Optimum design of sustainable sealed low volume roads using the Dynamic Cone Penetrometer (DCP)

Abstract

Sustainable upgrading of unsealed roads to a low volume sealed standard is best accomplished by maximising the use of the in situ materials within the prevailing road environment. Over the years and under traffic loading, unsealed roads achieve a significant degree of subgrade compaction, localised weak areas tend to become strengthened and an accumulation of residual gravel wearing course provides a sound support or foundation for the new road. Optimising the use of these conditions usually results in a reduction in the need to import large quantities of virgin material. Appropriate testing with the simple DCP test device can be used to assess the in situ conditions including material quality and moisture regimes along the road alignment. This information can be used to identify uniform sections; the in situ layer strength diagrams of each of these sections can then be analysed with respect to the estimated traffic to determine the layer quality and thicknesses for a sustainable design. Estimation of the expected traffic can often be a problem in such situations and guidelines to assist in this regard are presented. Data from various road sections in Southern Africa are used to support the discussion.