This thesis focuses on the investigation of the effect of load duration on preconsolidation stress and swelling pressure in oedometer testing on Søvind Marl. This type of clay has a highplasticity, highly overconsolidated and highly calcareous. Inaddition,it has a fissured structure that influenced the stiffness of the clay. These fissures were caused by the failure of the clay due to the load and unload of glaciers. As settlements and swelling are expected to cause damage to structure on these types of clays, it is of utmost important to determine the correct soil deformation characteristics on these clays by performing oedometer tests. In practice, most oedometer tests are performed as incremental loading test with 24hr measurements in order to save time. However, the more correct evaluation of oedometer test should consider the time for swelling to occur after the sample has been saturated and allows all settlements to be completed. Otherwise measurements of swelling and settlements on soil can be underestimated. Therefore, the main goal of this project is to investigate the effect of load duration by letting the sample to fully consolidate and obtain the exact pressure that can resist swelling during oedometer testing and compare it to the traditional 24 measurements.