Sustainability and Resilience of Transportation Infrastructure in African Countries

To address the global challenge of providing sustainable and resilient infrastructure for African countries, this proposal brings together leading researchers from Durham University with Kwame Nkrumah University of Science & Technology (Ghana), University of Pretoria (South Africa) and Nyaoro & Associates (Tanzania). The research outlined in this proposal will investigate (i) the use of sustainable (locally occurring) construction materials in road construction and (ii) the impacts of climate change on transportation infrastructure. A key common element will be the measurement of suction in laboratory and field testing, using high suction tensiometers developed at Durham University.

The use of locally available materials will be investigated for the design and construction of sustainable low volume roads (with traffic volumes of less than 300 vehicles per day). For low-volume sealed roads it is the road environment (controlled by climate, drainage and construction details) that is the most important factor influencing the road performance, rather than traffic loading. The novelty of the research proposed is to gain knowledge of the fundamental behaviour of road construction materials in tropical climate conditions through the principles of unsaturated soil mechanics. There is currently a disjoint between the requirements of specifications for road construction and observed performance. This can be explained by the lack of understanding of unsaturated conditions within the road base, due to a lack of field measurements of suction in these environments. Based on field measurements in different climatic conditions in Ghana and Tanzania, supported by water retention measurements in the laboratory, it will possible to address (i) adapting the specification and road design to suit local materials; or (ii) adapting or modifying the materials (by stabilisation) to suit a realistic specification.

Climate change in Africa has been manifest by extreme weather and changing rainfall patterns. To consider the impacts of climate change, suction and water content measurements will be obtained for a railway line in South Africa. These will be used to identify potential deterioration of transportation infrastructure due to wetting/drying cycles. This deterioration mechanism is likely to be exacerbated by climate change, when dry/wet cycles are expected to have greater amplitude, due to a reduction in precipitation (even drought) in dry seasons and more intense rainfall in wetter seasons. Another aspect related to the resilience of railway infrastructure in response to climatic and environmental influences is the performance of railway formation under heavy axle, cyclic loading. It is thought that the stiffness of the formation is linked to the unsaturated behaviour of the layerworks and that this relationship is key to understanding the long-term performance of the formation. These measurements will be interpreted in the light of existing historical data at this specific research site in South Africa, that spans a period of 12 years.

The project will demonstrate the following contributions to society and the economy:

1. It will demonstrate major economic impact in providing technologies that can reduce the costs to the economy of African countries:

(a) Construction of Low Volume Rural Roads (LVRR) using sustainable local materials. Experience in Botswana led to cost savings in excess of £16m (on the main road network alone). More recently, AFCAP have reported cost savings to construct low volume sealed roads of the order of £490m in Kenya and £10m in Malawi. Seventy percent of the cost of constructing LVRR roads is the material costs, so use of local materials (rather that unsustainable crushed rock with long haul distances) will provide major cost savings.

(b) Identifying potential deterioration of transportation infrastructure due to wetting/drying cycles. This deterioration mechanism is likely to be exacerbated by climate change, when dry/wet cycles are expected to have greater amplitude. The project will enable strategies to be developed for improving the resilience of infrastructure in response to shrink/swell action that causes damage to roads and railway formations.

2. It will have social impact through assisting in developing the rural road network in African countries that can provide opportunities for trade and for mobility and access to services of education and health.

3. It will provide contributions to public services and policy, by setting out clear advice on use of local materials that can be adopted by government roads departments and civil engineering contractors.

4. It will provide economic opportunities for geotechnical design consultants and geotechnical contractors as a potentially novel approach to road design that will have an international market.