Pub Date : 2023-10-04DOI: 10.17159/2309-8775/2023/v65n3a4
M Moelich, G van Zijl, W de Villiers
In the quest for sufficient and comfortable housing in South Africa, attention to building orientation and thermal transmittance principles has significantly improved thermal performance in local houses. Thermal simulation and monitoring of houses in the Joe Slovo Phase Three development in Cape Town confirms improved performance by solar radiation blockage and shading. This paper simulates the thermal performance of a housing unit in this development. The house was instrumented with thermocouples, and monitored from March to December 2013 by Sustainable Energy Africa in collaboration with the National Department of Human Settlements. Sustainable Energy Africa reported significant improvement when compared to a nearby traditional Reconstruction and Development Programme house that had been monitored during the same period. With the benefit of the monitored thermal data, complete drawings, and specification details of the Joe Slovo Phase Three unit, the current research modelled and calibrated a simulation model in DesignBuilder. DesignBuilder was selected given its accreditation status for Green Star Rating of buildings in South Africa. An additional motivation for investigating this unit was the availability of recorded weather data from the nearby Cape Town International Airport, captured in the DesignBuilder climate data base for 2013, which was assumed relevant in lieu of complete weather station data measured at the location of the housing unit. The study aimed to simulate the monitored temperatures in the house with acceptable agreement, and to investigate further potential improvement in occupant thermal comfort by alternative 3D-printed concrete walling developed by the authors. Systematic finite element analysis (FEA) iteratively solved cavity radiation and convection in wall cavities to calibrate thermal transmittance parameters for DesignBuilder. The FEA results acceptably simulated temperatures monitored in this physical wall experiment. The calibrated DesignBuilder model simulated the indoor temperatures of the monitored house with acceptable agreement, and predicted significant improvement in occupant thermal comfort if the walls were 3D-printed with a particular cross-sectional design.
{"title":"Thermal performance of cavities in 3DPC building façades","authors":"M Moelich, G van Zijl, W de Villiers","doi":"10.17159/2309-8775/2023/v65n3a4","DOIUrl":"https://doi.org/10.17159/2309-8775/2023/v65n3a4","url":null,"abstract":"In the quest for sufficient and comfortable housing in South Africa, attention to building orientation and thermal transmittance principles has significantly improved thermal performance in local houses. Thermal simulation and monitoring of houses in the Joe Slovo Phase Three development in Cape Town confirms improved performance by solar radiation blockage and shading. This paper simulates the thermal performance of a housing unit in this development. The house was instrumented with thermocouples, and monitored from March to December 2013 by Sustainable Energy Africa in collaboration with the National Department of Human Settlements. Sustainable Energy Africa reported significant improvement when compared to a nearby traditional Reconstruction and Development Programme house that had been monitored during the same period. With the benefit of the monitored thermal data, complete drawings, and specification details of the Joe Slovo Phase Three unit, the current research modelled and calibrated a simulation model in DesignBuilder. DesignBuilder was selected given its accreditation status for Green Star Rating of buildings in South Africa. An additional motivation for investigating this unit was the availability of recorded weather data from the nearby Cape Town International Airport, captured in the DesignBuilder climate data base for 2013, which was assumed relevant in lieu of complete weather station data measured at the location of the housing unit. The study aimed to simulate the monitored temperatures in the house with acceptable agreement, and to investigate further potential improvement in occupant thermal comfort by alternative 3D-printed concrete walling developed by the authors. Systematic finite element analysis (FEA) iteratively solved cavity radiation and convection in wall cavities to calibrate thermal transmittance parameters for DesignBuilder. The FEA results acceptably simulated temperatures monitored in this physical wall experiment. The calibrated DesignBuilder model simulated the indoor temperatures of the monitored house with acceptable agreement, and predicted significant improvement in occupant thermal comfort if the walls were 3D-printed with a particular cross-sectional design.","PeriodicalId":54762,"journal":{"name":"Journal of the South African Institution of Civil Engineering","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135646762","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-10-04DOI: 10.17159/2309-8775/2023/v65n3a1
J A du Plessis, S Masule
South Africa receives an average annual rainfall of about 450 mm. Hydraulic structures are typically constructed to either store or manage the excess water resulting from runoff. These hydraulic structures are designed and evaluated to withstand a particular flood peak that can occur in its catchment area. Adequate flow or rainfall records may often not be available to enable a reliable flood estimation. In South Africa an empirical estimation method (the Regional Maximum Flood (RMF)) that utilises regional envelope curves to estimate the maximum observed flood peaks that can be expected in a region, is available. The RMF method adopted by Kovács in 1980, and revised in 1988, is robust and simple to use. The current research revisits the method as applicable to South Africa, and presents an update of the method, taking more than 30 years of additional data and a revised regionalisation approach into consideration. Numerous previous researchers evaluated the RMF method and concluded that the method needs to be updated. It was identified that recently observed flood peaks exceeded the existing RMF envelopes. It was further identified that the Kovács regionalisation process is inconsistent, and a revised regionalisation approach was proposed. The revised regionalisation resulted in 15 RMF K regions and their associated envelope curves. The new RMF K regions are smaller, with the highest K value equal to 5.8 and the lowest value 2.8. The recommended envelope curves were drawn 15% above the maximum observed flood peaks for each region, allowing for possible future climate impacts. The revised RMF envelope curves are considered to adequately represent the RMFs in South Africa and are therefore applicable for determining the expected maximum regional flood at any site in South Africa.
