Coarse-Grained Debris-Flows: Hysteresis and Time-Dependent Rheology

Contreras, Samuel M.; Davies, Timothy R. H.

doi:10.1061/(asce)0733-9429(2000)126:12(938)

Cited by 32 publications

(23 citation statements)

References 10 publications

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“…When the large particle fraction is small compared to the amount of fine particle fraction, the colloidal fine fraction determines the rheological features of the mixture. Instead, as observed in different studies led using nonconventional rheometers on material mixtures, rheological properties are altered by addiction of larger particles (up to several centimeters) to the viscous fluid (Coussot and Piau, 1995;Contreras and Davies, 2000;Schatzmann 2005). Thus, rheological parameters determined by debris flow material of limited grain size with a conventional rheometer do not represent the bulk rheological behaviour of the complete natural material.…”

Section: Experimental Results and Model Fittingmentioning

confidence: 98%

“…It is considered that, for such a fluid, an abrupt change in flow behaviour exists around a given shear stress value, the yield stress τ y , which needs to be overcome before flow takes place. The viscoplastic character of debris flow mixtures has often been reported in literature Julien, 1984, 1988;Phillips and Davies, 1991;Major and Pierson, 1992;Coussot and Piau, 1995;Contreras and Davies, 2000;Ancey and Jorrot, 2001;Schatzmann, 2005;Kaitna et al, 2007). Phenomenological laws like the Bingham generalized model (or Herschel & Bulkley model) are usually used to describe the rheological behaviour of such mixtures (Major and Pierson, 1992;Nguyen and Boger, 1992;Coussot, 1997).…”

Section: Debris Flow Rheologymentioning

confidence: 99%

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Experimental study on the rheological behaviour of debris flow

Santolo

Pellegrino

Evangelista

2010

Nat. Hazards Earth Syst. Sci.

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Abstract.A model able to describe all the processes involved in a debris flow can be very complex owing to the sudden changing of the material that turns from solid into liquid state. The two phases of the phenomenon are analysed separately referring to soil mechanics procedures with regard to the trigger phase, and to an equivalent fluid for the postfailure phase. The present paper is devoted to show the experimental results carried out to evaluate the behaviour assumed by a pyroclastic-derived soil during the flow. A traditional fluid tool has been utilized: a standard rotational rheometer equipped with two different geometries. The soils tested belong to deposits that cover the slopes of the Campania region, Italy, often affected by debris flows. The influence of solid concentration C v and grain size distribution was tested: the soils were destructurated, sieved and mixed with water starting from the in situ porosity. All material mixtures showed a non-Newtonian fluid behaviour with a yield stress τ y that increases with a solid volumetric concentration and decreases for an increase of sand fraction. The experimental data were fitted with standard model for fluids. A simple relation between C v and τ y was obtained. The yield stress seems to be a key parameter for describing and predicting the post-failure behaviour of debris flows. These results suggest that in the field a small change in solid fraction, due to rainfall, will cause a slight decrease of the static yield stress, readily inducing a rapid flow which will stop only when the dynamic yield stress is reached, namely on a much smoother slope. This can explain the in situ observed post-failure behaviour of debris flows, which are able to flow over very long distances even on smooth slopes.

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Section: Experimental Results and Model Fittingmentioning

confidence: 98%

Section: Debris Flow Rheologymentioning

confidence: 99%

Experimental study on the rheological behaviour of debris flow

Santolo

Pellegrino

Evangelista

2010

Nat. Hazards Earth Syst. Sci.

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“…In the case of simple stress-strain relations (e.g., Bingham, Herschel Bulkley model), laboratory experiments have been conducted to derive material parameters for highly concentrated grain-fluid mixtures (e.g., Phillips and Davies, 1991;Major and Pierson, 1992;Contreras and Davies, 2000;. However, direct application of the results is complicated because scaled experiments together with the simple flow resistance models do not themselves represent full mixture dynamics of a real scale debris-flow (Iverson, 1997(Iverson, , 2003Ancey, 2006;Kaitna et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

Modeling debris-flow runout patterns on two alpine fans with different dynamic simulation models

Schraml

Thomschitz

McArdell

et al. 2015

Nat. Hazards Earth Syst. Sci.

