A generalised constitutive model for unsaturated compacted soils considering wetting/drying cycles and environmentally-stabilised line

A new Monash - Peradeniya - Kodikara (MPK) generalised model is presented, embodying a volumetric yield surface (i.e. loaded compaction yield surface) derived from constant water content testing, an environmentally-stabilised line representing the states achieved after a sufficient number of wetting/drying cycles, a constant plastic volumetric strain-based loading collapse yield curve and a soil water retention curve. The MPK generalised model has 16 parameters, including 10 parameters for mechanical behaviour. These 10 mechanical parameters can be determined by relatively simple constant water content tests, which is a major advantage of the model. The evolution of the plastic-strain-based soil water retention curves involves 6 parameters, some of which require calibration based on traditional SWRC testing under constant net stress. The equations for coupled hydro-mechanical behaviour were developed considering Bishop's effective stress for the wet side of the air transition line and independent stress for the dry side of the air transition line, and the stress/strain conjugates were finally transformed to Bishop's effective stress approach for the overall behaviour. The derived equations for the isotropic stress state were validated by reproducing a range of phenomenological observations, and the generalised MPK model is capable of reproducing most observed phenomenological behaviour, at least qualitatively.