Scielo RSS <![CDATA[Journal of the South African Institution of Civil Engineering]]> http://www.scielo.org.za/rss.php?pid=1021-201920190002&lang= vol. 61 num. 2 lang. <![CDATA[SciELO Logo]]> http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za <![CDATA[<b>Evaluation of empirical equations to predict bridge pier scour in a non-cohesive bed under clear-water conditions</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192019000200001&lng=&nrm=iso&tlng= Pier scour has been cited as the main mechanism responsible for the failure of bridges spanning rivers. Despite extensive research since the 1950s, there is no universally agreed upon procedure to accurately predict the equilibrium scour depth. Experimental data was generated by 48 tests with four flows and three pier shapes to evaluate the capability of 30 empirical equations to predict the local scour depth. Fine sand and crushed peach pips were used to address the scaling challenges of the equations by means of an equivalent movability number. The equations yielded a wide range of mostly unreliable results, particularly for the non-cylindrical pier shapes. Nevertheless, the HEC-18 models are recommended, in conjunction with Shen et al (1969), and Ali and Karim (2002), because they rely on the pier Reynolds number, a parameter which is significant in the vortex formation. Prediction models taking the horseshoe vortex into consideration could offer better scour depth predictions. Field data was analysed to improve the HEC-18 equation with new factors for pier shape and armouring for different confidence intervals. The armouring factor is based on the particle Reynolds number as opposed to the widely adopted critical velocity, and achieves considerably less scatter about the line of equality despite under-predictions for the cylindrical piers. Alternatively, a diagram comparable to the Modified Liu Diagram has the potential to predict bridge pier scour even though the pier structure parameters are omitted. Further research and improved prediction models should be considered, particularly advanced numerical models which are becoming increasingly feasible. <![CDATA[<b>The influence of gradient on saturation flow rate at signalised intersections</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192019000200002&lng=&nrm=iso&tlng= Saturation flow rate is the maximum hourly traffic volume per lane that can be accommodated through an intersection, and is used in the design and analysis of signalised intersections and traffic signal plans. The most widely applied method to estimate saturation flow rate is provided by the Highway Capacity Manual (HCM), which proposes default values obtained from USA empirical data for application in saturation flow rate calculations. This study considers the applicability of the HCM proposed base saturation flow rates, and particularly the adjustment factors for gradient on saturation flow in the South African context. The data for this research was collected by author ES Viljoen for use in her dissertation conducted in the final year of the BEng degree at Stellenbosch University. The influence of approach lane gradient on saturation flow rate was investigated for application in the South African environment. The results of this research indicate that the HCM underestimates the influence of approach gradient on saturation flow rate, a similar finding to other international research. The standard use of a base saturation flow rate of 1 900 passenger cars per hour per lane for South African conditions was also commented on. HCM methods do not take into account the influence of speed limit on saturation flow rate, which has been shown to significantly affect saturation flow rate in numerous research projects, and is also commented on in this paper for zones with a 60 km/h and 80 km/h speed limit. <![CDATA[<b>Artificial aeration of stepped spillways by crest piers and flares for the mitigation of cavitation damage</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192019000200003&lng=&nrm=iso&tlng= Stepped spillways are one of the oldest spillway designs dating back to 500 B.C. With technical advances in Roller Compacted Concrete (RCC) construction, the stepped spillway has become increasingly popular over recent decades. However, the use of this spillway is limited to a maximum safe unit discharge of 25 m²/s due to the risk of cavitation. In order to increase the discharge capacity on stepped spillways, various crest pier designs were introduced for flow aeration, thereby reducing the risk of cavitation damage. These pier designs were investigated on two physical models, constructed on a scale of 1:15 and 1:50, both with a standard ogee crest profile which transit to a stepped spillway chute. Air concentration was recorded along the pseudo-bottom, while pressures were measured at the step riser. The results of the 1:15 scale model indicated that the implementation of a short bullnose pier increased the safe unit discharge capacity to 30 rm/s. The innovative Flaring Gate Pier design, which was adapted on existing spillways in China, with reported design prototype unit discharges exceeding 200 m2/s, was investigated on the 1:50 scale model. Based on the experimental results of the current study, the safe unit discharge capacity (i.e. a discharge satisfying the relevant criteria defined for this study) was increased to 50 m2/s with an X-shape Flare Gate Pier (FGP) on the spillway crest. <![CDATA[<b>Understanding public transport needs in Cape Town's informal settlements: a Best-Worst-Scaling approach</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192019000200004&lng=&nrm=iso&tlng= A poor understanding of the needs of people living in informal settlements has often resulted in these needs being assumed and misunderstood due to the lack of proper public consultation or participation. Because of this, South Africa's transport sector, and by extension many other public sectors, faces various challenges. Knowing that public transport is the dominant mode of transport in informal settlements, a better understanding of its challenges as experienced by its commuters is essential for the development of informal settlement upgrading policies. The research in this paper uses Best-Worst-Scaling (BWS) - part of the family of discrete choice models - as a survey and analysis tool for rating and ranking public transport-related challenges of 290 randomly selected commuters from six different informal settlements in Cape Town. The most important features deduced from the public transport experience (PTE) study include (1) Walking Safety, (2) Personal Safety, (3) Unsafe Driving, (4) Overcrowding and (5) Walking Distance. There is no apparent trend in the variance between the choices of men and women. However, there is a significant variance of choices across the respective locations, and - for most attributes - between mode users. This suggests that, with respect to public transport infrastructure upgrading, contextual factors, determined by one's environment, dominate experiences and perceptions, rather than socio-demographic factors. <![CDATA[<b>Stormwater runoff quality on an urban highway in South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192019000200005&lng=&nrm=iso&tlng= Roadway sediment and stormwater runoff were sampled from a 15 km section of the R300 freeway located in the greater Cape Town area, South Africa. Grab samples were collected over a four-month period in 2016 and analysed for metals, hydrocarbons and nutrients. The metal concentration profiles were similar in sediment and runoff samples. The primary pollutants identified in the highway runoff were aluminium, copper, lead, manganese, nitrogen, phosphorus, zinc, total suspended solids (TSS), and oil and grease. The concentrations of each of these elements, barring lead, exceeded the national effluent water quality guidelines. Large volumes of macro pollutants such as cigarettes, plastic and packaging were also observed. The results of this research indicate that Sustainable Drainage Systems (SuDS) should be used in conjunction with highways, particularly where runoff may influence a sensitive or valuable aquatic ecosystem, as it can be a significant non-point source of pollution. <![CDATA[<b>The collapsible nature of residual granite soils of the Cape Granite Suite</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192019000200006&lng=&nrm=iso&tlng= Roadway sediment and stormwater runoff were sampled from a 15 km section of the R300 freeway located in the greater Cape Town area, South Africa. Grab samples were collected over a four-month period in 2016 and analysed for metals, hydrocarbons and nutrients. The metal concentration profiles were similar in sediment and runoff samples. The primary pollutants identified in the highway runoff were aluminium, copper, lead, manganese, nitrogen, phosphorus, zinc, total suspended solids (TSS), and oil and grease. The concentrations of each of these elements, barring lead, exceeded the national effluent water quality guidelines. Large volumes of macro pollutants such as cigarettes, plastic and packaging were also observed. The results of this research indicate that Sustainable Drainage Systems (SuDS) should be used in conjunction with highways, particularly where runoff may influence a sensitive or valuable aquatic ecosystem, as it can be a significant non-point source of pollution.