{"title":"Revised Regional Maximum Flood (RMF) method and regionalisation","authors":"J A du Plessis, S Masule","doi":"10.17159/2309-8775/2023/v65n3a1","DOIUrl":"https://doi.org/10.17159/2309-8775/2023/v65n3a1","url":null,"abstract":"South Africa receives an average annual rainfall of about 450 mm. Hydraulic structures are typically constructed to either store or manage the excess water resulting from runoff. These hydraulic structures are designed and evaluated to withstand a particular flood peak that can occur in its catchment area. Adequate flow or rainfall records may often not be available to enable a reliable flood estimation. In South Africa an empirical estimation method (the Regional Maximum Flood (RMF)) that utilises regional envelope curves to estimate the maximum observed flood peaks that can be expected in a region, is available. The RMF method adopted by Kovács in 1980, and revised in 1988, is robust and simple to use. The current research revisits the method as applicable to South Africa, and presents an update of the method, taking more than 30 years of additional data and a revised regionalisation approach into consideration. Numerous previous researchers evaluated the RMF method and concluded that the method needs to be updated. It was identified that recently observed flood peaks exceeded the existing RMF envelopes. It was further identified that the Kovács regionalisation process is inconsistent, and a revised regionalisation approach was proposed. The revised regionalisation resulted in 15 RMF K regions and their associated envelope curves. The new RMF K regions are smaller, with the highest K value equal to 5.8 and the lowest value 2.8. The recommended envelope curves were drawn 15% above the maximum observed flood peaks for each region, allowing for possible future climate impacts. The revised RMF envelope curves are considered to adequately represent the RMFs in South Africa and are therefore applicable for determining the expected maximum regional flood at any site in South Africa.","PeriodicalId":54762,"journal":{"name":"Journal of the South African Institution of Civil Engineering","volume":"36 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135646541","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-10-04DOI: 10.17159/2309-8775/2023/v65n3a2
A Ilemobade
It is mandatory in South Africa that water for firefighting is included in the demand estimates input when designing municipal water networks. To this end, guidelines for determining fire flows for different risk categories have been developed. The most commonly used guidelines are the South African National Standard (SANS) 10090 of 2018 and the Department of Human Settlements (DHS) guide of 2019 (also called the Red Book). The evolution of the built environment, firefighting technologies and approaches, and the availability of freshwater resources all require that the fire flows in the guidelines are current and adequately protect communities from the devastating impacts of fires - this while conserving depleting freshwater resources and contributing to optimal water network design. Currently, empirical research into the appropriateness of the fire flows in SANS 10090 and the Red Book to firefighting efforts in South African municipalities is limited. This paper therefore compares water for firefighting in these two guidelines with some international companions and local firefighting data, and also compares similar data from the six studies published on this topic in South Africa. Some highlights from this investigation include: (i) the fire risk categories and fire flows in SANS 10090 and the Red Book are misaligned, and are contradictory in at least one instance; (ii) when compared with firefighting data, the fire flows in SANS 10090 and the Red Book are conservative; (iii) a significant percentage of fires were extinguished between 30 and 120 minutes; (iv) 10 kl or less of water was employed to extinguish more than 87% of fires; and (v) the frequencies of fires were positively related to dry and/or cold weather conditions.
