Extended Barcelona Basic Model to the cyclic behaviour of unsaturated soils

Partially saturated soils can be loaded in different ways; for instance, mechanically and hydraulically. In addition, cycles of loading and unloading can be applied. The Barcelona Basic Model (BBM) is an extension of the Cam clay model that has become popular in applications involving unsaturated soils and, in particular, in simulations using the finite element method. This paper presents a modification of the BBM in order to simplify its computer implementation and also to permit the simulation of elasto-plastic behaviour during cycles of both mechanical and hydraulic loading. A unique, smooth yield surface is introduced and the two-yield surfaces concept is applied in order to represent the cyclic behaviour. The influence of the intermediate principal stress on the strength is also accounted for.