The lateral displacements developing in clay foundations under 21 different embankments during construction and consolidation have been analyzed. The development of a significant consolidation at the beginning of any embankment construction has been confirmed. As a result, lateral deformations initially develop in conformity to the theory of elasticity for a drained condition. Undrained shear distortions develop near the end of construction when the clay foundation has become partly or entirely normally consolidated. This sequence of drained and undrained response of the foundation governs both the magnitude and distribution with depth of the lateral displacements and is the main reason why previous displacement predictions based on undrained analysis have been unsuccessful. Delayed lateral deformations can be significant and develop linearly with the consolidation settlement, at least in the first years after the end of construction. The distribution of lateral deformations with depth is not modified during consolidation so that long-term predictions of deformations as well as of the behaviour of adjacent structures appear possible.