School of Civil & Environmental Engineering (ETDs)

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A Comparative Study of the Efficiencies of Vertical Bracing Practices
(University of the Witwatersrand, Johannesburg, 2023-11) Saunders, Shawn Wayne Valintino; Elvin, Alex
The 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, respectively
A decision support framework for grading of civil engineering contractors and evaluation of infrastructure project performance
(University of the Witwatersrand, Johannesburg, 2024) Chiloane-Nwabueze, Salome
The construction sector plays a key role in the economic development of a country. The management of this sector is thus crucial in maximising the performance of the sector and the economy. The South African construction sector performance has some level of inefficiencies that could be improved to enhance the sector’s performance outputs. Therefore, the study aimed to develop a framework for grading civil engineering contractors and the evaluation of project performance. To achieve this, the study reviewed the literature on relevant key concepts and CIDB processes and systems. The government of South Africa has mandated the registration and grading of contractors to the Construction Industry Development Board (CIDB). The CIDB grade is a license for trading with the government. It certifies contractors who are graded as capable of delivering projects up to a pre-determined contract value in each class of work. Currently, the grading system is based on two key determinants, which are the contractor’s track record (i.e., completed projects) and available capital. Presently, a contractor grade does not denote the contractors’ capabilities. However, contractor grading and performance evaluation should be a multi-criteria decision-making process. A questionnaire was developed and distributed to the key participants in the industry to establish whether there is a need for enhancing the current registration, grading, and performance evaluation of contractors in the construction sector and to establish relevant criteria. Of the 149 respondents, the results of the study have revealed that most of the respondents (88.6%) agree that enhancing the current construction sector entry requirements could assist in improving contractors’ capabilities. Moreover, 90.6% of the respondents have indicated that enhancing the current construction sector entry requirements will assist in improving the performance outputs of the construction sector. A multicriteria decision-making methodology using the Analytical Hierarchy Process (AHP) based on seven main criteria with seventeen sub-criteria was carried out for iii grading of contractors and performance evaluation of contractors. Thereafter, using the results obtained from the AHP, an enhanced framework was developed for registering, grading, and evaluating the performance of contractors. Relevant scenarios and CIDB grading scenarios were applied to test and validate the developed framework. The construction sector entry requirements have been proposed by the study based on the literature reviewed and results of the state of practice survey to improve the sector performance. One way of improving the sector’s performance is through entry regulation. Organisations and some countries worldwide have some form of entry regulation to manage the construction sector. To minimise business failure and poor performance, new entrants need to have at least a recognised technical qualification in the aspiring field of work. This will ensure that new entrants have the relevant knowledge of the field in which they aspire to enter. Having entry regulations and improved grading and performance evaluation systems may assist in improving the sector’s performance. Proposals on the enhancements that may be considered by the CIDB are made which may assist in improving the industry’s performance.
A linear vibration isolator integrating a non-linear energy sink (nes)
(University of the Witwatersrand, Johannesburg, 2024) Waite, Clinton; Li, Kuinian
This 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.
Addressing high dimensionality in water quality modelling in water distribution networks
(University of the Witwatersrand, Johannesburg, 2024-02) Machweu, Morongwa Ednah; Taigbenu, Akpofure
Water 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.
Assessment of in-service durability performance of natural draft cooling towers in a petrochemical environment
(University of the Witwatersrand, Johannesburg, 2024) Shaw, Kyle Lloyd; Otieno, Mike
Effective temperature control is an important operation requirement in petrochemical processes, where Cooling Towers (CT) play a key role in efficiently lowering water temperature for reuse in various chemical processes. Natural draft cooling towers function as heat extraction systems, dissipating thermal energy from hot water into the atmosphere through cold air. However, many reinforced concrete cooling towers have exhibited signs of deterioration over time, such as cracking, corrosion, and structural misalignment, posing the risk of structural failure. To address these issues, structural condition assessment programs, aiming to inspect, repair, and monitor cooling towers to prevent structural collapse are of significant importance. The focus of this study investigates the durability of natural draft cooling towers in an aggressive petrochemical environment. With a focus on Sasol Secunda Natural Draft Cooling Towers, the research aims to identify and characterize the various concrete deterioration mechanisms, quantify durability parameters, and explore mitigation measures for both new and existing cooling towers. Concrete deterioration is a significant concern in structures exposed to harsh environments, affecting their global stability and service life. The study examines the role of cover concrete quality in resisting corrosive agents and assesses durability using South Africa's three durability index (DI) tests, including water sorptivity, chloride conductivity, and oxygen permeability. The study comprised of on-site assessments and laboratory testing methods to determine the durability performance of cooling towers. The approach includes the three durability index tests. On-site assessments include visual inspections and non-destructive testing (NDT) near areas displaying signs of deterioration. The significance of this research relies on the operational efficiency of cooling towers in petrochemical plants, their vulnerability to harsh conditions, and the need for durability design considerations at Front End Loading (FEL) engineering and planning. It aims to shift from prescriptive to performance-based design approaches and provide insights for maintenance and mitigation strategies. This study contributes to the knowledge of concrete durability in challenging environments, aiming to enhance the longevity and performance of critical industrial infrastructure, particularly natural draft cooling towers.
