School of Civil & Environmental Engineering (ETDs)
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Item A linear vibration isolator integrating a non-linear energy sink (nes)(University of the Witwatersrand, Johannesburg, 2024) Waite, Clinton; Li, KuinianThis report investigates the integration of traditional linear vibration isolators with non-linear energy sinks (NES) to enhance vibration control in structures subjected to dynamic loading. Structures often respond to dynamic loads—such as machinery vibrations, seismic activity, and environmental factors—by vibrating at their natural frequencies, potentially leading to resonance and structural failure. Vibration isolation and damping systems, such as linear isolators and NES, mitigate these effects. Linear isolators are effective at higher frequencies but have limited performance at lower frequencies, while NES systems offer broader frequency- range effectiveness. This study explores the effectiveness of combining these systems to optimize vibration control. Through simulation of both simple and complex setups, the research compares the vibration response of traditional linear isolators, NES-integrated isolators, and NES systems combined with additional damping elements. Key findings demonstrate that integrating NES with linear isolators significantly reduces peak transmissibility and improves vibration reduction under harmonic and seismic loading. However, the integration's effectiveness varies depending on system configuration and specific loading conditions, highlighting the need for further optimization. The study also presents a parametric analysis for designing vibration control systems tailored to diverse applications, offering valuable insights for engineering practice in reducing structural vibrations.Item Emerging Contractor Development through the Provision of Low-cost Housing in the Eastern Cape(University of the Witwatersrand, Johannesburg, 2024) Joseph, Shati; Fitchett, AnneThe construction industry is an economic stimulant and enabler of growth particularly in developing nations such as South Africa. The industry’s low entry barriers and the nature of work being labour-intensive attract emerging contractors. These contractors create jobs, upskill the community and transfer wealth to the previously marginalised. However, studies have shown that despite these several benefits, emerging contractors are prone to fail. Therefore, this research investigated the challenges facing emerging contractors and in addition, examined the low-cost housing programme. The positivism paradigm was adopted because of the nature of the research questions, its efficiency in the collection of voluminous data, and its perceived credibility by the policymakers. The collated data from 66 out of 173 contractors on the Eastern Cape Department of Human Settlements database were statistically analysed. The findings showed that most of emerging contractors are typically owned by a black male with a tertiary education, employ less than 20 employees, are capable of work worth less than R20 million and do not have a background in construction. The findings presented that the government was the primary employer of emerging contractors while some rely on subcontracting. Several contractors reported that they spent between 30 to 60 per cent of the contract value on materials. The start-up funds for emerging contractors are largely from family’s savings due to limited access to low- interest loans. During operation, the contractors heavily depend on monthly payment certificates to meet their expenses hence the importance of promptly settling these certificates. Emerging contractors receive training, it is largely from unaccredited mentors, which limits the upskilling of these contractors and leads to poor performance. The study then proposed possible initiatives that can employed for a progressive developmental programme based on the findings.Item The Informal Waste Sector in the City of Ekurhuleni(University of the Witwatersrand, Johannesburg, 2024) Nyirenda, Irene N. Inan; Fitchett, AnneIn South Africa, landfilling has traditionally been the primary method for dealing with general municipal solid waste. However, in recent years, there has been a shift in focus towards promoting a circular economy, which has brought about a change in waste management practices. The focus is now on minimising waste generation and reducing the waste stream rather than simply disposing of it. This approach aligns with South African National Waste Management Strategy 2020, which encourages such practices. The study focused on City of Ekurhuleni and the opportunities that exist in the formalisation of the informal waste sector with particular focus on landfill waste pickers and by analysing the amount of waste disposed of at the landfill site over a six (6) year period and comparing it to the percentage of materials that informal waste pickers recovered and reclaimed, the study provided valuable insights. This study utilised a mixed-method design that involved collecting and analysing both quantitative and qualitative data through desktop surveys, face- to-face interviews, and questionnaires. The practice of informal recycling at landfill sites encounters numerous environmental and health hazards for those who reclaim materials, because the waste is not sorted before disposal. The municipality lacks adequate resources for waste reduction initiatives, regulatory framework and capacity, educational campaigns, and enforcements, unlike those carried out by private companies or organisations. The study highlighted that some of the key inconsistencies in the interpretation of informal sector activities and their integration thereof in the context of the municipal regulatory framework are vague and unsupported.Item Heavy metal contamination and its spatial distribution from mining wastesin receiving environments of Mazowe District, Zimbabwe(University of the Witwatersrand, Johannesburg, 