3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Combating the effects of rockbursts caused by seismically-induced shock waves(2017) Mudau, AvhaseiRockburst occurrences and their consequent damage remain a problem in modern mining, particularly at great depth. The problem of rockbursts has also escalated in deepcivilengineeringtunnelsduetohighlevelsofin-situstressatsuchdepths. Key advancementshavebeenmadetodatetohelpmitigatethedrasticimpactscausedby rockburstdamage,withrocksupportremainingalineofdefensetoprovidestability in rockbursting situations. There is, however, an ongoing inability of support to contain severe rockburst damage, especially conventional support systems. More than two decades ago, a support concept termed “sacrificial support” was proposed as a potential additional method to help inhibit rockburst damage. The philosophy behind a sacrificial support system is that, under dynamic loading conditions, support, in the form of a liner must fail (i.e. be ejected from rock surface), leaving behind, undamaged, what was once supported rock mass. It is because of this reason that this support is referred to as a sacrificial support due to its ability to protect the rock from damage whilst the support itself fails. Since the inception of this support idea, it was only recently that the behaviour of support in real rockburst events manifested the sacrificial behaviour in rockbursting, which warranted the need for further research. The sacrificial support concept stated here is applicable in situations where the source (i.e. seismic event) of the rockburst is located remote from where rockburst damage is likely to occur. To investigate the behaviour of sacrificial support, controlled laboratory experimentsbasedonthesplitHopkinsonpressurebar(SHPB)techniquewereconducted to study some aspects of dynamic rock fracturing in tension at high strain rates, and also the role a sacrificial layer plays in combating dynamic rock failure (i.e. rockburst damage). To achieve this, a single Hopkinson pressure bar configured for spalling tests, comprised of a relatively long cylindrical intact rock specimen attached at the bar free end, was impacted by a striker on the opposite free end of the bar in order to generate a dynamic stress pulse responsible for spall failure upon reflection from the specimen free end. Different liners and/or liner combinations were then introduced at the specimen free end as sacrificial support. This experimental arrangement allowed the role of, and failure mechanisms associated with, sacrificial support under dynamic loading to be demonstrated, and comparisons were made with “sacrificial support” behaviour observed in real rockburst events in a mine. Analysis of experimental results revealed that varying liner thickness and mechanical impedance between rock and support liner plays a significant role in helping to limit rockburst damage. Apart from experimental investigations, numerical simulations were undertaken to further probe the behaviour of sacrificial support under dynamic loading. Elastic models subjected to p-wave propagation indicated failure of the sacrificial layer, manifested by ejection of the liner due to reflection of compressive wave at the free surface. This failure mechanism was noticed for all the liners, independent of variation in liner thickness, and wavelength characteristic of the applied wave to the model. The sacrificial support method presented in this thesis presents an opportunity to further enhance safety in seismically active mines.Item A laboratory investigation of the effects of water content and waste composition on leachate and gas generation from simulated MSW(2012-07-04) Mudau, AvhaseiLeachate emitted by landfilled municipal solid waste may cause many and cumulative adverse effects ranging from health problems to environmental impacts. South Africa is one of the few countries in the developing world to have a sound regulatory framework for waste disposal by landfill. Municipal solid waste, however, is not differentiated by content. It is well established that the characteristics of waste produced by affluent suburbs are very different from poor suburbs and informal settlements. The regulatory framework for landfilling is presented as a set of the Minimum Requirements that specifies the design of landfills on the basis of the potential to generate leachate and the type of waste being disposed. The current study interrogates aspects of the Minimum Requirements classification system, namely the classification of waste and climatic water balance. The climatic water balance is used as a guiding tool to assess the potential for a landfill to generate leachate. The end result of this classification is a determination of the proposed site falls under B+ (water surplus) or B- (water deficient) class. The Minimum Requirements ensure that all sites which fall under the B+ class must be equipped with an underliner owing to the potential for leachate generation, while B- sites do not require any underliner since leachate will be only generated sporadically. However, there is no differentiation on the basis of the content of municipal solid waste from rich and poor suburbs. The present study investigates the generation of leachate from landfills situated on the borderline between B+ and B- sites, as well as the degradation of refuse having a range of basic constituents, and representing waste from rich and poor suburbs, as well as a mixture of the two. Laboratory lysimeters were filled with synthetic waste consisting of varying proportions of paper, putrescible material (grass cuttings) and coal ash (power station fly ash was used to ensure consistency). This was intended mimic the waste coming from “poor” and “rich” suburbs in South Africa. The effect of waste types grading from “poor” to “rich” on leachate quality was investigated. It has been found that a content of 60 % of ash on a dry mass basis, characterizing poor waste, has a neutralizing capacity which results in a better leachate quality than waste with little or no ash, mimicking rich waste. It has been also established that poor waste has lower leachate generation rates than a 1:1 mix of poor and rich waste as well as rich waste alone. A range of water applications was made bracketing the climatic divide between B+ and B-. It was also established that poor waste is characterized by high degradation owing to the high percentage of ash as compared to ash deficient rich waste. It was also noted that different standards for landfills receiving either only poor or only rich waste under the same climatic conditions (B+ and B-) in the Minimum Requirements may be advantageous. A relaxation of Minimum Requirements for landfills receiving poor waste could significantly reduce the cost of establishing a landfill under this range of climatic water balance conditions.