A. Veeraragavan, Professor, Civil Engineering. Indian Institute of Technology (IIT), Madras, Chennai, Tamil Nadu, India.
Research has clearly shown (and continues to do so) that as a result of changing global climatic patterns countries are becoming increasingly vulnerable to devastating damage to the infrastructure – for example through floods associated with hurricanes of increasing frequency and rise in sea water and ground water level. The Inter governmental Panel on Climate Change (IPCC) has stated that the frequencies of heavy precipitation, as well as rainfall from tropical cyclones, are likely to continue to increase in this century (Pachauri, 2012). As projected by the IPCC, rising sea levels is virtually certain (>99% probability of occurrence) to continue, and increases in intense precipitate events are highly likely (>90% probability of occurrence) to become more frequent in widespread areas of the world, and as a consequence, along coastal areas and low-lying river areas flooding will be expected to occur more frequently.
Pavements constitute the most widely used part of the nations’ infrastructure for the transportation of people and goods. Flooding can inflict significant damage to pavements, making them unserviceable – causing a major negative impact on the nation’s economy. Furthermore, in many cases the pavement may appear to be intact, but may not be structurally sufficient to support traffic. An example would be a pavement with voids that can cause sinkholes and devastating failures under traffic. On the other hand, if the damage can be determined, the highway agencies can make an informed decision to repair the damage and detour the traffic or to allow the traffic (to avoid negative economic impacts), based on the risk of such action, and when to allow emergency and repair vehicles. The ingress of moisture in pavements due to flooding can also accelerate the onset of other types of non-water related distress such as rutting and cracking. Finally, because of the ingress of water, there is a significant chance of contamination of the different layers by salts and pollutants. Knowledge about the potential of these chemicals for leaching out at a later time needs to be developed. When pavement materials are recycled it is not known what impact will these chemicals may have on the emissions that result during recycling.
The effect of flooding on the pavement structure is a serious research challenge as it is affected by a large number of factors (and their interactions) such as temperatures, material properties, hydraulic conductivity, hysteresis effect and loading conditions, and flood intensity (velocity of flow and depth) and flood duration. Significant information is required on the effect of the moisture susceptibility of the materials on flood induced damage and the rate of deterioration of the material properties as a result of flooding. This research area has not been developed fully yet, primarily because of the lack of the ability to realistically simulate flood conditions for pavements in the laboratory. And it is becoming clear that the challenge of assessing flood induced damage will become more common in the future.