Internal Erosion Research Articles

CFD-DEM based wind-deposited sand high concentration slurry pipe transport characteristics and erosion study

In order to study the conveying process of wind-accumulated sand slurry pipeline, this study simulates the flow process of wind-accumulated sand slurry at 1m/s inlet flow rate with straight pipe bend and uphill by coupled CFD-DEM method. The fluid flow, particle motion and position distribution, pipe erosion and force during the whole process are analyzed based on the selection of a suitable traction model. The results show that the flow velocity of highly viscous slurry at the wall of the pipe is small which can easily lead to the deposition of sand particles, which is proved by the particle velocity cloud diagram. The extent of erosion and the degree of erosion increase with time, and the peak of erosion occurs at the bend. The force changes along the Y-direction in different parts of the pipe show that the extreme values of force and erosion are located at the bend. This part is the weak point of the whole pipeline slurry flow and erosion project should pay attention to reinforcement or monitoring.

On the hydraulics of flow in cracks in embankment dam cores

A major hazard to embankment dams is internal erosion and piping arising from concentrated leaks through transverse cracks in the core near the crest due to differential settlement or desiccation. This contribution summarises experiments and a formal boundary layer analysis of flow through such transverse cracks subject to near-horizontal pressure gradients. The critical hydraulic gradients, at which erosion in such cracks may initiate, occur at the downstream end of the crack. This location and the maximum crack width defines the local point most vulnerable to erosion. The hydraulic laboratory measurements are shown to be consistent with equivalent international standards describing depths at free overflows, in spite of the narrow vertical profile of the cracks, provided that the tendency towards laminar flow in very narrow cracks is incorporated within the modelling. A backwater model based on conventional representations of flow in narrow channels is verified qualitatively by hydraulic laboratory data. Flow-depth relationships, maximum crack wall hydraulic stresses, normalised hydraulic wall stress profiles and depth profiles along cracks are presented for the two principal crack geometries present in embankment dams. These characterisations are a significant improvement on the simplified methods previously used to assess internal erosion in transverse cracks in dams.

Embankment Dam Design with Dispersive Soil: Solutions and Challenges

The configuration and safety factor of rockfill dams design depend on materials used in construction of the dam. In some regions, the available materials for using as impermeable element of the dam body are dispersive and it is inevitable to consider the dispersivity of the material in the design and construction. Internal erosion through cracks or other openings in the embankment is the most concern of using the dispersive soils. The authors have designed an embankment dam by using dispersive soil in East Africa after finalizing the dispersivity of materials based on the required tests. The foundation of dam and borrow areas consisted of dispersive soil and the effective measures has been considered in the design to safely deal with dispersivity according to recommendation of the design codes. The selected solution was the combination of chimney filter, filter drain, and selective placement of materials in the dam body as the effective solution considering the specification of the project. More precautions in addition to general recommendation have been incorporated into the design criteria due to placing the project in high hazard category. The local instability in the contact zones was the concerns of designers and bilinear parameters has been considered in the stability analysis as the base case. A drainage layer was added into half of the length of filter blanket and the feature of the design was determined according to nonlinear static and dynamic analysis of the dam body. This paper presents the measures and precautions that were taken into account in dealing with dispersive soil in order to ensure the safety of design.

Determining trigger factors of soil mass failure in a hollow: A study based in the Sichuan Province, China

Soil mass failure disasters are among the most destructive disasters in mountainous areas worldwide, and they continue to receive significant attention in the literature. However, factors that influence soil mass failure in hollows have not been explored via experimental approaches. In this study, we conducted a series of indoor hollow–flume experiments to exhibit how the three factors, namely, initial moisture content, slope angle, and clay content, influence the collapse of soil mass under surface runoff conditions. Our findings revealed that the major processes causing soil mass failure were internal seepage erosion resulting from subsurface runoff, migration of fine particles, development of tension cracks, increase in pore water pressure, and decrease in cohesion. Fluctuations in pore water pressure were characterized by two main trends: (1) an abrupt rise under static liquefaction and (2) a decrease before failure due to dilatancy. The time required for soil mass failure first decreased and then increased with the increase in moisture content. The soil mass with an initial moisture content of ∼12.5% was more critical to the failure. In addition, the time required for soil mass failure decreased with increasing slope angle, revealing a slope angle of 40° to be more prone to failure. The buildup of pore water pressure was found to increase with clay content; soil with a clay content of ∼7.5% required the shortest amount of time to initiate slides. Thus, our results provide a thorough insight into the processes and factors involved in the initiation and development of soil mass failure in hollow areas, which can be used by public agencies to improve monitoring, early warning, and forecasting systems. Notably, our study can help identify risk-prone source areas, and sensors can be installed to monitor potential mass failure locations.

