Mechanism of downcutting erosion of debris flow over a movable bed

Pan, Huali; Huang, Jiangcheng; Ou, Guoqiang

doi:10.1007/s11629-012-2523-2

Cited by 7 publications

(8 citation statements)

References 12 publications

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“…Pan et al. () found that experimental debris flows with a density of 1900 kgm −3 and a median grain size of 0.45 mm had a critical slope for erosion on a wet bed of 11.0°. This sediment is comparable with the reference mixture of our experiments, with a density of 1919 kgm −3 and a median grain size of 0.39 mm, although the critical slope was much larger in our experiments, probably because of the dry erodible bed used in our experiments.…”

Section: Discussionmentioning

confidence: 99%

Bed scour by debris flows: experimental investigation of effects of debris‐flow composition

Haas

Woerkom

2016

Earth Surf Processes Landf

108

110

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Debris flows can grow greatly in size by entrainment of bed material, enhancing their runout and hazardous impact. Here, we experimentally investigate the effects of debris-flow composition on the amount and spatial patterns of bed scour and erosion downstream of a fixed to erodible bed transition. The experimental debris flows were observed to entrain bed particles both grain by grain and en masse, and the majority of entrainment was observed to occur during passage of the flow front. The spatial bed scour patterns are highly variable, but large-scale patterns are largely similar over 22.5-35°channel slopes for debris flows of similar composition. Scour depth is generally largest slightly downstream of the fixed to erodible bed transition, except for clay-rich debris flows, which cause a relatively uniform scour pattern. The spatial variability in the scour depth decreases with increasing water, gravel (= grain size) and clay fraction. Basal scour depth increases with channel slope, flow velocity, flow depth, discharge and shear stress in our experiments, whereas there is no correlation with grain collisional stress. The strongest correlation is between basal scour and shear stress and discharge. There are substantial differences in the scour caused by different types of debris flows. In general, mean and maximum scour depths become larger with increasing water fraction and grain size, and decrease with increasing clay content. However, the erodibility of coarse-grained experimental debris flows (gravel fraction = 0.64) is similar on a wide range of channel slopes, flow depths, flow velocities, discharges and shear stresses. This probably relates to the relatively large influence of grain-collisional stress to the total bed stress in these flows (30-50%). The relative effect of grain-collisional stress is low in the other experimental debris flows (<5%), causing erosion to be largely controlled by basal shear stress.

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Section: Discussionmentioning

confidence: 99%

Bed scour by debris flows: experimental investigation of effects of debris‐flow composition

Haas

Woerkom

2016

Earth Surf Processes Landf

108

110

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“…Statistics show that the gully width of narrow-steep gully debris flow is mainly concentrated in 5-30 m. The flume width in this paper is designed at 0.18 m to maintain consistency in geometric similarity. According to the similar debris flow model experiments 19,25,29 , the width of the flume is within 0.09-0.3 m, implying that a flume width of 0.18 m can meet the experiment requirements. The width of the gully should be greater than 5 times the maximum grain size of the bed sediment, which should not exceed 10 mm for this experiment.…”

Section: Experiments Materialsmentioning

confidence: 86%

“…Zhu et al 16 obtained a calculation method for the scouring depth of dilute debris flows through theoretical analysis. Pan and You [17][18][19] found that the depth of debris flow scour is strongly influenced by the nature of the fluid, the longitudinal slope of the gully, and the composition of the sediment. However, most scour tests have mainly been done with a fixed slope or by varying the slope to a small extent and do not reflect the typical characteristics of the narrow-steep gully with steep longitudinal slopes and a wide range of slope variations [15][16][17][19][20][21][22][23] .…”

mentioning

confidence: 99%

“…Pan and You [17][18][19] found that the depth of debris flow scour is strongly influenced by the nature of the fluid, the longitudinal slope of the gully, and the composition of the sediment. However, most scour tests have mainly been done with a fixed slope or by varying the slope to a small extent and do not reflect the typical characteristics of the narrow-steep gully with steep longitudinal slopes and a wide range of slope variations [15][16][17][19][20][21][22][23] . Notably, Baggio et al 24 regarded the gully slope as the major control variable and further discovered that the correlation between slope and erosion depth becomes satisfactory only for slopes steeper than 14°, but low slopes (5.7°-12.4°) are associated with a great heterogeneity in erosion depth.…”

mentioning

confidence: 99%

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Experimental study of erodible bed scoured by the debris flow in the narrow-steep gully

