Soil Internal Erosion Research Articles

A Hydraulic Gradient and Stress-Controlled Erosion Apparatus for Assessing Soil Internal Erosion

Abstract Among the four dominant mechanisms of internal erosion, suffusion appears as one of the most complex. It is indeed the result of the combination of three processes: dislodgement of fine particles, transport of them, and filtration of some fluidized fine particles. These processes depend on the soil’s stress state and on the hydraulic gradient path. Thus, to ensure the repeatability of the suffusion test and to study with accuracy the influence of the aforementioned parameters, a new apparatus was developed. This apparatus is designed to test specimens under a vertical downward flow in hydraulic gradient controlled condition while controlling the confining pressure and the stress deviator, which can be either positive or negative. Ten tests on one cohesionless soil were performed in triaxial conditions, with the same mean effective stress and four different values of stress deviator. To compare with conventional suffusion results, one test is also performed in rigid wall conditions. For all performed tests, the same hydraulic gradient path was applied and particular attention is paid to the repeatability, which implies control of each test step. At the end of each test, the specimen was divided into four layers to measure post-suffusion grain size distributions. The time evolutions of the hydraulic conductivity and the erosion rate permit to identify four different phases. Each phase is characterized by two methods: one based on the hydraulic gradient and the second based on the expended energy by the fluid. The results show the great influence on the suffusion kinetics of the preferential flow paths, which localize in the body of the specimen in triaxial conditions and on the circumference in rigid wall ones. Under a constant mean effective stress, the effect of the stress deviator on the suffusion kinetics appears limited, for the tested soil and shear stress ratios.

The impact of Microbially Induced Calcite Precipitation (MICP) on sand internal erosion resistance: A microfluidic study

Fine particle internal erosion involves the detachment, transport, and deposition of fine particles within soil, significantly impacting agriculture, engineering, and environmental protection. Microbially induced calcite precipitation (MICP) has proven to be an effective method for controlling internal erosion. To optimize MICP protocols for effective erosion control, understanding the microscopic mechanisms by which MICP reduces fine particle erosion is essential but remains unclear. In this study, microfluidic chip experiments were conducted to observe the characteristics of calcium carbonate crystals and fine particles before and after MICP reinforcement and erosion. Through quantitative analysis of the calcium carbonate produced by MICP and eroded fine particles, the effects of bacterial density, concentration of cementation solution, and flow rate on the efficiency of MICP in resisting soil internal erosion were investigated. In addition, three primary mechanisms by which MICP reduces fine particle erosion were identified. Firstly, in situ sand stabilization occurs when calcium carbonate generated by MICP bonds and encapsulates fine particles, forming larger particles that remain stable under erosive flow conditions. Secondly, regional sand stabilization is achieved as MICP-produced calcium carbonate crystals narrow or block the flow channels, preventing extensive migration of fine particles. Lastly, adjacent particle stabilization is facilitated by calcium carbonate crystals, which remain stable during water flow erosion and alter the erosion flow lines, creating zones adjacent to the crystals where fine particle movement is minimized. These findings provide a deeper understanding of the role of MICP in erosion control and can inform the development of more effective erosion mitigation strategies.

Polymeric Products in Erosion Control Applications: A Review.

Among the various types of polymeric materials, geosynthetics deserve special attention. A geosynthetic is a product made from synthetic polymers that is embedded in soils for various purposes. There are some basic functions of geosynthetics, namely, erosion control, filtration, drainage, separation, reinforcement, containment, barrier, and protection. Geosynthetics for erosion control are very effective in preventing or limiting soil loss by water erosion on slopes or river/channel banks. Where the current line runs through the undercut area of the slope, the curvature of the arch is increased. If this phenomenon is undesirable, the meander arch should be protected from erosion processes. The combination of geosynthetics provides the best resistance to erosion. In addition to external erosion, internal erosion of soils is also a negative phenomenon. Internal erosion refers to any process by which soil particles are eroded from within or beneath a water-retaining structure. Geosynthetics, particularly geotextiles, are used to prevent internal erosion of soils in contact with the filters. Therefore, the main objective of this review paper is to address the many ways in which geosynthetics are used for erosion control (internal and external). Many examples of hydrotechnical and civil engineering applications of geosynthetics will be presented.

