Major wetting behaviour of compacted unsaturated soils in road embankments using the MPK framework

Major wetting events such as rainfall infiltration or flooding can induce substantial volumetric changes, including swelling, compression, or both, in compacted unsaturated soils used in road embankments and pavement subgrades. This study investigates the prediction of wetting-induced volumetric behaviour using the void ratio-moisture ratio-net stress ( e - e w - p ) space of the MPK (Monash-Peradeniya-Kodikara) framework. The MPK framework has previously been applied successfully to explain loading, unloading, wetting, collapse potential, and swelling behaviour of compacted soils using moisture ratio as a practical state variable. In this study, laboratory modelling considered a range of initial conditions, including moisture content, void ratio (or dry density), and operational stress. A hypothetical 30 m high road embankment with varying degrees of saturation and compaction levels was analysed to investigate field scale responses during major wetting events. A simplified hydric coefficient equation was developed to predict the swelling gradient during major wetting using operational stress, operational void ratio, and initial moisture ratio. The proposed equation was calibrated using laboratory data for compacted Merri Creek soil and validated against independent flooding experiments reported by Noorany and Stanley (1994). The results show that under operational stresses lower than the compaction stress, compacted soils may undergo swelling alone or a combination of swelling and compression, whereas increasing operational stress progressively suppresses swelling and promotes compression. Overall, the MPK framework, together with the proposed hydric coefficient equation, provides a practical engineering methodology for predicting the volumetric behaviour of compacted unsaturated soils during major wetting events in transportation earthworks.