Experimental Study of Internal Erosion in Granular Soil Subject to Cyclic Hydraulic Gradient Reversal

Numerous studies have been conducted to evaluate the influence of internal erosion on the geotechnical properties of soil under unidirectional seepage. Yet cyclic gradients prevail in natural or engineering systems, and the mechanical consequences of soil subjected to cyclic hydraulic gradient reversal have not been addressed in the literature. This paper reported the first batch of internal erosion tests on a modified stress-controlled triaxial apparatus that allows alteration of seepage direction and hydraulic gradient reversals. Three different schemes of hydraulic gradient application, namely monotonic stepwise loading, cyclic reversal after monotonic loading, and direct cyclic loading, were adopted. In each test, the cumulative particle loss, deformation, hydraulic conductivity, and posterosion shearing behavior were evaluated. It was found that the cyclically reversed hydraulic gradient resulted in more severe erosion at the same level of mean hydraulic gradient. Microscopic analysis was also conducted to investigate the mechanism of internal erosion under cyclic hydraulic gradient reversal, in which mitigation of clogging within the soil matrix was observed and found to facilitate the progression of internal erosion.

Numerical simulation of particle erosion in the vertical-upward-horizontal elbow under multiphase bubble flow

Pipe erosion is one of the main reasons for oil leakage and safety accidents in many engineering fields. The purpose of this study is to investigate the impact of gas volume fraction, elbow angle and rib installation position on pipe erosion under multiphase bubble flow. The computational fluid dynamics (CFD) simulation approach based on volume of fluid (VOF) model and discrete phase model (DPM) was adopted to analyze the effect of gas-liquid distribution and particle movement on pipe erosion under different gas volume fractions. A good agreement of pipe erosion distribution was observed between the simulation results and measurement values. Furthermore, the CFD simulation results show that the pipe erosion rate increases rapidly as the gas volume fraction increases. The erosion rate also increases as the elbow angle increases from 15° to 90°. The rib at small installation position angles can protect the pipe from the direct impact of particles.

Large-scale landslide dam breach experiments: Overtopping and “overtopping and seepage” failures

Landslide dams form when landslide materials reach rivers causing complete or partial blockage. It is known that overtopping water flows and seepage flows are two crucial processes that induce dam failure. In several instances, the landslide dams collapse is caused by the coupled influence of seepage flows and overtopping water. This study aims to evaluate the contribution of seepage flows to the overtopping failure of landslide dams in terms of dam stability, breach duration, and flow discharge. We conducted two field experiment tests to simulate landslide dam failure modes: overtopping failure and overtopping-seepage coupling. Results show that the internal erosion due to seepage induces the loss of fine particles, resulting in a fourfold increase in dam deformation relative to when seepage is minimal. In the case overtopping and seepage failure, the outburst duration is shortened by two-thirds, but the peak outburst discharge is increased by nearly two times compared with the pure overtopping failure. Sediments accumulate at the downstream channel for overtopping failure, but erosion is observed before accumulation when the “overtopping and seepage” failure occurs. Fine grain sizes are limited to the downstream bed for both failure modes, which indicates the equal mobility of sediments involved in the outburst flood from a landslide dam breach.

Assessing the internal erosion sensitivity of earth-fill-dam soils based on the phenomena of suffusion and suffosion

Assessing the internal erosion sensitivity of earth-fill-dam soils based on the phenomena of suffusion and suffosion

Temporal evolution of backward erosion piping in small-scale experiments

Backward erosion piping (BEP) is a form of internal erosion which can lead to failure of levees and dams. Most research focused on the critical head difference at which piping failure occurs. Two aspects have received less attention, namely (1) the temporal evolution of piping and (2) the local hydraulic conditions in the pipe and at the pipe tip. We present small-scale experiments with local pressure measurements in the pipe during equilibrium and pipe progression for different sands and degrees of hydraulic loading. The experiments confirm a positive relation between progression rate and grain size as well as the degree of hydraulic overloading. Furthermore, the analysis of local hydraulic conditions shows that the rate of BEP progression can be better explained by the bed shear stress and sediment transport in the pipe than by the seepage velocity at the pipe tip. The experiments show how different processes contribute to the piping process and these insights provide a first empirical basis for modeling pipe development using coupled seepage-sediment transport equations.

