3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Relationship between undrained shear strength and moisture content for red berea sand tailings(2001) Du Plessis, AlbertusThe project report deals with the relationship between the undrained shear strength and the moisture content of Red Berea sand tailings. The tailings were obtained from the Red Berea sand dunes near Richards Bay, Kwa-Zulu Natal, South Africa. The geology of the area consists of Miocene deposits of red clayey sand, classified as Berea Formation. A method for determining stability of a tailings dam for Red Berea sand tailings, was investigated. The general method of using the degree of saturation of the tailings to specify the rate of rise, is not applicable to this type of tailings. It was found that a relationship exists between the undrained shear strength of the tailings, and the moisture content. The moisture content can easily be measured and the undrained shear strength can then be calculated. The calculated undrained shear strength can be used in a total stress analysis to determine a factor of safety against failure. This project report consists of a discussion of the literature, which was used as the basis for the assumptions made, as well as a description of the tests performed to prove the above-mentioned relationship. Test results are given, interpreted and used in an illustrative example of a stability analysis.Item On the initiation and propagation of fatigue cracks in WC-Co(1998) Erling, GhitaThis research examines fatigue in WC-Co, both under compressive and tensile loading conditions. A new macro-mechanism for compression fatigue crack propagation is put forward, which contradicts existing data on compression fatigue cracks as being self-limiting. Evidence of this macro-mechanism is presented in the form of final crack length versus number of cycles data, and micrographs of the compression fatigue cracks. A finite element study of the stress distribution in the WC-Co microstructure during compression fatigue loading has been developed. This model verifies possible methods of compression fatigue crack initiation. Examination of tensile fatigue and fast: fracture surfaces is used to show that fatigue is a separate mechanism to fast fracture in WC-Co. Characteristic features of the fatigue fracture surface are presented. A possible fatigue crack propagation mechanism is also presented. Finally, fatigue crack growth rate data in the form of the Paris equation is presented for WC-Co grades T6 and G6.Item A photoelastic investigation into the stress concentration factors around rectangular holes in composite plates(1993) Eichenberger, Edward PeterThe stress concentration factors around rectangular holes in carbon-fibre reinforced epoxy plates, subject uniaxial loads, were investigated experimentally and theoretically. To obtain theoretical solutions, two approaches were adopted; the finite element method and the theory of elasticity using the method of complex variable functions. Reflective photoelasticity was used as the experimental method. The determination of the stress concentration factor around a rectangular hole in a glass-fibrereinforced plate was attempted using transmissive photoelasticity, but no meaningful results were obtained. [Abbreviated Abstract. Open document to view full version}Item Determination of rock material properties to design robust support at Unki Mine(2016) Mponya, EreckSince mining platinum started at Unki Mine in 2005, large and small geologically controlled falls of ground (FOG) have been problematic especially in 2011 where a FOG caused a fatality. This study is about determining the rock properties at Unki Mine and then using the results to design and recommend robust support to reduce the FOG problems that are continuously happening. The study analysed all the FOG data from the mine database from 2010 to 2015 using statistical methods. Rock properties of the hangingwall, ore zone and footwall were determined from the laboratory tests. The geological structures were also mapped carefully. The results were then used as input data to the numerical modelling softwares Phase2 and J-Block. The J-Block program was used to determine the number of keyblocks that were stable, unstable and failed with support in designated and specified bords. A probabilistic approach was used to evaluate the stable span with special reference from small to large hangingwall instabilities for different mining scenarios. It was found out using Phase2 that large spans at Unki Mine are possible provided appropriate and robust support system is adopted. To fully address the issue of FOG problem at Unki Mine, a probabilistic approach is recommended as this is considered to be more appropriate than a deterministic approach that has been the traditional design approach so far.Item The effect of liquids on the stress distribution in a glass fibre reinforced plastic road tanker(2016) Armbruster, Michael HermanThe absence of reliable design data for Glass Reinforced Plastic (GRP) road tankers has been considered an obstacle for the local design and manufacture of such vehicles. This has prompted the analysis, using Finite Element Methods (FEM) of a filament wound cylindrical shell for a monocoque road tanker. [Abbreviated Abstract. Open document to view full version]Item Investigations into the mechanism of fracture onset and growth in layered rock using physical and numerical modelling(2015) Dede, TufanOne of the major impediments in the field of numerical modelling in rock mechanics is limited knowledge of the mechanisms of fracture and failure of brittle rock. One important tool for improving the understanding of rock behaviour is the use of laboratory experiments under controlled conditions. The Displacement Discontinuity Method, capable of fracture growth simulation (DIGS), has been used to model fracturing in samples under punch loading. A Finite Difference Method, capable of plastic deformations due to its explicit time marching scheme (FLAC), has also been used to model the punch tests. By comparing numerical simulations with results from laboratory experiments of punch tests, it has been possible to define the basic failure mechanism for pillar foundation failure. Two different test set-ups were used namely, steel jacketed axisymmetric punch tests and long strip punch tests in the triaxial cell which is built for these specific tests. The layered structure of the test specimens and in the test procedure had significant effects on the fracture pattern as well as the failure load. When the layer is near to the punch area, then both the layer and the layer conditions had a strong effect on the failure load. When the layer was frictionless, the failure stress dropped by about 20 percent. The same result occurred in both the axisymmetry and strip loading tests. When shear fractures intersect a layer with either low or high friction it terminates. This is not the case for the tensile fractures, which can pass through the layer media. However, it is important to note that the tensile fractures which originate from near the cone area can not pass through the layers. They stop at the interface.