在南非，在设计市政供水网络时，消防用水必须包含在需求估算输入中。为此目的，制定了确定不同风险类别的火灾流量的准则。最常用的指南是2018年的南非国家标准(SANS) 10090和2019年的人类住区部(DHS)指南(也称为红皮书)。建筑环境的发展、消防技术和方法以及淡水资源的可用性都要求指南中的消防流是最新的，并充分保护社区免受火灾的破坏性影响，同时保护耗尽的淡水资源并促进最佳水网设计。目前，关于SANS 10090和红皮书中火灾流对南非市政消防工作的适当性的实证研究是有限的。因此，本文将这两份指南中的消防用水与一些国际伙伴和当地消防数据进行了比较，并比较了南非就此主题发表的六项研究的类似数据。本调查的一些亮点包括:(i) SANS 10090和红皮书中的火灾风险类别和火灾流不一致，并且至少在一个实例中存在矛盾;(ii)与消防数据相比，SANS 10090和红皮书中的火流是保守的;(iii)相当大比例的火灾在30至120分钟内被扑灭;(iv)灭火用水量不超过10千升(kl);(v)火灾的频率与干燥和/或寒冷的天气条件呈正相关。
{"title":"The status of water for firefighting in South Africa","authors":"A Ilemobade","doi":"10.17159/2309-8775/2023/v65n3a2","DOIUrl":"https://doi.org/10.17159/2309-8775/2023/v65n3a2","url":null,"abstract":"It is mandatory in South Africa that water for firefighting is included in the demand estimates input when designing municipal water networks. To this end, guidelines for determining fire flows for different risk categories have been developed. The most commonly used guidelines are the South African National Standard (SANS) 10090 of 2018 and the Department of Human Settlements (DHS) guide of 2019 (also called the Red Book). The evolution of the built environment, firefighting technologies and approaches, and the availability of freshwater resources all require that the fire flows in the guidelines are current and adequately protect communities from the devastating impacts of fires - this while conserving depleting freshwater resources and contributing to optimal water network design. Currently, empirical research into the appropriateness of the fire flows in SANS 10090 and the Red Book to firefighting efforts in South African municipalities is limited. This paper therefore compares water for firefighting in these two guidelines with some international companions and local firefighting data, and also compares similar data from the six studies published on this topic in South Africa. Some highlights from this investigation include: (i) the fire risk categories and fire flows in SANS 10090 and the Red Book are misaligned, and are contradictory in at least one instance; (ii) when compared with firefighting data, the fire flows in SANS 10090 and the Red Book are conservative; (iii) a significant percentage of fires were extinguished between 30 and 120 minutes; (iv) 10 kl or less of water was employed to extinguish more than 87% of fires; and (v) the frequencies of fires were positively related to dry and/or cold weather conditions.","PeriodicalId":54762,"journal":{"name":"Journal of the South African Institution of Civil Engineering","volume":"4 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135646542","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-10-04DOI: 10.17159/2309-8775/2023/v65n3a3
M C Ntaote, G Heymann
Active seismic surface wave tests are tests during which signals are generated by artificial sources such as sledgehammers, drop weights and fixed or variable frequency shakers. A number of active seismic surface wave tests have become popular in the geotechnical industry. Interestingly, different surface wave tests are popular in different regions of the world, presumably because the tests require different equipment, expertise and numerical analysis techniques. Few studies have been done to compare seismic surface wave tests directly. This study investigated the performance of three active seismic surface wave tests, namely the spectral analysis of surface waves (SASW), multi-channel analysis of surface waves (MASW) and continuous surface wave (CSW) tests. This paper reports the performance of the three tests with regard to repeatability, susceptibility to near-field effects, and maximum and minimum measurement depths at both a shallow and a deep bedrock site.
