scholarly journals Analyzing the effects of vertical acceleration and deceleration in multi-phase, debris-flow sediment-column experiments / by Christine Marie Williams.

2006 ◽  
Author(s):  
Christine Marie Williams
Keyword(s):  
Debris Flow ◽  
Column Experiments ◽  
Vertical Acceleration ◽  
Sediment Column ◽  
Acceleration And Deceleration ◽  
Multi Phase

scholarly journals On the evaluation of yield stress of soils for debris flow analysis

2019 ◽  
Vol 92 ◽  
pp. 05002
Author(s):  
Carlos Besso ◽  
Tácio Mauro Pereira de Campos
Keyword(s):  
Debris Flow ◽  
Yield Stress ◽  
Mass Movement ◽  
Flow Analysis ◽  
Rheological Parameters ◽  
Test Results ◽  
Slump Test ◽  
Acceleration And Deceleration ◽  
Cheap Alternative ◽  
Set Up

Debris flow materials behave as a fluid, hence its analysis requires rheological parameters such as yield stress and viscosity. Yield stress is associated to the start and the end of the mass movement downhill in the sense that it denotes the yield transition from the creep to the flow regime, i.e., passage from solid to fluid state. This paper presents an experimental study of the yield stress of a colluvium from Rio de Janeiro, through its determination in a modified set-up of the slump test and in a rotational parallel plate rheometer. Tests were performed in five different water contents above its liquidity limit, providing a fairly good relationship between yield stress and water content. While slump test provides yield stress related to the beginning of the movement (acceleration), rheometer results are related to flow's outset and stoppage. As a result, the percentual differences between yield stresses associated with acceleration and deceleration were less than 5% in all testes, which is related to the low hysteresis effect in the flow curves obtained in the rotational rheometer. Comparing the two methodologies, it is proposed a correction from rheometer to slump test results. Results obtained are compared with data presented in other studies involving soil's yield stress, showing a good acceptance of the slump test results as a cheap alternative to rheometers.

scholarly journals Debris-Flow Hazard Assessments: A Practitioner's View

2021 ◽  
Author(s):  
Matthias Jakob
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Three Dimensional ◽  
Extreme Value Statistics ◽  
Major Life ◽  
Two Factors ◽  
Hazard Assessments ◽  
Cost Efficient ◽  
Multi Phase ◽  
Debris Flow Hazard

ABSTRACT Substantial advances have been achieved in various aspects of debris-flow hazard assessments over the past decade. These advances include sophisticated ways to date previous events, two- and three-dimensional runout models including multi-phase flows and debris entrainment options, and applications of extreme value statistics to assemble frequency–magnitude analyses. Pertinent questions have remained the same: How often, how big, how fast, how deep, how intense, and how far? Similarly, although major life loss attributable to debris flows can often, but not always, be avoided in developed nations, debris flows remain one of the principal geophysical killers in mountainous terrains. Substantial differences in debris-flow hazard persist between nations. Some rely on a design magnitude associated with a specific return period; others use relationships between intensity and frequency; and some allow for, but do not mandate, in-depth quantitative risk assessments. Differences exist in the management of debris-flow risks, from highly sophisticated and nation-wide applied protocols to retroaction in which catastrophic debris flows occur before they are considered for mitigation. Two factors conspire to challenge future generations of debris-flow researchers, practitioners, and decision makers: Population growth and climate change, which are increasingly manifested by augmenting hydroclimatic extremes. While researchers will undoubtedly finesse future remote sensing, dating, and runout techniques and models, practitioners will need to focus on translating those advances into practical cost-efficient tools and integrating those tools into long-term debris-flow risk management.

A Dilatant, Two-Phase Debris Flow Model for Hazard Mitigation

2021 ◽  
Author(s):  
Guillaume Meyrat
Keyword(s):  
Debris Flow ◽  
Practical Problem ◽  
Flow Model ◽  
Flow Behavior ◽  
Test Site ◽  
Recent Analysis ◽  
Water Type ◽  
Two Phase ◽  
Flow Measurements ◽  
Multi Phase

