Constitutive model of unsaturated structured soils under cyclic loading

Unsaturated structured soil has been one of research focuses in geotechnical mechanics. This paper aims to investigate the influence of structure degradation and suction variation on unsaturated soils subjected to cyclic loading. Within the framework of plastic bounding surface model, the structure damage theory and unsaturated soil mechanics, an elasto-plastic model for unsaturated soils under cyclic loading has been elaborated. Firstly, on the basis of Barcelona Basic Model, the water retention curve is employed to unite the suction with mechanical stresses under constant water condition. Secondly, the size of yielding surface is assumed to depend on the soil structure damage, and a law of structure degradation is given, linking the structure damage with accumulated plastic strain increments. Besides, by incorporating the concept of mobile mapping origin, the bounding surface model is modified to unify the mapping rule used during both loading and unloading, to simulate the phenomenon of hysteretic properties under cyclic loading. Comparisons between experimental results or published data and model simulations show that the elaborated model is capable of describing unsaturated soil behavior under cyclic loading