{"title":"Experimental comparison of active seismic surface wave tests on shallow and deep bedrock sites","authors":"M C Ntaote, G Heymann","doi":"10.17159/2309-8775/2023/v65n3a3","DOIUrl":"https://doi.org/10.17159/2309-8775/2023/v65n3a3","url":null,"abstract":"Active seismic surface wave tests are tests during which signals are generated by artificial sources such as sledgehammers, drop weights and fixed or variable frequency shakers. A number of active seismic surface wave tests have become popular in the geotechnical industry. Interestingly, different surface wave tests are popular in different regions of the world, presumably because the tests require different equipment, expertise and numerical analysis techniques. Few studies have been done to compare seismic surface wave tests directly. This study investigated the performance of three active seismic surface wave tests, namely the spectral analysis of surface waves (SASW), multi-channel analysis of surface waves (MASW) and continuous surface wave (CSW) tests. This paper reports the performance of the three tests with regard to repeatability, susceptibility to near-field effects, and maximum and minimum measurement depths at both a shallow and a deep bedrock site.","PeriodicalId":54762,"journal":{"name":"Journal of the South African Institution of Civil Engineering","volume":"209 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135646564","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-06-27DOI: 10.17159/2309-8775/2023/v65n2a1
J. E. van der Merwe
Concrete has traditionally been considered as a material with favourable fire resistance. The development of modern concretes with low permeability has, however, resulted in the increased occurrence of spalling when exposed to fire. Recent fire damage in South Africa during the riots in July 2021 resulted in such damage. This paper presents an overview of explosive spalling of concrete in fire, recent local observations, and developments in the field. It is shown that various (often interrelated) factors influence the susceptibility of concrete to spall in fire, and that much research is still needed to fully understand the phenomenon and, specifically, how to accurately predict its occurrence. Recent observations in South Africa support conclusions in the literature that, as an accidental loading case or as life-safety performance criteria, overall structural integrity is rarely compromised. However, as the use of higher concrete grades increases, the relevance of this risk should be considered by practising engineers.
{"title":"Spalling of concrete in fire -an overview and local relevance","authors":"J. E. van der Merwe","doi":"10.17159/2309-8775/2023/v65n2a1","DOIUrl":"https://doi.org/10.17159/2309-8775/2023/v65n2a1","url":null,"abstract":"Concrete has traditionally been considered as a material with favourable fire resistance. The development of modern concretes with low permeability has, however, resulted in the increased occurrence of spalling when exposed to fire. Recent fire damage in South Africa during the riots in July 2021 resulted in such damage. This paper presents an overview of explosive spalling of concrete in fire, recent local observations, and developments in the field. It is shown that various (often interrelated) factors influence the susceptibility of concrete to spall in fire, and that much research is still needed to fully understand the phenomenon and, specifically, how to accurately predict its occurrence. Recent observations in South Africa support conclusions in the literature that, as an accidental loading case or as life-safety performance criteria, overall structural integrity is rarely compromised. However, as the use of higher concrete grades increases, the relevance of this risk should be considered by practising engineers.","PeriodicalId":54762,"journal":{"name":"Journal of the South African Institution of Civil Engineering","volume":" ","pages":""},"PeriodicalIF":0.4,"publicationDate":"2023-06-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42993527","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-06-27DOI: 10.17159/2309-8775/2023/v65n2a2
J. Wates
For more than 100 years upstreaming has been the dominant raising method for tailings storage facilities in Southern Africa. However, there is a growing view worldwide that upstreaming is inherently less safe than centreline or downstream raising of tailings storage facilities. Considering that more than 90% of the 250 plus operational tailings storing facilities in Southern Africa are upstream raised and cannot economically be converted to, or replaced by, downstream raised facilities, the arguments for and against upstreaming were examined in this study. It was found that no compelling reason exists to ban upstreaming in Southern Africa, provided that failure mechanisms are thoroughly considered to prevent serious design omissions. The ALARP (as low as reasonably practicable) approach is introduced as a practical method to deal with the risk of failure, and its hierarchical application is illustrated.
