Stiff clay samples from the Princess Elisabeth Zone show the presence of faults and fissures on various length scales. The presence of these discontinuities influences the mass strength and stiffness of the clay. This study aims to investigate the geological origin of the discontinuities and proposes laboratory testing and numerical modelling to quantify their effect on strength and stiffness of the soil surrounding monopile foundations. This is necessary to optimize the amount of primary steel for the foundations and follow up their lifetime through a digital twin model.