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A New Analytical Solution for the Stress State in Inclined Backfilled Mine Stopes
Geotechnical and Geological Engineering, 2017Co-Authors: Abtin Jahanbakhshzadeh, Michel AubertinAbstract: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.
N. Sivakugan - One of the best experts on this subject based on the ideXlab platform.
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Average Vertical Stresses in Underground Mine Stopes Filled with Granular Backfills
Geotechnical and Geological Engineering, 2016Co-Authors: P. Rajeev, P. R. Sumanasekera, N. SivakuganAbstract:Marston’s theory and its modifications are being used to deterMine the average vertical stress variation with depth within a cavity with vertical wall, backfilled with granular material. In the past, this has been applied in trenches, Mine Stopes and silos of different cross sections. In all situations, at very large depths, the vertical stresses become asymptotic. The laboratory model tests clearly suggest that this is not the case and that the average vertical stresses continue to increase. In this paper, an attempt is made to improve Marston’s model, in the light of laboratory test data. It is shown that the problem with Marston’s equation is its inability to model the shear stress correctly, which leads to an asymptotic vertical stress after a certain depth. The proposed equation is of the same form as Marston’s equation, and has two coefficients α and β that have to be deterMined from a laboratory model test.
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Lateral Variation of the Vertical Stress in Underground Mine Stopes Filled with Granular Backfills
Geotechnical and Geological Engineering, 2016Co-Authors: P. Rajeev, P. R. Sumanasekera, N. SivakuganAbstract:Marston’s theory and its modifications are widely used to predict the average vertical stress variation with depth within Mine Stopes. However, this does not model the lateral variation in vertical stress at a particular depth. In this study, a mathematical expression to simulate the vertical stress variation is developed using the experimental shear stress data of granular backfill. The developed model is validated against average vertical stress measured in the experiment. Therefore, the developed model has the advantage of determining both the average vertical stress and its distribution respectively, at a particular depth and a cross sectional area of the Mine stope.
P. Rajeev - One of the best experts on this subject based on the ideXlab platform.
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Average Vertical Stresses in Underground Mine Stopes Filled with Granular Backfills
Geotechnical and Geological Engineering, 2016Co-Authors: P. Rajeev, P. R. Sumanasekera, N. SivakuganAbstract:Marston’s theory and its modifications are being used to deterMine the average vertical stress variation with depth within a cavity with vertical wall, backfilled with granular material. In the past, this has been applied in trenches, Mine Stopes and silos of different cross sections. In all situations, at very large depths, the vertical stresses become asymptotic. The laboratory model tests clearly suggest that this is not the case and that the average vertical stresses continue to increase. In this paper, an attempt is made to improve Marston’s model, in the light of laboratory test data. It is shown that the problem with Marston’s equation is its inability to model the shear stress correctly, which leads to an asymptotic vertical stress after a certain depth. The proposed equation is of the same form as Marston’s equation, and has two coefficients α and β that have to be deterMined from a laboratory model test.
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Lateral Variation of the Vertical Stress in Underground Mine Stopes Filled with Granular Backfills
Geotechnical and Geological Engineering, 2016Co-Authors: P. Rajeev, P. R. Sumanasekera, N. SivakuganAbstract:Marston’s theory and its modifications are widely used to predict the average vertical stress variation with depth within Mine Stopes. However, this does not model the lateral variation in vertical stress at a particular depth. In this study, a mathematical expression to simulate the vertical stress variation is developed using the experimental shear stress data of granular backfill. The developed model is validated against average vertical stress measured in the experiment. Therefore, the developed model has the advantage of determining both the average vertical stress and its distribution respectively, at a particular depth and a cross sectional area of the Mine stope.
Rudd Rankine - One of the best experts on this subject based on the ideXlab platform.
