scholarly journals Effects of Barrier Stiffness on Debris Flow Dynamic Impact—I: Laboratory Flume Test

Water ◽  
2022 ◽  
Vol 14 (2) ◽  
pp. 177
Author(s):  
Yu Huang ◽  
Xiaoyan Jin ◽  
Junji Ji
Keyword(s):  
Debris Flow ◽  
Dead Zone ◽  
Peak Load ◽  
Buffer Effect ◽  
Engineering Structures ◽  
Impact Forces ◽  
Flume Tests ◽  
Run Up ◽  
The Impact

Debris flows often cause local damage to engineering structures by exerting destructive impact forces. The debris-flow–deformable-barrier interaction is a significant issue in engineering design. In this study, a large physical flume model test device was independently designed to repeatedly reproduce the flow and impact process of debris flow. Three physical flume tests were performed to investigate the effect of barrier stiffness on the debris flow impact. The flow kinematics of debris flow with three barrier stiffness values are essentially consistent with the process of impact–run-up–falling–pile-up. The development of a dead zone provided a cushion to diminish the impact of the follow-up debris flow on the barrier. The peak impact forces were attenuated as the barrier stiffness decreased. The slight deflections of a deformable barrier were sufficiently effective for peak load attenuation by up to 30%. It showed that the decrease of the barrier stiffness had a buffer effect on the debris flow impact and attenuated the peak impact force. And with the decrease of the barrier stiffness, when the barrier was impacted by the same soil types, the recoverable elastic strain will be larger, and the strain peak will be more obvious.

The Effects of Upstream Flexible Barrier on the Debris Flow Entrainment and Impact Dynamics on a Terminal Barrier

2021 ◽  
Author(s):  
Hervé Vicari ◽  
C.W.W. Ng ◽  
Steinar Nordal ◽  
Vikas Thakur ◽  
W.A. Roanga K. De Silva ◽  
...  
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Impact Force ◽  
Dynamic Pressure ◽  
Pressure Coefficient ◽  
Flexible Barrier ◽  
Impact Forces ◽  
Flexible Barriers ◽  
The Impact ◽  
Bed Entrainment

The destructive nature of debris flows is mainly caused by flow bulking from entrainment of an erodible channel bed. To arrest these flows, multiple flexible barriers are commonly installed along the predicted flow path. Despite the importance of an erodible bed, its effects are generally ignored when designing barriers. In this study, three unique experiments were carried out in a 28 m-long flume to investigate the impact of a debris flow on both single and dual flexible barriers installed in a channel with a 6 m-long erodible soil bed. Initial debris volumes of 2.5 m<sup>3</sup> and 6 m<sup>3</sup> were modelled. For the test setting adopted, a small upstream flexible barrier before the erodible bed separates the flow into several surges via overflow. The smaller surges reduce bed entrainment by 70% and impact force on the terminal barrier by 94% compared to the case without an upstream flexible barrier. However, debris overflowing the deformed flexible upstream barrier induces a centrifugal force that results in a dynamic pressure coefficient that is up to 2.2 times higher than those recommended in guidelines. This suggests that although compact upstream flexible barriers can be effective for controlling bed entrainment, they should be carefully designed to withstand higher impact forces.

scholarly journals Debris Flow Damage Assessment by Considering Debris Flow Direction and Direction Angle of Structure in South Korea

Water ◽  
2019 ◽  
Vol 11 (2) ◽  
pp. 328 ◽  
Author(s):  
Dong Nam ◽  
Man-Il Kim ◽  
Dong Kang ◽  
Byung Kim
Keyword(s):  
South Korea ◽  
Debris Flow ◽  
Debris Flows ◽  
Impact Force ◽  
Mountainous Areas ◽  
Mountainous Regions ◽  
Impact Forces ◽  
The Impact

