Masters Degrees (Civil Engineering)
Permanent URI for this collection
Browse
Recent Submissions
- ItemShoreline dynamics of South Africa using satellite imagery(Stellenbosch University, 2024-12) Theron, Danie; Theron, Andre Karl; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: Most South African beaches lack sufficient monitoring, which impedes a holistic understanding of shoreline dynamics amid increasing environmental and anthropogenic pressures. This study addressed this critical knowledge gap by utilising a satellite-derived shoreline algorithm (CoastSat) to rectify years of inadequate monitoring and to contribute to a thorough understanding of South African shoreline dynamics. Enhancements were made to the open-source CoastSat algorithm to enable a semi-automated, nationwide application. As a result, a pioneering database was created, spanning from 1984 to 2023 and covering nearly all sandy areas of the South African coastline. This extensive and coherent database represents the first of its kind for South Africa. The accuracy of the satellite-derived shoreline data (SDS) was assessed by comparing it with Lidar-surveyed data from 27km of beach area across six different beaches in the eThekwini Municipality. The results showed a very strong correlation (R = 0.95) between the SDS and the surveyed data, although an overall landward bias of 11.2m was observed. By incorporating wave runup in the analysis the accuracy was significantly improved, reducing bias by up to 79%. These findings were consistent with previous CoastSat studies from abroad. In addition to developing this extensive shoreline dynamics database, four local case studies and four regional assessments were carried out. These efforts served two primary objectives: to further the understanding of South African coastal dynamics both locally and regionally, and to demonstrate the utility of the database. For example, (i) A study of the Tugela River Mouth revealed shoreline erosion of several hundred metres from 2005 to 2023, which is important information for ongoing and planned catchment projects, such as large dams, that impact fluvial sand yield to the coast. (ii) The consistent extreme accretion south of the Richards Bay port entrance sharply contrasted with the extreme erosion to the north. This highlighted the impacts of various coastal engineering interventions, providing valuable insights into their effectiveness and guiding future coastal management strategies based on the lessons learned. (iii) Studies of the seasonal shoreline responses at St Helena Bay and Cape Town bays (Table Bay and False Bay) showed how the magnitude of these responses was related to the degree of wave exposure. (iv) Regional investigations found interesting distinctions in shoreline evolution: for instance, the west coast typically experienced shoreline retreat during winter, the south coast had less extreme winter erosion, and the east coast, particularly from Port St Johns northward, saw the greatest erosion shifting from winter to spring. This information is invaluable for informing local, regional, and provincial vulnerability assessments and guiding resource allocation more effectively. This study successfully established the first comprehensive database of shoreline dynamics for the entire South African sandy coastline. The data and insights provided could serve as a valuable resource for coastal managers, policymakers, engineers, researchers, and other stakeholders, facilitating the development of informed, effective, and sustainable coastal management strategies that address both current and future challenges. Future research can build on these data and insights by exploring new, unresearched avenues or enhancing methods and technologies to mitigate the identified errors and limitations.
- ItemStrength, durability, thermal performance and sustainability assessment of one-part geopolymer concrete masonry units.(Stellenbosch : Stellenbosch University, 2024-12) Bhayat, Moegamat Tashriq; Babafemi, Adewumi John; De Villiers, Wibke; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: South Africa currently faces a major backlog in the delivery of affordable housing units, which are typically constructed with conventional fired clay-based or cement-based masonry units. Additionally, the production of clay-based and cement-based masonry places a significant impact on the natural environment due to the clay firing and limestone calcination procedures, respectively. The need for alternative masonry units (AMUs) satisfying social, economic and environmental performance is evident. One-part geopolymer cement, produced from the alkali activation of aluminosilicate waste via solid alkali activators, has become an attractive low-carbon cement alternative showcasing superior mechanical, durability and thermal properties. Additionally, the use of alternative concrete aggregates is valuable toward mitigating the intense pressure placed on conventional aggregate resources by the built environment. This study investigated fly ash (FA), ground granulated blast furnace slag (GGBFS) and metakaolin (MK)-based one-part geopolymer concrete-based AMUs synthesised by solid alkali activators comprising sodium hydroxide (NaOH), sodium metasilicate pentahydrate (Na₂SiO₃.5H₂O) and calcium hydroxide (Ca(OH)₂). Additionally, expanded vermiculite (EV) and recycled plastic waste (RESIN8) were substituted as an alternative fine aggregate. The AMUs developed in this study include the FA and GGBFS-based (FABS) and the FA and MK-based (FAMK) units. EV was incorporated at 15% replacement in the development of the EV-based FA and GGBFS (FSEV) unit and the EV-based FA and MK (FMEV) unit. RESIN8 was incorporated at 5% replacement in the development of the RESIN8-based FA and GGBFS (FSR8) unit. All AMUs were subject to ambient curing. The AMUs were tested for their mechanical properties (compressive strength and elastic modulus) and density, durability properties (cold and boiled water absorption, initial rate of absorption, shrinkage and efflorescence extent), thermal properties (thermal conductivity, thermal resistance and thermal transmittance of wall specimens) and sustainability (cost analysis and lifecycle assessment). The average compressive strength of all AMUs satisfies the minimum strength requirement for masonry units. The elastic modulus for all