Erosion Function Apparatus Research Articles

Coupled CFD-DEM modeling of surface erosion in granular soils: Simulation of erosion function apparatus experiments

This study introduces a numerical modeling approach that couples the computational fluid dynamics (CFD) with the discrete element method (DEM) to simulate grain-scale soil erosion processes induced by water flows. In this modeling framework, CFD simulates fluid flows by solving the volume-averaged Navier-Stokes equations, and uses the k-ω turbulent model for turbulent flows. Simultaneously, DEM computes the displacement of solid particles by incorporating the fluid-particle interactions driven by fluid flows while adhering to Newton's laws of motion. These interactions encompass drag force, buoyancy force, pressure-gradient force, and viscous force exerted by fluid flows and acting on the particles. The coupled CFD-DEM modeling adeptly replicates soil erosion processes, demonstrating good alignment with results obtained from laboratory erosion function apparatus (EFA) tests. In particular, the DEM facilitates the estimation of shear stress acting on the soil surface based on fluid-particle interaction forces, which has been roughly approximated by empirical or semi-empirical models. This study underscores the capability of coupled CFD-DEM in providing valuable insights into the grain-scale behavior of soil particles subjected to fluid flows, with the potential for extension to address soil erosion and fines migration.

Spatio-temporal characterisation of local scour around a circular bridge pier in cohesive soil with different clay/silt ratio

This paper presents new data on scour around a vertical pier in cohesive soils. It specifically focuses on the temporal evolution of local scour hole around the pier with increasing the clay/silt ratio content. Series of flume tests were performed using soil mixtures made with 85% fine sand and 15% fines. The fines fraction used in the soil mixtures includes silt, kaolinite clay, and various combinations of both with different proportions. The water velocity during the tests was kept constant and slightly above the erosion critical velocity of the fine sand used in the mixtures. A 3D laser scanner was employed to continuously record the geometry of the scour hole. Results show that increasing the Kaolinite clay in the fine fraction reduces significantly the scour. The mixture with a range around 7.5–10% of kaolinite clay fines content provides the threshold composition for cohesive soil behaviour effect in scouring process, recognized through scour pattern change. As the clay content increases, notable reductions are observed in the dimensions of the scour hole. Furthermore, the temporal evolution of maximum scour depth measured in flume was in agreement with the results from SRICOS-EFA (Scour Rate in COhesive Soil - Erosion Function Apparatus) method.

Erosion Mitigation Using Grass, Riprap, Lime, and Enzymes

This paper presents the results of research on soil erosion and its mitigation by different methods such as grass, riprap, lime, and enzymes. The goal was to evaluate these methods for their degree of efficacy using laboratory erosion testing. The paper begins with a review of existing knowledge on erosion mitigation methods. The erosion resistance of natural and improved soil was investigated in the erosion function apparatus (EFA), a laboratory device for measuring erosion resistance in the velocity range of 0.3 to 6.5 m/s. EFA testing was performed on grass-covered soils, riprap-covered soils, enzyme-treated soils, and lime-treated soils. The erodibility of the soils before and after treatment was compared. The results of the EFA tests were also compared with a few large-scale field tests available in the published literature. The advantages, limitations, and range of applications of each erosion mitigation method are provided.

Enzymatic-Induced Calcite Precipitation (EICP) Method for Improving Hydraulic Erosion Resistance of Surface Sand Layer: A Laboratory Investigation