Comparative study of five country-specific labour-intensive infrastructure development programmes : implications for South Africa
(University of the Witwatersrand, Johannesburg, 2010) Quainoo, Harry Akyen; McCutcheon, R.T.
Unemployment and abject poverty in South Africa are widespread, persistent and disproportionately high. These problems are aggravated by inadequate capacity at all tiers of government and huge infrastructure backlogs in rural South Africa. Employment-intensive means of infrastructure delivery have been successfully implemented in several sub-Saharan African countries and elsewhere to generate employment and reduce poverty. It should be possible to replicate similar large-scale national programmes in South Africa. But South Africa has failed. Both prior to and since 1994, several supposedly employment-intensive programmes have been implemented in South Africa with poor results. In an endeavour to contribute to future South African policy and good practices regarding employment, this thesis describes and analyses in detail five major Sub-Saharan programmes and reaches conclusions regarding their achievements and shortcomings. Lessons derived bridge the knowledge gap between the large-scale programmes embarked upon in the sub-Saharan countries in the mid-1980s and the year 2007; these lessons should be applied to future endeavours in South Africa to generate significant employment per unit of expenditure and contribute to poverty alleviation. A major conclusion reached was that the success of employment-intensive infrastructure development programmes depends to a large extent on fundamental factors such as appropriate and implementable policy, government commitment, adequate and sustainable funding, adequate capacity and good preparation. Specifically, the thesis demonstrated that prior to implementation a sufficient timeframe is required for programme preparation in order to make significant contribution towards poverty reduction. Equally, national programme expansion requires a strategic balance between centralisation and decentralisation. In particular, for programme extension and decentralisation, due regard must be given to training and capability building and available resources. Deriving from the thesis’ major conclusions, the author developed three crucially important frameworks for anti-poverty infrastructure development programmes, namely; a four-phased model for evaluating the chances of success of infrastructure programmes, a five-phased result-oriented guidelines for testing the workability of infrastructure development policies, and a practical guideline for monitoring and evaluating employment-creation programmes that maximises the benefits thereof and pre-empts institutional memory loss through systematic knowledge management.
Determining the parameters for the sizing of sediment traps in the city of Johannesburg
(University of the Witwatersrand, Johannesburg, 2024) Raliengoane, Mankoe Francis; Fitchett, Anne
Urban land practices usually involve soil compaction and vegetation removal as cities expand and grow. This has led to increased flood peak flows and high stormwater runoff volumes associated with sediments, nutrients and other pollutants that load downstream water resources. To address these issues, there has been a growth of practices involving Sustainable Drainage Systems (SuDS) for managing stormwater runoff quantity and quality from urban areas. For example, this involves the application of attenuation ponds, and wetlands which temporarily store urban stormwater runoff, thereby reducing the sediment loads, pollutants, and release of peak flows to the downstream water resources at flow rates that mimic the pre-development flow patterns. This practice is gaining momentum in South African urban areas, which are supported by the policies and legislation set up by local authorities to address stormwater management. However, these stormwater application practices often do not perform according to their design capacities because they get filled with sediments and their effectiveness in attenuating peak flows is reduced. Therefore, it is important to reduce sediments coming into these structures by applying sediment traps and basins located at the head of such structures. The sediment trap’s main function is to slow down the stormwater runoff and help in the reduction of sediments before stormwater runoff is discharged out of the construction site and other disturbed areas. The City of Johannesburg Stormwater Management By-laws and Stormwater Design Manual have limited information for the management of sediment using sediment traps and basins and which parameters need to be considered when sizing sediment traps. Therefore, the main aim of the current research was to determine the parameters that should be considered when sizing sediment traps specifically for the city of Johannesburg. The following parameters: design rainfall, daily rainfall, catchment area, evaporation, land cover and land use, percentage of permeable and impermeable areas, topographical data, peak flow, runoff volume, catchment topography, soil types and infiltration characteristics, sediment particle size distribution, sediment settling velocity, sediment loading rate/yield were modelled through Personal Computer Stormwater Management Model (PCSWMM), ArcSWAT ArcGIS, and Excel Spreadsheet Models. Further, the sensitivity analysis was undertaken using different values of imperviousness and infiltration rates while observing peak flow and runoff volume changes in PCSWMM outputs. Modelling in PCSWMM showed that peak flows and runoff volumes increased due to an increase in the values of the imperviousness