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The liquid limit of clay is commonly determined through the Casagrande test or the fall-cone test, while the plastic limit is determined through the hand rolling method. The greatest issue with some of these techniques is their low repeatability and operator de- pendency. In order to minimize those issues, an indirect-extrusion based technique was evaluated as an alternative method to determine both consistency limits. The experimental work was carried out on mixtures of kaolin and bentonite to cover a wide range of plasticity. The results suggested that there is a specific extrusion pressure linked to each consistency limit and that the results are repeatable. The liquid limit obtained through the extrusion method closely matches the results of the fall-cone test. Similarly, the plastic limit out of extrusion closely matches the results of the hand rolling method.

The quality of a drilling fluid declines in salt water conditions. An engineered clay (HYPER clay) was developed for geosynthetic clay liners with enhanced resistance to aggressive conditions. This study investigates the potential of this superior clay for drilling fluids applied in salt water conditions. A sodium bentonite was treated with a carboxymethyl cellulose (CMC) polymer following the HYPER clay process method. Preliminary tests were performed to investigate suitability of HYPER clay for seawater resistant drilling fluids. Fluid performance was characterized by its thixotropic behavior, rheological properties (gel strength, yield point and viscosity), swell and bleeding behavior. Drilling fluid performance was analyzed at various polymer dosages and electrolyte concentrations. Polymer treatment improved the gel strength and swelling ability of the fluid, especially in electrolyte solutions. Moreover, filter press tests (API 13B-1, 76% seawater) showed that filtrate loss decreased due to polymer treatment.

A Geosynthetic Clay Liner (GCL) is a frequently used h ydraulic barrier system designed to impede the flow of contaminated leachate into the environment. The main objective of this barrier system is to maintain a low hydraulic conductivity that is determined by the bentonite fraction. In this study, calcium bentonite, natural sodium bentonites, and sodium activated bentonite were treated with the HYPER clay technique. This involves the adsorption of an anionic polymer, Sodium CarboxyMethylCellulose (Na-CMC) onto the surface of the clay material. The purpose of this research was to show the beneficial effect of the HYPER clay treatment on the swelling and hydraulic performance, while the bentonite is permeated with high concentration CaCl2 solutions. The test results showed that swelling and hydraulic performance increased with Na-CMC treatment, regardless of the type of bentonite that was used. Additionally, a powdered Na CMC configuration provided higher swelling and hydraulic performance compared to a granular configuration.

There is a growing need to better understand the relationship between time, strain rate, and temperature on the load-deformation behaviour of clay soils in engineering applications. These applications may include: infrastructure constructed in northern regions where climate change is a growing concern; disposal of nuclear waste; and, industrial structures, such as furnaces, foundries, and refrigeration plants. Temperature variations may induce changes in internal pressure in the soil, swelling and shrinkage, and affect the mechanical properties of the soil. This thesis presents thermal numerical modeling for two instrumented field sites in northern Manitoba. Thermal conductivity testing on samples from these sites and field data are used to calibrate these thermal numerical models. Various boundary conditions are examined. The capabilities of the models are evaluated to determine if the models adequately simulate and predict changes in temperature in geotechnical structures. A discussion is presented on the strengths and weaknesses in the models and the predictive capabilities of the models. The thesis then shifts into understanding the concepts of thermoplasticity and viscoplasticity and the mathematics relating these concepts. Mathematical models that describe these concepts are examined and compared with traditional soil mechanics approaches. The concepts of thermoplasticity and viscoplasticity are combined in an encompassing elastic thermo-viscoplastic (ETVP) model using a semi-empirical framework. A sensitivity analysis is used to evaluate quantitatively the response of the model. The model is then validated qualitatively against published laboratory data. Applications of the ETVP model are discussed.

