Two-flow model for piping erosion based on liquid-solid coupling

ABSTRACTOn the Chinese Loess Plateau, soil erosion models are often employed to predict erosion rates and responses to land‐use/‐cover changes (LUCCs). Previous Loess Plateau studies employed individual models with specific emphases but model comparisons have not been undertaken so the relative performance of different models is not known. In this study we employed two extensively applied models (RUSLE and PESERA) to investigate the impact of LUCCs during 1990–2000 and 2000–2011 on soil erosion rates for a typical Loess Plateau catchment (i.e. Huangfuchuan), and compared their modelling results. Land‐cover patterns for 1990, 2000 and 2011 were derived from Landsat images. The catchment was dominated by grassland (over 70%) and experienced considerable LUCCs: vegetation coverage increased from 38.3% in 1990 to 48.7% in 2011. Modelling results suggested that mean soil erosion rates of the catchment increased under the 1990–2000 LUCC and decreased under the 2000–2011 LUCC. Sandy land and scrubland were found to suffer from most severe soil erosion and thus should be the focus of future conservation work. Mean soil erosion rates on steep slopes (i.e. > 25°) were predicted to increase under the 2000–2011 LUCC, implying that further work is still needed to study soil erosion processes and their conservation on steep slopes. Model comparisons showed that RUSLE predictions were higher than PESERA predictions for most areas (particularly for steep slopes), and the former were generally closer than the latter to check‐dam sediment yield measurements. RUSLE and PESERA results were not linearly correlated, possibly due to differences in their underlying principles and their sensitivity to crucial parameters – RUSLE is more sensitive to slope gradients while PESERA is more sensitive to vegetation coverage. PESERA needs improvement to better account for steep slope erosion processes on the Loess Plateau, while RUSLE needs improvement in the description of vegetation effects. © 2019 John Wiley & Sons, Ltd.

This paper presents the findings of a preliminary research program that aimed to investigate the mechanisms governing the progression of piping erosion in organic soils and attempted to use the findings to reduce the severity of piping erosion of sand. The hypothesis was that the presence of organics within mineral soils results in a reduction in piping erosion progression. Erosion behaviors of the soils were quantified using a simple erosion test with a preformed hole to simulate an initial piping channel. The research was split into five test phases. In Phase 1, the influence of grain-size distribution was eliminated to develop a preliminary understanding of the role that organic matter plays in the erosion process. The results indicated that organic matter likely contributed to a reduction in piping erosion. The second phase excluded both grain-size distribution and individual particle shape as variables in the erosion process. The results further confirmed the connection between organic matter content and erosion resistance. The third phase revealed the positive correlation between the reduced piping erosion and increased organic matter content. The fourth phase investigated the quantitative relationship between certain biologically derived substances (polysaccharides and glomalin) and piping erosion reduction. The positive correlations that were preliminarily derived from this phase indicated that these substances likely play a major role in reducing piping erosion. The final phase comprised of introducing organic matter into mineral soil and quantifying the subsequent changes in geomechanic properties. The results suggested that the introduction of organic materials into mineral soil decreases strength, increases consolidation settlement, and reduces permeability.

HighlightsThis study provides data from internal erosion tests on four intermediate-scale homogeneous embankment dams.Soil properties influence the breach formation process and breach timing.Results showed that observed erosion rates of the internal flow path varied by several orders of magnitude.Quality control of embankment construction can greatly influence breach development.Abstract. Internal erosion and embankment overtopping are the two most common causes of embankment dam and levee failures and incidents. Internal erosion is the removal of soil material by the flow of water through a continuous defect, cavity, or crack within a compacted fill and/or its foundation. Internal erosion initiates from vulnerabilities within the embankment. The embankment soil material plays a key role in both the erosion process and rate of failure, but characterizing soil properties and how they relate to the rate of failure can be challenging. Soil properties such as texture, density, strength, moisture content, and erodibility can vary greatly; thus, it is important to study the effects of these properties on the breach formation process and breach timing. The USDA Agricultural Research Service performed internal erosion breach experiments on four intermediate-scale homogeneous earthen embankments constructed of soils ranging from a silty sand to a lean clay material. The embankments were constructed to a height of 1.3 m, a top width of 1.8 m, and upstream and downstream slopes of 3(H):1(V). The embankment materials were characterized by water content, density, texture, strength, and erodibility. Erodibility was measured using a jet erosion test (JET) apparatus. A 40 mm diameter, continuous steel pipe was placed through each embankment during construction and removed to form an open-ended void through the embankment connected to the upstream reservoir. The removal of the pipe initiated internal erosion. The objectives of the experiments were to observe the development of the internal erosion process over time and to examine the influence of soil properties on the erosion rate, breach timing, geometry of the breach opening, and breach outflow. The rate of erosion and failure observed in these tests varied by several orders of magnitude, with the silty sand embankment eroding most rapidly and the lean clay embankment with a mean moisture content of 18% dry basis at standard compaction eroding the slowest. These observations were indicative of the soil textures. Although the two lean clay embankments were constructed of similar soils, the difference in erosion rates speak to the importance of quality control (e.g., compaction moisture content) during construction. Soil properties including soil texture, erodibility, and compaction moisture content are key predictors of erosion rate and observed failure. Keywords: Breach, Dam failure, Dams, Embankments, Erodibility, Internal erosion, Levees, Overtopping.

