Choice of Sampling Strategy for Flexible Pavement Distress Survey

Periodical monitoring of the condition of the pavement is performed through functional and structural evaluation. For functional evaluation of the pavement, a distress survey is typically carried out. To minimise the cost and time involved, these distress surveys are carried out on representative sample units rather than the entire road network. Different sampling techniques such as simple random sampling, systematic sampling, and stratified sampling are used in this regard. The effectiveness of the individual sampling technique in closely representing the population varies and scarcely any guideline currently exists to guide the user on the choice of sampling technique. To evaluate the influence of sampling technique on the pavement distress survey, five study stretches, 1 km each, were chosen, and a manual distress survey was carried out. Eleven distresses were considered here and the PCI values were calculated for individual distresses and for the overall case. To assess the influence of individual sampling techniques, each study stretch was divided into 34 sample units. From the 34 sample units, three different datasets were manually created using each sampling technique. ANOVA was performed to observe the variability within a given dataset and between the three datasets obtained from a given sampling technique. It did not indicate any variability between different sampling techniques and the mean PCI values obtained from individual sampling techniques resembled closely with the population. However, the proportion of sample units present in each PCI range varied significantly among the three datasets, the degree depending on the choice of sampling technique. This variability was minimal in the case of stratified sampling indicating that irrespective of the choice of sample units, it always resembled closely with the population. A similar statement could not be made for the other sampling techniques. This was observed to be valid for the overall PCI and for the selected individual distresses.