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Geotechnical Aspects of Hydraulic Filling of Australian Underground Mine Stopes
Ground Improvement Case Histories, 2015Co-Authors: Nagaratnam Sivakugan, Kelda Rankine, Rudd RankineAbstract:Mining for Minerals creates large voids underground that have to be backfilled to provide regional stability for subsequent mining operations. Hydraulic fill is one of the most popular backfill materials used to fill these underground voids, and is generally placed in the form of a slurry at water contents in the range of 30–45%. Porous brick barricades are placed across horizontal access drives to retain the hydraulic fill, allowing free drainage and enabling the hydraulic fill to settle under its self-weight. Several accidents have been reported worldwide, where the porous brick barricades have failed, resulting in an inrush of the hydraulic fill slurry into the drives, claiming lives of Miners and causing heavy economic losses. An example of this is the barricade failure at Bronzewing Mine in Western Australia in 2000, where three Miners were killed. The problems associated with the hydraulic filling of Mine Stopes in Australia, with special references to the numerical modeling and laboratory studies carried out to improve the current state of the art in hydraulic filling of underground Mines, are discussed in this chapter. At James Cook University, extensive laboratory tests were carried out on more than 25 different hydraulic fills obtained from five different Mines, in an attempt to fully understand their behavior and to develop a geotechnical database for the Mines. The data from laboratory tests compare well with the in situ measurements. Tests were also carried out on two types of porous barricade bricks that are commonly used in Australia, to quantify their permeability and load-deformation characteristics. Fast Lagrangian Analysis of Continua (FLAC) and Fast Lagrangian Analysis of Continua in 3 Dimensions (FLAC 3D ) were used to numerically model the drainage through the hydraulic fills and the stress developments within the fill. Due to the arching mechanism, the vertical normal stresses within the Stopes are significantly reduced. Typical parameters for hydraulic fills and porous barricade bricks are given in this chapter and these are very valuable in numerical modeling exercises when no other data are available.
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Permeability of Hydraulic Fills and Barricade Bricks
Geotechnical and Geological Engineering, 2006Co-Authors: Nagaratnam Sivakugan, K.j. Rankine, Rudd RankineAbstract:Permeability is one of the most important parameters in the design of hydraulic backfilling of Mine Stopes. A simple and reproducible method was developed for preparing reconstituted hydraulic fill sample in the laboratory, that is representative of the hydraulic fill in the Mine stope, replicating the slurry sedimentation process taking place in the Mine. Constant head and falling head permeability tests were carried out on the samples, giving consistent results. A brick permeameter was developed to study the flow characteristics of the porous barricade bricks under one-dimensional flow, simulating the flow conditions in the Mine. Three different methods were used to deterMine the permeability of the brick and the results showed very good agreement. This is the first rational attempt to measure the permeability of the porous barricade bricks that are used to close the horizontal access drives in the Mines, thus retaining the hydraulic fill. The measurements show that the permeability of the barricade brick is about two to three orders of magnitude greater than that of the hydraulic fill.
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Geotechnical aspects of hydraulic filling of underground Mine Stopes in Australia
2005Co-Authors: Nagaratnam Sivakugan, Kelda Rankine, Rudd RankineAbstract:Mining for Minerals creates large voids underground which have to be backfilled to provide regional stability for subsequent mining operations. Hydraulic fill is one of the most popular backfill materials used to fill these underground voids, and is generally placed in the form of a slurry at water contents in the range of 30-45%. Porous brick barricades are placed across horizontal access drives to retain the hydraulic fill, allowing free drainage and enabling the hydraulic fill to settle under its self-weight. Several accidents have been reported worldwide, where the porous brick barricades have failed, resulting in an inrush of the hydraulic fill slurry into the drives claiming lives of Miners and causing heavy economic losses. A recent example of this is the barricade failure at Bronzewing Mine in Western Australia, where three Miners were killed. The problems associated with the hydraulic filling of Mine Stopes in Australia, with special references to the numerical modelling and laboratory studies carried out to improve the current state-of-the-art in hydraulic filling of underground Mines are discussed in this chapter. At James Cook University, extensive laboratory tests were carried out on more than 25 different hydraulic fills obtained from five different Mines, in an attempt to fully understand their behaviour and to develop a geotechnical database for the Mines. The data from laboratory tests compare well with the in situ measurements. Tests were also carried out on two types of porous barricade bricks that are commonly used in Australia, to quantify their permeability and load-deformation characteristics. Fast Lagrangian Analysis of Continua (FLAC) and Fast Lagrangian Analysis of Continua in 3-dimensions (FLAC3D) were used to numerically model the drainage through the hydraulic fills and the stress developments within the fill. Due to arching mechanism, the vertical normal stresses within the Stopes are significantly reduced. Typical parameters for hydraulic fills and porous barricade bricks are given in this chapter and these would be very valuable in numerical modelling exercises when no other data are available.