Physics-Informed Multifidelity Residual Neural Networks for Hydromechanical Modeling of Granular Soils and Foundation Considering Internal Erosion

Coupled hydromechanical finite-element modeling of granular soils, taking into account internal erosion, is computationally prohibitive. Alternative data-driven approaches require large data sets for training and often provide poor generalization ability. To overcome these issues, this study proposed a physics-informed multifidelity residual neural network (PI-MR-NN) modeling strategy. The model was first trained using low-fidelity data to focus on capturing the main underpinning physical laws. Subsequent training on sparser high-fidelity data was then used to calibrate and refine the model. Physical constraints, e.g., boundary conditions, were incorporated through modifications to the loss functions. Feedforward and long short-term memory neural networks were considered as the baseline algorithms for training models. The PI-MR-NN was first used to reproduce synthetic results generated by the soil constitutive model SIMSAND and a published internal erosion model. The developed data-driven model was then applied to simulate the breach of a practical dike-on-foundation case and to predict its temporal responses. All results indicated that the hydromechanical response of porous media can be accurately captured using the proposed PI-MR-NN model. The novel training strategy mitigates the dependency of model performance on the training data set and architecture of the neural network, and the use of physical constraints improves training efficiency and enhances the model’s predictive robustness.

An evaluation method for internal erosion potential of gravelly soil based on particle size distribution

An evaluation method for internal erosion potential of gravelly soil based on particle size distribution

Model Test on Backward Erosion Piping under a K0 Stress State

Piping is a major failure mechanism in both dams and dikes. In this work, we develop a transparent specimen tank that allows a camera to clearly record the piping formation process. In addition, this apparatus is able to maintain a constant hydraulic head and to apply K0 stress states. The eroded soil and the discharged water are measured using a collection system. We conduct a series of laboratory tests to investigate the evolution process and mechanisms of piping in gap-graded soils under a K0 stress state. Our results show that the piping process can be divided into three stages: seepage, pipe formation, and pipe wall erosion. No visible soil erosion and deformation is observed in the seepage stage. In the pipe formation stage, the flow channel is formed gradually from the position where water is injected into the exits. In the pipe wall erosion stage, grains are eroded mainly from the pipe wall. Moreover, erosion is more profound on the convex side than on the concave side of the pipe. From the sensitivity analysis, a large percentage of coarse grains can hinder the formation of the flow channel is observed. Finally, the transition mechanism from suffusion to piping based on different testing conditions is revealed.

Structural Health Monitoring of Dams Based on Acoustic Monitoring, Deep Neural Networks, Fuzzy Logic and a CUSUM Control Algorithm.

Internal erosion is the most important failure mechanism of earth and rockfill dams. Since this type of erosion develops internally and silently, methodologies of data acquisition and processing for dam monitoring are crucial to guarantee a safe operation during the lifespan of these structures. In this context, artificial intelligence techniques show up as tools that can simplify the analysis and verification process not of the internal erosion itself, but of the effects that this pathology causes in the response of the dam to external stimuli. Therefore, within the scope of this paper, a methodological framework for monitoring internal erosion in the body of earth and rockfill dams will be proposed. For that, artificial intelligence methods, especially deep neural autoencoders, will be used to treat the acoustic data collected by geophones installed on a dam. The sensor data is processed to identify patterns and anomalies as well as to classify the dam’s structural health status. In short, the acoustic dataset is preprocessed to reduce its dimensionality. In this process, for each second of acquired data, three parameters are calculated (Hjorth parameters). For each parameter, the data from all the available sensors are used to calibrate an autoencoder. Then, the reconstruction error of each autoencoder is used to monitor how far from the original (normal) state the acoustic signature of the dam is. The time series of reconstruction errors are combined with a cumulative sum (CUSUM) algorithm, which indicates changes in the sequential data collected. Additionally, the outputs of the CUSUM algorithms are treated by a fuzzy logic framework to predict the status of the structure. A scale model is built and monitored to check the effectiveness of the methodology hereby developed, showing that the existence of anomalies is promptly detected by the algorithm. The framework introduced in the present paper aims to detect internal erosion inside dams by combining different techniques in a novel context and methodological workflow. Therefore, this paper seeks to close gaps in prior studies, which mostly treated just parts of the data acquisition–processing workflow.