2024) Charema, Josiah; Taigbenu, Akpofure; Newete, SolomonThe purpose of this study was to investigate heavy metal contamination and its spatial distribution from mining wastes (especially artisanal/informal mining) and the impact of agriculture on heavy metal pollution in receiving environments of the Mazowe district, Zimbabwe. Agriculture and mining have considerably contributed to heavy metal and nutrient concentration into the world’s freshwater systems. This study aimed to improve the understanding of the contribution of agriculture and informal mining to heavy metal and nutrients pollution of Mazowe River. Also, the research aimed to establish the contribution of sulphates and phosphorous on heavy metal mobility in agricultural and mining areas. The research was conducted in Mazowe District in Mashonaland Central Province of Zimbabwe. Collection of the samples was carried out at five locations along Mazowe River, from its outlet at Mazowe dam to about 25 km downstream. The samples were preserved using WHO approved preservation methods and transported to a licensed laboratory in Harare for testing and analysis of heavy metals (Hg, Pb, Cr and Cd), extractable sulphates and phosphorus at Zim Labs laboratory, in Harare - Zimbabwe. Heavy metal analysis was done using the flame Atomic Absorption Spectrometer after wet digestion. The results indicated an average concentration of heavy metals in the river sediments ranging from 0.01mg/kg (Hg) to 26.68 mg/kg (Pb) during the wet season. During the dry season the levels of Hg, Pb, Cr and Cd were less than 0.01mg/kg. There were low detectable levels of heavy metals in the water samples for both wet and dry seasons. Significant differences in mean levels of phosphates and extractable sulphate pollutants were observed in the wet and dry season. The average phosphorus levels detected in the sediment samples during the wet season was 14.93mg/kg which was 93.7% higher than that of water samples which was at an average of 0.94 mg/l. The sampling points were small due to budget constraints and limited access to some areas because of property rights’ issues and national key points along Mazowe River. Thus, it would imperatively be unjustified to generalise the effects of the research outcome to other locations within Mazowe River Catchment or locations along Mazowe River downstream from the study area, without considering other land use patterns. The results showed that the presence of heavy metals in the sediment samples of Mazowe River could be highly attributed to informal mining along the river while extractable sulphates and phosphorous in both water and sediment samples could be attributed to agricultural activities. These findings may assist the environmental management and mining authorities to regulate the activities of artisanal mining to combat heavy metal contamination of rivers from mining activitiesItem Effect of pipeline pigging on raw water pipeline flow rate and energy consumption(University of the Witwatersrand, Johannesburg, 2024-02) Phillip, Neil Claude; Ndiritu, JohnPipeline pigging is a widely used method of pipeline cleaning to improve the hydraulic efficiency of a pipeline system, reduce deposits within a pipeline, reduce operational costs and improve water quality. With insufficient pipe cleaning, pipeline deposits accumulate within the pipeline which reduces the cross-sectional flow area of the pipeline and increases the friction losses in the pipeline. This subsequently reduces the operating flow rate, increases the pumping cost of the system, and reduces the water supply to the surrounding area. Therefore, the study aimed to investigate the hydraulic improvements and operational cost savings of a pipeline system after pigging and to determine when pigging should be done. A case study of the Tayside high lift pump station in South Africa was used for this investigation. Results indicate that pigging removes deposits and sediments from the pipelines thereby increasing the flow rate while reducing the cost of pumping substantially. The increase in flow rate calculated from the case study was 23.9% after one of the pigging operations in 2016. In addition, the pigging operations completed yearly also indicated a flow rate increase after pigging. The study showed that the increase in sediment levels of the raw water in the rainy season led to a reduction in the hydraulic capacity of the pipeline indicating an increase in sediment deposition in the pipeline. Life cycle cost analysis of the case study system obtained annual cost savings of R991,800.59 over a 50-year period. Based on the findings, a flexible routine for pigging based on the reduction in the hydraulic capacity of the pipeline is proposed to cater for the variability in levels of sediment in the raw water in alignment to the rainfall and streamflow patterns. This allows the pipeline to operate at the lowest energy cost and at the highest possible flow rate.Item Addressing high dimensionality in water quality modelling in water distribution networks(University of the Witwatersrand, Johannesburg, 2024-02) Machweu, Morongwa Ednah; Taigbenu, AkpofureWater quality models are the most effective tools for characterizing water quality conditions, assessing the effects of water pollution, and supporting decision-makers with water quality management. They can be utilised for detecting the variations in the water quality parameters. Despite the usefulness of water quality models, an appropriate and simple water quality descriptor for a particular application, considering the high dimensionality of various water quality parameters, remains a challenge (Chapman, 1992). To address this high dimensionality, a single dimensionless index is commonly used to describe water quality for a particular application. While pollution loads at various points in a river reach have been widely assessed by studies using water quality indices, little research has been done on water distribution networks