Earth Pressure at rest of Søvind Marl – a highly overconsolidated Eocene clay

The present study evaluated earth pressure at rest, K0, in highly overconsolidated Eocene clay called Søvind Marl, which exhibits extremely high plasticity indices of up to 300%, a highly fissured structure, and preconsolidation stresses up to 6,800 kPa. Continuous Loading Oedometer (CLO) tests with a constant rate of strain were conducted on Søvind Marl in the Danish Continuous Loading Oedometer Apparatus, which enables test water to be applied at 200 kPa, and measures the horizontal stresses via pressure gauges placed in a stiff oedometer ring. The horizontal and vertical stresses were measured from in situ stresses to various stress levels to estimate continuous K0 development in this highly overconsolidated clay. The normally consolidated earth pressure at rest was found for two different sample ages of Søvind Marl to be between 0.42 and 0.68. Results indicated the overconsolidated K0 reached values as high as 6 to 8 in the in situ stress range. Meyerhof’s (1976) reported correlation between K0(oc) and OCR was found inconsistent with K0(oc) development of in Søvind Marl. However, the development of OCRlab dependent on previous test stresses, as an alternative to preconsolidation stresses, showed congruent results using α = 1.05 independent of sample age.