Thixotropic Behavior of Reconstituted Debris-Flow Mixture

• Main Authors: Leonardo Schippa, Ferruccio Doghieri, Anna Maria Pellegrino, Elisa Pavesi
• Format: Article
• Language: English
• Published: MDPI AG 2021-01-01
• Series: Water
• Subjects: thixotropy; time-dependent rheology; debris-flow
• Online Access: https://www.mdpi.com/2073-4441/13/2/153

Time-dependent rheological properties and thixotropy of reconstituted debris-flows samples taken from channel bank deposits are examined using a commercial rheometer equipped with a vane rotor geometric system. Sweep tests and creep tests were carried out involving mixtures having different grain concentrations ranging between 50% and 58%. Different initial conditions of the mixtures were considered in order to analyze the effects of aging and rejuvenation (thixotropy) over a short period of time and long period of time. Tested slurries show viscosity bifurcation, yield stress and time-dependent behavior. According to the experimental results, three different regimes were identified: a lower shear rate regime, corresponding to a shear rate lower than the critical value; an intermediate banding shear rate regime characterized by static and dynamic yield stress level; and a higher shear rate regime where the flowing debris behaves as a non-Newtonian fluid characterized by a constant steady state ultimate apparent viscosity. In any case, the initial state of the mixture and the sediment concentration affects the ultimate steady state rheology and the time-dependent (thixotropy) slurries’ behavior.