Internal Erosion Research Articles

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.

Experimental investigations of groundwater inflow-induced piping phenonomenon in compacted bentonite buffers for HLW repository

This study introduces a series of laboratory-scale experimental tests of piping erosion in buffer in order to investigate the phenomenon of piping erosion around the buffer material when rapid groundwater inflow occurs in a disposal repository. In a cylindrical cell, specimens of compacted bentonite were exposed to continuous water injection under varying conditions of flow rate, chemical composition, and flow direction. The erosional behaviors of bentonite buffer in piping are analyzed, including the formation of piping channels, critical inflow water pressure, and self-healing. In addition, X-ray CT scanning was utilized to analyze the post-erosion characteristics of the bentonite buffer. The outcomes will inform the development of requirements for the reference design and construction of a secure HLW repository.

Impacts of upslope inflow and soil pipe collapse on slope water erosion in the typical Chinese Mollisol region

Understanding the effects of upslope runoff and soil pipe collapse on slope water erosion can provide scien-tific basis for preventing Mollisol degradation caused by soil erosion. We conducted an experiment to investigate the effects of upslope inflow rate and soil pipe collapse on slope water erosion and to quantify the contribution of soil pipe erosion to slope soil erosion. The experiment included three inflow rates (30, 40, and 50 L·min-1) and three near-surface soil hydrological conditions (without soil pipe: NP; with soil pipe but no pipe flow: PF0; with pipe flow: PF1). The results showed that: 1) Slope soil erosion increased with increasing inflow rates; when the inflow rate increased from 30 L·min-1 to 40 and 50 L·min-1, slope soil erosion increased by 100.0%-111.5% and 214.8%-289.2%, respectively. 2) The soil pipe occurrence and pipe flow formation aggravated the slope water erosion process. At inflow rates of 30, 40, and 50 L·min-1, slope soil loss under the PF0 and PF1 treatments were 1.4-1.6 times and 1.7-2.1 times of that under the NP treatment. The contribution of soil pipe erosion to slope soil loss was 26.7%-37.6% under the PF0 treatment and 40.5%-51.9% under the PF1 treatment. 3) Soil pipe collapse intensified the rill erosion process. Compared with the NP treatment at 30, 40, and 50 L·min-1 inflow rate, rill erosion amounts under the PF0 and PF1 treatments increased by 38.1%-66.0% and by 93.7%-128.4%, respectively. Our results suggested that increasing upslope inflow rate resulted in higher surface runoff velocity, which promoted runoff detachment and transport capacity, and then aggrandized the amount of slope soil erosion. Moreover, soil pipe collapse exacerbated rill erosion process. When the soil pipe collapsed, all surface runoff was converted to soil pipe flow, which accelerated flow velocity and slope soil erosion process, and then increased the amount of slope soil erosion.

Effects of soil inhomogeneity on seepage behavior within embankments

Heavy rain events that accompany recent climate change, have triggered disasters of embankment structures, such as road embankment and levee. Internal erosion, which is the migration of soil particles following seepage flow, causes inhomogeneity of the soil properties of the embankment. However, there are very few studies investigating the effects of soil inhomogeneities on the seepage behavior of groundwater within embankment. In this study, small-scale modelling tests were performed under repeated seepage flow histories. As a result, the groundwater table gradually increased in accordance with the number of seepage repetition. Modelling the fluctuation of permeability due to internal erosion following seepage flow was additionally performed using the soil/water/air coupled finite element analysis, and seepage behavior was investigated. In these analyses, the lower permeability of the toe of embankment was shown to possibly cause an increase in upward water pressure.

Examining the impact of the inter-coarse void ratio (ICVR) on suffusion susceptibility and erosion prediction model

Suffusion, one of the primary types of internal erosion, preferentially erodes fine grains inside the skeleton of coarse particles due to interstitial permeability. The occurrence of suffusion damages earthen dams and affects the living environment around these structures. To avoid the effect of suffusion, many previous studies in the literature have investigated physical parameters influencing suffusion triggers or predicted suffusion potential. Yet, the precise impact of physical parameters, namely the inter-coarse void ratio (ICVR), on suffusion susceptibility was not considered. Thus, the crucial objectives of this article are devoted to investigating the effects of ICVR on suffusion susceptibility. The results show that suffusion susceptibility decreases until the minimum value at ICVR is 1.1 before increasing again. In addition, models for erosion prediction were proposed based on two physical parameters: ICVR and grain size distribution, which are easily determined in the laboratory.

