The Effects of Particle Segregation on Debris Flow Fluidity Over a Rigid Bed

2020 ◽  
Vol 27 (1) ◽  
pp. 139-149
Author(s):  
Norifumi Hotta ◽  
Tomoyuki Iwata ◽  
Takuro Suzuki ◽  
Yuichi Sakai
Keyword(s):  
Shear Stress ◽  
Debris Flow ◽  
Debris Flows ◽  
High Speed ◽  
Particle Diameter ◽  
Flow Characteristics ◽  
Video Camera ◽  
Front Velocity ◽  
Flow Depth ◽  
Particle Segregation

ABSTRACT It is essential to consider the fluidity of a debris flow front when calculating its impact. Here we flume-tested mono-granular and bi-granular debris flows and compared the results to those of numerical simulations. We used sand particles with diameters of 0.29 and 0.14 cm at two mixing ratios of 1:1 and 3:7. Particle segregation was recorded with a high-speed video camera. We evaluated the fronts of debris flows at 0.5-second intervals. Then we numerically simulated one-dimensional debris flows under the same conditions and used the mean particle diameter when simulating mixed-diameter flows. For the mono-granular debris flows, the experimental and simulated results showed good agreement in terms of flow depth, front velocity, and flux. However, for the bi-granular debris flows, the simulated flow depth was less, and both the front velocity and flux were greater than those found experimentally. These differences may be attributable to the fact that the dominant shear stress was caused by the concentration of smaller sediment particles in the lower flow layers; such inverse gradations were detected in the debris flow bodies. Under these conditions, most shear stress is supported by smaller particles in the lower layers; the debris flow characteristics become similar to those of mono-granular flows, in contrast to the numerical simulation, which incorporated particle segregation with gradually decreasing mean diameter from the front to the flow body. Consequently, the calculated front velocities were underestimated; particle segregation at the front of the bi-granular debris flows did not affect fluidity either initially or over time.

Flume investigation of cylindrical baffles for dissipation of debris flow energy

2021 ◽  
Author(s):  
Chan-Young Yune ◽  
Beom-Jun Kim
Keyword(s):  
Energy Dissipation ◽  
Debris Flow ◽  
Debris Flows ◽  
High Speed ◽  
Flow Characteristics ◽  
Digital Camera ◽  
Major Effect ◽  
Small Scale ◽  
Design Guideline ◽  
Flow Energy

<p>A debris flow with a high speed along valleys has been reported to cause serious damages to urban area or infrastructure. To prevent debris flow disaster, countermeasures for flow-impeding structures are installed on the flow path of debris flows. Recently, an installation of cylindrical baffles which are open-type countermeasures has increased because of a low construction cost, filtering out rocks, and an increased hydraulic continuity. However, a comprehensive design guideline for specification and arrangement on cylindrical baffles has not yet been suggested. Moreover, the design of baffle installation is mainly based on empirical approaches as the influence of baffle array on debris mobility is not well understood. In this study, to investigate the effect of cylindrical baffles on the flow characteristics of debris flow, a series of small-scale flume tests were performed according to the varying baffle height and row numbers of installed baffles. High-speed cameras and digital camera to record the flow interaction with baffles were installed at the top and side of the channel. To reproduce the viscosity of debris flows caused by fine-grained soil in the flume, glycerin was mixed with debris materials (sand and gravel). After the test, the velocity and energy dissipation according to various baffle arrays were estimated. Test results showed that the installation of baffles reduced the frontal velocity of debris flows. Furthermore, taller baffles also increased the effect of the energy dissipation in debris flows, but additional rows of the baffle did not have a major effect on the energy dissipation. Thus, increasing the height of baffle led to an increased efficiency of energy dissipation of debris flows.</p>

Debris flow monitoring in China

2020 ◽  
Author(s):  
Xiaojun Guo
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Flow Characteristics ◽  
Western China ◽  
Flow Density ◽  
Flow Depth ◽  
Jinsha River ◽  
Flow Monitoring ◽  
Jiangjia Gully ◽  
Set Up