Internal erosion in granular soils with different microstructures under cyclically increased hydraulic gradients

Internal erosion is one of the leading causes of failures and accidents of embankment dams, dikes, and slopes. The hydraulic loading acts as the driving force to detach the soil particles, while the initial soil microstructure determines the susceptibility of particle loss. In engineering practices, the soil may be subjected to cyclic hydraulic loadings due to water level fluctuations by extreme weather of intensive rainfall and drought. Under such conditions, the soil internal erosion process will be different from that under the steady unidirectional seepage, which has not been fully studied and needs urgent investigation. Thus, in this study, the internal erosion process and hydraulic characteristics of soils with different microstructures were investigated by both laboratory seepage tests and the discrete element method (DEM) simulation. The results indicate that the soil with a higher fine content was more structurally stable, and required a larger hydraulic gradient for erosion initiation. Once the internal erosion occurred, the particle loss and the soil hydraulic conductivity increased with increasing fine content. Additionally, when the applied hydraulic gradient was essentially the same, the soil experienced a server erosion under the cyclically than monotonically increased hydraulic gradients, and the amount of eroded soils increased with the increasing gradient amplitude. The results of this study will expand our understanding of the physical mechanism and hydraulic behaviors of soils subjected to cyclically increased hydraulic gradients and with different microstrures.

Failure evolution and mechanism of ground collapse due to exfiltration of shallowly buried water pipeline

Exfiltration of defective water pipelines is one of the leading causes contributing to the frequent ground collapses in congested urban areas; hence, revealing the failure evolution and mechanism of this hazard is essential to its prevention and mitigation. In this study, comprehensive experimental model tests were conducted first to characterize the evolution of soil erosion and ground collapse due to exfiltration of shallowly buried defective water pipes and examine the effects of six critical parameters, i.e., opening size and location, pipe pressure and buried depth, groundwater level, and exfiltration condition. Three failure behaviors of strata around leaking waterpipe were identified, i.e., minor disturbance (slight), formation and collapse of an erosion cavity (moderate), and soil fluidization (severe). Moreover, the ground loosening zone induced by cavity collapse could be roughly estimated using the modified flow ellipsoid theory; soil fluidization would occur once the ratio of water pressure head inside the pipe to its buried depth was greater than 2. Subsequently, a validated computational-fluid-dynamics and discrete-element-method (CFD–DEM) coupling method was employed to explore the microscopic mechanism of cavity erosion under the exfiltration flow. It was disclosed that the formation and expansion of a temporary cavity resulted from internal soil erosion, including the emigration of massive fine particles and aggregation of coarse particles around the defective pipe. Finally, the numerical simulation results indicated that cavity erosion would be exacerbated by increasing flow velocity and particle size-ratio, reducing soil fines content, and changing the opening from the pipe crown to its invert.

Obliquely incident seismic response of subway stations following urban soil internal erosion

Urban groundwater infiltration resulting from tropical storm rainfall can lead to internal soil erosion and ground subsidence. The long-term effects of these phenomena may result in uneven settlement of the subway system, posing risks to its safety and operational integrity. Suffusion poses a significant hazard to long-term subway operation. It is a type of soil internal erosion characterized by the migration of fine particles from the pore channels between coarse particles. This study focused on the performance degradation of different gap-graded sands caused by internal erosion, observed through triaxial compression tests. Using the cap plasticity model and considering mechanical parameters before and after soil erosion, a refined two-dimensional finite element model of a soil subway station structure based on ABAQUS was developed to analyze the deformation and damage pattern of the subway structure resulting from soil internal erosion and earthquake. The results of this study demonstrated that localized internal soil erosion significantly contributes to uneven settlement in subway stations, potentially compromising their seismic performance during oblique seismic excitations.

