MICROSTRUCTURAL CHANGES ASSOCIATED WITH THIXOTROPIC PHENOMENA IN CLAY SOILS

Thixotropic phenomena in clay soils are accompanied by microstructural changes. The nature of these changes is unclear because of the short duration of the thixotropic processes and the difficulties involved in preparing a specimen at certain stages. However, these technological problems were overcome and SEM photographs were obtained of the thixotropic soil microstructure during deformation of samples in a rotary viscometer with and without vibration. The new data obtained clarify the mechanism of thixotropic phenomena. Soil microstructure was not ruptured by vibration during the shear process. On the contrary, it became more homogeneous over the entire volume and at the same time this induced a decrease in strengthin the system due to a reduction in cohesion at contacts. Disruption of some structural bonds is followed by their rapid restoration—the overall microstructure remaining intact. As a result, in all the samples studied the shear zone disappears. In kaolinite clay and coarser dispersed soils (si...