AMUs falls within an acceptable range for masonry materials. The water absorption for all AMUs falls under the absorption limit for concrete-based masonry units. The initial rate of absorption for all AMUs are within an acceptable range for masonry units. All AMUs exhibit higher shrinkage in comparison to conventional concrete. The extent of efflorescence for all AMUs was slight to none. The thermal resistance (R-value) for all AMU wall specimens does not meet the minimum requirement for external walls in South Africa, yet the walls still possess comparable R-values to that of conventional concrete-based masonry units used in South Africa. The cost of the AMUs is roughly two times higher than that of a conventional concrete-based masonry unit, highlighting the economic challenge of adopting one-part geopolymer concrete as an alternative to conventional masonry materials for affordable housing construction. A cradle to gate and cradle to grave life cycle analysis of all AMUs showcased a reduction between 30% to 90% in the carbon footprint when compared to conventional masonry units. Overall, the outcomes of this study showcase the potential of one-part geopolymer cement and alternative aggregates to replace conventional masonry materials.
- ItemAdaptive conversational systems harnessing human expertise in modern chatbots(Stellenbosch : Stellenbosch University, 2024-03) Van Eeden, Christiaan; Du Preez, Johan; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: Chatbots are a rapidly evolving technology integral to the automation of customer service. Traditionally designed around complex if-then-else statements, the technology has seen a paradigm shift towards deep learning techniques for improved flexibility and user interaction. This research proposes a novel approach for training chatbots to learn more effectively from human support agents within automated customer service. Capitalising on the extensive data generated by these agents, we develop a framework to train chatbot models to emulate human-like responses, encapsulating nuances of unique language and individual mannerisms. Using state-of-the-art machine learning and natural language processing techniques, we train these models, achieving more contextually appropriate and authentic responses that accommodate the subtle complexities of human interaction. While commercial large language models (LLMs) like ChatGPT have demonstrated proficiency in customer service automation, they present limitations that could hinder their practical use. Such models, being proprietary, are not available for modification, impeding a company’s capacity to customise them to their specific needs. The costs, both financial and technical, associated with training a bespoke LLM can also be prohibitive for many organisations. Furthermore, these models, with their billions of parameters, require substantial hardware resources and may struggle to manage high-volume, swift interactions typical in a customer service environment. Additionally, due to their general-purpose nature, these models can occasionally produce unpredictable or undesirable responses as they lack specific domain knowledge. Our proposed model, developed on the more manageable GPT-2, offers a tailored, cost-effective, and adaptive solution to these challenges. Although our research is limited in its scope, the findings indicate an improvement in the usability and effectiveness of chatbots trained with our proposed method. This study contributes to the broader field of AI-driven customer service by augmenting the development of more sophisticated and user-friendly chatbot systems.
- ItemEvaluating five mine residue disposal facility case studies using a limit equilibrium method of slices.(Stellenbosch : Stellenbosch University, 2024-03) Greyling, Deon; MacRobert, Charles; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: In this study, five slope failure case studies, associated with mine waste facilities, such as Tailings Storage Facilities and Waste Rock Dumps, are evaluated using the Morgenstern-Price Limit Equilibrium Method of Slices. The available information of each study has been studied and key information about its investigation, soil test work, pre-failure slope geometry, and the piezometric surface have been extracted to develop a set of limit equilibrium slope stability models. The models were used to search for the critical slip surface and to back-calculate the shear strength of the critical soil region that satisfies a computed factor of safety of unity. The critical slip surfaces, determined from the limit equilibrium models, closely resemble the observed performance of the studied slopes. The back-calculated shear strength parameters of the critical soil region are compared to shear strength parameters derived from laboratory test results and typical values published in the literature. The back-calculated values compared well to the shear strength values published in the literature for similar soils. However, in two cases the back-calculated values did not compare well to values derived from laboratory test results. In both cases, direct shear tests were completed on fine-grained soil, which may have led to erroneous results. In two case studies, the back-calculated values compared well to the test results, and in another, the back-calculated shear strength is between the peak and residual shear strengths derived from laboratory test results. For three case studies, an additional analysis was done where two empirical correlations was used to specify the fully softened shear strength and residual shear strength of finegrained soil. The results of the slope stability models showed that the stability of the slopes is sensitive to the porewater pressure regime, emphasising that it should always be appropriately accounted for in the analysis of a slope that has a consequence of failure. Furthermore, the results of the analyses highlight that the engineering properties of the soils comprising the slope and its foundation should be sufficiently characterised and verified through appropriate geotechnical laboratory and in situ test work. The analyses affirm that the Morgenstern-Price Limit Equilibrium Method of Slices is a suitable tool to investigate slope stability provided that the piezometric surface, soil parameters and slope geometry are accurately defined.
