A generalised water retention model with soil fabric evolution

This paper introduces a novel soil water retention curve model that considers two different mechanisms of water retention –namely capillarity and adsorption – and their evolution with soil fabric along a generalized stress path. The model is formulated based on a new developed framework, which is justified against experimental evidence and incorporates the following developments: (i) the characteristics of the capillary and adsorption water retention curves are identified, and an ad-hoc water retention model is developed for each mechanism; (ii) the capillary and adsorption water retention curves are related to the experimentally determinable water retention curve thanks to a newly defined parameter named “contribution factor”, which changes with the evolution of the fabric. The proposed model is an elastoplastic water retention model and it allows to describe satisfactorily the water retention capacity of different soils. All simulation results support the statement that the adsorptive mechanism plays a crucial rule in the high suction range while capillarity is important in the low suction range. Moreover, it is shown that the developed capillary water retention curve allows to easily compute, at any state of the soil, a suitable capillary degree of saturation; the latter, adopted within the generalised effective stress concept, makes it possible to interpret shear strength data under different saturation conditions properly.