The paper deals with a laboratory experimental techniques aimed at determining the viscous properties of materials that are produced during fast landslides type mud and debris flows. An experimental study of the rheological behavior of a natural pyroclastic soil remixed with water has been carried out with the help of an inclined plane tests and a rotational rheometer. It has been decided to use both inclined test and rotational rheometer because, unlike standard fluid rheometer, with the inclined plane test it has been possible to use much higher volume of mixtures of appropriate size and then, next to the real. The mixtures have been reconstituted at at different volumetric solid concentrations and different grain size distributions and maximum diameter of soil particles. In the studied range of solid volumetric concentration (in which the material behaves like an homogeneous fluid) the typical rheological behavior of these suspensions is that of a yield stress fluid exhibiting a static yield stress larger than its dynamic yield stress. The static and dynamic yield stresses of these materials widely increase from very low to very large values (several orders of magnitude). Inclined plane tests provide reasonable though still approximate values for the static and dynamic yield stresses. It has been also observed that the rheological behavior of this kind of material is strongly influenced by the particles size in the mixtures too. These results suggest that in the field during the debris flow motion, a small variation of the solid fraction or particle dimensions can lead to changing the behavior from “solid-like” to “fluid-like” and vice versa. The material starts to flow beyond a critical shear stress at a relatively large velocity. The critical shear stress, related to solid fractions and particle size, might explain the in situ observed post-failure behavior of pyroclastic debris flows, which are able to flow over very long distances even over smooth slopes
Experimental analysis for fine-grained and large-grained soils involved in debris-flow at the solid fluid transition
PELLEGRINO, Anna Maria;SCHIPPA, Leonardo
2013
Abstract
The paper deals with a laboratory experimental techniques aimed at determining the viscous properties of materials that are produced during fast landslides type mud and debris flows. An experimental study of the rheological behavior of a natural pyroclastic soil remixed with water has been carried out with the help of an inclined plane tests and a rotational rheometer. It has been decided to use both inclined test and rotational rheometer because, unlike standard fluid rheometer, with the inclined plane test it has been possible to use much higher volume of mixtures of appropriate size and then, next to the real. The mixtures have been reconstituted at at different volumetric solid concentrations and different grain size distributions and maximum diameter of soil particles. In the studied range of solid volumetric concentration (in which the material behaves like an homogeneous fluid) the typical rheological behavior of these suspensions is that of a yield stress fluid exhibiting a static yield stress larger than its dynamic yield stress. The static and dynamic yield stresses of these materials widely increase from very low to very large values (several orders of magnitude). Inclined plane tests provide reasonable though still approximate values for the static and dynamic yield stresses. It has been also observed that the rheological behavior of this kind of material is strongly influenced by the particles size in the mixtures too. These results suggest that in the field during the debris flow motion, a small variation of the solid fraction or particle dimensions can lead to changing the behavior from “solid-like” to “fluid-like” and vice versa. The material starts to flow beyond a critical shear stress at a relatively large velocity. The critical shear stress, related to solid fractions and particle size, might explain the in situ observed post-failure behavior of pyroclastic debris flows, which are able to flow over very long distances even over smooth slopesI documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