In slopes where a mixture of coarse and fine particles is present, the infiltration of rainfall can cause the migration of fine particles. This migration alters the hydraulic properties of the soil and has implications for slope stability. In this study, the slope under investigation is a tailings dam composed of loosely consolidated soil with a wide particle size distribution. Due to rainfall infiltration, fine particles tend to migrate within the voids of the coarse particle framework, leading to changes in hydraulic properties and inducing slope instability. The classical internal erosion constitutive model, known as the Cividini and Gioda erosion criterion, is commonly used to predict the behavior and effects of fine particle erosion in geotechnical engineering. However, certain parameters in this erosion criterion equation, such as long-term density, are challenging to obtain through experiments. To investigate the coupled evolution of seepage and erosion within landfill slopes under the influence of rainfall infiltration and to understand the mechanisms of slope instability, this research assumes the erosion of fine particle suspension and adopts the Worman and Olafsdottir erosion criterion to establish a coupled model of unsaturated seepage and internal erosion. The developed model simulates the coupled response of seepage and erosion in unsaturated landfill slopes under three different rainfall intensities. It is then combined with the infinite slope model to quantitatively analyze the impact of fine particle migration on soil permeability and slope stability. The numerical simulations provide the following findings: The Worman and Olafsdottir erosion criterion, unlike the Cividini and Gioda erosion criterion, only requires the determination of the soil’s gradation curve to estimate the erosion rate. Internal erosion primarily occurs within the leading edge of moisture penetration, accelerating the advancement of the wetting front and reducing slope stability. When the rainfall intensity is lower than the saturated permeability coefficient, the influence of internal erosion can be disregarded. However, under rainfall intensities equal to or greater than the saturated permeability coefficient, considering internal erosion results in a difference in the depth of the wetting front of up to 34.2 cm after 6 h in the R2 scenario. The safety factor without considering internal erosion is 1.12, whereas considering internal erosion yields safety factors between 1.08 and 1.09. In the R3 scenario, the difference in the depth of the wetting front reaches 53.8 cm after 6 h, with a safety factor of 1.12 without considering internal erosion and safety factors between 1.06 and 1.07 when considering internal erosion.

A meta-analysis of soil erosion rates across the world

Piping, as the result of internal erosion of embankments, is a primary cause of embankment breaks. Moreover, hollows or cavities of soil structures have been occasionally reported due to erosion within soils. The inner states of embankments are needed to be estimated to take appropriate measures for the prevention of the accidents of soil structures. In this study, simultaneous modeling of the internal erosion and the deformation of soils is carried out. As for the internal erosion, the equations governing the erosion and the transport of fine particles within a soil mass are derived with the concept of erosion rates of soils. Additionally, the constitutive model which can describe the deformation of soils caused by the internal erosion is proposed in this paper.

Internal erosion can induce significant changes in the mechanical properties of soils, posing various hazards to dam and dike structures. Despite its importance, our current understanding of this phenomenon remains incomplete. The influence of pre-shearing stress conditions on the mechanical behaviours of soils during the internal erosion process is particularly challenging, as existing experiments have not been able to maintain the constant pre-shearing stress ratios. To bridge this gap in knowledge, this paper presents a series of discrete element method (DEM) simulations focused on gap-graded cohesionless soil. The primary objective of these simulations is to investigate two specific cases of internal erosion: suffusion and suffosion processes. Soil specimens are subjected to different pre-shearing stress ratios in the standard triaxial tests before being submitted to different levels of erosion to study their constitutive responses. The results show that erosion-induced deformation (i.e. suffosion) only starts after a specific amount of mass loss. This mass loss and the pre-shearing stress ratio form a well-defined criterion for triggering suffosion, which is named “suffosion surface”. The volumetric strain is shown to be a better indicator to describe the suffosion process than the commonly used void ratio. The pre-shearing stress ratio significantly influences the suffosion response of the soil sample, with a higher pre-shearing stress ratio facilitating soil failure. Furthermore, soil specimens undergo both deviatoric and volumetric responses during the suffosion process. To this end, new DEM-based statistical equations were proposed to describe the observed mechanisms, which are helpful for the future development of constitutive models to describe internal soil erosion.