In the construction and maintenance of civil and industrial buildings there is an high risk for the worker to fall from high places. The worker has to be protect with a proper fall protection device able to prevent the human damage but, at the same time, which permits all the movements of the worker. Very effective protection systems are the Safety Lines. These systems are based on the positioning of fixed cables to which the user can be connected with a moving cable. In this way the safety of the worker is assured if the cables systems are dimensioned to resist to the worker weight increased by the dynamical effect, with a proper safety coefficient. However, the cable systems have a structural behaviour with a very low damping and the oscillations of the attached mass can be very large. Clearly, these systems have to arrest the fall minimizing the pendulum effect, therefore one or more dissipative devices have to be installed. In this paper a Safety Line installed by the Italian Society "Nuovo Modulo S.p.A." (BG) on its new buildings is investigated with the intention to show the importance of a proper design of the dissipation devices. Using a finite element program the authors investigated the dynamical behaviour of the installed safety system. The design of the mechanical properties of the dissipation devices was performed using a genetic algorithms approach.

Through-thickness reinforcement (stitching, z-pins, weaving) is a promising technology to develop fall-safe load bearing components for aeronautical structures and lightweight armor and combat vehicles with superior capabilities. The through-thickness reinforcement enhances the performance of laminates against delamination failure, improving impact and damage tolerance and rendering stable or even suppressing crack propagadon. The purpose of the work was to investigate basic aspects of the mechanics of through-thickness reinforced laminates. Focus has been on two problems. (1) The definition and validation of approximate mode I weight functions for orthotropic double cantilever beams. The weight functions allow the problem of large scale bridging delamination to be formulated as integral equations overcoming the limitations of beam theory approximations. (2) The formulation of a theoretical model to investigate the effectiveness of a through-thickness reinforcement in reducing the delamination-induced degradation of the dynamic properties of delaminated structures. The work performed under this contract has been published in (1-4).

These conferences provide a forum for discussion among people in the mining industry and environmental community regarding tailings and mine waste. Papers are presented in sections entitled: Regulatory (2 papers); Design, operation and disposal (13 papers); Paste technology (4 papers); Geotechnical considerations (18 papers); Liners, covers and barriers (8 papers); Groundwater and geochemistry (27 papers); Surface water quality (8 papers); Remediation and reclamation (11 papers); Reprocessing, utilisation and treatment (5 papers); and Case histories (3 papers). There is an author index., These conferences provide a forum for discussion among people in the mining industry and environmental community regarding tailings and mine waste. Papers are presented in sections entitled: Regulatory (2 papers); Design, operation and disposal (13 papers); Paste technology (4 papers); Geotechnical considerations (18 papers); Liners, covers and barriers (8 papers); Groundwater and geochemistry (27 papers); Surface water quality (8 papers); Remediation and reclamation (11 papers); Reprocessing, utilisation and treatment (5 papers); and Case histories (3 papers). There is an author index.

After an introductory paper on terminology, papers are presented in sections entitled: Regulatory (7 papers), Design and operation (6 papers), Geotechnical (11 papers), Liners, covers, barriers (8 papers), Disposal (8 papers), Ground water and geochemistry (15 papers), Surface water quality (4 papers), Remediation and reclamation (7 papers), Reprocessing, utilisation and treatment (3 papers) and Case histories (13 papers). Specific wastes discussed include uranium, copper, coal, sulphide ores, arsenic, phosphate and diamond. Case histories include dam flow failure at Merrispruit, South Africa, tailings consolidation and closure in the Bonanza mining district, Colorado, the Gibraltar mine cyclone tailings dam, British Columbia, Beauty Bay mine in Alaska, the Weavers open cast mine in New Zealand, a coal refuse impoundment in Illinois, tailings impoundment expansion at Kennecott Utah Copper, uranium tailings management in northern Saskatchewan and tailings dam reclamation at Hot Springs, Arkansas., After an introductory paper on terminology, papers are presented in sections entitled: Regulatory (7 papers), Design and operation (6 papers), Geotechnical (11 papers), Liners, covers, barriers (8 papers), Disposal (8 papers), Ground water and geochemistry (15 papers), Surface water quality (4 papers), Remediation and reclamation (7 papers), Reprocessing, utilisation and treatment (3 papers) and Case histories (13 papers). Specific wastes discussed include uranium, copper, coal, sulphide ores, arsenic, phosphate and diamond. Case histories include dam flow failure at Merrispruit, South Africa, tailings consolidation and closure in the Bonanza mining district, Colorado, the Gibraltar mine cyclone tailings dam, British Columbia, Beauty Bay mine in Alaska, the Weavers open cast mine in New Zealand, a coal refuse impoundment in Illinois, tailings impoundment expansion at Kennecott Utah Copper, uranium tailings management in northern Saskatchewan and tailings dam reclamation at Hot Springs, Arkansas.