with service reservoirs and a variation of loading conditions. In a water distribution network, service reservoirs function similarly to rivers in that they have complicated mixing mechanisms, are subject to a variety of water quality factors, and are sized and located differently. The most common water quality indices require the formation of subindices and weights to avoid ambiguity, eclipsing and rigidity. The Canadian Council of Ministers of the Environment Water Quality Index (CCME WQI) does not require the formation of sub-indices and weights, thus providing a simplified way of describing water quality. This study investigates the use of the CCME WQI to address high dimensionality in water quality modelling of water distribution networks, taking into consideration the locations of multiple service reservoirs. This study was carried out primarily for decision-making and design optimization purposes only. Using EPANET 2.2, four hydraulically optimised solutions (which satisfied minimum pressure requirements) were further analysed for water quality performance. This was achieved by incorporating simulated data on three water quality variables (chlorine residual, water age and THM concentration) into the CCME WQI for a hypothetical water distribution network, Anytown. The results indicate that two of the four hydraulically optimised solutions achieved excellent water quality levels. This study has demonstrated the usefulness of a dimensionless index as a proxy for multiple water quality variables of a water distribution system in facilitating decision-making.Item Improving the Penalty-Free Multi-Objective Evolutionary Design Optimization of Water Distribution Systems(University of the Witwatersrand, Johannesburg, 2024-02) Kambalame, Emily; Ndiritu, JohnWater distribution networks necessitate many investments for construction, prompting researchers to seek cost reduction and efficient design solutions. Optimization techniques are employed in this regard to address these challenges. In this context, the penalty-free multi-objective evolutionary algorithm (PFMOEA) coupled with pressure-dependent analysis (PDA) was utilized to develop a multi-objective evolutionary search for the optimization of water distribution systems (WDSs). The aim of this research was to find out if the computational efficiency of the PFMOEA for WDS optimization could be enhanced. This was done by applying real coding representation and retaining different percentages of feasible and infeasible solutions close to the Pareto front in the elitism step of the optimization. Two benchmark network problems, namely the Two-looped and Hanoi networks, were utilized in the study. A comparative analysis was then conducted to assess the performance of the real-coded PFMOEA in relation to other approaches described in the literature. The algorithm demonstrated competitive performance for the two benchmark networks by implementing real coding. The real-coded PFMOEA achieved the novel best-known solutions ($419,000 and $6.081 million) and a zero-pressure deficit for the two networks, requiring fewer function evaluations than the binary-coded PFMOEA. In previous PFMOEA studies, elitism applied a default retention of 30% of the least cost-feasible solutions while excluding all infeasible solutions. It was found in this study that by replacing 10% and 15% of the feasible solutions with infeasible ones that are close to the Pareto front with minimal pressure deficit violations, the computational efficiency of the PFMOEA was significantly enhanced. The configuration of 15% feasible and 15% infeasible solutions out performed other retention allocations by identifying the optimal solution with the fewest function evaluations.Item Hydraulic Performance Assessment and Upgrading of The Tswelopele Village (Gauteng) Water Distribution Network(University of the Witwatersrand, Johannesburg, 2024-02) Magabatela, Jonathan; Ilemobade, AdesolaThe hydraulic performance assessment of a water distribution network can reveal critical information that might help to address challenges experienced within that network. This study investigated the hydraulic performance and upgrading of the Tswelopele water distribution network to accommodate additional 35 yard connections. In line with the main objective of the study, the following were addressed, (1) modelling and simulating in EPANET the existing Tswelopele water distribution network and ascertaining the nodes experiencing below minimum pressures, (2) determining and incorporating upgrades required to accommodate current and future water demands, (3) optimization of the proposed upgraded water distribution network, initially using trial and error typically employed by industry and then using Wadiso software and (4) comparison of results obtained using the two approaches. Tswelopele Village comprises 89 households, and only 54 are connected to the existing water distribution network. The existing water distribution network was refurbished in 2015 but some households which are part of the water distribution network are still experiencing erratic water supply. A model of the existing network was prepared and simulated in EPANET. The analysis results indicated that only one node had a pressure value below the normally minimum accepted of 20m, but it was more than the minimum allowable pressure of 15m. Therefore, it is suspected that the water challenges might not be due to low pressure but to other reasons such as leakages, partially open valves or illegal connections. To accommodate the additional 35 households, an upgrade of the network incorporating future water demands was proposed. Optimization by trial and error was employed as per usual industry approach and was checked by optimization with Wadiso software. A comparison of the results revealed that based on July 2023 pipe cost estimates a 19.5% saving could be realised by using Wadiso optimization software as compared to the traditional trial and error.