Internal erosion is one of the most common causes of failure in hydraulic engineering structures, such as embankments and levees. It also plays a vital role in the geohazards (such as landslides and sinkhole developments) and more importantly, the earth landscape evolution, which has a broad environmental and ecosystem impacts. The groundwater seepage is multi‐directional, and its multi‐dimensional nature could affect the initiation and the progression of internal erosion. With a newly developed apparatus, we carry out nine internal erosion experiments under five different seepage directions. The results reveal that the critical hydraulic gradient increases as the seepage direction varies from the horizontal to the vertical. After a global erosion is triggered, preferential erosion paths distribute randomly from the bottom to the top of the specimen. If the seepage direction is not vertical, small preferential erosion paths merge into a large erosion corridor, in which the loss of fine particles is significant but negligible outside. Results of experiments manifest that the erosion is heterogeneous and three‐dimensional, even in the unidirectional seepage flow. The particles are rapidly eroded at the early stage of the erosion, indicating a high erosion rate. With the erosion time increasing, the particle loss slows down and even ceases if the time is long enough. The erosion rate increases if the seepage direction approaches a vertical direction. Overall, the erosion rate approximately decreases with erosion time exponentially. We proposed exponential equations to illustrate the variation of the erosion rate in the erosion process.

Excessive soil erosion and deposition is recognised as a significant land degradation issue. Quantifying soil erosion and deposition is a non‐trivial task. One of these methods has been the mathematical modelling of soil erosion and deposition patterns and the processes that drive them. Here we examine the capability of a landscape evolution model to predict both soil erosion rate and pattern of erosion and deposition. This numerical model (SIBERIA) uses a Digital Elevation Model (DEM) to represent the landscape and calculates erosion and deposition at each grid point in the DEM. To assess field soil redistribution rates (SRR) and patterns the distribution of the environmental tracer 137Cs has been analysed. Net hill slope SRR predicted by SIBERIA (a soil loss rate of 1.7 to 4.3 t ha‐1 yr‐1) were found to be in good agreement with 137Cs based estimates (2.1 – 3.4 t ha‐1 yr‐1) providing confidence in the predictive ability of the model at the hillslope scale. However some differences in predicted erosion/deposition patterns were noted due to historical changes in landscape form (i.e. the addition of a contour bank) and possible causes discussed, as is the finding that soil erosion rates are an order of magnitude higher than likely soil production rates. The finding that SIBERIA can approximate independently quantified erosion and deposition patterns and rates is encouraging, providing confidence in the employment of DEM based models to quantify hillslope erosion rates and demonstrating the potential to upscale for the prediction of whole catchment erosion and deposition. The findings of this study suggest that LEMs can be a reliable alternative to complex and time consuming methods such as that using environmental tracers for the determination of erosion rates. The model and approach demonstrates a new approach to assessing soil erosion that can be employed elsewhere. © 2018 John Wiley & Sons, Ltd.

Investigations on temporal and spatial variation of slope-scale SOC erosion and deposition

SummaryIt has been reported that sand production, which is a simultaneous production of soil particles along with gas and water into a production well, forced to terminate the operation during the world's first offshore methane production test from hydrate‐bearing sediments in the Eastern Nankai Tough. The sand production is induced by internal erosion, which is the detachment and migration of soil particles from soil skeleton due to seepage flow. The inflow of the eroded soil particles into the production well leads to damage of the production devices. In the present study, a numerical model to predict the chemo‐thermo‐mechanically coupled behavior including internal erosion during hydrate dissociation has been formulated based on the multiphase mixture theory. In the proposed model, the internal erosion is expressed as mass transition of soil particles from soil skeleton to the fluidized soil particles. Since the internal erosion is considered to depend on the soil particle size, mass of soil particles are divided into several groups that have different representative particle diameters, and the constitutive equations for the onset condition and the mass transition rate of the internal erosion are formulated for each group. Also, transportation of soil particles in the liquid phase is formulated for each particle size group in the proposed model. Finally, a simulation of the methane gas production from the hydrate‐bearing sediment by depressurization method is presented, and the internal erosion and the dissociation behavior are discussed.

