Abstract: The structure of unsaturated clays can significantly affect its mechanical properties. Based on the classical BBM (Barcelona basic model) and a hardening rule which can describe cyclic plasticity, an elastoplastic two-surface model is established to describe the static and dynamic mechanical properties of unsaturated structural clays under constant suction condition using the volumetric damage rate as the standard soil structural damage parameter. The proposed model includes a structural bounding surface and a loading surface which are geometrically similar to the yield surface of reconstituted unsaturated clays in the stress space. Based on the principle of radial mapping and movable memory center, the cyclic plastic characteristics and structural damage process of unsaturated structural clay under cyclic loading are reflected by the evolution of structural boundary and loading surface in stress space. By comparing with the relevant experimental results of unsaturated clays under controlled suction, it is shown that the model can well reflect the main mechanical behaviour of unsaturated structural clays under static loading, and the stress-strain behaviour predicted by the model under cyclic loading is also reasonable.

Key words: unsaturated soils, matric suction, structure, cyclic loading, elastoplastic two-surface model