- ItemThe influence of pristine graphene on conventional concrete(Stellenbosch : Stellenbosch University, 2024-02) Van Wyk, Abraham Erasmus; Combrinck, Riaan; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: Population growth and rapid urbanisation have brought forth the demand for infrastructure development and the need for durable, low cost and accessible materials. Material compositions such as concrete are commonly used in the built environment. Cement is the primary binding agent in concrete. To produce one metric ton of cement, 0.59 metric ton of CO2 is emitted into the atmosphere (IEA, 2022). The Global Cement & Concrete Association (GCCA) implemented the Net Zero Emissions vision 2050 to reduce the industry’s CO2 emissions. Significantly reducing the amount of cement used in concrete is a viable strategy to lower CO2 emissions during this transitional period towards Net Zero Emissions 2050. This can be achieved by increasing the mechanical and durability properties of concrete whilst reducing the cement content. This research study aims to substantially improve the mechanical and durability properties of conventional concrete by using pristine graphene (PG), which has the potential to ultimately reduce the carbon footprint of cement-based materials (CBMs). PG used in concrete has shown the potential to improve concrete’s mechanical and durability properties significantly, but to unlock the full potential of PG has been one of the greatest challenges. Thus, to unlock the potential of PG and improve the mechanical and durability properties of conventional concrete, different PG application techniques (PGATs) were developed. These PGATs are known as pre-dispersion methods and have two functions namely, 1) reduce the number of layered graphene (exfoliate) and 2) facilitate the distribution of graphene throughout the cementitious matrix. This is done by using three different pre-dispersion methods namely, 1) wet pre-dispersion, 2) dry pre-dispersion and 3) combined (wet and dry) pre-dispersion. All three pre-dispersion methods were used in this study. The PG was obtained from First Graphene Ltd Australia. Two PG forms namely, flake (PUREGRAPH) and agglomerate (PUREGRAPH AQUA) were used in this study. The PG in flake and agglomerate form that was used has a lateral platelet size of 56.9 μm and 52.1 μm, respectively. Additionally, the PGATs aims to resolve some of conventional concrete’s oldest problems. Concrete is described as a heterogeneous material. Therefore, concrete is not uniform in composition due to the difference in stiffness of each traditional constituent (sand, cement and coarse aggregate). The difference in stiffness causes predominantly smaller sized particles to be situated in a region near the surface or aggregates when concrete is formed. This causes porous crystalline structures to form in a region around aggregates which are susceptible to mechanical failure and durability issues. This region is known as the interfacial transition zone (ITZ). Thus, this study strategically positioned PG in the ITZ to improve the bond between the mortar matrix and the surface of coarse aggregate to improve the mechanical and durability properties of conventional concrete. The compressive and in-direct tensile splitting strength of conventional concrete were improved by 18.8% and 7.6%, respectively after 56 days of water curing. Additionally, the amount of crystalline growth on the surface of the coarse aggregate were investigated to determine the bond between the mortar matrix and the surface of the coarse aggregate. The bond strength between the mortar matrix and the surface of the coarse aggregate was quantified by using a direct tensile test referred to as the ITZ strength test. PG improved the bond strength by 22.1% after 28 days of water curing. Furthermore, the oxygen permeability and water absorption were reduced by 42.8% and 17.4%, respectively. Therefore, PG applied to conventional concrete have shown the potential to improve the ITZ which directly influences the mechanical and durability properties. Although significant research still needs to be conducted, this study shows that PG could facilitate greener, stronger and longer lasting concrete as well as provide a partial solution to decrease the global cement consumption which will lower carbon emissions of the cement industry.