Piping Stabilization of Clay Soil Using Lime

Construction of earth fill dams offers a cost-effective solution for various purposes. However, their susceptibility to internal soil erosion, known as piping, poses a significant risk of structural failure and resultant loss of life and property. Soil stabilization emerges as a practical technique to fortify these dams against such threats. This study investigated the impact of lime on the internal erosion properties of clay soils, focusing on CH and ML soil types. Specimens of different lime content were prepared and remolded at 95% relative compaction and optimum moisture content. Hole Erosion tests at varying lime concentrations and curing durations were adapted to conduct the investigation. This investigation aims to optimize lime content and curing time for cohesive soil stabilization against internal erosion. Findings revealed that 2% and 5% of quicklime, by dry weight of the soil, effectively stabilized CH and ML soils, respectively, against internal erosion, with a two-day curing period proving optimal. Furthermore, the addition of lime significantly enhanced erosion rate index and critical shear strength in clay soil, underscoring its efficacy in soil stabilization efforts.

The validation and application of electrical measurement for evaluating soil internal erosion under rainfall condition

The validation and application of electrical measurement for evaluating soil internal erosion under rainfall condition

Internal erosion of a gap-graded soil and influences on the critical state

Water retaining structures are critical elements of civil infrastructure. Internal erosion of soils forming the containment structures may occur progressively and lead to expensive maintenance costs or failures. The strength, stress–strain behavior and critical state of soils which have eroded, as well as the characteristics of the erosion, may be affected by hydraulic gradient, confining stress and relative density of the soil at the start of the erosion. Here, erosion and triaxial tests have been conducted on gap-graded soil samples. The tests and results are novel as the samples were prepared to be homogenous post-erosion and prior to triaxial testing by adopting a new sample formation procedure. The post-erosion homogeneity was evaluated in terms of particle size distribution and void ratio along a sample’s length. The erosion-induced mechanical property changes can then be linked to a measure of initial state, more reliably than when erosion causes samples to be heterogeneous. The results show that erosion causes the critical state line in the compression plane to move upwards. The movement is lesser than the increase in void ratio caused by erosion. The state parameter is therefore reduced, consistent with the soil’s reduced peak strength and its less dilative response. Regarding the erosion characteristics, the flow rate decreases with the increase in initial relative density or effective stress, but increases with the increase in the hydraulic gradient being applied. The cumulative eroded soil mass increases with the increase in hydraulic gradient and decreases with the increase in initial density and effective confining stress.

Sinkhole stability chart for geotechnical investigation

Sinkholes are a common geohazard in karst areas where soluble carbonate bedrock is present. Active groundwater flow causes internal soil erosion that creates cavities in the overburden soil layer. The subsurface cavity propagates upward due to the continuous erosion process, and ultimately, they reach to the ground surface, resulting in a sudden collapse. This cover-collapse type is generally a sudden event, particularly in the area where a thick cohesive soil layer is embedded. In this study, a sinkhole stability chart was developed to quantitatively evaluate the safety against the collapse-type sinkhole. Finite-element (FE) modeling was used to simulate the collapse of sinkhole. Field testing data collected from multiple sinkhole sites were used as input to the FE model. To simulate the progress of sinkhole activity, a number of different scenarios with varied size of cavity, strength of overburden soil were simulated, and the corresponding safety factors were determined. Even though each site has varied soil profile, a general trend of the safety factor was observed. The envelopes of safety factors (or equal-safety lines) were statistically determined by using a multivariate regression method. The chart that quantitatively evaluate the stability of sinkhole is used as a decision-making tool for further engineering investigation or mitigation.

Assessing the dam's stability of the pond at the ‘El Bosque’ renaissance garden (Béjar, Spain)

