In this study, the pre-failure behavior of a jointed rock block is modeled by an incrementally linear elastic anisotropic constitutive model (using an orthotropic model in 2D). In order to estimate the parameters in the constitutive model, a new technique was used in this dissertation. A 2D joint geometry generation code was used to generate finite size actual joint networks in 2D rock blocks. A 2D distinct element code (UDEC) was chosen as the stress analysis tool in this study. Fictitious joints were introduced into the rock blocks which contain finite size actual joints to discretize the problem domain into polygons. A number of stress analyses of rock blocks which contain only persistent joints were performed to estimate representative values for mechanical properties of fictitious joints to simulate the intact rock behavior. Finally, the rock blocks having different deterministic actual joint configurations with fictitious joints were subjected to 2D stress analysis under various stress paths using UDEC. Results of these stress analyses were used to estimate the deformational and strength properties of these rock blocks. Influence of joint geometry parameters on the mechanical properties of jointed rock blocks were found to be very significant. Plots are given to show how mechanical properties of rock blocks vary with joint intensity and joint size/block size for different joint orientations. These plots can also be used to estimate REV (Representative Elementary Volume) size and REV properties for rock masses. It is important to note that these REV property values depend on the chosen constitutive models for intact rock and joints. The concept of fracture tensor is reviewed at the 2D level. Relationships between the mechanical properties of jointed rock blocks and the fracture tensor parameters (its first invariant and components) are established. These relationships can be used to estimate the parameters of the chosen constitutive model for the rock block. This constitutive model has captured both scale dependent and anisotropic behaviors of rock masses. The possibility of obtaining the equivalent continuum properties (REV properties) of jointed rock blocks is explored by using the aforementioned relationships. (Abstract shortened by UMI.)

A bentonite grouting technology has been developed to meet the requirements of fracture sealing for nuclear waste isolation and environmental engineering. The work reported presents an experimental evaluation of the performance of the bentonite fracture sealing in densely welded tuff. Included are the study of grout stability and resistance to erosion, theoretical and numerical analyses of the grout penetration process, pressure distribution in the fracture during grouting, grout delivery distance, breakthrough pressure and rheological characterization. Bentonite suspensions with solids content of 18, 20 and 22% by weight have been injected into single fractures in rock samples at 0.07 to 3.45 MPa pressure. Bentonite grouting reduces the fracture hydraulic conductivity by 7 to 9 orders in magnitude, to the level of 10⁻⁷ to 10⁻⁹ cm/s. Grout stability and erosion have been studied with long-term flow testing at up to 121 kPa hydraulic pressure. After 1,000 to 5,000 hours of flow testing, at pressure gradients of up to 91 cm/cm, the hydraulic conductivity of the grouted fracture does not increase with test time. The hydraulic conductivity of the grouted fracture decreases with increasing pressure gradient up to the wash-out pressure. Analytical solutions have been derived for pressure distribution during grouting in wedge shaped fractures and in fractures with constant aperture. Influence factors on pressure distribution in a fracture have been identified. They are yield stress, fracture shape, original aperture, deformation properties of the rock mass and the fracture, mixing of air in a grout and sample size. A mathematical solution of grout delivery distance under a given injection pressure has been developed. The breakthrough pressure has been studied, based on the mechanical deformation of the fracture applied by a normal stress across the fracture and by the grout pressure within the fracture during grouting. Results indicate that bentonite grouting is a promising fracture sealing technology. Bentonite grout has great hydraulic conductivity reduction and chemical physical stability. Some disadvantages of bentonite grout have been identified, such as the formation of hydraulic fractures in the grout and the washing away of grout particles when the applied pressure gradient is high enough.

This investigation focuses on the uses of non-equilibrium plasmas to enhance the chemical reactions used in metallurgical process chemistry. The main emphasis of this work was the reduction of TiO₂ and FeTiO₃ in a hydrogen plasma. The plasma was maintained in a single resonant cavity using microwave energy (2.45 GHz). The reaction was monitored for volatile species by a quadrupole mass spectrometer. The extent of reaction during hydrogen reduction experiments was performed using an external standard X-ray diffraction technique. The effect of process variables (absorbed power, chamber pressure, time of plasma solid contact, applied voltages) on the extent of the reactions and the sample temperature were investigated. An investigation into the chlorination of TiO₂ in a chlorine plasma was also performed, however, the numerous side reactions that developed during these experiments made analysis difficult. Attempts were made to identify the volatile species from the mass spectra obtained during the chlorination experiments. The reduction of fused silica as a result of contact with the plasma is also investigated. Thermodynamic calculations suggest that the reduction proceeds by the formation of silane in the plasma; metallic silicon is formed by the subsequent thermal decomposition of silane in a non-oxidizing environment. A mechanism for the formation of silane is proposed. Finally, one proposed use for this technology is presented: The production of oxygen in situ form the lunar soil. Experimental values and thermodynamic data are used to develop a plasma process flow diagram for the production of oxygen. The mining requirements, the hydrogen flow rates and the power demands for this system are compared to more conventional process under consideration for the production of lunar oxygen.

