scholarly journals Stress anisotropy in natural debris flows during impacting a monitoring structure

Landslides ◽  
2021 ◽  
Author(s):  
Georg Nagl ◽  
Johannes Hübl ◽  
Roland Kaitna
Keyword(s):  
Debris Flows ◽  
Flow Direction ◽  
Vertical Wall ◽  
Force Plate ◽  
Frictional Resistance ◽  
Gravitational Mass ◽  
Analytical Models ◽  
Stress Anisotropy ◽  
Mass Flows ◽  
Stress Ratios

AbstractThe frictional resistance of rock and debris is supposed to induce stress anisotropy in the unsteady, non-uniform flow of gravitational mass flows, including debris flows. Though widely used in analytical models and numerical simulation tools, concurrent measurements of stresses in different directions are not yet available for natural flow events. The present study aims to investigate the relation of longitudinal and bed-normal stress exerted by two natural debris flows impacting a monitoring barrier in the Gadria creek, Italy. For that, a force plate in front of a barrier was used to continuously record forces normal to the channel bed, whereas load cells mounted on the vertical wall of the barrier recorded forces in flow direction. We observed an anisotropic stress state during most of the flow events, with stress ratios ranging between 0.1 and 3.5. Video recordings reveal complex deposition and re-mobilization patterns in front of the barrier during surges and highlight the unsteady nature of debris flows. These first-time in-situ measurements confirm the assumption of stress anisotropy in natural debris flows for gravitational mass flows, and provide data for model testing.

In-situ measurements of stress anisotropy in natural debris flows 

2021 ◽  
Author(s):  
Georg Nagl ◽  
Johannes Hübl ◽  
Roland Kaitna
Keyword(s):  
Debris Flows ◽  
Stress Ratio ◽  
Vertical Wall ◽  
Fluid Pressure ◽  
Pore Fluid ◽  
Gravitational Mass ◽  
Analytical Models ◽  
Pore Fluid Pressure ◽  
Stress Anisotropy ◽  
Mass Flows

<p>Stress anisotropy affects the motion of gravitational mass flows, including debris flows, rock and snow avalanches. Though widely used in analytical models and numerical simulation tools, direct measurements of stress anisotropy in debris flows are not yet available. The present study aims to investigate the ratio of longitudinal to normal pressure exerted by two natural debris flows impacting a monitoring structure in the Gadria creek, IT. The fin-shaped structure in the middle of the channel is equipped with a force plate upstream of the barrier and load cells on the vertical wall of the barrier, continuously recording forces in flow and bed-normal direction. Additionally, the flow height and basal pore fluid pressure were measured. Here we present data from surges of two debris-flow events with peak flow heights of 2.5 m and velocities up to 4 m/s. The ratio of pore fluid pressure to normal stress (often termed liquefaction ratio) reached values up to 0.8. We find an anisotropic stress state during most of the flow event, with stress ratios ranging between 0.1 and 3.5. Video recordings reveal complex deposition and re-mobilization patterns in front of the barrier during surges and highlight the unsteady nature of debris flows. We find a correlation of the stress ratio with flow depth. There is a weak correlation between stress ratio and liquefaction ratio during the falling limb of the surge hydrographs.  Our monitoring data confirm the assumption of stress anisotropy in natural debris flows and support the earth-pressure concept used for gravitational mass flows.</p>

scholarly journals The Heat of the Flow: Thermal Equilibrium in Gravitational Mass Flows

2018 ◽  
Vol 45 (20) ◽  
Author(s):  
Jan‐Thomas Fischer ◽  
Roland Kaitna ◽  
Kilian Heil ◽  
Ingrid Reiweger
Keyword(s):  
Thermal Equilibrium ◽  
Gravitational Mass ◽  
Mass Flows

A two-fluid model for avalanche and debris flows

2005 ◽  
Vol 363 (1832) ◽  
pp. 1573-1601 ◽  
Author(s):  
E. Bruce Pitman ◽  
Long Le
Keyword(s):  
Debris Flows ◽  
Fluid Model ◽  
Solid Material ◽  
Fluid Inertia ◽  
Two Phase ◽  
Engineering Research ◽  
Mass Flows ◽  
Two Fluid Model ◽  
Two Fluid ◽  
Geophysical Mass Flows

Geophysical mass flows—debris flows, avalanches, landslides—can contain O (10 6 –10 10 ) m 3 or more of material, often a mixture of soil and rocks with a significant quantity of interstitial fluid. These flows can be tens of meters in depth and hundreds of meters in length. The range of scales and the rheology of this mixture presents significant modelling and computational challenges. This paper describes a depth-averaged ‘thin layer’ model of geophysical mass flows containing a mixture of solid material and fluid. The model is derived from a ‘two-phase’ or ‘two-fluid’ system of equations commonly used in engineering research. Phenomenological modelling and depth averaging combine to yield a tractable set of equations, a hyperbolic system that describes the motion of the two constituent phases. If the fluid inertia is small, a reduced model system that is easier to solve may be derived.

