Relationships between size and velocity for particles within debris flows

Adam B. Prochaska; Paul M. Santi; Jerry D. Higgins

doi:10.1139/t08-088

Relationships between size and velocity for particles within debris flows

Canadian Geotechnical Journal ◽

10.1139/t08-088 ◽

2008 ◽

Vol 45 (12) ◽

pp. 1778-1783 ◽

Cited By ~ 5

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.

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

Canadian Geotechnical Journal ◽

10.1139/cgj-2021-0119 ◽

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 m3 and 6 m3 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.

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

Water ◽

10.3390/w11020328 ◽

2019 ◽

Vol 11 (2) ◽

pp. 328 ◽

Cited By ~ 4

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.

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

10.5194/egusphere-egu2020-134 ◽

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

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.

Experimental Study of the Debris Flow Slurry Impact and Distribution

Shock and Vibration ◽

10.1155/2018/5460362 ◽

2018 ◽

Vol 2018 ◽

pp. 1-15 ◽

Cited By ~ 1

Author(s):

Haixin Zhao ◽

Lingkan Yao ◽

Yong You ◽

Baoliang Wang ◽

Cong Zhang

Keyword(s):

Debris Flow ◽

Debris Flows ◽

Impact Force ◽

Influence Factors ◽

Flume Experiment ◽

Middle Point ◽

Laboratory Flume ◽

Critical Issues ◽

Maximum Impact Force ◽

The Impact

In this study, we present a new method to calculate debris flow slurry impact and its distribution, which are critical issues for designing countermeasures against debris flows. There is no unified formula at present, and we usually design preventive engineering according to the uniform distribution of the maximum impact force. For conducting a laboratory flume experiment, we arrange sensors at different positions on a dam and analyze the differences on debris flow slurry impact against various densities, channel slopes, and dam front angles. Results show that the force of debris flow on the dam distributes unevenly, and that the impact force is large in the middle and decreases gradually to the both sides. We systematically analyze the influence factors for the calculation of the maximum impact force in the middle point and give the quantitative law of decay from the middle to the sides. We propose a method to calculate the distribution of the debris flow impact force on the whole section and provide a case to illustrate this method.

A combined model approach for debris-flow impact forces

10.5194/egusphere-egu21-10777 ◽

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

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.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 &#8220;Debris flow impact forces on bridge super structures (DEFSUP)&#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.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&#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.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.The findings from these experiments contribute to a better prediction of debris-flows impact forces in terms of their material composition and flow behaviour.

Deriving sediment transport information from debris-flow impact force signals

10.5194/egusphere-egu2020-13054 ◽

2020 ◽

Author(s):

Hui Tang ◽

Yan Yan ◽

Kaiheng Hu

Keyword(s):

Debris Flow ◽

Physical Model ◽

Ground Motion ◽

Debris Flows ◽

Impact Force ◽

Sediment Flux ◽

Seismic Ground Motion ◽

Inversion Model ◽

Force Signal ◽

The Impact

Runoff-generated debris flow has hazardous implications for downstream communities and infrastructure in alpine landscapes. Our understanding of fluid mechanisms of debris flows is very limited, in part, by a lack of direct observations and measurements. Seismic ground motion-based observations provide new constraints on debris flow physics, but it is still not widely applied due to the missing of validated inversion models for interpreting the impact force which generates seismic ground motion. Here we propose a physical model for the high-frequency spectral distribution of impact force signal generated by debris flows. Then we present a new inversion model based on the physical model for the impact force signal and apply this to the devastating debris flows in Dongchuang, China, on 25 August 2004. The amplitude and frequency characteristics of the impact force data can enable the estimation of grain size, sediment concentration, and sediment flux. Results suggest that in-situ data from three sensors could have provided a reconstruction of sediment flux profile in the vertical direction. Meanwhile, an inversion model designed for debris flows impact force would potentially provide hydrodynamics information as well.

Numerical study on debris flow in step-pools channel using smoothed particle hydrodynamics method

10.5194/egusphere-egu2020-2813 ◽

2020 ◽

Author(s):

Shuai Li ◽

Xiaoqing Chen ◽

Chong Peng ◽

Jiangang Chen

Keyword(s):

Debris Flow ◽

Smoothed Particle Hydrodynamics ◽

Debris Flows ◽

Impact Force ◽

Numerical Study ◽

Particle Hydrodynamics ◽

Smoothed Particle ◽

Smoothed Particle Hydrodynamics Method ◽

The Impact ◽

Peak Impact Force

Drainage channel with step-pool systems are widely used to control debris flow. However, the blocking of debris flow often gives rise to local damage at the steps and baffles. Hence, the estimation of impact force of debris flow is crucial for design step-pools channel. This paper presents a numerical study on the impact behavior of debris flows using SPH (Smoothed Particle Hydrodynamics) method. Some important parameters, such as the baffle shape (square, triangle, and trapezoid) and the densities of debris flows are considered to examine their influence on the impact force. The results show that the largest peak impact force is obtained at the second last baffle, rather than the first baffle. Moreover, the square baffle gives rise to the largest impact force whereas the triangle baffle bears the smallest one among the three baffles. Generally, the peak impact force increases with increasing the inflow density. However, a threshold density, beyond which the peak impact force will decrease, is suggested by the simulations. Based on the numerical results, an improved expression to predict the impact force considering the inclined angle of baffle is proposed.

