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 Developing of a parametrically resonw1t vibrating screen, modelling, simulation and dynamic testing(University of the Witwatersrand, Johannesburg, 2023-07) Mohanlal, Mishal; Li, KuinianA novel coupled spring pendulum vibrating screen is proposed with the goal of developing efficient screening using parametric resonance. A simple spring pendulum is initially studied to provide the basis of the dissertation. The theoretical model of the proposed vibrating screen is developed using Lagrangian mechanics which includes damping and generalized forces. Two derivations of the vibrating screen are proposed, the first being a 4DOF (degree of freedom) system and the second being a 3DOF system. The 3DOF system is found to present better numerical stability and is thus utilized for the study. It is shown that the 3DOF system is comparable to the simple spring pendulum for the case where initial conditions are applied to similar coordinates. The proposed vibrating screen presents motion which is not indicative of traditional vibrating screens. It is found that a system where attributes are sized for parametric resonance requires far smaller excitation forces to achieve higher accelerations and displacements compared to traditional vibrating screens. The proposed vibrating screen is an unfeasible design due to the large displacements; high foundation loads and limitations on mechanical components. Discrete element method (DEM) simulations of the proposed vibrating screen are performed to study the efficiency with varying inclinations of the mesh deck. The results are compared to a linear motion vibrating screen. The proposed screen requires far less energy compared to traditional vibrating screens and achieves higher efficiencies with larger deck inclinations. The derived differential equations are verified by experimental testing using free vibrations. The numerical simulations and experimental tests present a good correlation. Signal processing is implemented to compare the natural frequencies from the experimental testing and numerical simulations, the results present a good correlation.Item Use of Multispectral Satellite Imagery to Monitor the Decant Pond of Tailings Dams(University of the Witwatersrand, Johannesburg, 2023-08) O’Donovan, Christopher Galen; Adam, Elhadi; Torres-Cruz, AlbertoTailings dam failures, such as the Jagersfontein failure in the Free State province and the Fundão and Feijão failures in Brazil, have brought into question the ability of the mining industry to operate safely, threatening its social license. To improve the safety of tailings dams, leading indicators of dam safety should be monitored. The location and historical behaviour of the tailings decant pond provides insight into several such leading indicators and can be used as a proxy to flag potential construction issues. This work investigates the use of public multispectral data collected by the Sentinel-2 satellite mission to monitor the supernatant tailings dam decant pond. This is achieved by leveraging the cloud-based Google Earth Engine platform and open-source GIS tools. Sentinel-2 acquires visible and near infrared spectrum data with a spatial resolution of 10 m and a revisit time of 5 days. Pond data is obtained by visual assessment and automated thresholding of Sentinel-2 imagery. Thresholds of near-infrared (NIR) reflectance and the normalised difference water index (NDWI) obtained by a least square error analysis are investigated. Implementation of the method at three South African tailings dams, constituting four decant ponds, illustrates the capabilities and limitations of Sentinel-2 imagery. High spatial resolution (<5 m) multispectral satellite imagery and natural colour aerial orthophotos (<0.25 m) serve as reference data. Visually assessed Sentinel-2 pond data presented a bias towards slight over estimation of the pond area compared to reference data. Other leading indicators did not show systematic bias across all sites. In general, the deviation between Sentinel-2 and the reference measurements was high, indicating that Sentinel-2 imagery should be used with caution for measurements critical to dam safety. Site-specific thresholds of NIR and NDWI indicated that automated thresholding of the NDWI is superior to NIR reflectance alone. It is shown that Sentinel-2 timeseries imagery can be used in tailings dam monitoring to supplement existing construction surveillance frameworks and provide historical pond data in the absence of such information.Item 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 A Comparative Study of the Efficiencies of Vertical Bracing Practices(University of the Witwatersrand, Johannesburg, 2023-11) Saunders, Shawn Wayne Valintino; Elvin, AlexThe efficiencies of cross sections and configurations applied to vertical bracing are investigated by evaluating reference configurations (RCs), composed of cross braced circular hollow section (CHS) members, against comparative configurations (CCs), consisting of cross-braced Angle members, and single-CHS members. The metrics used to evaluate efficiencies were mass, raw materials costs, and fabrication and erection costs. CCs were found to be more efficient than RCs for most analysed