Recently, human and property damages have often occurred due to various reasons—such as landslides, debris flow, and other sediment-related disasters—which are also caused by regional torrential rain resulting from climate change and reckless development of mountainous areas. Debris flows mainly occur in mountainous areas near urban living communities and often cause direct damages. In general, debris flows containing soil, rock fragments, and driftwood temporarily travel down to lower parts along with a mountain torrent. However, debris flows are also often reported to stream down from the point where a slope failure or a landslide occurs in a mountain directly to its lower parts. The impact of those debris flows is one of the main factors that cause serious damage to structures. To mitigate such damage of debris flows, a quantitative assessment of the impact force is thus required. Moreover, technologies to evaluate disaster prevention facilities and structures at disaster-prone regions are needed. This study developed two models to quantitatively analyze the damages caused by debris flows on structures: Type-1 model for calculating the impact force, which reflected the flow characteristics of debris flows and the Type-2 model, which calculated the impact force based on the topographical characteristics of mountainous regions. Using RAMMS a debris flow runoff model, the impact forces assessed through Type-1 and Type-2 models were compared to check reliability. Using the assessed impact forces, the damage ratio of the structures was calculated and the amount of damage caused by debris flows on the structures was ultimately assessed. The results showed that the Type-1 model overestimated the impact force by 10% and the Type-2 model by 4% for Mt. Umyeon in Seoul, compared to the RAMMS model. In addition, the Type-1 model overestimated the impact force by 3% and Type-2 by 2% for Mt. Majeok in Chuncheon, South Korea.

Relationships between size and velocity for particles within debris flows

2008 ◽  
Vol 45 (12) ◽  
pp. 1778-1783 ◽  
Author(s):  
Adam B. Prochaska ◽  
Paul M. Santi ◽  
Jerry D. Higgins
Keyword(s):  
Particle Size ◽  
Debris Flow ◽  
Particle Velocity ◽  
Video Analysis ◽  
Debris Flows ◽  
Impact Force ◽  
Analysis Software ◽  
Impact Forces ◽  
The Impact ◽  
Current Guidelines

Estimation of the impact forces from boulders within a debris flow is important for the design of structural mitigation elements. Boulder impact force equations are most sensitive to the inputs of particle size and particle velocity. Current guidelines recommend that a design boulder should have a size equal to the depth of flow and a velocity equal to that of the flow. This study used video analysis software to investigate the velocities of different sized particles within debris flows. Particle velocity generally decreased with increasing particle size, but the rate of decrease was found to be dependent on the abilities of particles to rearrange within debris flows.

scholarly journals Load model for designing flexible steel barriers for debris flow mitigation

2019 ◽  
Vol 56 (6) ◽  
pp. 893-910 ◽  
Author(s):  
Corinna Wendeler ◽  
Axel Volkwein ◽  
Brian W. McArdell ◽  
Perry Bartelt
Keyword(s):  
Debris Flow ◽  
Pressure Coefficient ◽  
Flow Characteristics ◽  
Field Tests ◽  
Load Model ◽  
Dynamic Part ◽  
Pass Through ◽  
Run Up ◽  
Water Saturated ◽  
The Impact

Light-weight flexible steel net barriers catch coarse debris, but let some of the fine material and water pass through the net. They are difficult to design so that they can withstand the impact pressures of both boulder-laden granular and water-saturated debris flows. Using results from laboratory and full-scale field tests, a debris flow load model has been developed for flexible barriers in torrent channels. The model accounts for the forces of initial impact as well as the filling process discretized stepwise over time (barriers in the field and laboratory fill continuously). Laboratory tests with fast debris flow front velocities revealed a run-up behaviour that was not observed in the field (“pile-up”). The load model divides the flow forces into a hydrostatic component and a dynamic part depending on a pressure coefficient, the flow velocity, and the density of the flow. This dynamic part, which is more complex to quantify, accounts for the wide-ranging debris flow characteristics from watery and muddy debris floods to granular friction-dominated mass flows.

scholarly journals Estimation of Velocity Profile in a Hyper-Concentrated Flow: a Critical Analysis of Bagnold Equation

10.29007/kd81 ◽  
2018 ◽  
Author(s):  
Donatella Termini ◽  
Antonio Fichera
Keyword(s):  
Velocity Profile ◽  
Debris Flow ◽  
Flow Velocity ◽  
Critical Analysis ◽  
Sediment Concentration ◽  
Concentrated Flow ◽  
Impact Forces ◽  
The Impact ◽  
The Vertical Distribution ◽  
Distribution Of Flow

Debris flow velocity is an important factor which influences the impact forces and runup. Due to the complexity of the phenomenon, it is difficult to define predictive methodologies. The present work reports some results of an experimental run conducted in order to investigate the velocity and sediment concentration distributions. A modified Bagnold’s approach to calculate the vertical distribution of flow velocity is presented.