Large Scale Physical Modelling Study of a Flexible Barrier under the Impact of Granular Flows

10.5194/nhess-2018-131 ◽

2018 ◽

Author(s):

Dao-Yuan Tan ◽

Jian-Hua Yin ◽

Wei-Qiang Feng ◽

Jie-Qiong Qin ◽

Zhuo-Hui Zhu

Keyword(s):

Debris Flows ◽

Large Scale ◽

Impact Force ◽

Granular Flows ◽

Physical Modelling ◽

Flexible Barrier ◽

Impact Forces ◽

Flexible Barriers ◽

Open Question ◽

The Impact

Abstract. Flexible barriers are being increasingly applied to mitigate the danger of debris flows. However, how barriers can be better designed to withstand the impact loads of debris flows is still an open question in natural hazard engineering. Here we report an improved large-scale physical modelling device and the results of two consecutive large-scale granular flow tests using this device to study how flexible barriers react under impact from granular flows. In the study, the impact force directly on the flexible barrier and the impact force transferred to the supporting structures are measured, calculated and compared. Based on the comparison, the impact loading attenuated by the flexible barrier is quantified. The hydro-dynamic and hydro-static approaches are also validated using the calculated impact forces.

Assessment of Building Vulnerability with Varying Distances from Outlet Considering Impact Force of Debris Flow and Building Resistance

Water ◽

10.3390/w12072021 ◽

2020 ◽

Vol 12 (7) ◽

pp. 2021

Author(s):

Man-Il Kim ◽

Jae-Hwan Kwak

Keyword(s):

Debris Flow ◽

Debris Flows ◽

Impact Force ◽

Vulnerability Index ◽

Physical Characteristics ◽

Brick Masonry ◽

Flow Depth ◽

Wood Material ◽

Masonry Material ◽

The Impact

Studies have been conducted to understand the physical characteristics of debris flows and quantitatively assess the vulnerability of the buildings nearby to mitigate damage from debris flow disasters. However, there remains a paucity of research on vulnerability assessments that discuss the impact force of debris flow and building resistance within certain sections, where debris flows spread from an outlet. In this regard, the study assesses the vulnerability of buildings to debris flows while considering the distance from an outlet. For this purpose, it selects the two sites of Chuncheon-shi in Gangwon-do and Cheongju-shi in Chungcheongbuk-do in South Korea, which are widely known for having experienced debris flow damage in 2011 and 2017, respectively. For the sites, the study conducts an inverse analysis through debris flow simulation to understand the physical characteristics of debris flows, including flow depth, flow velocity, and impact force. Then, the study assesses vulnerability by estimating the resistance of the materials of the buildings placed in the range where debris flows spread, which allows the calculation of a vulnerability index that a building material may have and the estimation of a safety distance from the outlet for each material of the buildings in the study sites. The result shows that with an increasing distance from the outlet, the flow depth, velocity, and impact force, which represent debris flow properties, tend to decrease. This again results in vulnerability being gradually reduced. The study also suggests that buildings are exposed to the risk of debris flow disasters at a sections 40 to 60 m from an outlet for wood material construction, 70 to 110 m for brick-masonry material construction, and all sections from an outlet for prefabricated material construction. Based on this result, the vulnerability index is estimated for the wood material (0.85), brick-masonry material (0.58), and prefabricated material (0.003).

Numerical Simulation of Non-Homogeneous Viscous Debris-Flows Based on the Smoothed Particle Hydrodynamics (SPH) Method

Water ◽

10.3390/w11112314 ◽

2019 ◽

Vol 11 (11) ◽

pp. 2314 ◽

Cited By ~ 4

Author(s):

Shu Wang ◽

Anping Shu ◽

Matteo Rubinato ◽

Mengyao Wang ◽

Jiping Qin

Keyword(s):

Debris Flow ◽

Water Content ◽

Smoothed Particle Hydrodynamics ◽

Debris Flows ◽

Sph Method ◽

Particle Hydrodynamics ◽

Sph Model ◽

Smoothed Particle ◽

The Impact ◽

Kinetic And Potential Energies

Non-homogeneous viscous debris flows are characterized by high density, impact force and destructiveness, and the complexity of the materials they are made of. This has always made these flows challenging to simulate numerically, and to reproduce experimentally debris flow processes. In this study, the formation-movement process of non-homogeneous debris flow under three different soil configurations was simulated numerically by modifying the formulation of collision, friction, and yield stresses for the existing Smoothed Particle Hydrodynamics (SPH) method. The results obtained by applying this modification to the SPH model clearly demonstrated that the configuration where fine and coarse particles are fully mixed, with no specific layering, produces more fluctuations and instability of the debris flow. The kinetic and potential energies of the fluctuating particles calculated for each scenario have been shown to be affected by the water content by focusing on small local areas. Therefore, this study provides a better understanding and new insights regarding intermittent debris flows, and explains the impact of the water content on their formation and movement processes.