<p>Guillaume Meyrat, Brian McArdell, Ksenyia Ivanova, Perry Bartelt</p><p>WSL Institute for Forest, Snow and Landscape Research, 8903 Birmensdorf, Switzerland</p><p> </p><p><strong>Keywords</strong>: Debris flows, multi-phase models, dilatancy, shear stress, density distribution</p><p> </p><p>To implement an accurate numerical tool to simulate debris flow hazard is a longstanding goal of natural hazard research and engineering. In Switzerland the application of numerical debris flow models has, however, been hampered by many practical and theoretical difficulties. One practical problem is to define realistic initial conditions for hazard scenarios that involve both the rocky (granular solid) and muddy (fluid) material. Still another practical problem is to model debris flow growth by entrainment [1]. These problems are compounded by theoretical uncertainties regarding the rheological behavior of multi-phase flows. Recent analysis of debris flow measurements at the Swiss Illgraben test-site [2] (shear and normal stresses, debris flow height) show that the shear force, and therefore the entire debris flow behavior, is largely influenced by the debris flow composition, i.e. the amount of solid particle and muddy fluid at any specific location within the debris flow body (front, tail, etc.). The debris flow composition is, in turn, determined by the initial and entrainment conditions for a specific event. As a consequence, we have concluded that the very first step to construct a robust numerical model is to accurately predict the space and time evolution of the solid/fluid flow composition for any set of initial and boundary conditions. To this aim, we have developed a two-phase dilatant debris flow model [3, 4, 5] that is based on the idea that the dispersion of solid material in fluid phase can change over time. The model is thus able to predict different flow compositions (rocky fronts, watery tails), using shallow-water type mass, momentum and energy conservation equations. This helps to predict when the solid phase deposits, and when muddy fluid washes and channel outbreaks in the runout zone can occur. The parameters controlling the evolution of debris flow density and saturation have been derived by direct comparison to the full-scale measurements performed at the Illgraben test site.</p><p> </p><p><strong>References</strong></p><p><strong> </strong></p><p> </p>

scholarly journals Three-dimensional simulation of non-uniform sediment transport based on multi-phase Eulerian approach: Application to debris flow

2018 ◽  
Vol 40 ◽  
pp. 05051
Author(s):  
Kazuyuki Ota ◽  
Hitoshi Suto ◽  
Takahiro Sato
Keyword(s):  
Numerical Model ◽  
Debris Flow ◽  
Large Scale ◽  
Three Dimensional ◽  
Flow Property ◽  
Size Segregation ◽  
Particle Collisions ◽  
Sediment Size ◽  
Dimensional Simulation ◽  
Multi Phase

To simulate 3D flow of a non-uniform and highly concentrated sediment, a numerical model using a multi-phase Eulerian method for air, water, and particles of various class size is developed. This model accounts for turbulence in pore water, particle-particle collisions, and enduring friction. To test its performance, simulations were performed for large scale debris-flow experiments. The numerical model reproduces successfully the flow property and sediment size segregation of the debris flow.

scholarly journals Numerical investigation and application of 3D multi-phase non-Newtonian rheology model for debris flow

2021 ◽  
Author(s):  
Rui Li ◽  
Yuliang Teng
Keyword(s):  
Experimental Data ◽  
Debris Flow ◽  
Flow Model ◽  
Good Accuracy ◽  
Flow Simulation ◽  
Field Investigation ◽  
Plane Case ◽  
Improved Model ◽  
Multi Phase ◽  
Rheology Model

Abstract A 3D multiphase debris flow model – DebrisInterMixingFoam was studied. An improvement to include the VOF field updating in the iteration of updating the flow field variables was proposed. The improved model was first validated by a debris flow deposition on slope plane case. Then the model was applied to two benchmark debris flow cases and a real debris flow event. In all cases, the model results were favorably compared with the experimental data or field investigation data. As there were only two key parameters to be calibrated in DebrisInterMixingFoam, it was easy to be used to model debris flow. The numerical results showed that this model can achieve good accuracy for debris flow simulation after calibrations of these two key parameters.

Some Applications of the U. S. Steel MVEM

1973 ◽  
Vol 31 ◽  
pp. 4-5
Author(s):  
J. S. Lally ◽  
L. E. Thomas ◽  
R. M. Fisher
Keyword(s):  
Electron Diffraction ◽  
Debye Temperature ◽  
Metals And Alloys ◽  
Critical Voltage ◽  
Dynamical Diffraction ◽  
Phase Structures ◽  
Structure Factors ◽  
Local Bonding ◽  
Diffraction Phenomenon ◽  
Multi Phase

A variety of materials containing many different microstructures have been examined with the USS MVEM. Three topics have been selected to illustrate some of the more recent studies of diffraction phenomena and defect, grain and multi-phase structures of metals and minerals.(1) Critical Voltage Effects in Metals and Alloys - This many-beam dynamical diffraction phenomenon, in which some Bragg resonances vanish at certain accelerating voltages, Vc, depends sensitively on the spacing of diffracting planes, Debye temperature θD and structure factors. Vc values can be measured to ± 0.5% in the HVEM ana used to obtain improved extinction distances and θD values appropriate to electron diffraction, as well as to probe local bonding effects and composition variations in alloys.

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