A methodology of pavement design for upgrading gravel roads

In many developing countries, roads start their lives as footpaths. These paths later develop into vehicle tracks, engineered natural surfaces, gravel roads and, eventually, bituminous roads. This paper is concerned with the stage of transition of roads from gravel to bituminous standard. This transition is common in many countries that have gravel roads as a significant proportion of the road network. On many gravel roads, it is not uncommon to find particles larger than 40 mm in the gravel matrix. During upgrading of a gravel road to a bituminous standard, it is common to incorporate some of the existing gravel layer in the new pavement. A dynamic cone penetrometer (DCP) is frequently used to assess the strength of the existing gravel layer. However, if the pavement being tested contains a high proportion of large and coarse gravels, a DCP will produce highly variable results. The issue therefore is how to assess adequately the strength of the existing layer in order to produce a more cost-effective pavement design. This paper proposes a method of combining deflection and DCP tests for an effective pavement design.