As a bio-inspired calcite precipitation method, bio-grouting via enzymatic-induced calcite precipitation (EICP) uses free urease enzyme to catalyze the urea hydrolysis reaction. This soil stabilization approach is relatively new and insufficiently investigated, especially for applications involving surface layer stabilization of sandy soil deposits for increasing hydraulic erosion resistance. This paper presents a laboratory investigation on the surface erosion resistance improvements for compacted medium-gradation quartz sand specimens mediated using 10 different EICP treatment protocols. They involved single- and two-cycle injections of the urease enzyme (activity of 2400 U/L) and 0.5, 0.75, or 1.0-M urea–CaCl2 cementation solution reagents. The urease enzyme was extracted from watermelon seeds. Erosion rates were determined for various hydraulic shear stresses applied using the erosion function apparatus. The spatial distribution and morphology of precipitated calcite within the pore-void spaces of the crustal sand layer were investigated with a scanning electron microscope. Compared to untreated sand, all 10 investigated EICP treatment protocols produced substantially improved erosion resistance, especially for the higher cementation solution concentration (1.0 M). Of these 10 EICP protocols, a single cycle of enzyme–1.0-M-cementation solutions injections was identified as the more pragmatic option for achieving near-optimum erosion resistance improvements. Highest and lowest amounts (18.8 and 5.0 wt%) of precipitated calcite corresponded to the best and worst performing EICP-treated specimens, although the calcite’s spatial distribution in treated specimens is another important factor.

Improvements in Test Procedure and Data Reduction for the Borehole Erosion Test

Abstract As the use of the borehole erosion test (BET) is increasing worldwide, lessons are being learned and procedures are being updated and refined. This article presents new developments including a more detailed field-testing procedure and recommendations, more advanced numerical simulations with the mesh morphing technique, an expanded data reduction process that now includes the computation of the borehole wall shear stress, more comparisons with the erosion function apparatus (EFA) laboratory test, the difference between using water and drilling mud, and advantages and limitations of the BET. The numerical simulations give the velocity and shear stress fields on and near the borehole wall associated with the water flow. They show how the bottom BET is like an in situ jet test while the lateral BET is a vertical hole erosion test. They also show that the bottom two diameters of the borehole flow do not develop a steady shear stress on the wall and should not be used. The data reduction process is expanded to include the profile of the shear stress on the borehole wall using simplifying assumptions. The comparison between the BET and the EFA indicates that the BET gives a soil erosion resistance higher than the EFA does; this may be attributed to sample disturbance for the EFA and testing under favorable in situ stresses for the BET. Two parallel BETs, one with water and one with drilling mud, shows 10 % more erosion with water than with the drilling mud. The main advantage of the BET is soil erodibility profiling through the borehole radius versus depth profile. The BET is not as useful to determine the erosion functions of the soil stratigraphy but more useful in identifying which layers are more susceptible to erosion. The BET profile helps to identify the location of samples for erosion laboratory testing.

Reducing the Erodibility of Sandy Soils Engineered by Cyanobacteria Inoculation: A Laboratory Investigation

Windblown and water-induced erosion cause substantial soil losses worldwide, especially for drylands. Any sustainable management program that increases soil organic matter and improves the stability of the crustal layer could considerably enhance soil productivity and the preservation of erosion-prone land. This paper presents a laboratory investigation of cyanobacteria-inoculated medium sand and fine sand soils studied for severe runoff conditions that were simulated using an erosion function apparatus (EFA). Loosely deposited sand specimens prepared by air-pluviation were inoculated with a single native filamentous-cyanobacterium strain (investigating both Nostoc sp. and Calothrix sp.) and then incubated under high exposure to white light for 32- or 48-day periods. Well-developed bio-crusts were produced on the specimens’ top surface that achieved substantial improvements in erosion resistance, as was demonstrated for a wide range of hydraulic shear stress investigated using EFA experiments. Relative improvements in hydraulic erosion resistance were explained in terms of the nature of the cyanobacteria-developed microstructures (cyanobacteria filament infiltration of pore-void spaces and exopolysaccharide excretion), as were observed by scanning electron microscope examinations. The developed microstructure depended on the cyanobacterium strain employed and the nominal pore-void sizes that are related to the sand gradation and density state. The encouraging findings of this experimental investigation suggest a tailored approach (i.e., employing a suitable native cyanobacterium strain chosen for its compatibility with the soil’s physical properties) could lay the basis for developing a novel technology for soil protection.

