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http://www.scielo.org.za/rss.php?pid=1021-201920190003&lang=en
vol. 61 num. 3 lang. en<![CDATA[SciELO Logo]]>http://www.scielo.org.za/img/en/fbpelogp.gif
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<![CDATA[<b>Developing a hydraulic jump length model on horizontal rough beds</b>]]>
http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192019000300001&lng=en&nrm=iso&tlng=en
Hydraulic jumps play an important role in the dissipation of kinetic energy downstream of hydraulic structures. The roughness of the stilling basin increases energy loss and will affect the hydraulic jump length. In this research, to estimate hydraulic jump length and consider roughness, a semi-analytical equation with unspecified coefficient was developed. Then, 244 sets of laboratory data were used to determine the coefficient of equation. The first series of data was related to a flume with a width of 20 cm and Froude number in the range of 1.1 to 5. The second series of data was obtained from a flume with a width of 50 cm and Froude number in the range of 1.02 to 9.19. USBR data was also used to increase the Froude number range as the third series of data. The results showed that the hydraulic jump length obtained from this model is a function of upstream and downstream depths, upstream Froude number, and bed roughness. It was found that the hydraulic jump length obtained from this model has an error of about 8% in comparison with observational values. In addition, according to the model, increasing roughness will reduce the length of the hydraulic jump.<![CDATA[<b>A case for the adoption of decentralised reinforcement learning for the control of traffic flow on South African highways</b>]]>
http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192019000300002&lng=en&nrm=iso&tlng=en
As an alternative to capacity expansion, various dynamic highway traffic control measures have been introduced. Ramp metering and variable speed limits are often considered to be effective dynamic highway control measures. Typically, these control measures have been employed in conjunction with either optimal control methods or online feedback control. One shortcoming of feedback control is that it provides no guarantee of optimality with respect to the chosen metering rate or speed limit. Optimal control approaches, on the other hand, are limited in respect of their applicability to large traffic networks due to their significant computational expense. Reinforcement learning is an alternative solution approach, in which an agent learns a near-optimal control strategy in an online manner, with a smaller computational overhead than those of optimal control approaches. In this paper an empirical case is made for the adoption of a decentralised reinforcement learning approach towards solving the control problems posed by both ramp metering and variable speed limits simultaneously, and in an online manner. The effectiveness of this approach is evaluated in the context of a microscopic traffic simulation model of a section of the N1 national highway outbound from Cape Town in South Africa's Western Cape Province.<![CDATA[<b>Implementation of a performance-grade bitumen specification in South Africa</b>]]>
http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192019000300003&lng=en&nrm=iso&tlng=en
South Africa has been experiencing higher traffic volumes and heavier loads over the past several years. This has been accompanied by an increase in premature asphalt failures. Selection of the appropriate asphalt binder is critical for improving performance. Empirical bitumen testing has increasingly failed to relate test results to pavement performance, as the traffic volume and loading have changed. Moreover, empirical tests cannot effectively characterise polymer-modified bitumens that are increasingly being used in South Africa. This changing environment calls for the establishment of specifications based on fundamental engineering properties which relate to actual pavement performance. This paper discusses the fundamental principles of the performance grade (PG) specification being introduced in South Africa. It explains how these fundamental principles create a rational framework for the specification, and present a clear set of compliance criteria to ensure the optimal selection of bituminous binders. The reasons for transitioning to a PG specification are discussed, along with the basis of the specification, rheological concepts, measurements required to characterise bituminous binders, and the simulation of ageing in relation to durability. The framework of the specification, including test procedures, provisional compliance limits and mandatory reporting of test results as an interim measure, are discussed in this paper. Finally, some test results received to date for selected typical South African binders are reported and evaluated. These results indicate that current binders being used in South Africa can easily conform to the proposed PG specification in terms of deformation requirements without any disruption to the processes of the refineries or secondary manufacturers. The fatigue properties of binders are still under evaluation and thus not included in the specification framework. Only information gathered will inform the final decision.<![CDATA[<b>Monitoring permeability potential of hot mix asphalt via binary aggregate packing principles correlated with Bailey ratios and porosity principles</b>]]>
http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192019000300004&lng=en&nrm=iso&tlng=en
Asphalt mix designs tend to optimise the load transfer via aggregate skeletons as main mechanism to provide rut resistance, often to the detriment of durability. Permeability, as a significant durability indicator, is more difficult to measure in the field than in the laboratory. Voids in the asphalt mix have a critical zone where an increase in voids is exponentially linked to permeability. This zone is where voids start to become increasingly interconnected. The aggregate grading envelope characteristics can provide an indication of the interconnectedness of the voids to enhance quality control. New rational Bailey Method Ratios (BMRs) were defined with contiguous aggregate fractions in the numerator and denominator. This allows also for porosity calculation using the Dominant Aggregate Size Range (DASR) method. The Binary Aggregate Packing (BAP) triangle porosity diagrams provide insight into the link between porosity and interconnected voids. The wall and the loosening effects create additional porosity (voids) with increased probability of interconnectedness. Clear threshold zones of interconnected voids can be determined with BAP coarse/fine mass ratios. The latter is the inverse of the rational BMRs. It allows for simple spreadsheet calculations of porosity and coarse/fine mass ratio as a screening tool for probable permeability via benchmark analysis. Reworked data sets demonstrated how the inverse of BMRs could show potential for interconnectedness of voids and, therefore, permeability propensity.<![CDATA[<b>Validating traffic models using large-scale Automatic Number Plate Recognition (ANPR) data</b>]]>
http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192019000300005&lng=en&nrm=iso&tlng=en
The development of reliable strategic traffic models relies on comprehensive and accurate data, but traditional survey methods are time-consuming and expensive. Manual surveys often yield small samples that require estimated expansion factors to enable the data to represent the population. Modellers have turned to new data sourced from various electronic devices to improve the reliability of the data. Automatic Number Plate Recognition (ANPR) data is one such data source that can be used to extract travel time, speed and partial origin-destination (OD) information. This study assesses ANPR data in terms of its comprehensiveness and accuracy, and shows how it can be used for the validation of strategic traffic models. Data was obtained from the Gauteng freeway system's Open Road Tolling (ORT) gantries for a period of several months. A new methodology is developed to process traffic model outputs such that they are directly comparable to the partial origin-destination outputs derived from the ANPR data. It is shown that comparing the model distribution against observed ANPR data highlights potential trip distribution issues that are not detected using standard model validation techniques.<![CDATA[<b>Estimating elastic moduli of sandstones using two-dimensional pore space images</b>]]>
http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192019000300006&lng=en&nrm=iso&tlng=en
The elastic moduli (shear modulus and bulk modulus) of two different sandstones are estimated from two-dimensional images of the pore space. An image analysis technique was used to extract the area and perimeter of each pore. The shearablity and compressibility of each pore were calculated using the boundary element method and a perimeter-area scaling law. The effective shear modulus and bulk modulus of the rock were then estimated using the area-weighted mean pore shearablity, pore compressiblity and the differential effective medium theory. The method was applied to Fontainebleau and Berea sandstones. Comparison with experimental values of the shear moduli and bulk moduli showed good agreement.