Rheology and Fluid Mechanics

Biography

Biography: Nina Stoppe

Abstract

Soils are multifunctional key resources for human beings–they provide food and water, renewable resources, construction grounds and habitats for animals and plants. At the same time, they regulate local and global cycles of substances and water and therefore affect climate. Nowadays soil degradation and the loss of beneficial soil functions, which are intertwined with soil structure and convenient pore geometry, are severe problems. As soil structure possesses many valuable functions, the quantification of structural stability is an important field of research. As a basic understanding of soil behavior requires knowledge of the processes at the microscale (i.e. particle scale), rheological investigations of natural soils receive growing attention and useful insights have been gained in recent years to understand the microstructural deformation behavior of soils. Several homogenized soil materials were analyzed with a modular compact rheometer MCR 300 (Anton Paar, Germany) and a profiled parallel-plate measuring system. Amplitude sweep tests (AST) with controlled shear deformation were conducted to investigate the viscoelastic properties of the studied soils under oscillatory stress. The gradual depletion of microstructural stiffness during AST can be characterized by the well-known rheological parameters G′, G″ and tan δ but also by the dimensionless area parameter integral z, which quantifies the elasticity of microstructure. Depending on soil texture, various physicochemical features significantly affect the elasticity of soil microstructure, such as soil organic matter, concentration of Ca²⁺, K⁺ and Na⁺, content of CaCO₃ and pedogenic iron oxides. Especially under consideration of the combined effects of these features, the rheological behavior of soils becomes explainable.