cases, metric and configuration dependent. The following results were found: i. Mass metric a. Crossed-Angle more efficient in 79% of analysed cases. b. Single CHS more efficient in 87% of analysed cases. ii. Raw materials costs metric a. Crossed-Angle more efficient in 92% of analysed cases b. Single CHS more efficient in 88% of analysed cases iii. Fabrication and erection costs metric a. Crossed-Angle more efficient in 90.4% of analysed cases b. Single CHS more efficient in 88.5% of analysed cases Inversions of the efficiency parameter findings, with RCs more efficient than CCs, were observed when: i. RC CHS member slenderness ratios were less than 80-90. ii. CC design loads were greater than 225 kN, 1200 kN and 1500 kN for mass, raw materials and total cost efficiency metrics, respectivelyItem Water for Firefighting in Sol Plaatje Municipality, Northern Cape, South Africa(University of the Witwatersrand, Johannesburg, 2023) Thage, Tumelo MacAurthur; Ilemobade, AdesolaIn South Africa, SANS 10090 (SABS, 2018a) and the Red Book (DHS & CSIR, 2019) recommend that for firefighting municipal water distribution systems must have and maintain the capacity to provide water for firefighting purposes. van Zyl & Haarhoff (2007) state that the provision of water for firefighting is a dominant design consideration as it influences the sizing and outputs of critical components. Scheepers (2012) argues that fire flows acts ‘as the most limiting demand condition’ as when it required it is extracted in large quantities for a short period. The most commonly used fire flow values in the SANS 10090 have largely remained unchanged for several decades. In other words, these values have not been revised to take account of the evolution of municipal water consumption over more than 30 years. This suggests that the recommended water requirements for firefighting may no longer be fit for purpose. The literature review revealed that the fire flows in the Red book violates the same in the SANS 10090 - this is illegal as the SANS 10090 specifies enforceable absolute limits. Furthermore, the Red book and SANS 10090 provide different fire risk classifications and values for the different parameters and as such, inconsistent and lack uniformity. It is important for design engineers to have accurate input data when planning and designing for fire flow requirements as any deficiency in basic design information could lead to an insufficient capacity to fight fires or an over-design of water supply infrastructure. A question arose from these observations, which provided inspiration for this study: Are fire flows in the SANS 10090 and Red book appropriate for current firefighting efforts? In answering this question, the first step of this study was to identify participating municipalities that were willing to release their datasets on firefighting for this study. Sol Plaatje municipality was one of the willing municipalities. This study thereafter categorised and analysed information contained in the 3236 fire incident reports that occurred within Sol Plaatje Municipality during the period 21 July 2017 to 21 August 2020, and compared actual fire flow volumes and flow rate data against the SANS 10090, Red book and previous South African studies. In order to provide context and aid better understanding of the datasets, structured interviews were conducted with municipal officials responsible for firefighting operations at Sol Plaatje municipality. Key highlights of this study indicated: ∼ 93.3% of fires in Sol Plaatje municipality were extinguished using 7 Kℓ or less of water. This result is similar to previous studies- In a 2014 study more than 90% of fires in 5 Western Cape Towns were extinguished using less than 10 Kℓ of water; In a 2019 study, 75% of fires in the City of Johannesburg were extinguished using less than 6.60 Kℓ of water; and In a 2022 study, 87% of fires in the City of Johannesburg were extinguished using 10 Kℓ or less of water. Overall, 75%-93% of fires were extinguished in the various study areas using 10 Kℓ or less of water. For large fires in Sol Plaatje municipality, the average water volume used to extinguish 85 large Category 2 fires was 8.56 Kℓ or less of water. This finding is similar to that of the Western Cape 2014 study and the 2022 City of Johannesburg study that found that 8.6 Kℓ and 9.63 Kℓ or less of water extinguished 77 and 89 large category 2 fires, respectively. What is evident from the results is that the volumes of water used in Sol Plaatje and previous studies are significantly less that the specified values in SANS 10090 and the Red book. An adverse consequence of higher values is that it leads to an over-design of water supply infrastructure as it increases the volume of municipal storage required for firefighting and consequently, increases the total capacity of municipal storage. Increased storage capacity increases resources that are expended, as well as water retention times, which negatively affects water quality. This study validates the recommendations of previous studies that the fire flows in the SANS 10090 and Red book need to be revised to enable the efficient conservation of scarce water resources and optimal design of water systems.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.