Reducing hydraulic erosion of surficial sand layer by inoculation of cyanobacteria

Biological approaches have captured the attention of researchers regarding the beneficial effects of cyanobacteria inoculation in improving surficial soil stability. However, a gap exists in the literature regarding the impact of inoculation by individual cyanobacteria on stability of sand under intense surface-water erosion. This study assesses the improvements achieved in erosion resistance for biological soil crust (BC) formed on medium–coarse silica sand. Specimen groups were inoculated with Nostoc sp. and Calothrix sp., incubated for 32- or 48 day periods and then tested using an erosion function apparatus (EFA), investigating a wide range of flow velocities (hydraulic shear stresses). The significance of BC attachment to (or detachment from) the specimen container sidewall was also investigated in the EFA testing. Compared with untreated sand, inoculated specimens had a significantly greater erosion resistance that increased with the incubation period, with Nostoc inoculum producing greater reductions in erodibility coefficients (45–75%) compared with Calothrix (16–67%). Contrasting bond structures introduced by Nostoc and Calothrix are highlighted by scanning electron microscopy images that showed long Nostoc filaments were entangled more strongly in sand pore voids compared with short Calothrix filaments. In conclusion, this study supports the idea of using cyanobacteria inoculation as an eco-friendly, cost-benefit and effective technique for mitigating land degradation.

Study on Parameters of Two Widely Used Cohesive Soils Erosion Models

The erosion rate of cohesive soils was typically modeled with the excess shear stress model and the Wilson model. Several kinds of research have been conducted to determine the erodibility parameters of the two models, but few attempts have been made hitherto to investigate the general trends and range of the erodibility parameter values obtained by the commonly used Erosion Function apparatus. This paper collected a database of 177 erosion function apparatus tests to indicate the variability of all erodibility parameters; the range of erodibility parameters is determined by data statistics and parameter theoretical value derivation. The critical shear stress (τc) and erodibility coefficient (Z0) in the over-shear stress model have a positive proportional relationship when the data samples are sufficient. However, there is no such relationship between the erodibility coefficient (b0) and erodibility coefficient (b1) in the Wilson model. It is necessary to express the soil erosion resistance by considering all erosion parameters in the erosion model. Equations relating erodibility parameters to water content, plasticity index, and median particle size were developed by regression analysis.

Evaluation of Incipient Motion of Sand Particles by Different Indirect Methods in Erosion Function Apparatus

An experiment was carried out in an acrylic glass-sided re-circulating closed conduit with a rectangular cross section, which is similar in construction to an erosion function apparatus. An adjustable sand box, made of acrylic glass, was attached to the bottom of the conduit as the sand zone or the test section. The hydraulics of the flow in the erosion function apparatus is complicated due to the limited part of the non-smooth and erodible soil surface attached to the closed conduit. As the bed shear stress changes with the bed roughness, even though the flow velocity does not change, establishing a method to estimate the incipient motion is an important challenge for an erosion function apparatus. The present study was conducted to explore the incipient motion of sands from bed shear stress estimated by four different indirect methods on both the sand bed and the smooth bed installed in the erosion function apparatus. In the experiment, particle image velocimetry (PIV) was used to investigate flow dynamics and incipient motion in terms of dimensionless critical bed shear stress. The experimental results show that the bed shear stress estimated from the log-law profiles in the sand zone and the smooth zones are relatively higher than those of the other indirect methods. The dimensionless critical bed shear stress of threshold condition evaluated by all indirect methods was found in good agreement with those of previous results in both zones. The Manning roughness and Darcy–Weisbach friction coefficients were evaluated based on the critical shear velocity at the incipient motion. Although these coefficients were found slightly greater in the smooth zone than in the sand zone, in both zones, they showed good agreement with previous studies.

