JournalTOCs

Journal of the South African Institution of Civil Engineering
Journal Prestige (SJR): 0.174

Number of Followers: 2

This is an Open Access Journal

Open Access journal
ISSN (Print) 1021-2019 - ISSN (Online) 2309-8775
Published by SciELO

[913 journals]

Water meter replacement and its impact on water consumption, utility
revenue and payback periods
- Abstract: Mechanical water meter accuracy degrades over time due to wear and tear. Based on this premise, many water utilities around the world undertake meter replacement projects. In many instances, these projects neither assess the potential or actual impacts of meter replacement on consumption and utility revenue, nor undertake meter replacement based on a best practice, customised metering policy. From 2013 to 2015, Johannesburg Water (SOC) Limited embarked on a project to replace more than 50 000 mechanical water meters that had not been read over a period of 180 days due to technical faults. This study obtained and analysed two databases of these meters and arrived at a sorted and validated database comprising 3 679 meter replacements. For each meter replacement, twelve months of water consumption data was obtained for the period prior to and after replacement. This study then investigated the impact of replacement on water consumption, utility revenue and payback periods. Some high-level highlights from the study include the following: (i) a metering policy that addresses such issues as efficient meter database management, and the optimum meter replacement age and/or volumetric reading, is critical for any water utility if it is to obtain the best results from meter replacement; (ii) in order to guarantee the highest returns on investment, bulk meters (40 mm and larger) should be prioritised for meter replacement over single-stand residential meters; (iii) the replacement of 20 mm and 25 mm meters with 15 mm meters resulted in more accurate metering of consumption by virtue of increased consumption; and (iv) payback of the 15 mm replacement mechanical meters was achieved within 12 months, with the replacement of 20 mm and 25 mm meters resulting in average monthly revenue increases per property of R266.70 and R203.08 respectively.
Laboratory performance and modelling behaviour of hot-mix asphalt with
recycled crushed glass
- Abstract: In South Africa research is currently under way to determine the suitability of using locally available recycled crushed glass as a partial fine aggregate substitute in the production of asphalt mixes. This paper characterises the laboratory performance of a dense-graded asphalt wearing course mix consisting of 15% recycled crushed glass. The influence of selected antistripping additives on moisture susceptibility was specifically assessed as a variable in the performance evaluation of the glass-asphalt mix as follows: (a) the effect of 1% hydrated lime, (b) the effect of 0.5% liquid antistripping additive, and (c) the effect without the addition of antistripping additive. The effect of these variables on the moisture susceptibility of the glass-asphalt mix was evaluated using the tensile strength ratio parameter supported with a microscopic imaging analysis. Additionally, the stiffness and permanent deformation properties of the glass-asphalt mix that demonstrated optimum resistance to moisture damage was compared to the same mix without crushed glass. The performance properties were evaluated using the Huet-Sayegh model and a polynomial model respectively, which were used particularly to develop performance characterisation models for the glass-asphalt mix. The findings of this study revealed that an anti-stripping additive is essential to meet moisture susceptibility criteria and alleviate moisture damage in dense-graded glass-asphalt mixes. In particular, moisture susceptibility was improved using hydrated lime rather than the liquid antistripping additive. Furthermore, the selected constitutive models were able to effectively characterise the laboratory performance of both mixes, with the glass-asphalt mix demonstrating improved resistance to permanent deformation when compared with the conventional asphalt mix.
Quantifying the economic benefits of gauge changes on the South African
core railway network
- Abstract: In its white paper, the Department of Transport (2017) envisages a future South African core railway network which requires the conversion and construction of over 8 500 km of standard-gauge railway track by 2050. The scale of the project would undeniably have a large cost attached to it, which needs to be well understood before any of the construction takes place. Numerous studies regarding railway gauge have been conducted within South Africa, but no single paper has addressed the issue of which specific railway corridors could economically benefit from a standard-gauge intervention. The purpose of this study was to identify which corridors in the South African core network could potentially benefit from a gauge change intervention. These identified corridors were then economically evaluated to determine which of the corridors would outperform the base case, which was set as the Market Demand Strategy (MDS) plan. Finally, it was determined if any of the corridors identified outperformed the base case, to simulate how the operations of the corridor would be affected. The conclusions of the study indicated that all the corridors in the South African core network should follow the plans proposed in the MDS to achieve the maximum return for the analysis period, except for the Natal corridor. It was identified that the Natal corridor would benefit most from a standard-gauge single line which would run concurrently with the narrow-gauge system transporting containers and other general freight along the corridor.
Physical model study of bedrock scour downstream of dams due to
spillway plunging jets
- Abstract: The erosive power of a free-falling high-velocity water jet, flowing from a dam spillway, could create a scour hole downstream of the dam, endangering the foundation of the dam. Despite extensive research since the 1950s, there is presently no universally agreed method to predict accurately the equilibrium scour depth caused by plunging jets at dams. These formulae yield a large range of equilibrium scour dimensions. The hydrodynamics of plunging jets and the subsequent scour of a rectangular, horizontal and vertical fissured rock bed were investigated in this study by means of a physical model. Equilibrium scour hole geometries for different fissured dimensions (simulated with rectangular concrete blocks tightly prepacked in a regular rectangular matrix), for a range of flow rates, plunge pool depths, and dam height scenarios were experimentally established with 31 model tests. From the results, non-dimensional formulae for the scour hole geometry were developed using multi-linear regression analysis. The scour depth results from this study were compared to various analytical methods found in literature. The equilibrium scour hole depth established in this study best agrees with that predicted by the Critical Pressure method.
The effect of lane blockage on signalised intersection performance
-analysing and modelling
- Abstract: Unexpected stops or entry/exit manoeuvres of vehicles on the road may cause the related lane to become blocked. When this blocking happens in a signalised intersection zone, it also affects intersection performance. Determining the extent of this effect will assist traffic engineers with intersection design and performance analysis. In this study, the effects of Lane Blockage (LB) on intersection performance under various traffic conditions were analysed according to two performance criteria. ANN (Artificial Neural Network) models were also developed to enable the prediction of intersection performance. As a result of the analysis, it was clearly determined that the effect of LB on intersection performance was limited at v/c