The detailed analysis of the pore pressures generated during construction under the center lines of four test embankments on a soft sensitive clay indicates a significant departure from the classical methods of pore pressure prediction.In the early stages of loading, the clay is overconsolidated and is characterized by a highCv. As a result a significant consolidation occurs even in the very short duration of the construction. Due to this consolidation the vertical effective stresses increase rapidly until they reach the preconsolidation of the clay. At this point the clay becomes normally consolidated, and further loading occurs at constant effective vertical stress.The YLIGHT model of clay behaviour proposed by Tavenas and Leroueil may be used to fully understand this behaviour.In Part II, it will be shown that these findings apply in fact under most embankments and a prediction method will be proposed.