Experimental Study on Critical Shear Stress of Cohesive Soils and Soil Mixtures

HighlightsErosion tests were performed to study the critical shear stress of cohesive soils and soil mixtures.Linear relationships were observed between critical shear stress and cohesion of cohesive soils.Mixture critical shear stress relates to noncohesive particle size and cohesive soil erodibility.A formula for calculating the critical shear stress of soil mixtures is proposed and verified.Abstract. The incipient motion of soil is an important engineering property that impacts reservoir sedimentation, stable channel design, river bed degradation, and dam breach. Due to numerous factors influencing the erodibility parameters, the study of critical shear stress (tc) of cohesive soils and soil mixtures is still far from mature. In this study, erosion experiments were conducted to investigate the influence of soil properties on the tc of remolded cohesive soils and cohesive and noncohesive soil mixtures with mud contents varying from 0% to 100% using an erosion function apparatus (EFA). For cohesive soils, direct linear relationships were observed between tc and cohesion (c). The critical shear stress for soil mixture (tcm) erosion increased monotonically with an increase in mud content (pm). The median diameter of noncohesive soil (Ds), the void ratio (e), and the organic content of cohesive soil also influenced tcm. A formula for calculating tcm considering the effect of pm and the tc of noncohesive soil and pure mud was developed. The proposed formula was validated using experimental data from the present and previous research, and it can reproduce the variation of tcm for reconstituted soil mixtures. To use the proposed formula to predict the tcm for artificial engineering problems, experimental erosion tests should be performed. Future research should further test the proposed formula based on additional experimental data. Keywords: Cohesive and noncohesive soil mixture, Critical shear stress, Erodibility, Mud content, Soil property.

Surface erosion behavior of biopolymer-treated river sand

The resistance of soil to the tractive force of flowing water is one of the essential parameters for the stability of the soil when directly exposed to the movement of water such as in rivers and ocean beds. Biopolymers, which are new to sustainable geotechnical engineering practices, are known to enhance the mechanical properties of soil. This study addresses the surface erosion resistance of river-sand treated with several biopolymers that originated from micro-organisms, plants, and dairy products. We used a state-of-the-art erosion function apparatus with P-wave reflection monitoring. Experimental results have shown that biopolymers significantly improve the erosion resistance of soil surfaces. Specifically, the critical shear stress (i.e., the minimum shear stress needed to detach individual soil grains) of biopolymer-treated soils increased by 2 to 500 times. The erodibility coefficient (i.e., the rate of increase in erodibility as the shear stress increases) decreased following biopolymer treatment from 1 x 10-2 to 1 x 10-6 times compared to that of untreated river-sands. The scour prediction calculated using the SRICOS-EFA program has shown that a height of 14 m of an untreated surface is eroded during the ten years flow of the Nakdong River, while biopolymer treatment reduced this height to less than 2.5 m. The result of this study has demonstrated the possibility of cross-linked biopolymers for river-bed stabilization agents.

Surface-erosion behaviour of biopolymer-treated soils assessed by EFA

Exocultured biopolymers are ecofriendly soil-stabilisation agents with superior particle bonding, hydrogel-formation characteristics and zero endoculture duration. However, the use of exocultured biopolymers for enhancing soil resistance against surface erosion by water flow is yet to be investigated. Using erosion function apparatus (EFA) in combination with an ultrasonic P-wave reflection monitoring device, the effect of exocultured biopolymers on the erosion parameters of critical shear stress and the erodibility coefficient was examined in this study in soils with different particle distributions. In this way, biopolymer soil treatment showed a ten-fold increase in critical shear stress along with a 90% reduction in erodibility coefficient; results which could be attributed to enhanced particle-to-particle contact and increased pore-fluid viscosity and pore clogging. The results of this study demonstrate the feasibility of using exocultured biopolymers in mitigating surface erosion of erosion-prone soils.

Erosion resistance capacity of dredged marine clay treated with basic oxygen furnace slag

This study investigates the erosion resistance capacity of dredged marine clay treated with basic oxygen furnace (BOF) slag. Samples are prepared in different slag contents, sizes, and various curing times to determine their effects on the erosion resistance capacity. Erosion function apparatus (EFA) tests are performed with various flow velocities and by changing the water flow direction to obtain the erosion resistance properties, including the erosion rate, shear stress, critical velocity, and critical shear stress. The results show that the BOF slag-treated clay has a high erosion resistance capacity, and that the erosion of all the samples commenced only beyond a flow velocity of approximately 1 m/s. The erosion rate and shear stress were observed to increase with the BOF slag content, size, curing time, and bidirectional flow, and a BOF slag content of 30% (determined to be the optimum content) incurs the lowest erosion rate of the samples. The study also reveals that the erosion resistance properties are in good agreement with the undrained shear strength of the samples, and that the BOF slag-treated clay has a higher erosion resistance capacity to the water flow than clay samples with the same undrained shear strength.

