Influence of stress state and stress history on the rate of secondary deformation for a high plasticity Paleogene clay

An increasing demand for construction of high-speed railway systems in Northern Europe has led to increased focus on deformation prediction due to the low tolerances for settlement/heave in such projects. With a design lifetime exceeding 100 years, a detailed description of secondary deformation is essential for adequate prediction of long-term settlement/heave. The creep deformations of high plasticity Paleogene clays challenge currently planned Danish projects. These deposits have a high clay content with significant amount of smectite. Subsequent burial and erosion by Neogene deposits has led to a high level of overconsolidation, generating also fissures and slickensides. This complicated stress history along with active mineralogy influences the secondary deformation behaviour, which displays a significant stress state dependency. As a part of the tendering phase of the currently planned “Fehmarnbelt Fixed Link” project, connecting Denmark and Germany, an extensive laboratory campaign of 1D IL consolidation tests was carried out. The results from these tests were eanalysed in the current study, in order to assess the time dependent behaviour of folded Røsnæs Clay in compression and swelling. The results indicate that there is a nonlinear relationship between the primary and secondary compression, while a similar trend could not be as clearly identified for the swelling behaviour.