Papers are presented in sections entitled: Regulatory considerations (4 papers), Design and operation (10 papers), Geotechnical considerations (5 papers), Liners, covers, barriers (13 papers), Groundwater and geochemistry (8 papers), Surface water quality and modelling (11 papers), Remediation and reclamation (5 papers), Reprocessing and utilisation (4 papers) and Case histories (8 papers)., Papers are presented in sections entitled: Regulatory considerations (4 papers), Design and operation (10 papers), Geotechnical considerations (5 papers), Liners, covers, barriers (13 papers), Groundwater and geochemistry (8 papers), Surface water quality and modelling (11 papers), Remediation and reclamation (5 papers), Reprocessing and utilisation (4 papers) and Case histories (8 papers).

The usefulness of numerical models is limited by their applicability. Hence all numerical models, when applied to design, must be continuously validated by qualitative or quantitative field observations. This is the goal of the observational modelling approach. Several examples are presented which illustrate how this approach assists in developing improved models, in applying existing models more effectively, and in solving complex problems with simple models. Three specific elements of modelling for deep mining are addressed: stress boundary conditions, stress change effects, and modelling of near wall, brittle failure processes. The implications for openings in burst-prone ground are discussed., The usefulness of numerical models is limited by their applicability. Hence all numerical models, when applied to design, must be continuously validated by qualitative or quantitative field observations. This is the goal of the observational modelling approach. Several examples are presented which illustrate how this approach assists in developing improved models, in applying existing models more effectively, and in solving complex problems with simple models. Three specific elements of modelling for deep mining are addressed: stress boundary conditions, stress change effects, and modelling of near wall, brittle failure processes. The implications for openings in burst-prone ground are discussed.

Sophisticated computer models are available that enable the static stress and strain regimes around a block cave to be analysed in both 2- and 3-D. Also available are models to analyse the flow of discrete particles in 2-D. A new 3-D particle flow code, PFC-3D, has been developed to overcome some of the problems with the above methods. It uses a simplified 3-D distinct element program in which blocks are modelled using spherical particles, which are initially bonded so as to represent the intact rock strength. It is intended to use the code in block cave modelling initially to investigate the sensitivity of draw point spacing and then to move into areas of draw control., Sophisticated computer models are available that enable the static stress and strain regimes around a block cave to be analysed in both 2- and 3-D. Also available are models to analyse the flow of discrete particles in 2-D. A new 3-D particle flow code, PFC-3D, has been developed to overcome some of the problems with the above methods. It uses a simplified 3-D distinct element program in which blocks are modelled using spherical particles, which are initially bonded so as to represent the intact rock strength. It is intended to use the code in block cave modelling initially to investigate the sensitivity of draw point spacing and then to move into areas of draw control.

The success or failure of numerical simulations of rock mass behaviour depends to a large degree on the selection of realistic rock mass strength parameters. The Hoek-Brown failure criterion is a recognised and reliable means of estimating the shear strength of intact rock and rock masses. A methodology is outlined for applying this criterion to numerical simulations, in combination with a rock mass classification system. A case study is presented in which realistic pillar modelling results were obtained by application of the methodology with the FLAC code., The success or failure of numerical simulations of rock mass behaviour depends to a large degree on the selection of realistic rock mass strength parameters. The Hoek-Brown failure criterion is a recognised and reliable means of estimating the shear strength of intact rock and rock masses. A methodology is outlined for applying this criterion to numerical simulations, in combination with a rock mass classification system. A case study is presented in which realistic pillar modelling results were obtained by application of the methodology with the FLAC code.