used. However, the range of infiltration rates for the soils in both sub- catchments S22 and S23 did not change the peak flows and runoff volumes. Though it was not the scope of the current study, it was observed that higher infiltration rates than the ones that were determined from the sub-catchments S22 and S23 indeed reduced peak flows and runoff volumes. On the other hand, particle settling velocity showed that gravel particles took a short time to settle and required a smaller sediment trap iii storage capacity. In comparison, silt particles took longer to settle and required a larger sediment trap storage capacity. Lastly, sediment yield from both sub-catchments S22 and S23 showed that sediment yield is driven by rainfall, whereby months with high rainfall had higher sediment yield than the months with low rainfall. It is therefore, concluded that the following parameters: design rainfall, daily rainfall, evaporation, land cover and land use, percentage of permeable and impermeable areas, topographical data, contributing catchment area, peak flow, runoff volume, catchment topography, soil types and infiltration characteristics, sediment particle size distribution, sediment settling velocity, sediment loading yield should be considered by the engineers, designers and planners when sizing sediment traps in the City of Johannesburg and possibly in other places as well.
Developing of a parametrically resonw1t vibrating screen, modelling, simulation and dynamic testing
(University of the Witwatersrand, Johannesburg, 2023-07) Mohanlal, Mishal; Li, Kuinian
A 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.
Effect of pipeline pigging on raw water pipeline flow rate and energy consumption
(University of the Witwatersrand, Johannesburg, 2024-02) Phillip, Neil Claude; Ndiritu, John
Pipeline 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.
Emerging Contractor Development through the Provision of Low-cost Housing in the Eastern Cape
(University of the Witwatersrand, Johannesburg, 2024) Joseph, Shati; Fitchett, Anne
The 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.
Groundwater resource exploration within the inner-city of Johannesburg
(2020) Tywakadi, Ondela; Taigbenu, Akpofure E.
This study examined the hydrogeological characterisation of the Johannesburg inner-city. Residents reported a high water table that has resulted in groundwater seepage into building basements, posing a safety threat and limited functionality of these structures. Although this high groundwater table triggered this investigation, it took a deeper and broader approach by seeking to quantify the amount of groundwater resource that is available to be used to supplement the existing municipal supply. The study also aimed at establishing long-term sustainable abstraction rates and viable fit-for-purpose use of the available groundwater. The study then evaluated the abstraction rates against the water table response in order to achieve a safe water table level at which groundwater seepage into building basements does not occur. The methodology employed included assessing and verifying the number and distribution of buildings affected by groundwater seepage. Information was gathered by circulating a survey in the form of a questionnaire to a network database of property owners and managers. Field work, in the form of drilling and testing boreholes, and subsequent data processing were carried out to characterise the aquifers and establish the quantity of the resource. In order to determine possible uses of the groundwater, water chemistry testing was carried out. The characteristics and recharge dynamics of the aquifers that were established served as inputs into a numerical model which estimated the quantity of groundwater that can be sustainably abstracted for utilisation, while ensuring the water table is sufficiently suppressed. An estimated 2.47 million-m3 (or billion-litres) of groundwater is available as a total yield potential within the Johannesburg inner-city. This water can be sustainably withdrawn from the ground at a safe yield (abstraction rate) of over 56 million-litres per annum (56 902m3/a) from the nine drilled boreholes. The system response corresponding to this abstraction rate is predicted to cause a 2.3m decline in the water table level compared to the current scenario. This desired pumping scenario would suppress the water table level to be at an average of 8.6m below ground. The average basement depth in the Johannesburg inner-city is 8m below ground and hence, most building basements would consequently not be flooded under this scenario. Currently, 60% of building basements are subjected to the risk of flooding, and this would reduce to 30%, which is made up of those deeper than 9m. The current water demand in the Johannesburg inner-city is approximated to be 80Ml/day. Therefore, the estimated groundwater yield to supplement the municipal supply is insignificant (0.2%), and does not justify an investment into retrofitting the groundwater infrastructure into the bulk infrastructure system. Thus, developing a groundwater source infrastructure for bulk water supply purposes is not volumetrically viable in the case of Johannesburg inner-city, but can be beneficial for building strategic reserves and resilience into the system. It is recommended that in future, fine-tuning and continuous calibration of the numerical model should be carried out when the boreholes are in operation. Further research is also required to examine the aquifer geo-mechanics in order to assess the risk of land subsidence with decreasing water table levels, especially in a possible future scenario of over-exploitation of the aquifer.