Internal igneous growth, doming and rapid erosion of a mature ocean island: the Miocene evolution of Maio (Cabo Verde)

Maio Island (Cabo Verde Archipelago) is composed of uplifted Early Mesozoic MORB-type pillow lavas and deep-sea sediments, unconformably overlain and intruded by Miocene igneous rocks. Combined structural analyses and 40Ar–39Ar dating were used to constrain the Miocene evolution of Maio. Structures and ages of uplifted Mesozoic sequences and crosscutting Miocene dykes showed that numerous intrusive events were associated with the intense growth of an igneous core complex in the middle to upper crust, causing semi-circular doming and partial disruption of the Mesozoic strata. Two nosean nephelinite dykes cut the Valanginian Batalha Formation and yielded phlogopite 40Ar–39Ar ages of 10.405 ± 0.033 Ma and 10.570 ± 0.053 Ma (2σ errors). A nosean nephelinite dyke that cuts the overlying Valanginian to Early Aptian Morro Formation yielded an age of 9.273 ± 0.020 Ma. Combined with existing K–Ar and 40Ar–39Ar ages, this confirmed a main period of island growth between ~ 16 and 8.7 Ma. We re-interpreted extensive polymict conglomerates, which occur below the Late Miocene Monte Penoso Formation, as landslide deposits. A nephelinite lava clast yielded a phlogopite 40Ar–39Ar age of 8.666 ± 0.0274 Ma, which represents a maximum age for these landslides and thus confined a period of large-scale flank collapses and erosion to between 8.7 and 6.7 Ma. Flank collapses and further mass wasting during this period may have rejuvenated the igneous activity, i.e., resulting in the formation of the Tortonian/Messinian Monte Penoso and Malhada Pedra Formations, due to decompression-induced melting at upper mantle depths. Such interaction between flank collapses and rejuvenated volcanism may be a key to better understand ocean island evolution worldwide.

Detection of soil pipe network by geophysical approach: Electromagnetic induction (EMI) and electrical resistivity tomography (ERT)

AbstractStudying soil pipes is a methodological challenge that needs improvement in detection methods in order to better recognize the role of piping erosion in land degradation and hillslope hydrology. This study explores electromagnetic induction (EMI) and electrical resistivity tomography (ERT) in order to identify soil pipes. The study was conducted in a mountainous area (the Bieszczady Mountains, SE Poland) under a temperate climate, where pipes develop in silty‐clayey soils. In the plot area, eight profiles were measured by the conductivity meter at different depths and then interpolated to present apparent electrical conductivity (ECa). Also, six ERT profiles were carried out using the Wenner‐Schlumberger electrode configuration. The ECa values measured by EMI are not very diversified, suggesting its lower sensitivity to changes in the ECa, whereas the ECa values measured by ERT are characterized by greater fluctuation, that is, better detection possibilities. ERT has revealed soil pipes as zones of higher electrical resistivity (ER >268 Ωm) than their surroundings (characterized below pipes by ER <105 Ωm) underlying the air filling of pipes (ER >427 Ωm), whereas EMI has revealed its higher sensitivity to water content. The EMI results have shown the lowering of the water table in the lower part of the slope, perhaps because of the drainage by a complex pipe network. EMI allows quick measurements of ECa providing information on water content, and thus indirectly soil pipes, but, it cannot delineate individual pipes. Only the integration of geophysical methods supported by field recognition provides an effective method to detect soil pipes.

Mechanical Consequence Observation and Microscopic Visualization of Internal Erosion Using Developed Plane Strain Erosion Apparatus

Abstract Internal erosion has been frequently reported and has caused failures and instabilities of geotechnical structures. A plane strain erosion apparatus is developed in this study to allow the subsequent conduction of drained compression test after seepage test and the microscopic observation of particle movement through a transparent window. A drained compression test preceded by a seepage test is performed on specimens containing the same initial fines contents to investigate the mechanical consequence impacts of seepage-induced internal erosion. Experimental results reveal that, compared with uneroded soils, internally eroded soils show a larger secant stiffness at a small strain level (∼1 %). At medium strain level (∼15 %), the soils with erosion show smaller deviator stress comparing with soils without erosion. The analysis of images recorded by the microscope proves that the fines contacted with coarse particles possibly transferring the load are distinct between the soils with and without internal erosion at both small and medium strain levels during the drained compression test, which indicates that the soil fabric could affect the mechanical behaviors of soils subjected to internal erosion. Our designed equipment and microscopic observation could throw some light on the research of internal erosion from the view of particle scale.