Seasonal freeze-thaw processes have led to severe soil erosion in the middle and high latitudes. The area affected by freeze-thaw erosion in China exceeds 13% of the national territory. So understanding the effect of freeze-thaw on erosion process is of great significance for soil and water conservation as well as for ecological engineering. In this study, we designed simulated rainfall experiments to investigate soil erosion processes under two soil conditions, unfrozen slope (UFS) and frozen slope (FS), and three rainfall intensities of 0.6, 0.9 and 1.2 mm/min. The results showed that the initial runoff time of FS occurred much earlier than that of the UFS. Under the same rainfall intensity, the runoff of FS is 1.17–1.26 times that of UFS; and the sediment yield of FS is 6.48–10.49 times that of UFS. With increasing rainfall time, rills were produced on the slope. After the appearance of the rills, the sediment yield on the FS accounts for 74%–86% of the total sediment yield. Rill erosion was the main reason for the increase in soil erosion rate on FS, and the reduction in water percolation resulting from frozen layers was one of the important factors leading to the advancement of rills on slope. A linear relationship existed between the cumulative runoff and the sediment yield of UFS and FS (R2>0.97, P<0.01). The average mean weight diameter (MWD) on the slope erosion particles was as follows: UFS0.9 (73.84 µm)>FS0.6 (72.30 µm)>UFS1.2 (72.23 µm)>substrate (71.23 µm)>FS1.2 (71.06 µm)>FS0.9 (70.72 µm). During the early stage of the rainfall, the MWD of the FS was relatively large. However, during the middle to late rainfall, the particle composition gradually approached that of the soil substrate. Under different rainfall intensities, the mean soil erodibility (MK) of the FS was 7.22 times that of the UFS. The ratio of the mean regression coefficient C2 (MC2) between FS and UFS was roughly correspondent with MK. Therefore, the parameter C2 can be used to evaluate soil erodibility after the appearance of the rills. This article explored the influence mechanism of freeze-thaw effects on loess soil erosion and provided a theoretical basis for further studies on soil erosion in the loess hilly regions.

Engineering geomorphology at the cutting edge of land disturbance: erosion and sediment control on construction sites

Backward erosion piping is an important failure mechanism for water-retaining structures. It results in the formation of shallow pipes at the interface of a sandy or silty foundation and a cohesive cover layer. This paper analyzes the depth of these erosion pipes through small-scale experiments. The development of the pipe depth reveals a lot of information on the backward erosion process, but it had never been measured systematically during the erosion process. Our analysis shows that the pipes are extremely shallow (in the order of mm) and that the pipe depth increases slightly, as piping progresses. Furthermore, a relation is found between pipe depth, grain size, soil permeability, and pipe length. The experimentally obtained depths are in good agreement with those obtained with theoretically determined pipe depths based on pipe hydraulics. Finally, the experiments are compared to 2D numerical simulations using Sellmeijer’s mathematical model and 3D numerical simulations with the correct pipe dimensions.

Internal erosion often occurs in earthen water-retaining structures such as embankment dams, levees, and dikes. This erosion is caused by seepage flows through soils or other porous materials containing a mixture of coarse and fine particles. The internal erosion process, also known as suffusion, involves the transport of fine particles carried away from the soil structure by seepage. Internal erosion can weaken the soil, create voids or cavities, and ultimately lead to structural collapse, posing a significant risk to earthen water-retaining structures. This research investigates the internal erosion behavior of gap-graded sands with various fine fraction contents through a series of upward seepage tests. Using an in-house-developed apparatus to measure hydraulic gradient and permeability, this study examines the initiation and progression of internal erosion in detail. Additionally, it explores the effects of vertical stress and relative density on erosion behavior, as well as methods to control or mitigate erosion by incorporating different cement contents as an improvement measure for internal erosion control. Results indicate that internal erosion begins at a critical hydraulic gradient, with the migration of fine particles intensifying as the gradient increases. Vertical stress and relative density significantly influence erosion behavior, with higher stress and density improving resistance to erosion. Cement stabilization effectively mitigated erosion by reducing fine particle loss and enhancing soil stability. These findings contribute to a deeper understanding of seepage-induced internal erosion and support the development of strategies to improve the resilience of earthen structures.