<p><strong>Abstract: </strong>Debris flow monitoring provides valuable data for scitienfic research and early warning, however, it is of difficulty to sucessfully achive because of the great damage of debris flows and the high cost. This report introduces monitoring systems in two debris flow watersheds in western China, the Jiangjia gully (JJG) in Yunnan Province and the Ergou valley in Sichuan Province. JJG is loacted in the dry-hot valley of Jinsha River, and the derbis flows are frequent due to the semi-arid climate, deep-cut topography and highly weathered slope surface. A long-term mornitoring work has been conducted in JJG and more than 500 debris flows events has been recorded since 1965. The monitoring system consists of 10 rainfall gauges and a measuring section, with instruments to measure the flow depth and velocity; and flow density is measured through sampling the fresh debris flow body. Ergou lies in the Wenchuan earthquake affected area and the monitoring began in 2013 to investigate the characteristics and development tendency of post-earthquake debris flows. Three stations were set up in the mainstream and tributaries, with instruments to measure the flow depth, velocity, and density. Over 10 debris flow events were recorded up to date.</p><p>Based on the monitoring output, the rainfall spatial distribution and thresholds for debris flows are proposed. The debris flow dynamics characteristics are analyzed, and the relations between the parameters, e.g. density, velocity, discharge and grain compositions are presented. The debris flow formation modes and the mechanisms in different regions are discriminated and simulation methods are suggested. It is anticipated that the monitoring results will promote understanding of debris flow characteristics in the western China.</p><p><strong>Keywords:</strong> Debris flow, monitoring, rainfall, discharge, formation. </p>

scholarly journals Comparison of measurement methods of the front velocity of small-scale debris flows

2015 ◽  
Vol 46 (4) ◽  
pp. 129 ◽  
Author(s):  
Francesco Bettella ◽  
Gian Battista Bischetti ◽  
Vincenzo D'Agostino ◽  
Simone Virginio Marai ◽  
Enrico Ferrari ◽  
...  
Keyword(s):  
Debris Flow ◽  
High Speed ◽  
Video Camera ◽  
Significant Loss ◽  
Front Velocity ◽  
Small Scale ◽  
Mean Flow ◽  
Digital Video Camera ◽  
Transport Zone ◽  
Kinematic Behaviour

Debris flow is a gravity-driven process, which is characterized by a travelling dense surge including large boulders, and it is followed by a more fluid tail. These characteristics make difficult the measurement of the mean flow velocity by means of common hydraulic techniques. Different methods can be used at real scale and small-scale to measure the front velocity but a dedicate comparison between available methods is still lacking. This research aims to compare the front velocity measurements in the transport zone of a miniature debris flow using three devices: i) a common digital video camera (29 frames per second); ii) a high speed thermo camera (60 fps); and iii) a laser photoelectric sensors system. The statistical analysis of data has highlighted no significant differences exist between front velocities obtained by means of the video camera and the thermo camera, whereas photocells data statistically differ from those achieved via the other systems. Some lack of data recorded by photocell was documented, while the thermo camera technique did not show significant loss of information being also helpful to detect the kinematic behaviour of single particles. Finally, the tests confirmed the influence of the solid volumetric concentration in the debris-flow mechanics, which promotes, <em>ceteris</em> <em>paribus</em>, the debris-flow slowing down.

scholarly journals Acoustic module of the Acquabona (Italy) debris flow monitoring system

2005 ◽  
Vol 5 (2) ◽  
pp. 211-215 ◽  
Author(s):  
A. Galgaro ◽  
P. R. Tecca ◽  
R. Genevois ◽  
A. M. Deganutti
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Regression Line ◽  
Front Velocity ◽  
Peak Discharge ◽  
Physical Parameters ◽  
Flow Depth ◽  
Ground Vibrations ◽  
Mountain Areas ◽  
Flow Monitoring