AbstractThe renaissance botanical garden of ‘El Bosque’ in Béjar (Salamanca, Spain) presents a pond bounded by a dam in its western part. The latter is formed by two masonry walls interconnected by buttresses. Cubic spaces in between are filled with a variable grain‐size material (silty sand) that allows limited water flow. In recent years, the southern part of the dam has experienced localized and random subsidence that jeopardizes the entrance to part of the garden. To regain access, a proper and reliable diagnosis of the origin, magnitude and relevance of the subsidence must be made. In this regard, we have undertaken a microgravity survey in the dam area to identify places with an anomalous distribution of the filling material in order to foresee further sinking or potential collapsing areas. The precise positioning (2 mm resolution) and accurate terrain correction needed in this kind of high‐resolution gravity surveys (points every 1.5 m) were achieved by creating a detailed digital terrain model (cm resolution) with a remotely piloted aircraft. In addition, we performed three electric resistivity tomography (ERT) profiles at different levels of the garden: (i) on the dam itself; (ii) right on the foot of the dam and parallel to it (5 m below and ∼17 m to the W); and (iii) a bit farther, but also parallel to the dam (8 m below and ∼27 m to the W). The ERT profiles identified high conductivity in water‐saturated areas and determined the paths that rainfall and pond's seepage water follow in the dam and its underground, formed by granites. The geophysical studies were paired with geotechnical analyses of the sunk materials. The study concluded that the thinnest fraction of the dam's filling material (i.e., silts) is being washed away, leaving behind sand with less density and stability, susceptible to collapse. Thus, the observed sinking is related to soil piping, that is to soil internal erosion and compaction issues that force the soil material to re‐adjust geometrically and volumetrically.

Effects of pre-shearing stress ratio on the mechanical behaviours of gap-graded soils subjected to internal erosion

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.

Prediction ability of discrete element model of loose granular media subjected to complex loadings

The discrete numerical method is recognized today as a powerful method to describe the constitutive behaviour of granular media at both the scale of particles and the scale of the representative elementary volume. This method is also more and more used to address boundary value problems in particular when large deformations may occur or when fluid-solid interactions are involved as, for instance, for internal soil erosion problems. Such discrete numerical models are often calibrated and validated with respect to direct shear tests or drained triaxial compressions. However, even if the models provide satisfying results for these loading paths compared to experimental measurements, their validation with respect to more complex loading paths as the isochoric compression or the path at constant stress deviator still present difficulties, in particular for initially loose granular assemblies. This article investigates the importance of the description of the anisotropy of the initial fabric and of the inter-particle friction law in the simulated responses of loose granular assembly to different kinds of loading paths. It shows how the combination of both can modify importantly the simulated responses to some kinds of loading paths. This investigation is carried out for a numerical discrete model made of spheres by comparison with experimental results on sand. The real shape of particles is considered by introducing rolling resistance at contacts into the model, in order to keep a relatively light model and the possibility to tackle further boundary value problems with a limited computational cost.

Conducting a Comprehensive Physical Investigation on Uncontrolled Internal Soil Erosion Leading to Sinkholes in Anambra State, Nigeria

Uncontrolled infiltration of water poses a significant environmental threat, capable of causing severe damage to structures and farmland if left unaddressed. In the context of Anambra state, Nigeria, uncontrolled infiltration has emerged as the primary cause of internal erosion, leading to the formation of numerous sinkholes scattered throughout the region. Consequently, this study aimed to analyse the physical dynamics of the soils surrounding these sinkholes within the state. The investigation was conducted across three distinct locations: Awka site 1 (6.2232°N and 7.0824°E), Awka site 2 (6.2220°N and 7.0819°E), and Agulu (6.3401°N and 7.1233°E). A total of 24 soil samples were collected and analysed, comprising of 15 samples from the immediate vicinity of the sinkholes and 9 samples obtained from areas located at least 2Km or more from the sinkholes. The parameters examined included pH, Electrical Conductivity (EC), Total Dissolved Solids (TDS), Organic Carbon (OC), Organic Matter (OM), erodibility Factor (K), Moisture Content (MC), Bulk Density, Total Porosity and soil texture. The results revealed a range of pH values, with the piping zone exhibiting a pH of 5 and below, while the non-piping zone predominantly displayed a pH of 6 and above. This discrepancy indicates soil sodicity, suggesting potential challenges in terms of soil quality. Furthermore, the electrical conductivity values varied from 2.21 to 7.21 \(\mu\)S/cm, signifying differing levels of ion concentration within the examined areas. Additionally, the analyses indicated a substantial depletion of organic content, with the piping zone registering a meager organic content value of 2.43. Investigations of soil texture within the piping regions highlighted a notably low clay content, ranging from 2.5% to 6.7%. This finding suggested that significant drainage of the soil has potentially influenced the overall soil stability and the observations underscoring the presence of dispersive processes within the soil, further contribute to the prevailing conditions.