The effects of increasing panel width on power support loading and the stability of longwall face and gate entry systems under both strong and weak roof conditions were investigated. 3-D finite element models were built which considered panel layout, power supports, and the gob effect in a longwall panel. Based on the simulation results, stability analysis was performed by analysing the stress distribution around the longwall face and gate entry system. It is concluded that an increase in longwall panel width will have limited effects on the power support loading and gate entry stability. The effects, in general, become insignificant when the panel width is larger than 213.4 m., The effects of increasing panel width on power support loading and the stability of longwall face and gate entry systems under both strong and weak roof conditions were investigated. 3-D finite element models were built which considered panel layout, power supports, and the gob effect in a longwall panel. Based on the simulation results, stability analysis was performed by analysing the stress distribution around the longwall face and gate entry system. It is concluded that an increase in longwall panel width will have limited effects on the power support loading and gate entry stability. The effects, in general, become insignificant when the panel width is larger than 213.4 m.

Rock related accidents most frequently take place at stope faces and in gullies near the face. A review is presented of the challenges of modelling deep level excavations. Recent efforts by CSIR Miningtek to use numerical models to evaluate various aspects of stope and gully support systems are described. Both FLAC, an explicit finite difference code and UDEC, a distinct element code, also based on a finite difference method, were used to: model the influence of backfill stiffness and distance to the face on hangingwall stability; investigate the effect on the stability of the stope hangingwall of the spacing of support units, support unit force and areal coverage of support; and to assess the relationship between gully pack force and gully sidewall damage. Good modelling results can be obtained where mechanisms influencing global rock mass behaviour and stability are active, but modelling of local mechanisms associated with the local stability of blocky hangingwalls still requires development., Rock related accidents most frequently take place at stope faces and in gullies near the face. A review is presented of the challenges of modelling deep level excavations. Recent efforts by CSIR Miningtek to use numerical models to evaluate various aspects of stope and gully support systems are described. Both FLAC, an explicit finite difference code and UDEC, a distinct element code, also based on a finite difference method, were used to: model the influence of backfill stiffness and distance to the face on hangingwall stability; investigate the effect on the stability of the stope hangingwall of the spacing of support units, support unit force and areal coverage of support; and to assess the relationship between gully pack force and gully sidewall damage. Good modelling results can be obtained where mechanisms influencing global rock mass behaviour and stability are active, but modelling of local mechanisms associated with the local stability of blocky hangingwalls still requires development.

Computer modelling of production ring blasts have become a standard procedure at De Beers Consolidated Mines. As productivity is dependent on optimum fragmentation, the emphasis at Koffiefontein mine has not only been the optimisation of burden and spacing, but also the timing of large compound rings, used in the sublevel stoping operations. At the Dutoitspan mine, where mining of the kimberlite pipe is by block caving, the importance of achieving 100% extraction on the undercut level by ring blasting is essential. If this is not achieved pillars are formed which not only inhibit the caving process but also concentrate load onto the extraction level, causing damage. The Julius Kruttschnitt Mineral Research Centre 3x3 Win and Qfrag programs were used in both cases to analyse the problem., Computer modelling of production ring blasts have become a standard procedure at De Beers Consolidated Mines. As productivity is dependent on optimum fragmentation, the emphasis at Koffiefontein mine has not only been the optimisation of burden and spacing, but also the timing of large compound rings, used in the sublevel stoping operations. At the Dutoitspan mine, where mining of the kimberlite pipe is by block caving, the importance of achieving 100% extraction on the undercut level by ring blasting is essential. If this is not achieved pillars are formed which not only inhibit the caving process but also concentrate load onto the extraction level, causing damage. The Julius Kruttschnitt Mineral Research Centre 3x3 Win and Qfrag programs were used in both cases to analyse the problem.

The success of block caving depends on the size of the caved fragments since they are required to pass through drawpoints and need to be handled by loading equipment. During the planning of a block cave it is necessary to estimate the distribution of the rock fragments which will be produced to plan production rates, secondary blasting and to allow for delays due to ore hanging up in the drawpoints. A model for predicting block cave fragmentation, the first to do this, is presented. It combines basic rock mechanics principles and the experience of block cave operators and provides predicted fragmentation distributions. Good correlation has been found between the model results and an operating mine: 5-7% better fragmentation was predicted by the program than that which was observed., The success of block caving depends on the size of the caved fragments since they are required to pass through drawpoints and need to be handled by loading equipment. During the planning of a block cave it is necessary to estimate the distribution of the rock fragments which will be produced to plan production rates, secondary blasting and to allow for delays due to ore hanging up in the drawpoints. A model for predicting block cave fragmentation, the first to do this, is presented. It combines basic rock mechanics principles and the experience of block cave operators and provides predicted fragmentation distributions. Good correlation has been found between the model results and an operating mine: 5-7% better fragmentation was predicted by the program than that which was observed.