Numerical three-dimensional modeling of earthen dam piping failure

A physically-based numerical three-dimensional earthen dam piping failure model is developed for homogeneous and zoned soil dams. This model is an erosion model, coupled with force/moment equilibrium analyses. Orifice flow and two-dimensional (2D) shallow water equations (SWE) are solved to simulate dam break flows at different breaching stages. Erosion rates of different soils with different construction compaction efforts are calculated using corresponding erosion formulae. The dam's real shape, soil properties, and surrounding area are programmed. Large outer 2D-SWE grids are used to control upstream and downstream hydraulic conditions and control the boundary conditions of orifice flow, and inner 2D-SWE flow is used to scour soil and perform force/moment equilibrium analyses. This model is validated using the European Commission IMPACT (Investigation of Extreme Flood Processes and Uncertainty) Test #5 in Norway, Teton Dam failure in Idaho, USA, and Quail Creek Dike failure in Utah, USA. All calculated peak outflows are within 10% errors of observed values. Simulation results show that, for a V-shaped dam like Teton Dam, a piping breach location at the abutment tends to result in a smaller peak breach outflow than the piping breach location at the dam's center; and if Teton Dam had broken from its center for internal erosion, a peak outflow of 117 851 m3/s, which is 81% larger than the peak outflow of 65 120 m3/s released from its right abutment, would have been released from Teton Dam. A lower piping inlet elevation tends to cause a faster/earlier piping breach than a higher piping inlet elevation.

Effects of seepage flow on liquefaction resistance of uniform sand and gap-graded soil under undrained cyclic torsional shear

Internal erosion is the transportation of soil particles from within or beneath geotechnical structures, caused by seepage flow, that impacts the subsequent mechanical and hydraulic behaviour of the soil. However, it is difficult to predict the liquefaction resistance of eroded soil due to several factors related to the soil fabric. The present study investigates the impact of seepage flow on the undrained cyclic behaviour of two types of soil: uniform sand and gap-graded soil with a fines content of 20%, using a novel erosion hollow cylindrical torsion shear apparatus. From the results for the uniform sand, the soil fabric formed by moist tamping (MT) leads to higher liquefaction resistance than that formed by air-pluviation (AP). However, after applying seepage flow, the liquefaction resistance of the eroded MT specimens becomes even lower than that of the non-eroded AP specimen. Therefore, the liquefaction resistance of soil is expected to decrease due to the rearrangement of the initially stable coarse particles during seepage flow. On the other hand, the liquefaction resistance of the gap-graded soil tends to increase after the removal of fines as the number of stable contacts between the coarse particles is increased. Under these test conditions, the latter effect is found to be greater for the given gradation, leading to a slight increase in the liquefaction resistance of the tested gap-graded soil after internal erosion. Furthermore, the intergranular void ratio and small-strain shear modulus are seen to be well correlated with the liquefaction resistance of the tested soil.

The work input to saturated porous media undergoing internal erosion

The mechanism of internal erosion in porous media involves the microstructural evolutions induced by washing out of fine particles under different loading and seepage flow actions. Consequently, the effective stress on the solid skeleton is governed by the transition in velocity and stress of fine particles due to their detachment from the skeleton and then transport through pore channels, in addition to pore pressure. This study is to develop a formulation of work input to account for the interactions and mass exchanges between solid and fluid phases. Coupled mechanical-hydraulic erosion processes can be properly reflected through mass, momentum and energy balances based on Biot’s mixture theory of a three-phase model. This leads to three separate stress-like variables, effective stress, erosion force and hydraulic gradient, in conjugation with three strain-like variables, strain, mass loss and seepage velocity, respectively. The effective stress tensor, different from the classical form by Terzaghi due to the effect of erosion, and coupled hydro-mechanical-erosion criteria are naturally derived from the proposed work input. They consider grain scale mechanisms describing the transition of erodible particles from the solid skeleton to the fluidized state. Systematic formulations and discussions are presented to highlight the promising features of our approach.

Alteration of soil structure following seepage-induced internal erosion in model infrastructure embankments

The flooding of infrastructure embankments has the potential to cause lasting destabilisation through seepage-driven internal erosion development. To understand the effects of such erosion on slope behaviour it is imperative to identify where in slopes material alteration most commonly occurs. Laboratory testing on scale models of transportation embankments was undertaken to identify the locations within slopes where material movement, and likely property alteration occurs, caused by seepage through slopes. Changes in material properties were most commonly found to occur along the base of slopes and in regions of slopes adjacent to water inflow. Slope toes were found to have a greater proportion of fine material than elsewhere, with the mean grain size of the slope toe region 4.5% smaller and the coefficient of curvature 9% higher than in the main slope body, suggesting the development of a low permeability region towards the slope toe. The source zone for material deposited at the toe of slopes was the section of slopes adjacent to water inflow and the base of slopes away from the toe, shown by a coarsening of sediment in these zones. Material alteration following flooding was best identified using a combination of coefficient of curvature and mean grain size data. These results have implications for the stability of earthworks during and after flood events, and for the design of earthwork inspection and maintenance regimes.

