Designing a Paved Road Using Geogrids to Reduce the Thickness of the Pavement Layers

Abstract

Performance and durability of road pavements are significantly dependent on the strength and stability of the underlying soil layers, most especially the subgrade pavement layer. Currently, in Uganda most roads are constructed through low lying areas characterized by soft, hence weak, clay soils. The main practice, of improving the strength of such subgrade layers, has been to import stronger lateritic soils and dump them in layers over the weaker soils in thicknesses of more than 1.0 m. This is expensive, especially in terms of the haulage costs, and not environmentally friendly. Additionally, the lateritic soils are also getting depleted. Hence the need to utilize alternative means of increasing the strength of weak subgrades. This study focused on the application of Geogrids in pavement layers to reduce their overall thickness and life cycle costs of the road. A low-lying section on the Bajjo road, a bypass connecting Mukono to Seeta, was used as a case study. According to the AASHTO classification system of subgrade materials, the subgrade soils fell under the soil ranges of A-7, A-7-6, and A-6 group, therefore a poor subgrade material requiring stabilization. The average CBR was determined as 19%. The inclusion of the Geogrid reduced the overall layer works thickness by 25% and it’s cost effective by 42% over the whole lifecycle of the road.