Performance Enhancement of Flexible Pavements Founded on Expansive Subgrades

Abstract

Volume changes in expansive subgrade soils are responsible for the swelling and shrinkage. The volume changes cause major distress in flexible pavements such as rutting, alligator cracks, etc. This hampers the performance of pavements. Moisture variations in such expansive soils are primarily responsible for volume changes. The active zone within which these volume changes take place is up to 1 to 1.5 m depth from the natural ground level. Therefore, researchers have tried to control swelling of expansive soils by using various materials and techniques for stabilizing these soils within this active zone depth. (Katti 1978) have tried to replace the expansive soils in this active zone depth by Cohesive Non-Swelling (CNS) materials. However, this method is uneconomical where availability of such stabilizing materials for replacing expansive soils is a problem. (Sahoo and Pradhan 2010a) have observed that, the CNS methodology is ineffective after first swell- shrink cycle. In addition, disposal of removed expansive clay is another issue to be resolved. (Sahoo et al. 2008), as well as (Indian Road Congress(IRC-37) 2012), have suggested the concept of using strain resisting buffer layers for protecting pavement embankments from swelling displacements. These suggestions necessitate further in-depth studies. Therefore, instead of a mere buffer layer, a combination of buffer layer and vertical cut-off forming a lime stabilized C -shaped capping is examined in this study. This will provide an enclosed zone under the embankment, which will help to reduce the swelling displacements due to moisture. The present study suggests the use of this C -shaped capping and attempts to characterize the suitability of the capping material through laboratory studies and the efficacy of the capping by numerical modelling carried out by Finite Element Method (FEM).The results of the laboratory investigation were used as input parameters in software PLAXIS 3D, based on Finite Element Method.