Abstract. Monitoring of debris flows aimed to the assessment of their physical parameters is very important both for theoretical and practical purposes. Peak discharge and total volume of debris flows are crucial for designing effective countermeasures in many populated mountain areas where losses of lives and property damage could be avoided. This study quantifies the relationship between flow depth, acoustic amplitude of debris flow induced ground vibrations and front velocity in the experimental catchment of Acquabona, Eastern Dolomites, Italy. The analysis of data brought about the results described in the following. Debris flow depth and amplitude of the flow-induced ground vibrations show a good positive correlation. Estimation of both mean front velocity and peak discharge can be simply obtained monitoring the ground vibrations, through geophones installed close to the flow channel; the total volume of debris flow can be so directly estimated from the integral of the ground vibrations using a regression line. The application of acoustic technique to debris flow monitoring seems to be of the outmost relevance in risk reduction policies and in the correct management of the territory. Moreover this estimation is possible in other catchments producing debris flows of similar characteristics by means of their acoustic characterisation through quick and simple field tests (Standard Penetration Tests and seismic refraction surveys).

Deciphering the seismic and normal-force fluctuation signatures of debris flows: an experimental assessment of the effects of flow composition and dynamics

2021 ◽  
Author(s):  
Tjalling de Haas ◽  
Amanda Aaberg ◽  
Fabian Walter ◽  
Zhen Zhang
Keyword(s):  
Debris Flow ◽  
Size Distribution ◽  
Debris Flows ◽  
Large Particle ◽  
Normal Force ◽  
Flow Volume ◽  
Flow Depth ◽  
Water Fraction ◽  
Force Fluctuations ◽  
Seismic Vibrations

&lt;p&gt;Debris flows are gravity-driven mass movements that are common natural hazards in mountain regions worldwide. Previous work has shown that measurements of ground vibrations are capable of detecting the timing, speed, and location of landslides and debris flows. A remaining question is whether or not additional flow properties, such as grain-size distribution, flow depth, and impact stress can be inferred reliably from seismic data. Here, we experimentally explore the relation of seismic vibrations and normal-force fluctuations with debris-flow composition and dynamics. We show that seismic vibrations and normal-force fluctuations induced by debris flows are strongly correlated, and that both are strongly affected by debris-flow composition. We find that the effects of the large-particle distribution on seismic vibrations and normal-force fluctuations are substantially more pronounced than the effects of water fraction, clay fraction, and flow volume, especially when normalized by flow depth. We further show that for flows with similar coarse-particle distributions seismic vibrations and normal-force fluctuations can be reasonably-well related to flow depth, even if total flow volume, water fraction, and the size distribution of fines varies. Our experimental results shed light on how changes in large-particle, clay, and water fractions affect the seismic and force-fluctuation signatures of debris flows, and provide important guidelines for their interpretation.&lt;/p&gt;

scholarly journals Effect of Density and Total Weight on Flow Depth, Velocity, and Stresses in Loess Debris Flows

Water ◽  
2018 ◽  
Vol 10 (12) ◽  
pp. 1784 ◽  
Author(s):  
Heping Shu ◽  
Jinzhu Ma ◽  
Haichao Yu ◽  
Marcel Hürlimann ◽  
Peng Zhang ◽  
...  
Keyword(s):  
Normal Stress ◽  
Debris Flows ◽  
High Speed ◽  
Goodness Of Fit ◽  
Flow Behavior ◽  
Fluid Pressure ◽  
Pore Fluid ◽  
Flow Depth ◽  
Pore Fluid Pressure ◽  
Mixture Density

Debris flows that involve loess material produce important damage around the world. However, the kinematics of such processes are poorly understood. To better understand these kinematics, we used a flume to measure the kinematics of debris flows with different mixture densities and weights. We used sensors to measure pore fluid pressure and total normal stress. We measured flow patterns, velocities, and depths using a high-speed camera and laser range finder to identify the temporal evolution of the flow behavior and the corresponding peaks. We constructed fitting functions for the relationships between the maximum values of the experimental parameters. The hydrographs of the debris flows could be divided into four phases: increase to a first minor peak, a subsequent smooth increase to a second peak, fluctuation until a third major peak, and a final continuous decrease. The flow depth, velocity, total normal stress, and pore fluid pressure were strongly related to the mixture density and total mixture weight. We defined the corresponding relationships between the flow parameters and mixture kinematics. Linear and exponential relationships described the maximum flow depth and the mixture weight and density, respectively. The flow velocity was linearly related to the weight and density. The pore fluid pressure and total normal stress were linearly related to the weight, but logarithmically related to the density. The regression goodness of fit for all functions was >0.93. Therefore, these functions are accurate and could be used to predict the consequences of loess debris flows. Our results provide an improved understanding of the effects of mixture density and weight on the kinematics of debris flows in loess areas, and can help landscape managers prevent and design improved engineering solutions.