Briefing: Improving erosion resistance of sand using nano-silica additive

This briefing paper examines the improvement in the hydraulic erosion resistance of medium silica sand achieved using 1–4% nano-silica (NS) additive. The erodibility of the different soil blends (prepared by mixing NS solutions prepared at required concentrations with the dry test sand) was investigated at bench scale by testing compacted treated sand specimens using the erosion-function apparatus. The NS addition produced a viscous gel property for the soil mixtures, allowing the mobilisation of an effective cohesion (surface bond strength). A 1·5% NS addition was identified as the optimum amount in terms of the greatest erosion resistance for the particular sand investigated; that is, a 92% reduction in the erodibility coefficient value and an approximately six-fold increase in the critical shear stress value were achieved relative to the untreated sand. Further, these improvements in the erosion-resistance properties of the compacted sand–NS mixtures were achieved within a significantly shorter time period (i.e. 1 d specimen curing period adopted in the current investigation) when compared with that typically required for traditional cement and lime additives.

Experimental Investigation on the Erosion Threshold and Rate of Gravel and Silty Clay Mixtures

Abstract. The field of cohesive and noncohesive mixture erosion is not fully understood because of the numerous factors that influence soil erodibility. In this study, erosion experiments were conducted on mixtures of gravel and silty clay in proportions varying from 0% to 100% by weight. The critical shear stress of erosion and the erosion rate were quantified using an erosion function apparatus (EFA). Experimental data revealed that the mixture critical shear stress first decreased and then increased with an increasing cohesive fraction for mixtures with silty clay contents up to 50%. The critical shear stress of the mixture showed an increasing trend as the silty clay content varied from 60% to 100%. A transition from noncohesive to cohesive erosion behavior occurred at silty clay contents between 30% and 35%. The appropriateness of a dimensionless nonlinear excess shear stress model and the Wilson model was tested based on the EFA experimental data. The dimensionless excess shear stress model was shown to be appropriate for noncohesive mixtures, while the Wilson model performed better than the dimensionless excess shear stress model for cohesive mixtures. Keywords: Critical shear stress, Erosion rate, Dimensionless nonlinear excess shear stress, Soil mixture, Wilson model.

Experimental evaluation of the effect of the incidence angle and consolidation pressure on the hydraulic resistance capacity of clayey soils

The primary aim of this study is to examine the variations in erosion and hydraulic resistance capacity of clayey soils with a changing water flow under variable flow conditions. Clayey soils were artificially prepared with various kaolin-sand ratios and consolidation pressures. A laboratory flume apparatus, called an erosion function apparatus (EFA), is improved to measure the scour rate and critical shear stress of samples with changing water flow directions. A series of tests that use the improved EFA was performed for artificial clayey soils considering various directional changes in the water flow at incidence angles of 0°, 90°, 135°, and 180°. Based on the test results, the undrained shear strength indicated the highest correlation with the critical shear stress. Furthermore, the critical shear stress decreased and the scour rate increased with an increasing incidence angle. Finally, the characteristics of the hydraulic resistance capacity, the variations in critical shear stress, and the scour rate changed with the magnitude of consolidation pressure of the clayey soils.

Recent understanding on the hydraulic erosion of vegetated HPTRM system

In recent years, High Performance Turf Enforcement Mat (HPTRM) has been widely noticed and used in revetment projects due to its advantages in both erosion resistance and landscape ecology. Studies have shown that the vegetated HPTRM system has a much better performance in erosion resistance than vegetation lining while it has similar landscape and ecological benefits with vegetation lining. In this paper, firstly a brief overview of existing researches on the hydraulic erosion of vegetated HPTRM System is given, and then a series of experimental and numerical studies on the erosion process of vegetated HPTRM system are introduced, including full scale fume experiments, Erosion Function Apparatus (EFA) tests, high-speed open-channel flow tests and numerical flume tests that conducted by the authors from 2009 to 2018. Based on the test results, new understanding on the erosion characteristics of vegetated HPTRM system is presented, e.g., the feature of erosion development and “upper limit” of erosion. Some useful equations are also given. The vegetated HPTRM system performs effectively in the resistance of hydraulic erosion of open channel flow up to 6 m/s. At last, problems that need to be solved and prospects on future studies are suggested.

