Rheological investigations in soil micro mechanics: upscaling microstructural processes

Rheological methods have been introduced to soil micro mechanics within the last few years. Rheometry can be seen as a linking tool for upscaling processes in geoscience, hydrology, and soil science.

A rotational rheometer with a parallel-plate measuring device is used to achieve parameters, which may define soil as viscoelastic material. Hence, latest data deriving from conducted amplitude sweep tests with controlled shear deformation will be presented.

Test results are mainly influenced by physical as well as physicochemical properties of both, disturbed and undisturbed saturated and predrained soil samples. Water content, texture, organic matter compounds, contents and kind of clay minerals, carbonate, (hydr)oxides, and cations may have an effect on stiffness, structural stability, shear behaviour, and shrinkage/swelling potential. Storage modulus G’ and loss modulus G’’, yield point and yield area, loss factor tan d and the linear viscoelastic range (LVE range) characterize microstructural properties of soil on the particle-to-particle scale. A comparison of clay rich kaolinitic and smectitic samples, well-structured material originating from Rothamsted research plots amongst others lead to significant differences in structural stability and may function as link to shrinkage/swelling potential. In addition, a classification of rigid-nonrigid or elastic-viscous material can be done considering the loss factor.