scholarly journals Relationship between the accumulation of sediment storage and debris-flow characteristics in a debris-flow initiation zone, Ohya landslide body, Japan

2017 ◽  
Vol 17 (11) ◽  
pp. 1923-1938 ◽  
Author(s):  
Fumitoshi Imaizumi ◽  
Yuichi S. Hayakawa ◽  
Norifumi Hotta ◽  
Haruka Tsunetaka ◽  
Okihiro Ohsaka ◽  
...  
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Laser Scanning ◽  
Flow Characteristics ◽  
Sediment Supply ◽  
Physical Analysis ◽  
Saturated Flow ◽  
Initiation Zone ◽  
Landslide Body ◽  
Steep Terrain

Abstract. Debris flows usually occur in steep mountain channels and can be extremely hazardous as a result of their destructive power, long travel distance, and high velocity. However, their characteristics in the initiation zones, which could possibly be affected by temporal changes in the accumulation conditions of the storage (i.e., channel gradient and volume of storage) associated with sediment supply from hillslopes and the evacuation of sediment by debris flows, are poorly understood. Thus, we studied the relationship between the flow characteristics and the accumulation conditions of the storage in an initiation zone of debris flow at the Ohya landslide body in Japan using a variety of methods, including a physical analysis, a periodical terrestrial laser scanning (TLS) survey, and field monitoring. Our study clarified that both partly and fully saturated debris flows are important hydrogeomorphic processes in the initiation zones of debris flow because of the steep terrain. The predominant type of flow varied temporally and was affected by the volume of storage and rainfall patterns. Fully saturated flow dominated when the total volume of storage was  <  10 000 m3, while partly saturated flow dominated when the total volume of the storage was  >  15 000 m3. Debris flows form channel topography which reflects the predominant flow types during debris-flow events. Partly saturated debris flow tended to form steeper channel sections (22.2–37.3°), while fully saturated debris flow tended to form gentler channel sections ( <  22.2°). Such relationship between the flow type and the channel gradient could be explained by a simple analysis of the static force at the bottom of the sediment mass.

Comparison of the surface velocity of a debris flow at the Gadria creek using pulse compression radar and digital particle image velocimetry (DPIV).

2020 ◽  
Author(s):  
Tobias Schöffl ◽  
Georg Nagl ◽  
Johannes Hübl
Keyword(s):  
Particle Image Velocimetry ◽  
Debris Flow ◽  
Debris Flows ◽  
Pulse Compression ◽  
Particle Image ◽  
Video Camera ◽  
Digital Particle Image Velocimetry ◽  
Surface Velocity ◽  
Image Velocimetry ◽  
Pulse Compression Radar

&lt;p&gt;&lt;strong&gt;Comparison of the surface velocity of a debris flow at the Gadria creek using pulse compression radar and digital particle image velocimetry (DPIV).&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;&amp;#160;&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Tobias Sch&amp;#246;ffl, Georg Nagl, Johannes H&amp;#252;bl&lt;/p&gt;&lt;p&gt;Institute of Mountain Risk Engineering, University of Natural Resources and Life Sciences, Vienna, Austria&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;A central aspect of protection against debris flows is the understanding of the process. The flow velocity is an important parameter which is used, for example, in the dimensioning of protective structures, for technical building protection and for early warning systems. The measurement of the surface velocity which is regarded as the maximum velocity occurring within a debris flow, is therefore an essential link in the chain of fundamental process research and applied protection against natural hazards.&lt;/p&gt;&lt;p&gt;Due to the further development of various technologies such as video technology and high-frequency radar technology, the non-contact measurement of the surface speed of a debris flow has improved significantly in recent years. Radar technology provides a wide aspect of applications in alpine mass movements such as debris flows, avalanches and rockfall and is able to detect such processes up to a range of 2500 meters in distance. An additional beneficial feature is the possibility of non-contact measurement of the surface velocity. In the catchment area of the Gadria basin (South Tyrol, Italy), the measuring station, which has been in operation since 2016, has been extended by a pulse compression radar and a new HD video camera. On July 26, 2019 a debris flow consisting of several surges was recorded with both the radar and the HD video camera. To obtain surface velocity data from the video material, the material was analyzed and evaluated using digital particle image velocimetry by making use of the MATLAB software and its freely accessible ADD-On &quot;PIVlab&quot;.&lt;/p&gt;&lt;p&gt;The results of the compared surface velocity data showed a value of up to 0.74 according to the statistical mean of the coefficient of determination. The results demonstrate the high effectiveness of the pulse compression radar and the DPIV analysis in a wide range of the assessment of surface velocity of natural debris flows. There is great potential in both measuring systems and the chosen comparative analysis provides a blueprint for future recorded debris flows.&lt;/p&gt;

