Effects of Compaction Moisture Content on Permanent Deformation of Soils Subjected to Repeated Triaxial Load Tests

Water content is one of the key parameters that can cause variations in the elastic and plastic deformation of pavement layers. More specifically, both the compaction moisture and the post-compaction moisture should be carefully controlled. The objective of this study is to analyze the effects of compaction moisture on the accumulation of permanent deformation when unbound materials are subjected to repeated triaxial loads. The moisture contents were defined according to the compaction curve of each soil, being one above and one below the optimum moisture content which has been typically considered for the design of asphalt pavements in Brazil. The four soils evaluated in the study are commonly used in flexible pavements and have different classifications according to the Brazilian Miniature, Compacted, Tropical (MCT) methodology tailored to classify tropical soils. Specimens were subjected to permanent deformation tests and the results obtained show that the moisture content can significantly affect the mechanical behavior of soils. That effect is significant on both sides of the compaction curve, but the permanent deformation increases as the compaction moisture content increases on the wet side. This work is part of a broader and comprehensive research project in progress in Brazil to continuously update the current version of the Brazilian mechanistic-empirical pavement design guide. The proper understanding and characterization of the resistance to permanent deformation of unbound materials is a key part of that design guide.