Scielo RSS <![CDATA[Journal of the South African Institution of Civil Engineering]]> vol. 62 num. 2 lang. es <![CDATA[SciELO Logo]]> <![CDATA[<b>Mechanical behaviour of semi-rigid connections coupling two concrete segmental linings</b>]]> This paper describes the use of segment joints in shield-driven tunnel linings. The opening of segment joints due to the application of a bending moment under different levels of axial stress is studied. The main focus is the mechanical behaviour of the joints, which are considered to be semi-rigid, and the moment-rotation behaviour of the joint. A physically based mathematical model is proposed based on the joint dimensions and material properties. Considering joints connected by two long curved bolts as an example, the model parameters are evaluated, and the moment-rotation curves for the joint are presented. The model distinguishes joint behaviour before and after opening, and agrees well with the real mechanical behaviour of the joints. A comparison with previous experiments on segment joints and with Janssen's and Gladwell's models is provided, and the proposed model is found to be accurate and universal. <![CDATA[<b>Laboratory and field investigations in granular soils to correlate relative density, relative compaction and grain size</b>]]> An attempt has been made to correlate relative density and relative compaction based on laboratory and field test data. In this investigation, 185 sandy soil samples were tested in the laboratory. The experimental investigations include classification tests, maximum and minimum density tests, and standard and modified Proctor and in-situ density tests. The values of the dry unit weight of these samples obtained by performing different tests fall between 14.7 kN/m³ and 20.8 kN/m³. Based on these results, linear and multivariate regression analyses were carried out to (a) relate relative compaction and relative density, (b) relate maximum (e max) and minimum void ratios (e min), and (c) express e max and e min in terms of median grain size (D50) and uniformity coefficient (Cu). Experimental and predicted values varied ± 5%, with a 95% confidence interval for the relation between relative compaction and relative density, and for other relations the variation was ± 10%. The proposed equations were validated using a new data set which had not been used for the development of the correlations. Proposed equations were also compared with equations presented by various other researchers. Validation of the proposed equations suggests that these equations may be used for future prediction of the respective variables. <![CDATA[<b>The liquefaction potential of the upper quaternary sands of the Cape Flats, Western Cape, South Africa</b>]]> Liquefaction of saturated cohesionless soils as a result of earthquake-induced ground shaking is a major concern for structures constructed within or on these soils. During an earthquake, shear waves propagate through the ground, generating shear stresses and strains that are cyclic in nature, causing the soil grains to rearrange into a denser state of packing. This process is too rapid for drainage to occur, which results in an increase in pore water pressure and a decrease in effective stress and shear resistance of the soil. The occurrence of a seismic event associated with the Milnerton Fault line extending below the Cape Flats, a low-lying sand-covered area connecting the Cape Peninsula with the southwestern Cape mainland of South Africa, can cause extensive damage to the largely inadequate infrastructure characterising the area. To evaluate the susceptibility of Cape Flats sand to undergo liquefaction during and after a seismic event, the empirical SPT-based method put forth by Idriss & Boulanger (2004) was used to assess the cyclic liquefaction potential of dense, dilative sands, whereas the CPT-based method published by Robertson (2016) was used to assess the volumetric response of the sands during undrained shear. Resistance of the Cape Flats sands to liquefy at probable earthquake moment magnitude and acceleration values of M = 6.0 and a max= 0.15 g respectively, was noted. Robertson's normalised Soil Behaviour Type (SBTn) chart revealed mostly dilative sands and silty sands susceptible to cyclic liquefaction. Loose, contractive sands prone to flow liquefaction are present, although limited in occurrence and extent. <![CDATA[<b>Warrants for roundabouts and other traffic control devices</b>]]> There are many warrants for traffic signals, but no definitive warrant for roundabouts. Some references (e.g. TRB 2000) give guidelines, and refer to the capacities of roundabouts and TWSC (two-way stop control), but capacities address the upper limit of the control device, not the lower values which would justify, or warrant, a change in control. Other references refer to the need for a roundabout warrant but do not develop one. One paper by Sampson and Meijer (1999) discussed potential warrants, but no recommendation was made. In this paper the role of roundabouts and mini-circles in filling the large gap between where stop control is no longer ideal, and where traffic signals are required, is examined. It is found that there are many considerations in addition to volume or delay that need to be taken into account when deciding on whether to implement roundabout type control, but as a rule of thumb, if the average queue at a stop control exceeds two (2Q) during the peak hour, roundabouts will improve the traffic flow, and if the queue totals around ten or more (10Q), then the roundabout is likely to have reached its capacity. <![CDATA[<b>The cost-effectiveness of water augmentation and management: Assessing the Unit Reference Value</b>]]> As societies develop, the problem of securing and mobilising adequate water resources to support and sustain economic and social activities increases in complexity. As a cost-effectiveness measure the use of the Unit Reference Value (URV) has become standard practice in South African water resource management and development. It is informative and easy to understand. These two attributes inspire confidence and an ever-greater uptake of its use in evaluating suggested courses of action to be taken by society in ensuring their future. Deviations in how an URV is calculated emerge due to both the diversification of its user base and the dynamic nature of the contexts in which it is applied. Such developments add to the pluralistic framings within which research and decision-makers operate. We provide three sub-types of URV application, and caution against comparing URVs across categories. To mitigate possible confusion, we propose the development of standards/rules for the interpretation of URVs.