An Investigation of Flame Expansion Speed With a Strong Swirl Motion Using High-Speed Visualization

2003 ◽  
Vol 125 (2) ◽  
pp. 485-493
Author(s):  
S. H. Joo ◽  
K. M. Chun ◽  
Y. Shin ◽  
K. C. Lee
Keyword(s):  
High Speed ◽  
Combustion Process ◽  
Flow Characteristics ◽  
Video Camera ◽  
Frame Rate ◽  
Superposition Method ◽  
Linear Superposition ◽  
Compression Stroke ◽  
Engine Cylinder ◽  
Expansion Speed

In this study, a simple linear supposition method is proposed to separate the flame expansion speed and swirl motion of a flame propagating in an engine cylinder. Two series of images of flames propagating in the cylinder with/without swirl motion were taken by a high frame rate digital video camera. A small tube (4 mm ID) was installed inside the intake port to deliver the fuel/air mixture with strong swirl motion into the cylinder. An LDV was employed to measure the swirl motion during the compression stroke. Under the assumption that flame propagates spherically from the each point of the flame front, a diameter of small spherical flames can be calculated from the two consecutive images of the flame without swirl motion in the cylinder. Using the normalized swirl motion of the mixture during the compression stroke and the spherical flame diameters, the flame expansion speed and swirl ratio of combustion propagation in the engine cylinder can be obtained. This simple linear superposition method for separating the flame expansion speed and swirl motion can be utilized to understand the flow characteristics, such as swirl and turbulence, during the combustion process.

scholarly journals Laboratory Analysis of Debris Flow Characteristics and Berm Performance

Water ◽  
2021 ◽  
Vol 13 (16) ◽  
pp. 2223
Author(s):  
Kukhyun Ryou ◽  
Hyungjoon Chang ◽  
Hojin Lee
Keyword(s):  
Debris Flow ◽  
Flow Velocity ◽  
Flow Characteristics ◽  
Flow Depth ◽  
Volumetric Concentration ◽  
Runout Distance ◽  
Deposition Area ◽  
Lateral Width ◽  
Channel Slope ◽  
Study Laboratory

In this study, laboratory tests were used to determine the deposition characteristics (runout distance, lateral width, and deposition area) of debris flow and their relationships with the flow characteristics (flow velocity and flow depth) according to the presence of a berm. An experimental flume 1.3 to 1.9 m long, 0.15 m wide, and 0.3 m high was employed to investigate the effects of channel slope and volumetric concentration of sediment with and without the berm. The runout distance (0.201–1.423 m), lateral width (0.045–0.519 m), and deposition area (0.008–0.519 m2) increased as the channel slope increased and as the volumetric concentration of sediment decreased. These quantities also increased with the flow velocity and flow depth. In addition, the maximum reductions in the runout distance, lateral width, and deposition area were 69.1%, 65.9%, and 93%, respectively, upon berm installation. The results of this study illustrate general debris flow characteristics according to berm installation; the reported relationship magnitudes are specific to the experimental conditions described herein. However, the results of this study contribute to the design of site-specific berms in the future by providing data describing the utility and function of berms in mitigating debris flow.

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