Figure 1 - uploaded by Phil Paige-Green
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Prediction of expansive clay soils.
Source publication
The construction of new roads over virgin ground often results in the necessity to cope with problem subgrades. The most problematic of these in southern Africa include expansive soils, collapsible soils, dispersive/erodible soils, saline soils, karst areas, very soft soils and wet areas. These naturally occurring problems are all common in souther...
Contexts in source publication
Context 1
... their nature, smectites will also tend to be more plastic than other clay minerals and a measure of the plasticity index, or better still the activity (ratio of plasticity index to clay fraction) is a good indication of the presence of smectites, this being one of the earliest methods used to indicate potentially expansive soils in South Africa. This culminated in the development of the chart shown in Figure 1 for the preliminary identification of expansive soils (van der Merwe, 1976). It should be noted that the estimates for the degree of swell do not take into account the initial moisture content of the material, assuming that they move from a state of dryness normally used in the laboratory to wet. ...
Citations
... Unproclaimed roads, which are at best gravel roads that do not offer allweather access is a prime example of sub-par infrastructure. According to Paige-Green (2008) these types of roads can have a significant negative impact on the economic well-being of the affected communities and also result in negative environmental impacts (i.e., soil lost due to erosion, dust clouds). ...
... Drainage problems are caused by a lack of diversion of rainwater, which can lead to deterioration of the road structure or pavement surface. This is mostly due to moisture retention within the road prism and in particular within the subgrade soils relating to typical subgrade problems, as described in Table 1 (Paige-Green, 2008). The adverse effects of increase in moisture content on the soil behaviour have also been a major concern among geotechnical and pavement engineers. ...
In situ soil modification is required in order to improve the primary engineering properties of the material to meet a road construction standard. Bio-stabilised soil is an environmentally friendly, cost-effective alternative to imported granular fills, concrete, costly hauling of materials or export to a landfill. In-service soil performance and required maintenance is highly dependent on methods of stabilisation, ranging from expensive mechanical stabilisation to chemical processes. As such, many alternative materials originating from bio-based sources are being explored as potential stabilising additives to improve weak subgrade soils (i.e., dispersive, erodible and collapsible soil, and soft or expansive clays). Some key solutions include the use of bio-derived enzymes, microbes, and polymeric additives to avert road failure caused by water penetration and/or erosion. The role of microbial substrate specialisation has been largely unexplored, since the level of research done on alternative stabilisers consists mostly of small ad hoc studies. In addition, research has focused on a reduction in permeability and an increase in compressive strength using enzymes and polymers, however, the complexity of these products and their implementation for a wide range of soil types and structural applications remain limited. Currently there is a need for more supporting research methodologies and systematic approaches on the implementation of bio-based materials for infrastructure development. This also includes the simplification of bio-based products for potential construction applications. This review provides (a) an overview of soil stabilisation techniques, (b) the primary challenges that lay ahead for future research in bio-based stabilisation products application in the road sector and (c) innovations to address the challenges of using modernised techniques in the road construction industry (i.e., weak subgrade and the required maintenance thereof, as well as the development of potential bio-based additives for unpaved road construction application).
Long distance strategic road and rail transport is one of the four themes of the high-volume transport (HVT) applied research programme funded by Department for International Development (DFID). The HVT programme has been set up to identify transport research priorities in low-income countries (LICs) in Sub-Saharan Africa and South Asia and to deliver a research programme to meet these needs. Closely associated with identifying the research priorities is assessment of the capacity building requirements as well as dissemination of the research outcomes to the relevant authorities in the countries of the two regions to ensure maximum uptake. This final report on long distance strategic road and rail transport provides DFID with information on which to base the decision on the direction and strategy for research to be carried out in Part 2 of the HVT Programme. The report sets out the findings of literature reviews and the research priorities identified for long distance road and rail transport in LICs in Sub-Saharan Africa and South Asia. The research priorities are directed to ensuring long distance transport contributes more effectively to economic and social development. They are closely aligned with the development goals for these regions and specifically with the approaches advocated by UK Aid Direct in support of DFID strategic objectives. The research priorities identified in this study also contribute to achieving the UN Sustainable Development Goals (SDGs) and to the goals of the World Bank initiative of Sustainable Mobility for All (SuM4All).