This study presents the results of laboratory-scale experimental, analytical and numerical investigations on the sealing performance of crushed tuff concrete plugs in the welded brown unit of the Apache Leap tuff. Included are experimental studies of the bond strength, of the hydraulic conductivity, and of geochemical interactions between cement and the crushed tuff aggregate. The bond strength is measured by means of a total of 37 push-out tests on concrete borehole seals emplaced in hollow cylinders of welded tuff. Lateral stress is applied to 17 rock cylinders during push-out testing. Results are presented of an extensive finite element analysis of the stress distribution during push-out testing. Particular attention is paid to tensile zones in the plug and the host rock. Geochemical interaction analysis includes tests for alkali-silica reaction between the cement and crushed tuff aggregate. ASTM standard tests for the determination of alkali-silica reactivity of aggregates, in addition to uranyl acetate staining test have been performed. Hydraulic conductivity tests include constant head tests on plugged tuff cylinders and falling head tests on fractures induced by push-out testing along the plug/rock interface. The falling head tests have been conducted after the plugs were left to dry for two years in a laboratory environment. The main conclusion from the analysis of push-out tests is that high tensile stresses develop in plugs with a modulus ratio of 1.09 and length-to-diameter ratio of 1. Application of lateral stress to rock cylinders reduces the volume of plug under tension. Results of tests on alkali-silica reactivity indicated that Apache Leap tuff reacts with the alkalies in cement and expand. Replacement of cement 33% by weight with low-calcium Class F fly ash reduces the expansion 50%. Hydraulic conductivity of concrete plug and plug/rock interface interpreted from constant head tests is in the range of 10⁻¹⁰ cm/s. Hydraulic conductivity of fractures along the interface decreased from 10⁻² cm/s to 10⁻⁶ cm/s upon wetting of the concrete, due to the expansion of the cement.

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A thesis submitted to the Faculty of Engineering, University of the Witwatersrand, Johat.nesburq, in fulfilment of the requirements for the degree of Doctor of Philosophy Johannesburg, 1998 / This thesis contributes to accurate, practicable techniques of ascertaining and assessing site performance of large refrigerating machines chilling water 'for cooling deep South African mines. It applies to all vapourcompression machines cooling fluids in steady, continuous processes. To assess whether a water chilling machine is performing satisfactorily, both its actual performance, and the corresponding normal or optimal performance of which it is capable, must be ascertained. Both requirements r esent difficulties on site. in particular, the traditional "heat balance" method of verifying the apparent performance obtained from measurements in the water circuits does not prove that such performance is accurate. The calibration of typical site instrumentation is not assured, so an "acceptable" heat imbalance may conceal large but similar errors - which thus also balance out - in the apparent constituents of the heat balance. Three methods of independently ascertaining actual performance, so verifying apparent performance, are presented, The first is an enhanced method, applicable to custom-built machines as well as conventional ones, of ascertaining the efficiency of the actual refrigerating process from measurements in the refrigerant circuit. This detects errors concealed in an "acceptable" heat balance. Where some refrigerant-circuit measurements are unavailable, an inexact version of this method still indicates the relative likelihood of the apparent performance being acceptably accurate. The third method, where these two are inadequate, is ascertaining actual performance using available measurements and fundamental machine modelling. Such modelling is also the most versatile method of predicting corresponding normal or optimal performance. A computer program simulating complete mine water chilling installations is used here. Actual performance can then be meaningfully assessed and appropriate remedial action justified, as shown in seven case studies. An outcorr.e for conventional water chillinq machines with a centrifugal compressor is that keeping heat exchangers clean may prejudice efficiency under part-duties lf a machine has been designed for optimum efficiency at full duty. An alternative control philosophy of maximising the machine load may then yield better performance. If these techniques are included ill an automated system of fault diagnosis, they will be of most use to burdened mine staff, who are generally not refrigeration experts.

This report investigates the application of digital computer simulation models to the analysis and optimization of complex mine water reticulation systems- A simulation program is developed and documented, Guidelines in the construction and use of mine water models are applied in a case study of water quality and quantity aspects of Unisel Gold Mine.

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering. / The reliability of using isotropically consolidated specimens in the laboratory determination of liquefaction characteristics of cohesionless sands, as is common practice today, is evaluated. Two series of triaxial tests involved the conventional undrained loading of isotropically and anisotropically consolidated specimens. The third series of tests utilized anisotropically consolidated specimens loaded by following special undrained stress paths. Test results revealed that liquefaction characteristics obtained from isotropically and anisotropically consolidated specimens are different. The effective angles of friction mobilized at peak shear stress and at steady state were greater for anisotropically consolidated specimens. Loading stress path is seen to have no effect on the liquefaction characteristics derived from conventional loading of anisotropically consolidated specimens. The critical stress ratio line is observed to be the line determining the initiation of liquefaction so that any stress path attempting to cross this line, regardless of direction of approach, immediately shows strain-softening behavior leading to liquefaction. / AC 2018