  On the basis of plastic bounding surface model, the damage theory for
structured soils and unsaturated soil mechanics, an elastoplastic model for
unsaturated loessic soils under cyclic loading has been elaborated. Firstly,
the description of bond degradation in a damage framework is given, linking the
damage of soil's structure to the accumulated strain. The Barcelona Basic Model
(BBM) was considered for the suction effects. The elastoplastic model is then
integrated into a bounding surface plasticity framework in order to model
strain accumulation along cyclic loading, even under small stress levels. The
validation of the proposed model is conducted by comparing its predictions with
the experimental results from multi-level cyclic triaxial tests performed on a
natural loess sampled beside the Northern French railway for high speed train
and about 140 km far from Paris. The comparisons show the capabilities of the
model to describe the behaviour of unsaturated cemented soils under cyclic
loading.