Slip and Fall Characterization of Floors

2004 ◽  
Author(s):  
Peter J. Poczynok ◽  
Ralph L. Barnett
Keyword(s):  
General Theory ◽  
Contact Point ◽  
Force Plate ◽  
Frictional Resistance ◽  
Value Theory ◽  
Reliability Theory ◽  
Duty Cycles ◽  
Time Period ◽  
Five Disciplines

During ambulation, every maneuver causes the feet to impose a tangential loading at each contact with the floor. If the frictional resistance at the contact point is less than the associated tangential loading, slipping occurs and sometimes falling. There are five disciplines, some recently developed, that enable one to develop the general theory for predicting the number of walkers who will slip within a given time period on a statistically homogeneous and isotropic floor. These include force-plate studies, floor duty cycles, tribometry, extreme value theory of slipperiness, and floor reliability theory. When used with some additional bookkeeping notions, the general theory will be extended to real floors traversed by walkers with multiple ambulation styles and wearing a variety of footwear. In contrast, conventional slip and fall theory does not account for floor usage, different footwear and various ambulation styles, nor can it be used to determine the number of walkers who actually slip on a given floor.

scholarly journals Biomechanical assessment of various punching techniques

2020 ◽  
Author(s):  
Jiri Adamec ◽  
Peter Hofer ◽  
Stefan Pittner ◽  
Fabio Monticelli ◽  
Matthias Graw ◽  
...  
Keyword(s):  
High Speed ◽  
Vertical Wall ◽  
Force Plate ◽  
Physical Parameters ◽  
Time Curve ◽  
Biomechanical Assessment ◽  
Sports Science ◽  
General Terms ◽  
Force Time ◽  
The Impact

Abstract Punches without the use of instruments/objects are a common type of body violence and as such a frequent subject of medicolegal analyses. The assessment of the injuries occurred as well as of the potential of the assault to produce severe body harm is based on objective traces (especially the documented injuries of both parties involved) as well as the—often divergent—descriptions of the event. Quantitative data regarding the punching characteristics that could be used for the assessment are rare and originate mostly in sports science. The aim of this study was to provide physical data enabling/facilitating the assessment of various punching techniques. A total of 50 volunteers took part in our study (29 males and 21 females) and performed severe punches with the fist, with the small finger edge of the hand (karate chop), and with the open hand with both the dominant and the non-dominant hands in randomized order. The strikes were performed on a boxing pad attached to a KISTLER force plate (sampling frequency 10,000 Hz) mounted on a vertical wall. The punching velocity was defined as the hand velocity over the last 10 cm prior to the contact to the pad and ascertained by using a high-speed camera (2000 Hz). Apart from the strike velocity, the maximum force, the impulse (the integral of the force-time curve), the impact duration, and the effective mass of the punch (the ratio between the impulse and the strike velocity) were measured/calculated. The results show a various degree of dependence of the physical parameters of the strikes on the punching technique, gender, hand used, body weight, and other factors. On the other hand, a high degree of variability was observed that is likely attributable to individual punching capabilities. In a follow-up study, we plan to compare the “ordinary” persons with highly trained (boxers etc.) individuals. Even though the results must be interpreted with great caution and a direct transfer of the quantitative parameters to real-world situations is in general terms not possible, the study offers valuable insights and a solid basis for a qualified forensic medical/biomechanical assessment.

Critical bed shear for initial movement of sediments on a combined lateral and longitudinal slope

2004 ◽  
Vol 35 (2) ◽  
pp. 153-164 ◽  
Author(s):  
Subhasish Dey
Keyword(s):  
Shear Stress ◽  
Flow Direction ◽  
Side Wall ◽  
Shear Stresses ◽  
Bed Shear Stress ◽  
Conduit Flow ◽  
Sloping Bed ◽  
Stress Ratios ◽  
Closed Conduit ◽  
Initial Movement

An experimental study on critical bed shear-stress for initial movement of non-cohesive sediment particles under a steady-uniform stream flow on a combined lateral (across the flow direction) and longitudinal (streamwise direction) sloping bed is presented. The aim of this paper is to ascertain that the critical bed shear-stress on a combined lateral and longitudinal sloping bed is adequately represented by the product of critical bed shear-stress ratios for lateral and longitudinal sloping beds. Experiments were carried out with closed-conduit flow, in two ducts having a semicircular invert section, with three sizes of sediments. In laboratory flumes, the uniform flow is a difficult – if not impossible – proposition for a steeply sloping channel, and is impossible to obtain in an adversely sloping channel. To avoid this problem, the experiments were conducted with a closed-conduit flow. The critical bed shear-stresses for experimental runs were estimated from side-wall correction. The experimental data agree satisfactorily with the results obtained from the proposed formula.

