Increasing design life of pavements built over expansive soils

Abstract

The load or stresses that the flexible pavements have to resist during their lifetime can be divided into two main categories: (i) due to traffic, and (ii) due to environmental factors. The loads due to environmental factors primarily occur due to variation of moisture in the subgrade below the pavement. The seasonal variation of temperature and rainfall at a site can lead to change in subgrade moisture. Further, the edges of the pavement are prone to moisture variation as compared to the centre of the pavement, which tends to remain at constant moisture or at compacted moisture level. If the subgrade below the pavement is expansive in nature, the soil would shrink and swell with the moisture variation causing additional stress on the pavement surface. The primary result of this moisture variation below the pavement is the formation of longitudinal cracks that are found predominantly on the edges of the pavement. Longitudinal cracks are undesirable, as they provide a pathway for moisture infiltration and increased ease of base course particle migration, both of which accelerate roadway degradation. These environmental conditions are generally not fully evaluated as part of the design of pavements, which focuses more directly on traffic conditions. In recent decades, reinforcement geosynthetics have been used successfully to prevent the propagation of the micro cracks upward from the subgrade in pavements constructed over highly plastic, expansive clay subgrades. This paper reviews some of the traditional treatment methods for expansive soils, and presents the details of the geosynthetic method as the most recent advanced cost effective solution. This includes the mechanism, of controlling the cracks, test results, and full-scale trials and long term field monitoring achievements.