The design of soil-nailed walls involves the assessment of the internal and external stability of the monolith created by the reinforcing elements. Limit equilibrium and closed-form elastic analyses are available for the assessment of external and internal stability calculations respectively, subject to simplified load and displacement boundary conditions. Nonlinear numerical analysis techniques are available to integrate the internal and external stability aspects as well as the contribution of the reinforcing nails and cable bolts. These methods of analysis are considered and it is concluded that the use of the traditional, more cost efficient methods, can be advantageously used in the design of numerical models to achieve optimum results., The design of soil-nailed walls involves the assessment of the internal and external stability of the monolith created by the reinforcing elements. Limit equilibrium and closed-form elastic analyses are available for the assessment of external and internal stability calculations respectively, subject to simplified load and displacement boundary conditions. Nonlinear numerical analysis techniques are available to integrate the internal and external stability aspects as well as the contribution of the reinforcing nails and cable bolts. These methods of analysis are considered and it is concluded that the use of the traditional, more cost efficient methods, can be advantageously used in the design of numerical models to achieve optimum results.

The US Bureau of Mines has implemented a geophysical instrumentation programme in a southern Wyoming mine to study changes in roof stability during development mining. The case study was unique in providing integrated measurements of a mine roof, floor and pillar, and tracking failure growth around mining excavations. Lithology and roof conditions were mapped and cores were tested at the beginning and end of monitoring to assess structural damage. It was shown that failure initiated in the mine floor and spread to the pillar and roof. The field measurements were essential for understanding strata interaction and provided essential input for numerical models. In particular a model incorporating the strain-softening material behaviour for the floor showed best agreement between measured deformation patterns and the calculated results., The US Bureau of Mines has implemented a geophysical instrumentation programme in a southern Wyoming mine to study changes in roof stability during development mining. The case study was unique in providing integrated measurements of a mine roof, floor and pillar, and tracking failure growth around mining excavations. Lithology and roof conditions were mapped and cores were tested at the beginning and end of monitoring to assess structural damage. It was shown that failure initiated in the mine floor and spread to the pillar and roof. The field measurements were essential for understanding strata interaction and provided essential input for numerical models. In particular a model incorporating the strain-softening material behaviour for the floor showed best agreement between measured deformation patterns and the calculated results.

A method is presented that allows a 3-D interpretation of 2-D FLAC results of a strike stabilising pillar model. A history of average pillar stress with respect to distance to mining face is calculated using MINSIM-D. The FLAC model is controlled by means of a user function such that the MINSIM-D generated stress history is duplicated in the FLAC average pillar stress history. A third dimension is thus implicitly introduced into FLAC. In this way various stages of failure in the FLAC model can be related to a distance to mining face by referring the FLAC average pillar stress to the MINSIM-D curve and reading off a distance to face. This tool could prove useful to mine planners to provide information about local hangingwall and regional support conditions in the planning stage., A method is presented that allows a 3-D interpretation of 2-D FLAC results of a strike stabilising pillar model. A history of average pillar stress with respect to distance to mining face is calculated using MINSIM-D. The FLAC model is controlled by means of a user function such that the MINSIM-D generated stress history is duplicated in the FLAC average pillar stress history. A third dimension is thus implicitly introduced into FLAC. In this way various stages of failure in the FLAC model can be related to a distance to mining face by referring the FLAC average pillar stress to the MINSIM-D curve and reading off a distance to face. This tool could prove useful to mine planners to provide information about local hangingwall and regional support conditions in the planning stage.

