Masters Research Reports (Civil Engineering)
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Item An investigation into the sub-contractor selection process in the South African construction industry.(2003) Fenton, Graeme Stuart.; Pearl, Robert Gilfillan.; Rennie, Keith.This dissertation acknowledges that there is a need for improvement within the South African construction industry. Due to the broad need for improvement in the construction industry, this dissertation has investigated only one of the important possible areas of improvement i.e. the sub-contractor selection process. This dissertation investigates the existing sub-contractor selection methods used by sixteen established construction companies. Field research has been conducted by means of a questionnaire and all results have been compiled and analysed. Improvement of the sub-contractor procurement process can be achieved by benchmarking against practices used in the South African petroleum industry. This industry has had similar problems yet succeeded in improving their quality, safety, timeous completions, health and environmental issues. The construction of refineries are implemented under conditions similar to those experienced by the construction industry yet "best practice" procurement methods have been achieved. Sub-contractors presently undertake a large portion of the construction industries' activities and therefore should be more committed and responsible for their workmanship. This could be achieved by principal contractors establishing a wellstructured sub-contractor selection process, benchmarked against the petroleum industry. The petroleum industry believes that by procuring better contractors, they ensure better products. Their selection process ensures that all contractors meet certain requirements, which results in client satisfaction. The hypothesis, states that by benchmarking South African construction industry processes in respect of sub-contractor procurement, against the South African petroleum industry contractor procurement process, all stakeholders in the construction industry will achieve higher standards. If the principal contractors have well-structured sub-contractor selection processes, this will ensure the selection of the best sub-contractor for a particular project. The research and results prove this hypothesis. Without a paradigm shift by all stakeholders in the South African construction industry, establishing "best practice" in the sub-contractor procurement process will be unattainable. All stakeholders need to change their paradigms and invest in better processes. The petroleum industry sub-contractor selection process can be utilized by the construction industry positively and thereby establish higher satisfaction levels for clients.Item Characterisation and management of landfill emissions under a sub- tropical climate using full-scale landfill cells.(2002) Bowers, Aiden James.; Trois, Cristina.; Schreiner, Hilson Deneys.It is now widely understood that landfills, compnslng municipal solid wastes, typically undergo biological degradation processes in what are referred to as Bio-Reactor Landfills. These microbiological processes cause the release of gaseous and liquid emissions, which are commonly called landfill gas (LFG) and landfillleachate respectively. They are formed through mass transfer and biodegradation processes, which occur between percolating water and the solid waste matrix. Such emissions, if not correctly managed, may pose a threat to the natural environment surrounding landfills, and, specifically, landfill leachate may cause significant pollution of the ground water regime. The changes that landfilled wastes undergo to achieve a relatively stable, methanogenic state of decompQsition are now well understood, however little is known on the rate at which biodegradation processes take place, and particularly the timescale over which degradation of waste materials is completed. This dissertation presents research work demonstrating the behaviour of landfill emissions under specific climatic conditions encountered in South Africa in three containment landfill cells situated within the Bisasar Road and Mariannhill Landfill Sites. The containment cells, which are equipped with leachate extraction systems, proved to be ideal full-scale 'pilot plants' where changes in leachate and biogas emissions could be monitored. The characterisation of the landfill emissions allowed for the qualitative determination of the time-scales involved in reaching methanogenic conditions under a sub-tropical climate. Using this information, two landfill gas production models (adapted for the prevalent climatic conditions) were applied to two containment cells in order to predict the volume and duration of gas emissions. The results of the emissions characterisation show that the management of landfill developments in the form of small cells within the larger landfill footprint ('cellular' landfilling) can enhance waste degradation processes, and hence achieve desired levels of stabilised waste conditions relatively quickly. The results of the landfill gas models show that relatively large volumes of gas are emitted early in the lifetime of a landfill cell, and that the maximum emissions will be produced within a relatively short period of time (six to twelve months) after the last deposition of waste. This would allow for the extraction and treatment of landfill gas almost immediately after the closure of a cell, thereby shortening the time span over which potentially harmful emissions can occur.Item Nitrate removal using compost and pine bark as a carbon source.(2010-09-03) Pisano, Giulia.Emissions resulting from waste degradation processes have a high polluting potential and are responsible for negative impacts on the environment. Landfill leachate is hazardous for the human health and the environment and requires treatment before being discharged, in order to comply with the South African legislation indicated in the Government Gazette, 1999. However, treated leachate may still contain high levels of nitrate that require an additional denitrification step. Biological denitrification occurs with the addition of a carbon source that increases the operational costs of the process, particularly if chemical compounds are employed (such as methanol). This research aims to explore the efficiency of denitrification using low cost carbon sources such as garden refuse compost and pine bark, easily available in South Africa and currently disposed of in general waste landfills. Denitrification processes in fixed bed reactors were simulated in laboratory scale leaching columns packed with immature compost and pine and irrigated with biologically treated leachate from the Mariannhill landfill site Sequencing Batch Reactor (SBR). The overall objective is to assess efficiency, kinetics and performance of the substrates using batch tests and columns tests. A secondary objective is to assess the feasibility of using organic waste compost and pine bark as by product of an integrated waste management system to denitrify landfill leachate.