Numerical Modeling of Bank Instability by Seepage Erosion Undercutting of Layered Streambanks

Chu-Agor, M. L.; Wilson, George Grafton; Fox, Garey A.

doi:10.1061/(asce)1084-0699(2008)13:12(1133)

Cited by 58 publications

(40 citation statements)

References 29 publications

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“…Development and size of the undercut depended on the bulk density of the soil, which influenced hydraulic conductivity, cohesion, internal angle of friction, and critical hydraulic gradients to induce seepage particle mobilization. Chu-Agor et al (2008b) demonstrated that a stable bank could quickly become unstable due to seepage erosion undercutting, leading to bank failure.…”

Section: Introductionmentioning

confidence: 99%

Seepage-Induced Streambank Erosion and Instability: In Situ Constant-Head Experiments

et al. 2013

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The effects of seepage on streambank erosion and failure are less understood compared to fluvial processes, especially the linkage between surface water and groundwater mechanisms. Field data are needed to validate laboratory seepage erosion and instability conclusions and to understand how engineering tools and methods may be applied to field conditions. An innovative trench injection system was utilized to provide a constant head on a near-streambank groundwater system when filled with stream water. This research was performed on a streambank of Dry Creek, a deeply incised stream with near-vertical banks located in Mississippi. Experiments included installing a trench (2.8 m from the bank and 2 m below ground surface) and a network of tensiometers and observation wells to measure soil-water pressures and water table elevations. Bank stratigraphy consisted of a sloping, conductive loamy sand layer between cohesive streambank layers. Groundwater conditions were monitored during a series of induced-seepage experiments. The bank face was outfitted with a seepage collection device to measure seep flow rates and sediment concentrations. Seepage flow rates (as high as 0.4 L=min) and corresponding erosion rates (as high as 0.86 kg=min) were proportional to estimated hydraulic gradients in the near-streambank region and followed an excess flow rate equation. However, flow paths and hydraulic gradients were largely nonuniform due to local variability in streambank stratigraphy, suggesting difficulty when attempting to apply engineering analyses of bank erosion and stability for seepage processes without accounting for this heterogeneity. Seepage flow and erosion became restricted when small-scale bank failures due to undercutting blocked flow pathways and limited particle mobilization, termed temporary self-healing. Seepage erosion was shown to be an important mechanism of streambank failure, especially when acting in concert with fluvial erosion processes that prevent permanent self-healing of seeps.

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Section: Introductionmentioning

confidence: 99%

Seepage-Induced Streambank Erosion and Instability: In Situ Constant-Head Experiments

et al. 2013

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“…The theoretical model described in this paper can explain this effect effectively. For the unstable soil, d θk is much larger than d 15 , which leads to a smaller Π. Therefore, the calculated critical hydraulic gradient was significantly smaller than that of the stable soil.…”

Section: Effect Of the Soil Internal Instabilitymentioning

confidence: 91%

“…The finer particles can be removed by the flow easily. As suggested by Kezdi [33], d 15 is assumed to be the largest movable particle in Equation (8), and, thus, D = d 15 . Figure 4 shows the distribution of the critical hydraulic gradients that were predicted under different relative exposure degrees (∆ = 0.05, 0.1, 0.2) and different porosities (e = 0.43, 0.67, 1).…”

Section: Qualitative Analysismentioning

confidence: 99%

“…The initiation probability of particles D is: (15) where f (∆ ) is the probability density function of ∆ . In Ahlinhan's test [22], for hydraulic gradients of 0.2, 0.4 and 0.6 in a horizontal seepage, the initiation probabilities of soil samples A1 and E1 are shown in Figure 10, assuming that ∆ is uniformly distributed between 0 and 1.…”

Section: Exposure Degree and Particle Initiation Probabilitymentioning

confidence: 99%

“…Friction force d 15 Grain diameter for which 15% of the grains by weight are finer d c, 15 Grain diameter for which 15% of the grains by weight of the coarse soil are finer d f, 85 Grain diameter for which 85% of the grains by weight of the fine soil are finer G Gravity …”

Section: Conflicts Of Interestmentioning

confidence: 99%

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A Theoretical Model to Predict the Critical Hydraulic Gradient for Soil Particle Movement under Two-Dimensional Seepage Flow

Huang

Bai

et al. 2017

Water

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Abstract:The soil particle movement under seepage flow is one of the predominant mechanisms responsible for incidents and failures of dams and streambanks. However, little attention has been paid to the critical hydraulic gradient under two-dimensional (2-D) seepage flow. In this study, a theoretical model was established under 2-D seepage flow to predict the critical hydraulic gradients for soil particle movement. In this model, the sediment particle rolling theory was used, while taking into account the relative exposure degree of the soil grains and the seepage direction. The model was validated through qualitative analysis and comparison with previous data, and showed considerable superiority over Terzaghi's model. In addition, the effect of the soil internal instability, implying that the critical hydraulic gradient of unstable soil is lower than that of stable soil, was discussed. Various parameters of the model were also analyzed. The results showed that the seepage direction angle was positively related to the critical gradient, whereas the void and the mean diameter of the soil were negatively related to it. Finally, the model proposes a calculation method for the particle movement initiation probability, which is regarded as a key parameter in the sediment transport model.

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Mechanisms of ephemeral gully erosion caused by constant flow through a continuous soil‐pipe

Wilson

2009

Earth Surf Processes Landf

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Ephemeral gully erosion is considered to be driven by convergent surface fl ow while the role of subsurface fl ow is often overlooked. This study sought to characterize and quantify the soil erosion mechanisms associated with ephemeral gully erosion by pipe fl ow. A soil pipe (1 cm o.d.) was formed in a 10 cm soil bed immediately above a 5 cm water restricting layer. Flow into the soil pipe was established at steady-state rates of 190 and 284 l h −1 . Experiments were performed for pipe fl ow alone and with rainfall. Despite a constant fl ow rate into soil pipes, pipe fl ow was highly unstable due to internal mass wasting clogging soil pipes until pressure increases forced the debris plug out of the pipe. Short (10-20 Seconds) periods of negligible fl ow were followed by surges in fl ow with high sediment concentrations that included a high proportion of aggregates. Increases in soil water pressures associated with these debris fl ows were observed but were likely not representative of the pressures inside the soil pipes due to hydraulic non-equilibrium between the soil pipe and soil matrix. Hydraulic non-equilibrium resulted in hydraulic gradients in the opposite direction of fl ow through the soil pipe during early stages of pipe fl ow. Pipe fl ow rates and sediment concentrations during debris fl ow periods were likely more extreme than observed due to integration over the three minute sample collection interval. The Slot Erosion Test (SET) was extended to conditions of constant fl ow rate through an internal soil pipe that was observed at the front face of a soil bed. The modifi ed SET provided estimates of shear stress between 2·2 to 5·3 kg m −1 s −2 , however, the technique did not prove effective for estimation of the soil erodibility coeffi cient. Published in

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Numerical Modeling of Bank Instability by Seepage Erosion Undercutting of Layered Streambanks

Cited by 58 publications

References 29 publications

Seepage-Induced Streambank Erosion and Instability: In Situ Constant-Head Experiments

Seepage-Induced Streambank Erosion and Instability: In Situ Constant-Head Experiments

A Theoretical Model to Predict the Critical Hydraulic Gradient for Soil Particle Movement under Two-Dimensional Seepage Flow

Mechanisms of ephemeral gully erosion caused by constant flow through a continuous soil‐pipe

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