{"title":"Design criteria for upstream raised tailings storage facilities","authors":"J. Wates","doi":"10.17159/2309-8775/2023/v65n2a2","DOIUrl":"https://doi.org/10.17159/2309-8775/2023/v65n2a2","url":null,"abstract":"For more than 100 years upstreaming has been the dominant raising method for tailings storage facilities in Southern Africa. However, there is a growing view worldwide that upstreaming is inherently less safe than centreline or downstream raising of tailings storage facilities. Considering that more than 90% of the 250 plus operational tailings storing facilities in Southern Africa are upstream raised and cannot economically be converted to, or replaced by, downstream raised facilities, the arguments for and against upstreaming were examined in this study. It was found that no compelling reason exists to ban upstreaming in Southern Africa, provided that failure mechanisms are thoroughly considered to prevent serious design omissions. The ALARP (as low as reasonably practicable) approach is introduced as a practical method to deal with the risk of failure, and its hierarchical application is illustrated.","PeriodicalId":54762,"journal":{"name":"Journal of the South African Institution of Civil Engineering","volume":"1 1","pages":""},"PeriodicalIF":0.4,"publicationDate":"2023-06-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41703330","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-06-27DOI: 10.17159/2309-8775/2023/v65n2a4
K. Braun, N. Bakas, G. Markou, S. Jacobsz
Capturing and understanding the ultimate limit state behaviour of reinforced concrete piles embedded in soil requires the use of advanced tools or the performance of expensive tests. An experiment was performed where reinforced concrete piles embedded in a stiff unsaturated clay profile were load-tested on-site. However, even though in-situ experiments can provide engineers with valuable insight, their cost and time limitations come with restrictions, especially when dealing with a parametric investigation on the soil's material properties, the size of the piles, or the piles' material properties. The objective of this research work was to numerically model the nonlinear mechanical behaviour of laterally loaded full-scale piles through detailed 3D modelling, and perform an in-depth parametric investigation to provide answers to unknown factors that the actual physical experiment could not answer. Furthermore, this work serves as a pilot project that will be used to pave the way in developing multiple soil-structure interaction models that will be used to generate a dataset that helps the creation of predictive models through machine learning algorithms. For the needs of this research work, the reinforced concrete piles were discretised with 8-noded isoparametric hexahedral elements that accounted for cracking through the smeared crack approach. Steel reinforcement bars and stirrups were simulated as embedded rebar elements, while the soil domain was also discretised through 8-noded hexahedral elements. Most of the required material properties assumed during the nonlinear analyses were defined according to relevant laboratory experiments. According to the numerical investigation, it was found that the proposed numerical model has the ability to reproduce the experimental results with high accuracy, while providing in-depth insight on the failure mechanisms for both the soil and reinforced concrete domains.
{"title":"Advanced numerical modelling of the nonlinear mechanical behaviour of a laterally loaded pile embedded in stiff unsaturated clay","authors":"K. Braun, N. Bakas, G. Markou, S. Jacobsz","doi":"10.17159/2309-8775/2023/v65n2a4","DOIUrl":"https://doi.org/10.17159/2309-8775/2023/v65n2a4","url":null,"abstract":"Capturing and understanding the ultimate limit state behaviour of reinforced concrete piles embedded in soil requires the use of advanced tools or the performance of expensive tests. An experiment was performed where reinforced concrete piles embedded in a stiff unsaturated clay profile were load-tested on-site. However, even though in-situ experiments can provide engineers with valuable insight, their cost and time limitations come with restrictions, especially when dealing with a parametric investigation on the soil's material properties, the size of the piles, or the piles' material properties. The objective of this research work was to numerically model the nonlinear mechanical behaviour of laterally loaded full-scale piles through detailed 3D modelling, and perform an in-depth parametric investigation to provide answers to unknown factors that the actual physical experiment could not answer. Furthermore, this work serves as a pilot project that will be used to pave the way in developing multiple soil-structure interaction models that will be used to generate a dataset that helps the creation of predictive models through machine learning algorithms. For the needs of this research work, the reinforced concrete piles were discretised with 8-noded isoparametric hexahedral elements that accounted for cracking through the smeared crack approach. Steel reinforcement bars and stirrups were simulated as embedded rebar elements, while the soil domain was also discretised through 8-noded hexahedral elements. Most of the required material properties assumed during the nonlinear analyses were defined according to relevant laboratory experiments. According to the numerical investigation, it was found that the proposed numerical model has the ability to reproduce the experimental results with high accuracy, while providing in-depth insight on the failure mechanisms for both the soil and reinforced concrete domains.","PeriodicalId":54762,"journal":{"name":"Journal of the South African Institution of Civil Engineering","volume":" ","pages":""},"PeriodicalIF":0.4,"publicationDate":"2023-06-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45953024","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-06-27DOI: 10.17159/2309-8775/2023/v65n2a3
O. Gericke, V. H. Williams
At a flow-gauging weir, the stage or flow depth is normally measured continuously and converted into discharge using a stage-discharge (SD) rating curve (RC). During flood events, the observed water levels often exceed the flow-gauging weir's designed measuring capacity or structural limit. Subsequently, the standard calibration of the flow-gauging weir becomes irrelevant and the extension of the SD RC for above-structure-limit flow conditions is required. This paper attempts to identify a one-size-fits-all approach for the extension of SD RCs by assessing seven indirect hydraulic extension methods and a one-dimensional HEC-RAS modelling approach against direct SD measurements or extension methods at selected flow-gauging sites in South Africa. In considering a ranking-based selection procedure and associated goodness-of-fit (GOF) criteria, the stepped backwater analysis, slope-area method, and 1-D HEC-RAS steady flow modelling proved to be the most appropriate. The other indirect extension methods resulted in larger statistical differences between the at-site benchmark and modelled values. Given that the extension of RCs is significantly more affected by the site and river reach geometry, initial hydraulic conditions, flow regimes, and level of submergence at high discharges than the actual extension method used, it was confirmed that a one-size-fits-all approach cannot be applied for the extension of SD RCs in South Africa.
