CLAY model in PARATIE has been conceived to reasonably model the behavior of clays in both drained or undrained conditions. As for stage analysis of retaining walls, undrained behavior is of most interest. To permit the change from undrained to drained conditions and vice versa, the model is formulated in terms of effective stress behavior in both conditions. Drained stress paths are reproduced in a very straightforward way, which is the same as for granular materials. Failure conditions are determined by effective stress failure criteria. Water pressures do not change due to mechanical load changes or soil deformations but only depend on hydrostatic or steady state hydrodynamic conditions, which in turn do not depend on mechanical behavior of the soil skeleton. Pore pressures are essentially uncoupled from soil skeleton, like in granular material behavior.