Geotechnical properties of Søvind Marl — a plastic Eocene clay

Abstract

Results are presented of the analyses of the geotechnical properties of a fissured and highly plastic Danish tertiary clay: Søvind Marl. The analyses demonstrate the difficulties that can arise when dealing with this particular clay due to its unique characteristics. To characterize Søvind Marl and its pore water, samples were collected at multiple depths from five different borings located at the same site at Aarhus Harbour, Denmark, and all encountering the same Søvind Marl strata. Although Søvind Marl was deposited under circumstances very similar to those of London Clay, its properties show a poor resemblance to London Clay or other known clays. One of the key properties of Søvind Marl was found to be its extremely high plasticity, which can exceed 300%. Søvind Marl has high concentrations (up to 95%) of clay minerals, with a particularly large portion of smectite. Several key index parameters are presented and discussed including natural water content, Atterberg limits (plasticity in the typical range of 100%–250%), and calcite content (up to 65%). Results of vane shear tests and cone penetration tests are also presented. Oedometer tests yield two very different values for the preconsolidation stress level, although only one of these is correct. The dual calculation is associated with the fissured nature of Søvind Marl, which may confound traditional interpretation of test results, but must be taken into account for understanding of test results leading to proper classification of the material.