Effects of internal erosion on the cyclic and post-cyclic mechanical behaviours of reconstituted volcanic ash

Internal erosion is the transportation of soil particles from within or beneath the main structure inside the ground due to seepage flow. Internal erosion impacts the mechanical and hydraulic behaviour of soil. The present study investigates the impact of internal erosion on the cyclic and post-cyclic mechanical behaviours of volcanic ash sampled from Satozuka, Japan. A series of experiments using volcanic ash with loose, medium, and dense conditions have been performed using an erosion triaxial apparatus. Further, reconsolidation after application of cyclic loading was considered to study the impact of reconsolidation on the post-cyclic mechanical behaviour. The results show that the cyclic resistance of eroded specimens is improved regardless of the percentage of eroded fines and the initial relative density. The higher cyclic resistance for the eroded specimens is found to be due to a decrease in the intergranular void ratio after the erosion, change in fabric, and pre-strain history during erosion. Reduction in the critical state friction angle (φcri) and peak stress ratio (Rpeak) for the monotonic loading due to cyclic loading is greater for the eroded specimens. However, reconsolidated eroded specimens show increases in φcri and Rpeak, which are lower than those of the non-eroded and eroded specimens without cyclic loading. This could be due to the change in the soil fabric during cyclic loading where the positive impact of erosion is lost after cyclic loading. Such limited recovery of deviatoric stress with deformation is density-dependent.

Errors in finite element analysis of backward erosion piping

Backward erosion piping (BEP) is a type of internal erosion responsible for the failure of many dams and levees. BEP occurs when small, shallow erosion channels progress upstream through foundation sands beneath the structure. As analysis of BEP involves coupling two different sets of flow equations to describe the groundwater flow and erosion pipe flow, the solution contains a singularity in the gradient field at the juncture of the soil and pipe domains. In addition, the erosion process is highly localized, often occurring over length scales of 1 cm or less. While it is well known that singularities and localized phenomena cause high errors in numerical solutions, there has been no assessment of the magnitude of these errors in BEP numerical models. This study evaluates the magnitude of error in BEP finite element models through comparison of numerical results to measurements from a highly instrumented BEP experiment. The results indicate that discretization errors related to the pipe geometry can cause 50%–300% error in the solution near the pipe tip when the pipe is represented via linear, 1D elements. These errors are significant and must be considered for models that assess pipe progression based on the local solution near the pipe tip. Results also indicate that the pipe width must be modeled as twice the physical pipe width to accurately represent the pipe flow when assuming a rectangular cross sectional shape for the erosion pipe.

Foundation cutoffs for flood-detention reservoirs

In design and periodic safety reviews of flood-detention reservoirs one of the key issues, in terms of sustainability, affordability and safety, is the need for a positive cutoff through foundation strata to prevent internal erosion. Such strata often involve alluvial or terrace deposits, which are of variable composition and lithology. The authors will describe the considerations that affect the decision as to when a positive cutoff such as sheet piles, or a bentonite cutoff wall is required, and conversely when it can be omitted, with the potential consequences of such an omission. The latter is likely to include additional requirements for surveillance and monitoring. The paper will describe the investigations that are necessary to inform that decision, including desk study, understanding geological context, site-specific intrusive investigations and arrangements for inspections and so on during construction. The paper will conclude with key issues to be evaluated in deciding when a positive cutoff is necessary.

Sensitivity of tidal hydrodynamics to varying bathymetric configurations in a multi‐inlet rapidly eroding salt marsh system: A numerical study

AbstractWe describe the development of a high‐resolution, two‐dimensional hydrodynamic model for a multi‐inlet rapidly eroding tidal wetland on the western shore of Delaware Bay, using the finite‐volume, primitive equation community ocean model (FVCOM). Topo‐bathymetric surveys, together with water surface and current velocity measurements during calm and stormy conditions, have been conducted to support model validation. The tested model is then used to quantify the tide‐induced residual transport and asymmetry at major inlet entrances to determine the governing hydrodynamics. We chose a skewness method to calculate the tidal asymmetry and serve as a proxy for sediment transport estimates. The effects of the dredging of an artificial entrance channel and progressive channel deepening in shifting wetland hydrodynamics are shown by developing a scenario analysis. Model results show that the artificially dredged channel has altered the volume exchange at other inlet entrances and increased the net seaward export. The changes in the characteristic frequency of the frictional dissipation in the channel and the system's natural frequency are investigated using a simple ocean–inlet–bay analytical model. Subsequently, we have compared the channel friction scale to the inertia scale and observed that the new connection and gradual channel deepening reduce the overall frictional dominance. Ultimately, the study has shown how the short‐ and long‐term channel bathymetry changes, mainly the artificially dredged channel and progressive channel deepening, can affect the connected system's net circulation and trigger internal marsh erosion.