Elastodynamic codes such as FLAC, UDEC, WAVE, 3DEC, TWO4D AND VOLSIM, have been used to investigate a large variety of mining-related problems in both 2- and 3-D, and under linear and non-linear conditions. Insights into seismological parameters, dynamic support, rock mass behaviour and failure mechanisms have been obtained. The development of elastodynamic computer programs, using boundary element, finite difference and finite element methods, is traced and research efforts, mainly within the Rock Mass Behaviour project of CSIR's Mining Technology Division, Johannesburg, are summarised. Possible future research directions are indicated., Elastodynamic codes such as FLAC, UDEC, WAVE, 3DEC, TWO4D AND VOLSIM, have been used to investigate a large variety of mining-related problems in both 2- and 3-D, and under linear and non-linear conditions. Insights into seismological parameters, dynamic support, rock mass behaviour and failure mechanisms have been obtained. The development of elastodynamic computer programs, using boundary element, finite difference and finite element methods, is traced and research efforts, mainly within the Rock Mass Behaviour project of CSIR's Mining Technology Division, Johannesburg, are summarised. Possible future research directions are indicated.

Human beings are not naturally good at consciously building models to solve engineering and scientific problems. The philosophy of modelling and the thought process that underlies the approach to problem solving by conscious modelling is discussed. Three principal types of models are available: physical, analytic or closed-form solutions, and numerical simulation techniques. In engineering problem solving it is argued that modelling should only be carried out against a backdrop of specific questions that are enumerated before any analytical or computer analyses are undertaken. In complex cases involving inelastic material behaviour, the notion of an organic or self-adaptive modelling paradigm should be introduced., Human beings are not naturally good at consciously building models to solve engineering and scientific problems. The philosophy of modelling and the thought process that underlies the approach to problem solving by conscious modelling is discussed. Three principal types of models are available: physical, analytic or closed-form solutions, and numerical simulation techniques. In engineering problem solving it is argued that modelling should only be carried out against a backdrop of specific questions that are enumerated before any analytical or computer analyses are undertaken. In complex cases involving inelastic material behaviour, the notion of an organic or self-adaptive modelling paradigm should be introduced.

Physical modelling can provide a useful means of calibrating nonlinear numerical models although care must be exercised in designing physical experiments and in understanding loading conditions and the implied principal stress orientations that are to be analysed numerically. Both the mechanisms of failure as well as load-deformation characteristics must be reproduced. A case study is used to illustrate the utility of physical modelling in the formulation of rules for the simulation of fracture growth. This has highlighted the need to extend the concept of tension extension fracturing when strong shear driving forces occur next to the corners of openings., Physical modelling can provide a useful means of calibrating nonlinear numerical models although care must be exercised in designing physical experiments and in understanding loading conditions and the implied principal stress orientations that are to be analysed numerically. Both the mechanisms of failure as well as load-deformation characteristics must be reproduced. A case study is used to illustrate the utility of physical modelling in the formulation of rules for the simulation of fracture growth. This has highlighted the need to extend the concept of tension extension fracturing when strong shear driving forces occur next to the corners of openings.

Elastic MINSIM type modelling is likely to continue as the primary modelling tool for regional mine layout and support design for some time. Two important practical issues, the practice of Young's Modulus reduction of the host rock by 20-40% and the application of MINSIM-D to pillar design are investigated. An alternative approach to reducing the Young's Modulus of the host rock, in which the stoping width is reduced to account for irrecoverable bulking of the immediate hanging- and foot-wall was tested against some accurate off-reef displacement measurements taken at East Rand Proprietary Mines (ERPM). The computation and use of average pillar stress, the application of quarter grid adjustment and the influence of grid size on results in MINSIM-D is clarified. Several principles for the improved application of MINSIM type elastic models to regional layout designs are set out., Elastic MINSIM type modelling is likely to continue as the primary modelling tool for regional mine layout and support design for some time. Two important practical issues, the practice of Young's Modulus reduction of the host rock by 20-40% and the application of MINSIM-D to pillar design are investigated. An alternative approach to reducing the Young's Modulus of the host rock, in which the stoping width is reduced to account for irrecoverable bulking of the immediate hanging- and foot-wall was tested against some accurate off-reef displacement measurements taken at East Rand Proprietary Mines (ERPM). The computation and use of average pillar stress, the application of quarter grid adjustment and the influence of grid size on results in MINSIM-D is clarified. Several principles for the improved application of MINSIM type elastic models to regional layout designs are set out.