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, Solomon
The 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 activities
Hydraulic Performance Assessment and Upgrading of The Tswelopele Village (Gauteng) Water Distribution Network
(University of the Witwatersrand, Johannesburg, 2024-02) Magabatela, Jonathan; Ilemobade, Adesola
The 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.
Improving bulk water pump station policies and operations in conditions of uncertain and changing demand
(University of the Witwatersrand, Johannesburg, 2024) Mudau, Thendo David
South Africa is facing growing and complex changes in water demand; furthermore, acute water scarcity challenges due to drought and degradation of surface water resources threaten its ability to manage the demands. Industrial and power generation sectors in some regions are plagued with water shortages, requiring inter-basin transfer schemes for bulk water transfer to these regions. The complexity in the water demand is further exacerbated when the demand that bulk water transfer systems are designed to manage varies from the demand projections. This has resulted in inefficient pumping operations and unnecessary costs, which are causing great concern as a result of the current water crisis and the increasing cost of electricity in South Africa. This was an investigation to find out how the increasing energy costs and inefficiencies due to uncertainties in demand could be mitigated in bulk water transfer schemes in South Africa. This was done through determination of the impact demand changes and uncertainties have on bulk water transfer pump stations’ adherence to the operational policy, performance, and costs. Approaches to reduce costs associated with the changes in the demand and improve the operational performance of the pump station were proposed. The Jericho pump station in the Mpumalanga province, South Africa, was used as a case study to assess the impact demand changes have on the pump station’s operation and control, as well as the operational energy costs. The results of the assessment showed that all these three aspects of the pump station had been negatively affected by the variability in the demand, particularly the energy costs with operational costs due to pumping operations during peak periods contributing to 33% of the estimated energy costs during the study period. Optimal pump scheduling and a capital investment in the form of a booster pump station to assist the Jericho pumping system and changes to the pump station control policy are proposed, and it is determined that they would ensure a 17.02% saving in annual energy costs. Furthermore, it is shown that operational costs due to pumping operations during peak Time- of-Use (TOU) periods are more than three times the standard and off-peak tariffs, and as such pumping operations during peak periods should be minimized. This research report showed the significance of optimal pump scheduling and how operational policies of bulk water transfer systems should continuously be reviewed and improved if required, especially with the ever-changing demands.
Improving the Penalty-Free Multi-Objective Evolutionary Design Optimization of Water Distribution Systems
(University of the Witwatersrand, Johannesburg, 2024-02) Kambalame, Emily; Ndiritu, John
Water 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.