scholarly journals DAMAGE TO REINFORCED CONCRETE BUILDINGS AND COASTAL TREES DUE TO THE 2011 OFF THE PACIFIC COAST OF TOHOKU EARTHQUAKE TSUNAMI

2012 ◽  
Vol 1 (33) ◽  
pp. 51 ◽  
Author(s):  
Hideo Matsutomi ◽  
Eriko Yamaguchi ◽  
Kazunori Naoe ◽  
Kenji Harada
Keyword(s):  
Pacific Coast ◽  
Vertical Section ◽  
Flow Direction ◽  
Vertical Wall ◽  
Field Tests ◽  
Tohoku Earthquake ◽  
Simple Method ◽  
Field Surveys ◽  
The Pacific ◽  
Damage Condition

Macroscopic conditions of the damage to RC building and coastal black pine tree in the 2011 Off the Pacific Coast of Tohoku Earthquake Tsunami are discussed through field surveys and field tests. Effects of RC building’s location and arrangement, submerged vertical section area in the tsunami inundation flow direction, ratio of the area of submerged windows and/or doorways to the area of submerged vertical wall on the side hit by the inundation flow (so-called, aperture ratio), and foundation piles on the damage condition of the building are examined. The damage condition of the coastal tree is also discussed from the viewpoints of the drag force and moment assessed using inundation flow velocity estimated by a simple method. Moreover, effects and limits of coastal woods on the tsunami energy and force reductions are illustrated through the field surveys.

scholarly journals Modelling erosion and deposition in geophysical granular mass flows

2021 ◽  
Vol 52 (1) ◽  
pp. 29-32
Author(s):  
Sylvain Viroulet ◽  
Chris Johnson ◽  
Nico Gray
Keyword(s):  
Debris Flows ◽  
Large Scale ◽  
Laboratory Experiments ◽  
Pyroclastic Flows ◽  
Small Scale ◽  
Snow Avalanches ◽  
Erosion And Deposition ◽  
Granular Rheology ◽  
Scale Models ◽  
Mass Flows

During hazardous geophysical mass flows, such as rock or snow avalanches, debris flows and volcanic pyroclastic flows, a continuous exchange of material can occur between the slide and the bed. The net balance between erosion and deposition of particles can drastically influence the behaviour of these flows. Recent advances in describing the non-monotonic effective basal friction and the internal granular rheology in depth averaged theories have enabled small scale laboratory experiments (see fig. 1) to be quantitatively reproduced and can also be implemented in large scale models to improve hazard mitigation.

Influence of Upstream Conditions and Gravity on Highly Inertial Thin-Film Flow

2008 ◽  
Vol 130 (6) ◽  
Author(s):  
Roger E. Khayat
Keyword(s):  
Thin Film ◽  
Free Surface ◽  
Flow Field ◽  
Film Flow ◽  
Flow Direction ◽  
Vertical Wall ◽  
Galerkin Projection ◽  
Thin Film Flow ◽  
Thin Film Equations ◽  
Horizontal Wall

Steady two-dimensional thin-film flow of a Newtonian fluid is examined in this theoretical study. The influence of exit conditions and gravity is examined in detail. The considered flow is of moderately high inertia. The flow is dictated by the thin-film equations of boundary layer type, which are solved by expanding the flow field in orthonormal modes in the transverse direction and using Galerkin projection method, combined with integration along the flow direction. Three types of exit conditions are investigated, namely, parabolic, semiparabolic, and uniform flow. It is found that the type of exit conditions has a significant effect on the development of the free surface and flow field near the exit. While for the parabolic velocity profile at the exit, the free surface exhibits a local depression, for semiparabolic and uniform velocity profiles, the height of the film increases monotonically with streamwise position. In order to examine the influence of gravity, the flow is studied down a vertical wall as well as over a horizontal wall. The role of gravity is different for the two types of wall orientation. It is found that for the horizontal wall, a hydraulic-jump-like structure is formed and the flow further downstream exhibits a shock. The influence of exit conditions on shock formation is examined in detail.

Floor Reliability With Respect to “Slip and Fall”

2005 ◽  
Author(s):  
Ralph Lipsey Barnett ◽  
Peter Joseph Poczynok
Keyword(s):  
Force Plate ◽  
Frictional Resistance ◽  
Reliability Theory ◽  
Extreme Value Statistics ◽  
Horizontal Resistance ◽  
Friction Forces ◽  
Statistical Characterization ◽  
Friction Resistance ◽  
First Time

For a given community of walkers and a specific type of ambulation, force-plate studies have established the required level of horizontal resistance for stable locomotion. This stochastic floor loading is resisted by friction forces which must be great enough to prevent slipping. A statistical characterization of frictional resistance has recently been developed using extreme value statistics. Reliability theory provides a method for combining the floor loading and friction resistance which, for the first time, enables one to determine in a rational manner the probability of slipping. This paper presents a formula describing the “slip and fall” reliability of a floor/footwear couple.

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