PhD Project: Geotechnical properties of highly plastic tertiary clay

In recent years, large and prestigious buildings and structures have been planned in Denmark on sites where the soil consists of highly plastic tertiary clays. Currently, a high-rise building in Aarhus and the planned Fehmarn Belt link represent a challenge not before seen on highly plastic clays. Building on highly plastic tertiary clay is a challenging task within the field of geotechnology. This is due to the unique strength and deformation properties of the clay. The mineral composure of the highly plastic tertiary clays is causing it to swell strongly when the clay is unloaded while being surrounded by water and this can cause severe deformation problems. Highly plastic tertiary clays are often highly fissured, causing an anisotropic behavior. This can influence tests performed in the field and cause inaccurate results. It is therefore necessary to carry out laboratory testing to obtain an understanding of the clays’ behavior and properties. A low permeability of highly plastic tertiary clay makes laboratory testing a long and time consuming process. As a result, there is a need for constitutive models to describe the behavior of the clay.



The above mentioned issues will be clarified through the following activities:

- Through literature study, where the existing literature is reviewed for a description of the known challenges that exist when building on highly plastic tertiary clays, and to create an overview of existing knowledge and known issues.

- Through laboratory testing, to determine the behavior of highly plastic tertiary clay. Possible tests can be:

Consolidation tests to determine the deformation and swelling properties of the highly plastic tertiary clay and determine the preconsolidated stresses of the clay. The tests will be strictly loading tests and un- and reloading tests to demonstrate the different aspects of the stiffness of the clay under different load situations and to find the preconsolidation stresses and determine which aspects can have an influence on the interpretation of this. Furthermore, triaxial test is carried out to determine the deformation and strength parameters of the clay.