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Abstract. Predicting potential deposition areas of future debris-flow events is important for engineering hazard assessment in alpine regions. To this end, numerical simulation models are commonly used tools. However, knowledge of appropriate model parameters is essential but often not available. In this study we use two numerical simulation models, RAMMS-DF (rapid mass movement system-debris-flow) and DAN3D (dynamic analysis of landslides in three dimensions), to back-calculate two well-documented debris-flow events in Austria and to compare the range and sensitivity of input parameters for the Voellmy flow model. All simulations are based on the same digital elevation models and similar boundary conditions. Our results show that observed deposition patterns are best matched with a parameter set of µ [-] and ξ [m s −2 ], ranging between 0.07 to 0.11 and 200 to 300 m s −2 , respectively, for RAMMS-DF, and between 0.07 to 0.08 and 300 to 400 m s −2 , respectively, for DAN3D. Sensitivity analysis shows a higher sensitivity of model parameters for the DAN3D model than for the RAMMS-DF model. This contributes to the evaluation of realistic model parameters for simulation of debris-flows in steep mountain catchments and highlights the sensitivity of the models.

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“…However, the impediments to a full fluid-mechanics approach are many: a wide range of particle size (often in the 10 −6 to 1 m range), composition that may change with time and/or position, ill-known boundary conditions (e.g., erodible basal sur- face) and initial conditions, time-dependent flows with abrupt changes (e.g., surge front, instabilities along the free surface), etc. Even with the construction of specifically devoted large rheometers [62,67,158,190], testing the rheometrical properties of samples collected in the field remains difficult. To give examples of materials involved in rapid mass movements, Fig.…”

Section: Introductionmentioning

confidence: 99%

Plasticity and geophysical flows: A review

Ancey

2007

Journal of Non-Newtonian Fluid Mechanics

352

277

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The objective of this review is to examine how the concept of plasticity is used in geophysical fluid dynamics. Rapid mass movements such as snow avalanches or debris flows involve slurries of solid particles (ice, boulder, clay, etc.) within an interstitial fluid (air, water). The bulk behavior of these materials has often been modeled as plastic materials, i.e., a plastic material yields and starts to flow once its stress state has significantly departed from equilibrium. Two plastic theories are of common use in fluid dynamics: Coulomb plasticity and viscoplasticity. These theories have little in common, since ideal Coulomb materials are two-phase materials for which pore pressure and friction play the key role in the bulk dynamics, whereas viscoplastic materials (e.g., Bingham fluids) typically behave as single-phase fluids on the macroscopic scale and exhibit a viscous behavior after yielding. Determining the rheological behavior of geophysical materials remains difficult because they encompass coarse, irregular particles over a very wide range of size. Consequently, the true nature of plastic behavior for geophysical flows is still vigorously debated. In this review, we first set out the continuum-mechanics principles used for describing plastic behavior. The notion of yield surface rather than yield stress is emphasized in order to better understand how tensorial constitutive equations can be derived from experimental data. The notion of single-phase or two-phase behaviors on the macroscopic scale is then examined using a microstructural analysis on idealized suspensions of spheres within a Newtonian fluid; for these suspensions, the single-phase approximation is valid only at very high or low Stokes numbers. Within this framework, the bulk stress tensor can also be constructed, which makes it possible to give a physical interpretation to yield stress. Most of the time, depending on the bulk properties (especially, particle size) and flow features, bulk behavior is either Coulomb-like or viscoplastic in simple-shear experiments. The consequences of the rheological properties on the flow features are also examined. Some remarkable properties of the governing equations describing thin layers flowing down inclined surfaces are discussed. Finally, the question of parameter fitting is tackled: since rheological properties cannot be measured directly in most cases, they must be evaluated from field data. As an example, we show that the Coulomb model successfully captures the main traits of avalanche motion, but statistical analysis demonstrates that the probability distribution of the friction coefficient is not universal.

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Coarse-Grained Debris-Flows: Hysteresis and Time-Dependent Rheology

Cited by 32 publications

References 10 publications

Experimental study on the rheological behaviour of debris flow

Experimental study on the rheological behaviour of debris flow

Modeling debris-flow runout patterns on two alpine fans with different dynamic simulation models

Plasticity and geophysical flows: A review

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