Effect of compaction on the hydraulic conductivity of granular subbase layers in road pavements

It is a well-known fact that the provision of adequate surface and sub-surface drainage to prevent premature failures in pavements. The presence of an excessive quantity of water in the pavement layers, namely the bases, subbases and subgrade, can cause the pavement to fail prematurely if it is not drained as soon as possible. The granular subbase (GSB) layer is provided as a sub-surface drainage layer in flexible pavements. The Ministry of Road Transport and Highways (MoRTH) through the Indian Roads Congress suggested six gradations for the GSB layer. Though it is strongly believed that the hydraulic conductivity of these GSB options may vary with the type and amount of compaction, no studies have been reported to have investigated this aspect so far. It is in this direction that the present study is being carried out to evaluate the post compaction permeability characteristics of GSB layer as per the Indian specifications and validate the same with AASHTO specifications. Extensive laboratory investigations on the samples collected from the field were being carried out on all the six GSB MoRT&H gradations, and it was concluded that the gradation III and IV are meeting requisite Indian standards while satisfying the AASHTO specifications also.