{"title":"Could a one-size-fits-all approach apply to the extension of stage-discharge relationships at flow-gauging weirs?","authors":"O. Gericke, V. H. Williams","doi":"10.17159/2309-8775/2023/v65n2a3","DOIUrl":"https://doi.org/10.17159/2309-8775/2023/v65n2a3","url":null,"abstract":"At a flow-gauging weir, the stage or flow depth is normally measured continuously and converted into discharge using a stage-discharge (SD) rating curve (RC). During flood events, the observed water levels often exceed the flow-gauging weir's designed measuring capacity or structural limit. Subsequently, the standard calibration of the flow-gauging weir becomes irrelevant and the extension of the SD RC for above-structure-limit flow conditions is required. This paper attempts to identify a one-size-fits-all approach for the extension of SD RCs by assessing seven indirect hydraulic extension methods and a one-dimensional HEC-RAS modelling approach against direct SD measurements or extension methods at selected flow-gauging sites in South Africa. In considering a ranking-based selection procedure and associated goodness-of-fit (GOF) criteria, the stepped backwater analysis, slope-area method, and 1-D HEC-RAS steady flow modelling proved to be the most appropriate. The other indirect extension methods resulted in larger statistical differences between the at-site benchmark and modelled values. Given that the extension of RCs is significantly more affected by the site and river reach geometry, initial hydraulic conditions, flow regimes, and level of submergence at high discharges than the actual extension method used, it was confirmed that a one-size-fits-all approach cannot be applied for the extension of SD RCs in South Africa.","PeriodicalId":54762,"journal":{"name":"Journal of the South African Institution of Civil Engineering","volume":" ","pages":""},"PeriodicalIF":0.4,"publicationDate":"2023-06-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49336191","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-06-27DOI: 10.17159/2309-8775/2023/v65n2a5
J. Bunk
Sinkholes are a common occurrence on dolomitic land in South Africa. Different methods have been used in the past to classify the risk of sinkhole occurrence. The inherent hazard classifications (IHC) of boreholes are compared in this article to actual sinkhole occurrences. The national sinkhole database and the ENGEODE database of boreholes, both belonging to the Council for Geoscience (CGS), were used for this comparison between the IHC of the borehole and the size of the sinkhole that occurred within a 50 m radius. Thus, the sinkholes in the database were used for this comparison that had a borehole located within 50 m from the sinkhole. Four regions were identified and described separately, namely the Far West Rand, the Tshwane and Ekurhuleni Municipalities as separate areas, and the fourth group as the Johannesburg and Sedibeng Municipalities and the Mpumalanga, North West and Northern Cape Provinces. Although a very high percentage has been underestimated (ranging from 42% to 59% for the different regions), there is a relatively good IHC correlation between the hazard classification of the boreholes and the sinkholes (between 56% to 67%). Another problem is that an IHC of 1 to 4 (low to medium risk) was assigned to the boreholes in 17% to 29% of the cases for the different areas, yet sinkholes still formed. These areas are more problematic, since the risk from the drilling has been underestimated. The current methodology to classify boreholes has not proved to be one hundred percent accurate to predict the size of the sinkhole for the area, and several factors have been highlighted that should be taken into account when boreholes are classified. Further research needs be carried out around the discrepancies between the IHC of boreholes compared to actual sinkholes.
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Pub Date : 2023-03-23DOI: 10.17159/2309-8775/2023/v65n1a3
F. Calitz
Urban development in South Africa should be preceded by a preliminary stage geotechnical investigation to facilitate decision-making regarding site selection and project feasibility, and to aid the Environmental Impact Assessment process. These desk studies generally rely on information obtained from published sources, including regional geotechnical maps, typically only available for major urban centres. It is proposed that use be made of pedological information contained in published land type inventories available for most of the country, or resulting from detailed soil mapping surveys. The proposed refined Soils Effects Grouping (SEG) system provides a relatively simple scientifically based tool that allows conversion of pedological information into the relevant geotechnical parlance in accordance with industry-standard parameters suitable for use in preliminary stage geotechnical investigations. Application of this system over a period of more than a decade has provided cost-effective and reasonably accurate results in support of urban planning and Environmental Impact Assessments.
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