Influence of particle shape on the erodibility of non-cohesive soil: Insights from coupled CFD–DEM simulations

Soil erosion is a critical process that is being studied in soil science, hydraulic engineering, and geotechnical engineering. Among many societal and environmental impacts, soil erosion is a major cause for the failures of bridges. The erodibility of soil is determined by its physical and geochemical properties and is also affected by surrounding biological activities. In most of the current models for soil erosion, erodibility of non-cohesive soil is characterized by its median grain size (D50), density, and porosity. The contribution to erodibility of the irregular shape of soil grains, which plays an important role in the mechanical and hydraulic properties of coarse-grained soils, is generally ignored. In this paper, a coupled computational fluid dynamics and discrete element method model is developed to analyze the influence of the shape of sand grain on soil erodibility. A numerical model for the drag force on spherical and non-spherical particles is verified by using the results from physical free settling experiments. Erosion of sand grains of different shapes is simulated in a virtual erosion function apparatus, a laboratory device used to measure soil erodibility. The simulation results indicate that the grain shape has major effects on erodibility. Spherical particles do not show a critical velocity because of their low rolling resistance, but a critical velocity does exist for angular particles owing to grain interlocking. The erosion rate is proportional to the flow velocity for both spherical and non-spherical particles. The simulation result for angular particle erosion is fairly consistent with the experimental observations, implying that grain shape is an important factor affecting the erodibility of non-cohesive soils.

Erosion Rate Prediction Model for Levee-Floodwall Overtopping Applications in Fine-Grained Soils

Characterizing soil erosion and predicting levee erosion rates for various levee soils and storm conditions during floodwall overtopping events is necessary in designing levee-floodwall systems. In this study, a series of laboratory scaled levee-floodwall erosion tests were conducted to determine erosion characteristics of fine grained soils subject to overtopping from different floodwall heights with variable flow-rates. A decreasing rate of erosion was observed as a pool of water was generated in the created scour hole at the crest of the levee model. The erosion rates were also assessed using jet erosion test (JET) and erosion function apparatus (EFA) tests. The results of levee-floodwall overtopping along with soil geotechnical characteristics such as plasticity index, compaction level, and saturation level of the levee soils as well as hydraulic parameters such as water overtopping velocity were used to develop a levee-floodwall erosion rate prediction model. Then, the results of JET and EFA were integrated to develop another prediction model for levee-floodwall erosion rate estimation. Consequently, the prediction models were evaluated by conducting additional tests and comparing the prediction results with the actual measured erosion rates.

Erosion Characteristics of Silty to Clayey Soils Using EFA and Lab-Scaled Levee-Floodwall Tests

The erodibility of levee material has an influence on scour generation in levee-floodwall systems. In this investigation, the effect of various soil parameters including compaction level, plasticity index, and saturation ratio on erosion rates was studied using two methods: lab-scaled physical models of levee-floodwall systems and the Erosion Function Apparatus (EFA). For physical models, a 1:20 scale of a typical levee on the banks of the Mississippi river was constructed. The effect of the floodwall and its inclination on levee erosion were investigated. For EFA tests, the soil samples were prepared in the same way as the materials prepared for physical model tests in order to compare the erosion rate characteristics of these methods. EFA test results show that the erosion rate for soils with more than 60 % saturation levels is more sensitive to change in saturation levels than changes in plasticity index or compaction levels. An erosion rate prediction model was developed for various soils using EFA tests. The levee-floodwall tests show that the erosion rates at the crest are significantly more sensitive to soil parameters than at the slope. The erosion rates for levee-floodwall tests are much greater than the ones for EFA tests. Furthermore, the effect of floodwall inclination and presence in levees are discussed.