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Solid Earth An interactive open-access journal of the European Geosciences Union
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Volume 8, issue 1
Solid Earth, 8, 177-188, 2017
https://doi.org/10.5194/se-8-177-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Solid Earth, 8, 177-188, 2017
https://doi.org/10.5194/se-8-177-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 16 Feb 2017

Research article | 16 Feb 2017

Combined effects of grain size, flow volume and channel width on geophysical flow mobility: three-dimensional discrete element modeling of dry and dense flows of angular rock fragments

Bruno Cagnoli1 and Antonio Piersanti2 Bruno Cagnoli and Antonio Piersanti
  • 1Istituto Nazionale di Geofisica e Vulcanologia, Via Donato Creti 12, 40128 Bologna, Italy
  • 2Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, 00143 Rome, Italy

Abstract. We have carried out new three-dimensional numerical simulations by using a discrete element method (DEM) to study the mobility of dry granular flows of angular rock fragments. These simulations are relevant for geophysical flows such as rock avalanches and pyroclastic flows. The model is validated by previous laboratory experiments. We confirm that (1) the finer the grain size, the larger the mobility of the center of mass of granular flows; (2) the smaller the flow volume, the larger the mobility of the center of mass of granular flows and (3) the wider the channel, the larger the mobility of the center of mass of granular flows. The grain size effect is due to the fact that finer grain size flows dissipate intrinsically less energy. This volume effect is the opposite of that experienced by the flow fronts. The original contribution of this paper consists of providing a comparison of the mobility of granular flows in six channels with a different cross section each. This results in a new scaling parameter χ that has the product of grain size and the cubic root of flow volume as the numerator and the product of channel width and flow length as the denominator. The linear correlation between the reciprocal of mobility and parameter χ is statistically highly significant. Parameter χ confirms that the mobility of the center of mass of granular flows is an increasing function of the ratio of the number of fragments per unit of flow mass to the total number of fragments in the flow. These are two characteristic numbers of particles whose effect on mobility is scale invariant.

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The purpose of our research is to understand the mechanisms that determine the mobility of granular flows of rock fragments. Since rock avalanches and pyroclastic flows are too dangerous to be studied at close range, we use numerical simulations and laboratory experiments. We focus on the fundamentals upon which new numerical models will be built to predict the behaviors of natural flows. These fundamentals include the effects of grain size, flow volume and channel width.
The purpose of our research is to understand the mechanisms that determine the mobility of...
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