Experimental study on contact erosion at the interface between the weak interlayer and the crushed zone

Contact erosion, one type of internal erosion, is a significant risk to the dam’s safety. Weak interlayer, one of the weakest elements in rock foundations, is vulnerable to contact erosion. In this study, a newly developed triaxial apparatus was employed to investigate the contact erosion at the interface between the weak interlayer and the crushed zone under high triaxial pressure and high water-head. The effects of confining pressure, fines content, and crack width on the initiation of contact erosion were analyzed. The test results reveal that: (1) with increasing confining pressure, the critical hydraulic gradient increased linearly; (2) contact erosion initiated at a relatively low hydraulic gradient in low fines content soil and the critical hydraulic gradient nonlinearly increased with the increase of fines content, which was mainly caused by the contact force distributions of various contact types; (3) increasing crack width linearly reduced the critical hydraulic gradient; (4) the combined effects of confining pressure, fines content, and crack width on the critical hydraulic gradient revealed that fines content had the most significant impact at lower values of fines content, while confining pressure had the most significant impact at higher values of fines content. The experimental results here can be applied to estimate the onset and development of contact erosion at the interface between the weak interlayer and the crushed zone. Furthermore, they also can provide guidance for the embankment dam safety analysis.

Early detection of internal erosion in earth dams: combining seismic monitoring and convolutional AutoEncoders

ABSTRACT Levees/earth dams are critical infrastructures for supplementing clean water, flood management, and energy production, prone to progressive failures due to internal erosion. Current inspection methods are unable to detect internal erosion until its exterior manifestation when it is too late to prevent the often-catastrophic failures. Therefore, finding innovative methods for the early detection of internal erosion is crucial. Despite the knowledge about the general mechanism of internal erosion, its early detection (and prevention) has remained a gap. This study introduces a novel artificial intelligence (AI) method to identify the temporal patterns within the passive seismic monitoring data, which can be associated with internal erosion initiation in earth dams. The proposed approach implements Convolutional AutoEncoders, an emerging deep-learning algorithm for anomaly detection in time-series data. Through an unsupervised learning framework, the AutoEncoders are trained using passive seismic monitoring data collected from a full-scale test embankment. In addition to the approximate initiation time, this algorithm can evaluate the initiation location by identifying the first sensors demonstrating internal erosion signs. The proposed deep learning framework combined with continuous seismic monitoring can serve as a basis for developing advanced early warning systems for internal erosion in earth dams.

Micro-characterization of the adhesion properties and mechanisms at the asphalt-silica aggregate interface under combined thermal-oxygen aging and chloride salt erosion

In this investigation, various Atomic Force Microscopy (AFM) probes were used to characterize changes in the adhesion properties of aged asphalt under different concentrations of chloride salt. The characterization included analyzing the surface morphology, roughness parameters, height-height correlation function (HHCF), and force-distance curves of the asphalt. Additionally, Molecular Dynamics (MD) simulation was employed to reveal the underlying mechanisms that govern changes in adhesion properties between aged asphalt and aggregate when subjected to chloride salt erosion. Interfacial erosion and internal erosion models were constructed to facilitate a comprehensive analysis from multiple perspectives. The results demonstrate that chloride salts interact with the interface between asphalt and silica aggregates, engaging in competitive adsorption with the asphalt. The strength of this competitive adsorption is influenced by the constituents of the asphalt and the concentration gradient of chloride salts both within and outside the asphalt matrix. Under this concentration gradient, polar components are attracted to the asphalt surface by chloride ions, forming triangular adsorption structures with water molecules and aggregates such as asphaltene. Components with lower polarity exhibit distinct distributions and diffusion states due to variations in molecular weight and spatial configuration. As the concentration of chloride salts increases, the concentration gradient intensifies, resulting in enhanced transformations, migrations, and dissolutions of asphalt components. Consequently, the micro-morphology of the asphalt tends to smoothen, the HHCF undergoes significant modifications, roughness decreases, and the adhesion performance between asphalt and aggregate weakens. Moreover, at higher concentrations, the formation of precipitated chloride salt crystals disrupts the continuity of the asphalt, further compromising interfacial adhesion performance. This study is expected to provide theoretical guidance for the modification of asphalt and the improvement of asphalt pavement lifespan in complex service environments.