Wu,

Ji,

et al. 2023

Sci Rep

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In recent years, debris flows have frequently erupted in the narrow-steep gully of the earthquake-hit Wenchuan region, displaying high flow velocities and powerful scouring abilities. However, few scouring studies in the narrow-steep gully have been conducted. A model experiment simulated the debris flow scouring process in a narrow-steep flume, in which several important physical parameters, including the debris flow density (ρ), flume slope (θ), and grain size of the sediment (D), were varied to investigate their influences on the erodible strength. The experimental flows were composed of 50 L of water and grains, which scoured 2.3 m of erodible bed down a steeply inclined flume. A high-speed camera photographed the scouring processes, while a 3D laser device captured the final bed shapes. The experiments show that the debris flow first collides with the sediment at the head of the gully to form a pit, which is enlarged by continuous impact; the velocity of the debris flow out of the pit is significantly reduced due to the change in flow direction, resulting in a much lesser scouring effect after the pit; and finally, the gully bed presents the shape of a pit at the entrance and a groove in the middle and rear. The critical scour slope, where the gully bed shows scouring, increases with increasing debris flow density but decreases with increasing grain size of sediment. Following scouring, the maximum scouring depth is further positively correlated with the flume slope. In narrow-steep gullies, the gully bed is extremely susceptible to scouring by debris flow with a low density, and even headward erosion appears, at which the maximum scouring depth only increased from 148.04 to 149.97 mm, but the erosion amount had a significant increase of 36.9%. The research results have an important significance for revealing the disaster-causing phenomena and mechanisms of debris flows in the narrow-steep gully.

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“…Analyzing in terms of energy, when the debris flow passes through the drainage channel, it overcomes the shear resistance of the structural surface, and some of the energy is dissipated [30]. At the same time, some of the energy will be dissipated when the fluid collides with the structure's surface and with the particles inside the fluid.…”

Section: Composition and Influencing Factors Of Abrasion Systemmentioning

confidence: 99%

Abrasion Behavior and Anti-Wear Measures of Debris Flow Drainage Channel with Large Gradient

Yang

You

Zhao

et al. 2020

Water

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Debris flow gullies have high potential energy and geomorphic characteristics including a steep longitudinal slope and abundant loose material sources. They often experience debris flow with a strong impact force and a large instantaneous flow. Drainage engineering measures are most commonly used for mitigation in these gullies. However, the abrasion of drainage channels with large gradients (DCLG) is complex and strong because of the high-speed flushing of debris. In this study, the abrasion behavior of debris flow in DCLG is analyzed based on the kinematic characteristics and the theory of composite abrasive wear. Energy dissipation and anti-wear measures are suggested, and their effects are summarized with reference to a case study and in situ observation. The results show that there are four main types of wear morphology in drainage channels. The abrasion system of drainage channels shows the characteristics of system dependency, time dependency and multidisciplinary coupling. Energy dissipation and anti-wear measures include prefabricated reinforced concrete boxes as substrate, transverse roughening belts, adding a wear-resistant admixture, etc. The flow velocity of the debris flow is reduced by 5.7–37.1% after passing through the energy dissipation section. The distribution of abrasion and the mud depth show that the variation trend of the flow velocity in the channel is ”acceleration → deceleration → reacceleration“. According to tracking observations during two flood seasons, the energy dissipation and anti-wear measures are the most effective.

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Mechanism of downcutting erosion of debris flow over a movable bed

Cited by 7 publications

References 12 publications

Bed scour by debris flows: experimental investigation of effects of debris‐flow composition

Bed scour by debris flows: experimental investigation of effects of debris‐flow composition

Experimental study of erodible bed scoured by the debris flow in the narrow-steep gully

Abrasion Behavior and Anti-Wear Measures of Debris Flow Drainage Channel with Large Gradient

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