Swelling properties of a Danish Paleogene clay: a multiscale study on structure

Abstract

Paleogene clays are highly plastic, stiff clays deposited between 65.5 and 43 millions of years ago, frequently met in northern Europe. As they were deposited before the Quaternary, they experienced the glacial cycles that occurred in that period. The evolution and movement of the ice masses above the Paleogene clays highly influenced their stress history. During the interglacial periods the glaciers melted, unloading the underlying formations while during the glacial periods the glaciers mass loaded the Paleogene clays and sheared their shallower layers. Previous studies examined the compressibility and swelling of Danish Paleogene clays, and showed an early preconsolidation stresses, lower than that associated with the overburden pressure. This phenomenon was attributed to the effects of the glaciers movements. Other factors that have not been investigated yet and influence the deformation behaviour, can be associated with the micro and nano structure, meaning the particle orientation, and the mineralogical composition of the clays. This study focuses on a Danish Paleogene Formation called Røsnæs clay and the aim is to investigate the macromechanical swelling behaviour and its relation with particle rearrangement. A combination of 1D compression tests, microscopy imaging, mercury intrusion porosimetry and X-ray diffraction tests were performed on reconstituted and undisturbed samples in order to investigate the fabric, the pore structure and the mineralogy of the soil. A synthetic saline solution reproducing the in situ water was used to prepare the reconstituted samples and for the water bath. Variations with the swelling index were correlated with the clay particles rearrangement taking in to account the mineralogical composition. The compression curves and the scanning electron microscope micrographs were correlated with the mercury intrusion porosimeter results.