A novel technique for the construction industry to mitigate dispersibility and internal erosion problems of sodium rich clays by using Water-Soluble potassium rich ions material

Dispersibility and soil internal erosion are principal problems in clays having high amounts of exchangeable/dissolved sodium (Na) cations in their porewater. The most frequently utilized method for treating such clays is the chemical treatments that can supply calcium (Ca), which exile Na. The construction industry frequently uses expensive, environmentally harmful materials to mitigate such problems. Therefore, an alternative novel, eco-friendly, and economical approach could be needed. However, problems mitigation with water-soluble K cations are likely to be unknown. This study aims to investigate the effectiveness of using potassium-rich ash (KRA) to depose Na and control the dispersion/erosion problems of two clays (QS and PBS). Byproduct KRA is sustainable, environmentally friendly, and rich in water-soluble K cations. For this, many dispersibility and erosion tests, including double hydrometer, crumb, pinhole, and cylindrical dispersion tests, were carried out with different KRA percentages (0–30%). Physio-chemicals and water-soluble ions tests were also performed to witness changes in chemical characteristics. The experimental results revealed that KRA significantly reduced the dispersion and erosion of clays by exchanging Na with K. For 28 days curing, 15% and 10% KRA for QS and PBS clays, respectively, are found to be enough to mitigate the dispersion/erosion problems. The 62–64% and 76–79% Na are expelled in both clays with 15% KRA after 28 and 60 days, respectively. Physio-chemical study indicates the KRA enhanced the properties by creating a more stable structure through flocculation, agglomeration, and electrostatic processes.

A coupled CFD-DEM investigation into hydro-mechanical behaviour of gap-graded soil experiencing seepage erosion considering cyclic hydraulic loading

The internal erosion of soils is a critical factor that can cause infiltration damage in slope and embankment works. Under conditions of heavy rainfall, storm surge, and waves, the soil is subjected to the cyclic changing hydraulic loads that are different from constant or monotonically changing hydraulic gradient loads, resulting in significant differences in the internal erosion response. The internal erosion response of gap-graded soil under cyclic hydraulic gradient is investigated in microscopic view based on the three-dimensional coupled computational fluid dynamics and discrete element (CFD-DEM) method. Three average hydraulic gradients (i.e., i¯= 7, 9, 11) and different cyclic hydraulic gradient amplitudes (i.e., Δi = 2 ∼ 10) are considered. It is found that the erosion mass me is significantly increased under cyclic hydraulic loading, as the amplitude of the cyclic hydraulic gradient increases, the erosion ratio gradually increases. The particle migration in the upstream layer is more susceptible to the influence of cyclic hydraulic gradients, and the distribution of fine particles is more uniform after erosion with the increase of Δi. The mechanism of the effect of cyclic hydraulic gradient is revealed from a micro perspective, including coordination number, connectivity distribution, particle force characteristics, local packing profile and the force chain evolution, it is found that the cyclic hydraulic loading affects the erosion process mainly by disturb or destroy the local clogging. The work provides insights into the effect of more complex hydraulic loading on internal erosion from a micromechanical perspective.

Soil Erosion Due to Defective Pipes: A Hidden Hazard Beneath Our Feet

Sinkholes are a significant underground hazard that threatens infrastructure and lives and sometimes results in fatalities. The annual cost of sinkhole damages exceeds $300 million, although this estimate is likely underestimated due to the need for national tracking. Sinkholes can also alter natural drainage patterns, leading to increased flood risk. While natural sinkholes occur, those in urban areas are predominantly manmade, caused by soil erosion from defective pipes, typically due to aging. Climate change, storm surges, and urbanization have accelerated subsidence in urban environments, posing greater risks to critical infrastructure and densely populated areas. Extensive research has focused on soil erosion in dams; however, this knowledge does not necessarily apply to erosion through orifices, where gravity and other factors play significant roles. This paper presents a critical literature review on internal soil erosion due to defective pipes (SEDP). The review highlights that hydraulic loading, backfill type, and pipe conditions (defect shape, size, and depth) influence SEDP. Key findings from experiments and numerical studies are summarized, while mechanisms and knowledge gaps are identified. However, it is concluded that the current understanding in this field remains limited, underscoring the urgent need for further experimental and numerical research to expand the knowledge base on SEDP.

