Scielo RSS <![CDATA[Journal of the South African Institution of Civil Engineering]]> vol. 51 num. 1 lang. pt <![CDATA[SciELO Logo]]> <![CDATA[<b>Practical implications of the relation between the clay mineral content and the Plasticity Index of dolerite road construction material</b>]]> Naturally occurring road building materials, suitable for the higher-quality upper strata of road pavements (base and subbase layers), are systematically being depleted, resulting in the haulage of alternative material over increasing distances or the introduction of more expensive commercially manufactured materials. For this reason the naturally occurring materials have to be better assessed and utilised. The weathered rock most widely used for road construction in South Africa, yet also notorious for its variability and propensity to marginal behaviour, is dolerite. Tests developed for assessing the suitability of road building materials have, in the case of dolerite, often misled design engineers and technicians, to the point that the material is rather avoided if there is any suspicion of its quality being marginal. If the behaviour of dolerite under various environmental conditions were to be better understood, the assessment tests might also be improved, as well as being more effectively applied. This paper deals with the findings and recommendations resulting from research in this regard, especially the relationship between the Plasticity Index (PI) and the smectite content of dolerites in areas where the Weinert N-value is below 3, and its implications. It was found that there is a distinct correlation between the PI of decomposed dolerite gravel and its smectite content, and also that using the minus 0,425 mm material for the standard PI test does not adequately expose the smectite in freshly crushed dolerite rock. A rational explanation is presented for the short-term decomposition of stockpiled weathered dolerite. The results of this investigation indicate that for optimum durability, even dolerite gravel with a barely measurable smectite content should be treated (i.e. with lime) when used for base and subbase layers, and crushed dolerite rock intended for Crushed Rock (G1) base should be treated similarly. <![CDATA[<b>Public standpipe design and maintenance for rural South Africa</b>]]> The public standpipe is the user interface of most rural water systems in South Africa. Despite the renewed focus on providing safe water for all South Africans, field surveys throughout the country show that public standpipes are generally in a deplorable condition. As these standpipes contribute only about 1% or less to the overall cost of rural water-supply systems, this paper argues that the public standpipe deserves more engineering attention during design, construction and maintenance, without having a significant cost implication. The paper systematically lists the relatively simple design considerations, with quantitative guidelines where applicable, and gives multiple illustrations of common mistakes encountered during three field surveys conducted in the Venda region during 2006, 2007 and 2008. <![CDATA[<b>Experimentally applied earthquakes and associated loading on a full-scale dry-stacked masonry structure</b>]]> This paper describes some practical aspects of testing full-scale structures under realistic earthquake loading. A method of filtering earthquake signals so that they can be applied by servo-hydraulic test machines with limited displacement capabilities is presented. Two standard high-pass filtering methods, the moving average and the 4th order Butterworth, are considered. Both filters produce very similar results. The El Centro, Northridge and Llolleo earthquakes are considered as case studies. They were filtered and applied to a shaking table carrying a full-scale dry-stacked masonry structure. The table's displacements and accelerations were measured and compared with the filtered curves. The measured displacements showed good agreement with the filtered earthquake signal. The error in the actual applied (measured) accelerations was much greater due to the fact that the tests were carried out in displacement (not acceleration) control, and to the testing system noise (around 13 Hz). The response spectra for the filtered, unfiltered and measured accelerations for the three earthquakes were computed and compared with design earthquake spectra. It was found that at the natural period of the test structure considered, the response spectrum from the original earthquake accelerations and from the filtered/applied accelerations were almost the same. <![CDATA[<b>The issue of personal safety on dolomite</b>: <b>a probability-based evaluation with respect to single-storey residential houses</b>]]> In refining the principles supporting the safe and judicious use of land, the Council for Geoscience (CGS) is researching the use of a risk-based evaluation of the influence of development density on personal safety. This paper considers single-storey dwelling houses and is the first in a series that will also consider multi-storey and mixed-use developments. In much the same way that rainfall statistics are used to calculate flood events in order to control development by restricting it to above a fixed return period flood line, is it proposed to expand and apply the frequencies of sinkhole occurrence in order to arrive at a more rigorous expression of acceptable development densities for the eight "Inherent Risk Classes". A number of probability concepts are used in determining the development density. Depending on the incidence of each probability, it has been possible to determine the risk associated with development on dolomite for a single-storey dwelling. Recommended population densities are proposed for each Inherent Risk Class, with the exceptions of Risk Classes 6, 7 and 8, where no residential development is catered for, in line with industry standards.