Internal erosion and permeability of Na CMC-treated and PAM-treated geosynthetic clay liners

This paper investigates the occurrence of internal erosion and the variation of the permeability of geosynthetic clay liner (GCL) with respect to its geotextile component, polymer type and polymer amount added to its bentonite component, hydraulic head, and subgrade material by performing extensive triaxial permeability tests on the GCL specimens. To do this, Na carboxymethyl cellulose (CMC) and polyacrylamide (PAM) were treated with the bentonite component of the GCLs. Then, the GCLs were placed over poorly graded gravel (GP) and poorly graded sand (SP). Consequently, they were tested with two different woven geotextile components under the hydraulics heads of 0.3 m and 10 m. Results showed that only GCLs tested with woven geotextile, having lower tensile strength, lower mass/area and lower thickness over the gravel at a hydraulic head of 10 m, experienced internal erosion. Critically, Na CMC and PAM treatment caused 2–2.5 orders of magnitude decrease in the permeability. Actually, 2% Na CMC and 1% PAM treatment by dry mass were found to be the optimum polymer contents. Both the environmentally friendly biopolymer Na CMC and the synthetic polymer PAM can effectively be treated with Ca bentonite to enhance the hydraulic performance of the GCLs.

Mechanical behavior of gap-graded soil subjected to internal erosion: comparison of suffusion and concentrated erosion

Internal erosion causes massive damage to the soil local and integral fabric with loss of fine particles. In order to further compare the mechanical consequence of different internal erosion scenarios, a series of dissolution tests were designed to simulate suffusion and concentrated erosion by using small amounts of salt particles. For both salt-free clean sand specimens and erodible salt-sand specimens, drained triaxial compression tests combined with bender element measurement were performed to evaluate the degradation of stiffness and strength after internal erosion. Experimental results showed that the shear wave velocity decreased during water saturation. The concentrated erosion resulted more reduction in the shear wave velocity compared to suffusion at same mass erosion fraction of 1%. In general, all the relevant mechanical parameters, e.g. shear wave velocity, peak shear strength and volumetric strain, showed more significant decreasing characteristics in case of concentrated erosion, which indicated that concentrated erosion at key local positions would lead to more critical damage to the soil fabric.

An insight into the interaction between fluid and granular soil based on a resolved CFD-DEM method

Fluid-solid interaction is an essential scientific issue interested many researchers in geological and geotechnical fields, which always holds the key to understanding the meso-mechanism underlying the water-induced geohazards of granular soils such as debris flow, piping erosion, and soil liquefaction. Therefore, this study utilized a resolved coupling method of computational fluid dynamics (CFD) and discrete element method (DEM) to investigate the fluid-solid interaction and its underlying meso mechanics within the granular soils. Three representative cases including single particle free setting, seepage in narrow tubes with dense-packed particles, and one-dimensional consolidation of particle column were implemented to validate the accuracy and efficiency of the resolved CFD-DEM in granular soils. Moreover, the influence of the mesh size and timestep were evaluated in dilute and dense particle systems, respectively. All the numerical results indicated well agreement with the experimental or analytical results reported in literatures. Furthermore, the nonlinear behaviours of the fluid-solid interaction (e.g., wake flow and wall effect) and authentic characteristics at pore scale level were fully depicted in this study. These novel findings provided a deep insight into the meso-mechanics of the complicated fluid-solid interaction within saturated granular soils.

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.

Numerical Study of Resistance Loss and Erosive Wear during Pipe Transport of Paste Slurry

Cemented paste backfill (CPB) as a solid waste treatment technology that prepares tailings as aggregate into a highly concentrated slurry to be transported to the underground mining area, is now widely used in mines. However, the pipeline resistance loss and erosion wear during CPB slurry transportation considering the coupling effect of inlet velocities, viscosities, and particle sizes have not yet been well evaluated and analyzed. Hence, the CFD-based three-dimensional network simulation of CPB slurry flow in an L-shaped pipe at different combinations of the three parameters was developed using COMSOL Multiphysics software. The results showed that the pipe resistance loss was most affected by the inlet velocity and viscosity, with the minimum pipe resistance loss occurring at an inlet velocity of 1.5 m/s, a viscosity of 2.0 Pa·s, and a particle size of 150 μm. In particular, pipe erosion wear was severest at the bend and was positively correlated with inlet velocity and particle size, and negatively correlated with slurry viscosity, with maximum pipe erosion wear occurring at an inlet velocity of 3.5 m/s, a viscosity of 3.0 Pa·s, and a particle size of 2000 μm. The findings would be important for the design of the CPB pipeline transportation, which will improve the safety and economic level of a mine.

