Scielo RSS <![CDATA[Journal of the South African Institution of Civil Engineering]]> vol. 62 num. 4 lang. en <![CDATA[SciELO Logo]]> <![CDATA[<b>Geotechnical characterisation and back analysis of a landslide in marl deposit: A case study of Algiers Sahel (coast), Algeria</b>]]> The purposeof this study isto present the results of geotechnical investigations and landslide analysis in a marl deposit at the Sahel (coast) of Algiers in northern Algeria, where many landslides take place in the Plaisancian marls, particularly following rainfall periods each year, causing severe damage to infrastructures and buildings. The physico-mechanical characteristics of the soils obtained from three different sites (El-Achour, Daly-Brahim and Ouled-Fayet) were analysed to identify the mechanism of these landslides. In the study, the laboratory test results providing grain-size distribution, Atterberg limits, water content, shear strength, and compressibility were analysed. The findings showed that, although the soils were characterised by slightly higher plasticity at Ouled-Fayet, they were generally homogeneous in the studied sites. The upper soils, generally weathered, exhibited low shear strength parameters, which are lower than the undisturbed formation beneath. The stability analysis based on limit equilibrium methods (LEM) showed the significant influence of pore water pressures on slope stability, suggesting that the weathered soils are prone to instability processes due to the effect of long rainy periods. <![CDATA[<b>The interception capabilities of slotted drains as pavement surface drainage systems</b>]]> The following two slotted drain installation scenarios were reviewed in this paper: a slotted drain operating individually without a median barrier and a slotted drain operating with an adjacent barrier installed along the longitudinal length of the drain. The interception capability of the two installation scenarios was experimentally reviewed and compared while imitating various conditions typically expected on South African pavements. The applied sheet flow, slotted inlet sizes and pavement slopes (longitudinal and cross slopes) were varied throughout the experiment. Interception efficiencies of the slotted inlets were experimentally calculated as a ratio of total intercepted sheet flow to the total sheet flow applied to the pavement layouts. The sheet flow applied during the experiment was analysed to estimate the rainfall intensities and flow depths that can typically occur on the different pavements for which the interception capability of the slotted inlets was reviewed. It was estimated that rainfall intensities of more than 1 000 mm/hr and flow depths higherthan 10 mm were imitated during the experiment. More than 98% of the maximum applied sheet flow of approximately 3.0 £/s/m was intercepted by the 30 mm slotted inlets regardless of the pavement slope values and type of slotted drain layout. The conclusion reached was that both these slotted drain installation scenarios operating in practice for the conditions tested would have the capability to sufficiently remove the surface water to promote road safety during wet pavement conditions. <![CDATA[<b>Estimation of areai reduction factors using daily rainfall data and a geographically centred approach</b>]]> This paper presents the estimation of geographically centred and probabilistically correct areal reduction factors (ARFs) from daily rainfall data to explain the unique relationship between average design point rainfall and average areal design rainfall estimates at a catchment level in the C5 secondary drainage region in South Africa as a pilot case study. The methodology adopted is based on a modified version of Bell's geographically centred approach. The sample ARF values estimated varied with catchment area, storm duration and return period, hence confirming the probabilistic nature. The derived algorithms also provided improved probabilistic ARF estimates in comparison to the geographically and storm-centred methods currently used in South Africa. At a national level, it is envisaged that the implementation and expansion of the methodology will ultimately contribute towards improved ARF estimations at a catchment level in South Africa. Consequently, the improved ARF estimations will also result in improved design flood estimations. <![CDATA[<b>Methodological approach for the compilation of a water distribution network model using QGIS and EPANET</b>]]> This paper presents the development of a methodological approach based on the integration of free-of-charge open-source software, e.g. QGIS and EPANET, and engineering practices applicable to water distribution network design. The use of QGIS and EPANET, as well as the integration thereof with sound engineering practices and judgement, proved to be both viable and practical to enable practitioners to create a water distribution network model of an existing network in smaller developments or towns. Typically, in the latter smaller developments or towns, the professional cost associated with the additional time required when commercial licensed software is used, could be lower than the actual cost associated with the procurement of the licensed software itself. Hence, the developed process flow diagrams will not only potentially save time and money in comparison to a traditional, manual approach in EPANET, but will also provide guidance to practitioners and assist smaller municipalities in southern Africa facing challenges in terms of outdated records and budget constraints. It is envisaged that the implementation of the overall methodology will contribute to improved water infrastructure planning, design and management, especially in the southern African context where water resources are scarce and service delivery remains a pressing issue. <![CDATA[<b>Effects of the skew angle and road embankment length on the hydraulic performance of bridges on compound channels</b>]]> The flow pattern and bed shear stress are important factors to determine the scour potential regions in river bridges. This study has developed a 3D numerical model to simulate the flow around bridge abutments in a compound channel, and study the simultaneous effects of the bridge skew angle and contraction ratio (i.e. the roadway embankment length normal to the flowto the floodplain width) on the velocity distribution and the bed shear stress. After the model performance was verified, 13 cases were considered with different skew angles and contraction ratios. The results showed that the flow was more complex around the flow-splitting embankment than around the flow-guiding one, because of the flow-roadway embankment confrontation. At a zero skew angle, an increased contraction ratio increased the velocity around both abutments significantly; velocity increased by 67% and 40% when the contraction ratio rose from 0.25 to 0.50 and from 0.50 to 0.75, respectively. This velocity increase around the flow-splitting embankment was also visible for 15°, 30° and 45° angles; unexpectedly, the increase was less for the 45° angle than for the other cases. A shear stress study around the flow-guiding embankment showed that in all three cases an increased skew angle reduced the maximum shear stress mildly at contraction ratios of 0.25 and 0.50, and severely at 0.75. The trend of the maximum shear stress variations around the flow-splitting embankment was different for different contraction ratios - at a contraction ratio of 0.25 it was the highest at 45°, but for contraction ratios of 0.50 and 0.75, the maximum was 30°.