Rheology in Soils
Rheology Greek: rhei (ρει): flow; logos (λογοσ): science; science of flow behavior.
ta panta rhei (τα παντα ρει) Everything flows (Heraklit, ~2500 year BP).
Rheology is a science dealing with the mechanical behavior of fluids and plastic bodies when subjected to external stresses. Hooke’s law for a perfect elastic body, Newton’s law for ideal fluids, and finally, Bingham’s yield represent terms on which rheology is based (Bingham, 1922). Theoretical aspects of rheology are the relation of the flow/deformation behavior of material and its internal structure (e.g., the orientation of particles) and the flow/deformation behavior of materials that cannot be described by classical fluid mechanics or elasticity.
Fundamentals of rheology: thixotropy and rheopexy
Amplitude sweep test conducted with a rotational rheometer (MCR 300 Paar Physica Co., Ostfildern, Germany) in oscillatory mode, with controlled shear deformation (CSR): γ = 0.0001… 100%, frequency f = 0.5 Hz, 30 measuring points, duration of one test: 15–18 min (depending on the texture and water content). Parallel plate measuring system: upper oscillating plate 25 mm in diameter with profiled surface, fixed plate at bottom: 50 mm in diameter also with profiled surface, plate distance: 4 mm. A constant temperature (20°C) is controlled by a Peltier unit. Stiffness degradation (= distance-controlled work in Nm) is detected online; shear moduli G′ and G″ (Pa) and/or loss factor tan δ (−) vs. deformation γ (%) are plotted simultaneously. The calculation of the linear viscoelastic (LVE) range and integral z can be done by using the same software which controls the measuring system: US 200 (Paar Physica Co., Ostfildern, Germany).
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