A comprehensive experimental study of enhanced solid particle erosive resistance on the inner/outer surface of graphene nanoplatelets modified basalt/epoxy composite pipe

AbstractBasalt fiber reinforced polymer (BFRP) composite pipe is an excellent alternative to glass and carbon fiber reinforced composite pipes in industry and promising in high recycling for polymer composite used in aerospace, marine, and automotive. To enhance the solid particle erosion (SPE) properties of filament‐wound BFRP composite pipe while preserving its mechanical properties, reinforced BFRP composite pipes were prepared to employ non‐functionalized graphene nanoplatelets (GnPs) at a reinforcement concentration of 0.25 wt.% and ultrasonication mixing technique. The SPE behavior of GnPs reinforced and non‐reinforced BFRP composite pipes were characterized by axial and radial positioning of the inner and outer surfaces of the pipes. In each case, the erosion rates of these composite pipes were evaluated at five impingement angles (30°, 45°, 60°, 75°, and 90°) and an impact velocity of 34 m/s. The erosion response of both BFRP composite pipes' outer surfaces showed a semi‐ductile in the axial positioning, with a maximum erosion rate at a 60° impingement angle. However, these composite pipes' inner surfaces in the same positioning presented a maximum erosion rate at a 45° impingement angle. Besides, it is explored that the GnPs contribute to an improvement of approximately 10%–55% in erosive wear resistance of the non‐reinforced BFRP composite pipes. The damage analysis of eroded surfaces was examined through scanning electron microscopy (SEM), and the GnPs effect upon composite pipes' erosion micromechanisms was presented and discussed in detail.Highlights GnPs increased the BFRP composite pipe's erosion resistance. Erosion rate on the inner surface increases due to particle accumulation. GnPs improved erosion behavior via solid lubrication and mechanical properties.

Experimental Research on Backward Erosion Piping Progression

Internal erosion is caused by seepage body forces acting on the soil particles. One of the most dangerous modes of internal erosion at hydraulic structures is backward erosion piping, which usually initiates at the downstream end of a seepage path, e.g., at the downstream toe of the dam. The progress of backward erosion and the development of erosion pipes were tested in a newly developed laboratory device for three types of sand with grain sizes of 0/2, 0.25/2, and 0.25/1. The piezometric head along the gradually developing seepage “pipe” was observed by seventeen piezometers and seven pressure sensors. The seepage amount was measured by the volumetric method. The critical hydraulic gradient was determined and related to the soil porosity. The progression of the seepage path and relevant characteristics such as the piezometric and pressure heads and the amount of trapped sediment were observed by two synchronous cameras. Based on the analysis of the results of 42 tests, a new empirical formula for the backward erosion rate was proposed. The characteristics of lateral erosion were evaluated and compared with the available literature, which provided reasonably good agreement.

Numerical investigation into hydrodynamic behavior of graded aggregates of high-speed ballastless track considering the degree of saturation

The ballastless track inevitably suffers from some functional defects, such as expansion joint cracking, due to the long term combined effect of dynamic train loads and environmental factors. As a result, water can be somehow retained in the graded aggregates of the roadbed surface layer under ballastless track, which is a key structural component subject to high-speed train loads. Accordingly, it is of significance to study the hydrodynamic behavior of roadbed surface layer that can be prone to depend on variation of the degree of saturation (Sr) in graded aggregates. A coupled hydrodynamic model of roadbed surface layer under ballastless track subject to high speed train loads was established based on homogenization theory and elastic wave theory involving Sr of graded aggregates. The proposed model is validated by degrading to Biot's dynamic model in saturated porous medium and analytical method of unsaturated soil. The effect of different Sr on the pore fluid pressure, spatial seepage velocity of graded aggregates is investigated based on this model with the practical seepage boundaries in ballastless track considered. On this basis, the influence of different spatial locations on the dynamic seepage index is discussed, and the differences in the stress paths in the roadbed surface layer under different Sr at different depths are analysed. The numerical results show that the increase of Sr has a spatial and critical effect on the increase of pore water pressure and seepage velocity in the roadbed surface layer. When the expansion joint of ballastless track cracks, the hydrodynamic erosion in the surface layer of ballastless track roadbed has been accumulating continuously. The erosion is more serious within the depth of 15 cm under the surface of roadbed. For Sr above 0.7, extra attention should be given to prevent internal erosion diseases in the roadbed surface layer during maintenance of ballastless track.