Passive Vibration Isolation Systems Integrated with Dynamic Vibration Absorber
(University of the Witwatersrand, Johannesburg, 2023-02) Thakadu, Katlego; Li, Kuinian
Isolating vibration using an isolator and/or vibration absorber are the two commonly used measures of vibration control in practice. The presented investigation explores multiple passive vibration isolator configurations, integrated with a dynamic vibration absorber, to improve the performance of vibration isolating. In the first section, A Passive vibration Isolator Integrated with a Skyhook and Groundhook Vibrational Absorber is investigated. The dynamic behaviour of the proposed isolators with the lumped mass, fixed to an inertial reference, is investigated using force, and displacement transmissibility equations. The force and displacement transmissibility equations are derived by modelling the dynamic system as a two-degree-of-freedom system. Derivations for both configurations of the isolator, integrated with a skyhook and groundhook are presented, including numerical simulations and parameter sensitivity analyses. The analysis conducted, indicates that both configurations, is indeed a passive linear isolator, which can support a static load whilst achieving significant vibrational isolation, employing a relatively low damping element. Additionally, the practical applications of the proposed configurations are plausible with the currently available material, which makes the research viable within the field of engineering. In the second section, A Passive vibration Isolator Integrated a Dynamic Vibration Absorber with Negative Stiffness Spring is investigated. The dynamic behaviour of the isolator supporting a lumped mass, is investigated using force and displacement transmissibility equations of the isolator. The force and displacement transmissibility are derived by modelling the dynamic system as a two-degree-of-freedom system. A unique constraint on the negative stiffness ratio, α, for the isolator’s stable operation, is developed. The optimal design of such an isolator was demonstrated with a design example. Extensive numerical simulation and parameter studies on the isolator were performed, which revealed attractive dynamic characteristics of the isolator. It is a passive linear isolator, without any non-linear elements, spring or damper. However, it can bear a large static load and, at the same time, achieve a greatly increased vibration isolation. These two effects are considered mutually exclusive in linear isolator and can be overcome in some extent by properly configured nonlinear isolators only. Moreover, numerical simulation and parameters study shows that the negative stiffness ratio and the mass ratio required can be very small, which makes the implementation of such an isolator in practice convenient. All these make the isolator attractive for engineering application. The third section of this research is on the optimal design of a two-stage isolator, a isolator integrated with another isolator. Performance of a passive two-stage vibration isolator and its design was rigorously evaluated and recorded in this study. It is revealed that the vibration isolating performance of a linear passive two-stage vibration isolator depends on the configurational parameters of the isolator. The transmissibility, a non-dimensional parameter used to quantify the effectiveness of an isolation system, of the passive two-stage vibration isolator was derived. A numerical optimization on the transmissibility of the isolator was developed and performed using the Minimax algorithm. It is demonstrated that an optimally designed linear passive two-stage vibration isolator produces significantly better isolating than a single-stage linear isolator at all frequencies, high and low. The proposed linear passive two-stage isolator is not only effective against high-frequency isolation, which used to be the primary use of a passive two-stage isolator but shows outstanding isolation performance at all frequencies. The proposed linear passive two-stage vibration isolator outperforms many complicated nonlinear isolators, including both single-stage or two-stage isolators. Parameter selection, dynamic performance driven optimal design and potential application of the proposed isolator were also investigated and presented.
Prospects of gibbsite-rich laterite as a source of aluminosilicates in geopolymerisation
(University of the Witwatersrand, Johannesburg, 2024) Gilayeneh, Victor Saye; Nwaubani, Sunday; Otieno, Mike
Laterite, an iron-rich soil widely found in the tropical and subtropical regions of the world, has shown promise for the development of eco-friendly construction materials through geopolymerisation. However, this material varies greatly in composition based on location, prevailing climate conditions, and even in depth within a given lateritic profile. The top layer of most lateritic profiles is usually low in kaolinite but rich in aluminium or iron hydroxide minerals. Despite these variations, research on the use of laterite in geopolymerisation has predominantly focused on materials rich in kaolinite. Therefore, this study explores the potential of aluminium-rich laterite as a source of aluminosilicates in geopolymerisation. In this study, the reaction kinetics, setting times, flow behaviour, strength development, phase composition, and pore structure of geopolymer derived from aluminous laterite were examined. This study also considered both calcined and uncalcined laterite as well as the influence of calcium minerals, namely calcium carbonate (CaCO3) and Portland cement, which replaced 40% of the laterite. In addition, the influence of the laterite’s properties on the performance of the derived geopolymer was also examined. The flow behaviour of the paste was found to be influenced by the viscosity of the activating solution, while the setting times and heat of reaction varied according to the type of laterite and the presence of calcium carbonate or Portland cement, which reduced the setting times and accelerated the rate of heat liberation within the first hour of the isothermal calorimetry test. The geopolymer mix based on calcined laterite displayed the highest amount of heat liberated, while its uncalcined laterite counterpart showed the lowest. All mixes within the calcined laterite series exhibited higher compressive strength than those in the uncalcined series, but only the calcined laterite mixes containing calcium minerals achieved structural strength. The uncalcined laterite mixes experienced strength regressions, with samples of the uncalcined laterite mix containing calcium carbonate developing cracks and subsequently disintegrating. The phase assemblage, porosity and pore structure were also influenced by the type of laterite and the presence of calcium carbonate or Portland cement. However, the presence of calcium carbonate also led to severe efflorescence and subflorescence, which negatively impacted the porosity and structural integrity. Also, the dissolution of gibbsite initiated the development of unstable phases in the uncalcined laterite mixes within the geopolymer and hybrid categories. Conversely, in the absence of activators, especially sodium hydroxide, as demonstrated in the binary mix containing uncalcined laterite, the dissolution of gibbsite is inhibited, resulting in the formation of stable phases.