Internal Erosion Stabilization of Cohesionless Soil Using Lime

Soil embankments are valuable for the adequate reserve and supply of water to multiple industries. However, they are susceptible to internal soil erosion, which may ultimately lead to structural collapse. To counteract this issue, soil stabilization is practiced in the construction industry. This paper proposes the internal erosion stabilization of cohesionless soil using quicklime. For this research, two cohesionless soil types were investigated and treated with quicklime: poorly graded and well-graded cohesionless soils. For poorly graded soil, the lime percentage varied from 0.0% to 6.0% based on the soil’s weight, while for well-graded soil, it ranged from 0.0% to 3.0%. All the soil specimens were cured for 24 h and tested using the hole erosion test (HET) to replicate the internal erosion effortlessly. The analyzed results demonstrated the efficiency of quicklime as an internal erosion stabilizer for cohesionless soils. The optimum lime content for poorly graded cohesionless soils was 5.0%; for well-graded, the percentage was approximately 3.0%. Moreover, adding lime significantly improved the strength, critical shear stress, and erosion rate index of the soil.

Effect of Curing Time on Lime-Stabilized Sandy Soil against Internal Erosion

One of the key challenges geotechnical engineers face is the failure of embankments due to internal soil erosion. Therefore, soil stabilization against internal erosion becomes necessary to prevent embankment failure. This paper aims to use lime to stabilize sandy soil against internal erosion. Two types of sandy soil (poorly graded and well-graded) were treated with different percentages of lime (based on the dry weight of the soil) and curing times (1 day, 2 days, and 7 days). For poorly graded soil, the different lime percentages used were from 0.0% to 6.0% with an increment of 1% by dry weight of soil. While for well-graded soil, the lime percentages used were 0.0%, 1.0%, 2.0%, and 3.0% by dry weight of soil. The hole erosion test (HET) was utilized to analyze the erosion parameters of the soil samples. Results proved that lime is an effective soil stabilization agent against the internal erosion of sandy soil. Moreover, for optimum stabilization against internal erosion, poorly graded and well-graded sandy soil required about 5.0% and 3.0% of lime, respectively, with a curing time of 2 days. Significant reduction in erosion rate and improvement in the erosion rate index and critical erosion stress were observed at optimum soil stabilization. In addition, the results demonstrated that the curing time increases the erosion rate index and reduces soil erosion.

Coupled CFD–DEM Investigation of Erosion Accompanied by Clogging Mechanism under Different Hydraulic Gradients

Soil internal erosion refers to any process that the finer grains are eroded from the matrix of coarser grains due to seepage. A coupled computational fluid dynamics and discrete element method (CFD–DEM) analysis of internal erosion is conducted on bimodal soils. The coupled influences of hydraulic gradient i and fine content Fc on different domination process of internal erosion is investigated. It is found that the erosion degree does not always increase as i increases for “underfilled” soil (e.g. Fc = 10 % and Fc = 20 %), there is a hydraulic gradient threshold ith above which local particle clogging plays a dominant role, resulting in a smaller erosion degree instead, the ith is larger for larger Fc, when Fc is equal to 10, the ith is 2 or less, while ith is 4 for the soil with a fine content of 20 %. For “transitional” soil (e.g. Fc = 30 %), no obvious clogging domination under larger i is observed. The mechanism is revealed through both macro- and microquantity perspectives. It is found that local clogging is formed by particle bridge formation under larger i values. These findings are highly significant for further understanding the influence of i on the erosion process and establishing the erosion law.