Properties of very soft clays: A study of thixotropic hardening and behavior under low consolidation pressure

In a study on the properties of very soft clays, bender element testing was used to evaluate thixotropic hardening behavior; that is, to measure the stiffness with resting time under constant volume and water content. A laboratory vane test, which measures the undrained shear strength of the materials, was also carried out for comparison purposes. To investigate the mechanism of the thixotropic phenomenon, a consolidation test with very low pressure was also performed in a cell equipped with bender elements. The most important findings from this study are as follows: (1) regardless of soil types, the effect of thixotropy was significant around the liquid limit state and less remarkable at the lower and higher ranges; (2) the shear modulus at the liquid limit after 24 h resting is around 200 kPa; (3) the correlation between the shear modulus and the undrained shear strength of very soft clays is similar to that of cement-treated soil proposed by Seng and Tanaka (2011); (4) the increment of the shear modulus developed in the thixotropy process appears to be noticeably higher than that in the secondary consolidation process. It is believed that these findings are very useful to establish a new theory for the consolidation of ground filled by very soft clays or dredged soils with extremely high water content as well as to understand the effects of ageing on the consolidation properties of natural soils.