The impact of incorrectly sized bulk meters on water consumption and municipal revenue
(University of the Witwatersrand, Johannesburg, 2024) Rabé, Magdeleen; Ilemobade, A.
South Africa is a water-scarce country, characterised by lower-than-average rainfall and high water consumption rates, with Non-Revenue Water increasing despite water conservation efforts. Literature shows that bulk water meters are often incorrectly sized, increasing Apparent Losses from metering inaccuracies, resulting in revenue loss and negating the municipality’s water conservation and water demand management initiatives. This study investigates the impact of incorrectly sized bulk water meters (sized 40mm – 150mm installed at non-residential and multi-residential facilities) on municipal revenue by analysing flow logging data and metered consumption characteristics of 42 users. The methodology combines flow logging to analyse actual water consumption characteristics, assessment of meter operating flow ranges for optimal sizing, calculation of weighted accuracy for Apparent Loss estimation, and literature review on meter sizing and alternatives to consider regarding fire demand requirements. Highlights from this study are (a) the consumer profiling findings underscore the importance of aligning meter size with consumer water use patterns: consumption below the meter’s starting flow is observed at 50% of the stands analysed in the dataset, indicating over-sized meters; (b) 57% of the stands had on-site leakage, occurring at low flow rates where meters are most inaccurate; (c) two examples demonstrate the impact of incorporating fire demand, resulting in meter size changes from a 15mm to 100mm, and a 25mm to 150mm, respectively; (d) resizing meters for 35 stands is estimated to result in an additional municipal revenue gain of R636,876.92 within one year. Overall, the study highlights the importance of accurate meter sizing for reducing Non-Revenue Water, improving revenue generation, and enhancing water conservation efforts.
The Impact of South Africa’s Response to Informal Settlements and Affordable Housing Development when compared to the responses adopted in Brazil and India
(University of the Witwatersrand, Johannesburg, 2024) Mlotsa, Cebile; Biyela, Precious
In South Africa, informal settlements are prevalent in all the major urban centers, including some long-established informal settlements, such as ones within Alexandria township in the City of Johannesburg, Nyanga in the City of Cape Town and Kennedy Road in the City of eThekwini. New informal settlements are continuing to develop across South Africa’s urban centers. Various policies and interventions have been implemented to address this phenomena. This study aimed to investigate the impact and effectiveness of South Africa’s policies and interventions on informal settlements and compared them to policies and interventions of India Brazil. The study begins with a literature review of the policies and strategies of the three countries alongside best practices recommended by international organizations such as UN-Habitat and the World Bank. The effectiveness of the policies was assessed, and the general issues that affect informal settlements globally were identified. Research questions were formulated based on the literature review to gain further insights into South Africa's response strategies. Semi-structured Interviews were conducted with three professionals working in organizations addressing informal settlements across different provinces, focusing on current strategies, their impact and effectiveness, and potential improvements. A field visit to Mahlakong informal settlement in Limpopo was also carried out which included interviews with two residents to understand challenges and interventions underway to address them. The study found some progressive policies and strategies underway in South Africa, such as the strong emphasis on participation and approval by residents of informal settlements when interventions are carried out, and incremental construction of infrastructure in informal settlements. The study also identified areas that if addressed can improve South Africa’s response to informal settlements, such as recognizing multi-storey inner city buildings as informal settlements, encouraging private developers to invest in affordable housing development, and diversifying tenure legalization option.
The Informal Waste Sector in the City of Ekurhuleni
(University of the Witwatersrand, Johannesburg, 2024) Nyirenda, Irene N. Inan; Fitchett, Anne
In 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.