Hartebeestfontein is unique in its use of cave mining for the extraction of deep, tabular gold reserves, which it has practised for 30 yrs. Attempts to substantiate caving theories by means of numerical modelling have been severely limited by the lack of suitable programs. The recently available distinct element code UDEC, was used to simulate the discontinuous nature of rock surrounding a stope at great depth and the collapse of the back area. Three intuitive models were created to confirm principles which would be difficult to isolate in more sophisticated models. Two dynamic models followed: simulating a stope face advancing through an elastic, discontinuous rockmass; and a stope face advancing through a discontinuous, strain softening rock mass. Both could not simulate the decrease of stress ahead of the face. It was concluded that the role of failure and dilationary processes ahead of the face which generate shear displacements on bedding planes requires further investigation. Many plots from the program are included., Hartebeestfontein is unique in its use of cave mining for the extraction of deep, tabular gold reserves, which it has practised for 30 yrs. Attempts to substantiate caving theories by means of numerical modelling have been severely limited by the lack of suitable programs. The recently available distinct element code UDEC, was used to simulate the discontinuous nature of rock surrounding a stope at great depth and the collapse of the back area. Three intuitive models were created to confirm principles which would be difficult to isolate in more sophisticated models. Two dynamic models followed: simulating a stope face advancing through an elastic, discontinuous rockmass; and a stope face advancing through a discontinuous, strain softening rock mass. Both could not simulate the decrease of stress ahead of the face. It was concluded that the role of failure and dilationary processes ahead of the face which generate shear displacements on bedding planes requires further investigation. Many plots from the program are included.

The results of research into human computer interaction have been combined with expert system technology to design interfaces to complex rock engineering analysis programs to make the life of the practical rock mechanics engineer easier. A prototype interface, InFrEnd1 (Intelligent Front End), is presented which produces a data input file for use with the discontinuum code UDEC., The results of research into human computer interaction have been combined with expert system technology to design interfaces to complex rock engineering analysis programs to make the life of the practical rock mechanics engineer easier. A prototype interface, InFrEnd1 (Intelligent Front End), is presented which produces a data input file for use with the discontinuum code UDEC.

Mining of the gold reefs in Central Witwatersrand has resulted in subsidence. Knowledge of this subsidence and its extent is usually not available and mining records are often poor. Non-linear finite difference modelling has been carried out to determine the potential differential movements that could occur. Structural and architectural techniques can then be used to minimise the effects of subsidence on buildings. The method was applied to two sites in the area. The magnitudes of total subsidence predicted from the analyses compared well with magnitudes known to have occurred., Mining of the gold reefs in Central Witwatersrand has resulted in subsidence. Knowledge of this subsidence and its extent is usually not available and mining records are often poor. Non-linear finite difference modelling has been carried out to determine the potential differential movements that could occur. Structural and architectural techniques can then be used to minimise the effects of subsidence on buildings. The method was applied to two sites in the area. The magnitudes of total subsidence predicted from the analyses compared well with magnitudes known to have occurred.

The extraction of the Bracken shaft pillar was unique in that it involved twin shafts, both of which had to remain operational since they represented the only means of access to the underground workings. Difficult steel arrangements within the shafts coupled to small clearances between conveyances and shaft linings posed formidable design challenges. It is demonstrated that computer codes such as MINSIM D can be used to predict stresses and displacements with sufficient accuracy provided that allowances are made for bed separation within the zone of tension. In shallow mines, satellite pillars can be used to good effect for limiting elastic and non elastic displacements. All the vital ancillary excavations and both vertical shafts were in excellent operating condition until the final closure of the mine. A new adjustable bracket design replaced fixed brackets on the guides and coped with all displacement and ride movements., The extraction of the Bracken shaft pillar was unique in that it involved twin shafts, both of which had to remain operational since they represented the only means of access to the underground workings. Difficult steel arrangements within the shafts coupled to small clearances between conveyances and shaft linings posed formidable design challenges. It is demonstrated that computer codes such as MINSIM D can be used to predict stresses and displacements with sufficient accuracy provided that allowances are made for bed separation within the zone of tension. In shallow mines, satellite pillars can be used to good effect for limiting elastic and non elastic displacements. All the vital ancillary excavations and both vertical shafts were in excellent operating condition until the final closure of the mine. A new adjustable bracket design replaced fixed brackets on the guides and coped with all displacement and ride movements.