A combined model approach for debris-flow impact forces

2021 ◽  
Author(s):  
Lukas Reider ◽  
Anna-Lisa Fuchs ◽  
Lisa Dankwerth ◽  
Susanna Wernhart ◽  
Roland Kaitna ◽  
...  
Keyword(s):  
Debris Flow ◽  
Correction Factor ◽  
Debris Flows ◽  
Flow Behaviour ◽  
Material Composition ◽  
Correction Factors ◽  
Additional Pressure ◽  
Impact Forces ◽  
Pressure Term ◽  
The Impact

&lt;p&gt;For the design of mitigation measures knowledge of debris-flow impact forces, usually estimated based on hydrostatic, hydrodynamic, or combined approaches, is essential. As these approaches are based on Newtonian fluids, they must be adjusted by empirical correction factors to account for the solid-fluid nature of debris flows. The values for the correction factors shown in the literature vary over a wide range and several studies showed a clear dependence with the Froude regime of debris flows.&lt;/p&gt;&lt;p&gt;To better understand the correction factors and to be able to calculate them using parameters that describe the flow behaviour a total of 32 experiments were conducted in the course of the project &amp;#8220;Debris flow impact forces on bridge super structures (DEFSUP)&amp;#8221;, funded by the Austrian Science Fund (FWF). Two different material compositions, different water contents as well as a total impact and a bypassing of the measuring block were tested.&lt;/p&gt;&lt;p&gt;The experimental setup designed within the project consists of a 4 m long semi-circular channel with a diameter of 300 mm and an inclination of 20&amp;#176;. The material is released from a rectangular reservoir in a dam-break scenario and accelerated with zero roughness on a length of 1.2 m and transferred to the semi-circle profile. The subsequently introduced roughness with a grain diameter of 1-2 mm generates a stationary phenomenological debris flow until it hits the measuring setup. With a starting volume of 50 kg, flow heights between 8 and 12 cm and velocities from 0.8 to 2.2 m/s were achieved according to the material composition and different water content. With these different mixtures a Froude-range from 0.6 to 3.6 was covered. In addition, normal stresses and pore water pressures were measured at the exact same point.&lt;/p&gt;&lt;p&gt;A detailed analysis of the measured impact forces together with the above mentioned measured parameters showed that the hydrodynamic correction factor is a constant mainly corresponding to the liquification ratio of the debris-flow mixture. Hence, the hydrodynamic correction factor can be regarded as a drag coefficient and seems to depend mainly on the internal friction of the flowing medium. At low Froude numbers measured impact forces exceed even a full momentum transfer if the mean bulk density is used for the calculation. This indicates that the impact forces can no longer be described by the hydrodynamic approach alone. For this reason, an additional pressure term based on a hydrostatic approach is considered in the combined concept. This additional pressure term depends on the dynamics of flow (Froude number) and can be modelled via a dynamic earth pressure coefficient.&lt;/p&gt;&lt;p&gt;The findings from these experiments contribute to a better prediction of debris-flows impact forces in terms of their material composition and flow behaviour.&lt;/p&gt;

An experimental evaluation of impact force on a fiber bragg grating (FBG)-based device for debris flow warning

2020 ◽  
Author(s):  
Shaojie Zhang
Keyword(s):  
Debris Flow ◽  
Fiber Bragg Grating ◽  
Debris Flows ◽  
Impact Force ◽  
Dynamic Strain ◽  
Bragg Grating ◽  
New Device ◽  
Impact Forces ◽  
Measured Strain ◽  
The Impact

&lt;p&gt;Conventional sensors for debris flow monitoring suffer from several drawbacks including low service life, low reliability in long-distance data transfer, and stability in severe weather conditions. Recently, fiber Bragg grating (FBG)-based sensors have been developed to monitor debris flows. However, they can be easily damaged by the impact forces of boulders within debris flow. This paper presents a new FBG-based device to measure the strain induced by the impact force of debris flow with high reliability and effectiveness. The effects of the impact forces of debris flows have been investigated. Then, the relationship between the strain and the debris flow energy correlating with the damage to building structures has been established. It is shown that this new FBG-based device is capable of monitoring and warning about debris flows. The impact experiment results show that the peak value of dynamic strain on the fixed end of the new device is positively correlated with the external impact force. Using an impact force, we establish a relationship between the measured strain and the potential of a debris flow resulting in damage to structures was established. This follows the general rule that a larger measured strain corresponds to a higher level of debris flow. Using this relationship, we can quantify a dangerous level of debris flow using the monitored strain data. Our new device is capable of monitoring and warning about dangerous debris flows, allowing for more effective debris flow mitigation.&lt;/p&gt;

scholarly journals Effects of Barrier Stiffness on Debris Flow Dynamic Impact—II: Numerical Simulation