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Chapter 18 Geotechnical aspects of hydraulic filling of underground Mine Stopes in Australia
Ground Improvement — Case Histories, 2005Co-Authors: Nagaratnam Sivakugan, Kelda Rankine, Rudd RankineAbstract:Abstract Mining for Minerals creates large voids underground which have to be backfilled to provide regional stability for subsequent mining operations. Hydraulic fill is one of the most popular backfill materials used to fill these underground voids, and is generally placed in the form of a slurry at water contents in the range of 30–45%. Porous brick barricades are placed across horizontal access drives to retain the hydraulic fill, allowing free drainage and enabling the hydraulic fill to settle under its self-weight. Several accidents have been reported worldwide, where the porous brick barricades have failed, resulting in an inrush of the hydraulic fill slurry into the drives claiming lives of Miners and causing heavy economic losses. A recent example of this is the barricade failure at Bronzewing Mine in Western Australia, where three Miners were killed. The problems associated with the hydraulic filling of Mine Stopes in Australia, with special references to the numerical modelling and laboratory studies carried out to improve the current state-of-the-art in hydraulic filling of underground Mines are discussed in this chapter. At James Cook University, extensive laboratory tests were carried out on more than 25 different hydraulic fills obtained from five different Mines, in an attempt to fully understand their behaviour and to develop a geotechnical database for the Mines. The data from laboratory tests compare well with the in situ measurements. Tests were also carried out on two types of porous barricade bricks that are commonly used in Australia, to quantify their permeability and load-deformation characteristics. Fast Lagrangian Analysis of Continua (FLAC) and Fast Lagrangian Analysis of Continua in 3-dimensions (FLAC3D) were used to numerically model the drainage through the hydraulic fills and the stress developments within the fill. Due to arching mechanism, the vertical normal stresses within the Stopes are significantly reduced. Typical parameters for hydraulic fills and porous barricade bricks are given in this chapter and these would be very valuable in numerical modelling exercises when no other data are available.
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The geotechnical characterisation and stability analysis of BHP Billiton's Cannington Mine paste fill
2004Co-Authors: Rudd RankineAbstract:BHP Billiton's Cannington Mine is a silver-lead-zinc Mine located in North West Queensland, which utilizes post-placed backfill technology in tailings disposal. The backfill is known as paste fill. Paste fill is simply Mine tailings, with typical effective grain size of 5 μm, mixed with a small percentage of cement binder. As Mine Stopes are removed, the paste fill is used to backfill the empty space. Paste fill provides substantial benefits to mining operations including an effective means of tailings disposal, improvement of local and regional rock stability, greater ore recovery and greatly reduced environmental impacts. The studies undertaken as part of this dissertation has included extensive laboratory testing to study the geotechnical behaviour of paste fill. The testing programme included direct shear, triaxial, UCS in addition to the index property tests. These were prepared and cast in the laboratory and cured over different times to include short, medium and long term properties. The study period ranged from less than 24 hours to one year. Additional in-situ testing was conducted at Cannington Mine with James Cook Universities' dynamic cone penetrometer to identify the variation of strength with depth. Additional in-situ samples were taken and tested, with the results compared to the laboratory prepared samples. FLAC³ᴰ was used to study the stress development in paste, taking into account the geometric properties of the stope and material properties of the paste fill. A sensitivity analysis was done on the geometry and material properties of the paste to measure the effect on stress development. Artificial neural networks were used as a predictive tool to tie all the outputs from the geotechnical characterisation phase and stress modelling phases. By combining the two phases of the study an integrated model for the prediction and optimisation of the cement content in the backfill masses was achieved. The results of which have been presented within the findings. The stability of fill barricades was also investigated and a relationship between the horizontal stress and the stope geometry, drive location and fill rate developed.