This paper presents some of the considerations made in connection with the planning of the advanced laboratory tests conducted for the design of the Fehmarnbelt Fixed Link. Two design solutions have been proposed: a cable stayed bridge and an immersed tunnel. The soil below the Fehmarnbelt consists, among others, of Palaeogene formations of fissured, very high plasticity clays. The different loading situations for the two designs and the properties of the Palaeogene clays have formed the basis for selecting appropriate laboratory tests and testing programs. This is clearly seen in the planning of the oedometer tests with either loading or unloading after the consolidation phase, and in the determination of the undrained shear strength. The latter is determined by either triaxial compression, triaxial extension or direct simple shear tests since the results of these tests depend on the field conditions. Additionally, the swelling pressure and magnitude needs to be clarified by oedometer tests before any further testing is started. Otherwise, misleading results will come out of the tests.