Water ◽  
2022 ◽  
Vol 14 (2) ◽  
pp. 182
Author(s):  
Yu Huang ◽  
Xiaoyan Jin ◽  
Junji Ji
Keyword(s):  
Debris Flow ◽  
Smoothed Particle Hydrodynamics ◽  
Impact Force ◽  
Time History ◽  
Appreciable Effect ◽  
Engineering Structures ◽  
Dynamic Component ◽  
Particle Hydrodynamics ◽  
Smoothed Particle ◽  
The Impact

The destructive and impactful forces of debris flow commonly causes local damage to engineering structures. The effect of a deformable barrier on the impact dynamics is important in engineering design. In this study, a flow–structure coupled with Smoothed Particle Hydrodynamics model was presented to investigate the effects of barrier stiffness on the debris impact. A comparison of the results of physical tests and simulation results revealed that the proposed smoothed particle hydrodynamics model effectively reproduces the flow kinematics and time history of the impact force. Even slight deflections of the deformable barrier lead to obvious attenuation of the peak impact pressure. Additionally, deformable barriers with lower stiffness tend to deform more downstream upon loading, shifting the deposited sand toward the active failure mode and generating less static earth pressure. When the debris flow has a higher frontal velocity, the impact force on the barrier is dominated by the dynamic component and there is an appreciable effect of the stiffness of the deformable barrier on load attenuation.

Impact of dense avalanches on civil engineering structures: demarcating depth-dependent from velocity-squared impact forces

2020 ◽  
Author(s):  
Thierry Faug
Keyword(s):  
Civil Engineering ◽  
Impact Force ◽  
Control Volume ◽  
Analytic Form ◽  
Influence Zone ◽  
Engineering Structures ◽  
Impact Forces ◽  
Hydrostatic Force ◽  
Civil Engineering Structures ◽  
The Impact

&lt;p&gt;Recent well-documented measurements on full-scale snow avalanches impacting civil engineering structures have identified an impact force regime for which the pressure exerted on the obstacle is depth-dependent, rather than being controlled by the square of the avalanche speed. In addition, these measurements have shown that the depth-dependent force could be many times greater than the hydrostatic force associated with the thickness of the incoming avalanche-flow. The present paper proposes a general analytic form for the impact force of dense avalanches on any kind of structure, with the help of the depth-averaged hydrodynamics applied to a control-volume surrounding the influence zone of the obstacle. This form extends the recently established force models for wall-like and pylon-like obstacles impacted by flows of dry granular materials. A criterion to distinguish between the depth-dependent force regime and the velocity-square force regime is derived. It is demonstrated that the size of the influence zone of the obstacle, relative to the dimension of the obstacle and/or the avalanche thickness, is a key ingredient---in addition to the traditional Froude number---to demarcate the depth-dependent from velocity-square impact forces. There is still a need for further developments to unravel the size and shape of the influence zone of any kind obstacle for any type of flowing snow, and then being able to hone this criterion as well as to predict the force amplification in the depth-dependent regime. However the present study takes a step forward for a better understanding of granular avalanche impact force on civil engineering structures.&lt;/p&gt;

scholarly journals Influence of debris flow solid fraction on rigid barrier impact

2017 ◽  
Vol 54 (10) ◽  
pp. 1421-1434 ◽  
Author(s):  
D. Song ◽  
C.W.W. Ng ◽  
C.E. Choi ◽  
G.G.D. Zhou ◽  
J.S.H. Kwan ◽  
...  
Keyword(s):  
Debris Flow ◽  
Solid Fraction ◽  
Impact Pressure ◽  
Frontal Impact ◽  
Rigid Barrier ◽  
Pile Up ◽  
Run Up ◽  
The Impact ◽  
Fluid Interaction ◽  
Fluid Phases

The dynamics of debris flows are fundamentally governed by the interaction between the solid and fluid phases. However, current approaches used to estimate impact load treat debris flow as an equivalent fluid without considering solid–fluid interaction separately from other factors. In this study, a series of centrifuge tests was carried out to investigate the influence of interaction between solid and fluid phases on single-surge debris flow impact on a rigid barrier. The effect of solid–fluid interaction was studied by varying the solid fraction of the flows. A model rigid barrier was instrumented to capture induced bending moment and impact pressure. Test results demonstrate that the transition from a pile-up mechanism to a run-up mechanism is governed by the solid fraction and thus the grain contact stresses. The rigid barrier design for the impact with a pile-up mechanism is mainly dominated by the static load. Contrary to the hydrodynamic approach, which assumes that the frontal impact is the most critical, the frontal impact of a run-up mechanism contributes less than 25% of the total force impulse. The consideration of static loading leads to the development of a new impact model with a triangular distribution of the impact pressure.

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