Dilatancy effects in simulation of dry and solid/fluid granular flows
Abstract
Describing grain/fluid interaction in debris flows model is still a challenging issue with key impact on hazard assessment [1]. We present a two-phase two-thin-layer model for fluidized debris flows that takes into account dilatancy effects. It describes the compression/dilatation of the granular media and its interaction with the pore fluid pressure [2]. The model is derived from a 3D two-phase model proposed by Jackson [3] and a weak compressibility relation, making it possible to obtain a well-posed model.
The occurrence of dilation or contraction of the granular material in the model depends on whether the solid volume fraction is respectively higher or lower than a critical value. As an example, when dilation occurs, the fluid is sucked into the granular material, the pore pressure decreases and the friction force on the granular phase increases. To account for this transfer of fluid into and out of the mixture, a two-layer model is proposed with a fluid or a solid layer on top of the two-phase mixture layer. Mass and momentum are transferred between the two layers. A thin-layer approximation is used to derive average equations. We extend this model to deal with in-depth variations by developing a multi-layer approach. Interestingly, when removing the role of water, our model reduces to a dry granular flow model including dilatancy. For the first time, we show the complex role of dilatancy in dry granular flows, with varying states of compression/dilatation as a function of time and space. Our results suggest that dilatancy plays a role in the establishment of a low velocity regime following the collapse of granular columns. Then, by quantitatively comparing the results of simulation and laboratory experiments on submerged granular flows, we show that our model contains the basic ingredients making it possible to reproduce the interaction between the granular and fluid phases through the change in pore fluid pressure. [1] R. Delannay, A. Valance, A. Mangeney, O. Roche, P. Richard, J. Phys. D: Appl. Phys., 50, 053001 (2017). [2] F. Bouchut, E. D. Fernández-Nieto, A. Mangeney, G. Narbona-Reina, J. Fluid Mech., 801, 166-221 (2016). [3] R. Jackson, Cambridges Monographs on Mechanics (2000).- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMEP52A..08M
- Keywords:
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- 0742 Avalanches;
- CRYOSPHERE;
- 1810 Debris flow and landslides;
- HYDROLOGY;
- 1862 Sediment transport;
- HYDROLOGY;
- 3022 Marine sediments: processes and transport;
- MARINE GEOLOGY AND GEOPHYSICS