A fully-resolved micromechanical simulation of piping erosion during a suction bucket installation

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

Loose wide-grading soils are commonly found in the source areas of debris flows, and in landslides after an earthquake. During rainfall events, fine particles (fines) in the soils gradually migrate downward, and eventually the loss of fines results in an increase in the pore volume of the soil and a reduction in the stability of the soil skeleton, which can lead to subsequent slope failure. To gain more understanding of the fine migration process at the microscopic scale, a 3D discrete element-fluid flow sequentially coupled model is developed, based on Darcy’s Law, to simulate fluid flow through a porous medium and calculate the transportation of soil solids. The erosion model is verified using experimental data. Parametric studies are carried out to investigate the effects of coarse particle size. The results reveal that changes in pore structure caused by fine particle migration can change the local permeability of the material. For the case of the average pore throat diameter to fine particle ratio ( $$J$$ ) of 2.41, changes in local porosity with time from internal erosion in the sample can be divided into four stages: (1) a rapid increase with some variations in porosity, (2) a slow increase in porosity, (3) a rapid increase in porosity, and (4) a steady state with no change in porosity. Not all stages are present for all value of $$J$$ . Stages (1) (2) (4) are present for 2.48 ≤ $$J\le$$ 2.58 and stages (1) (4) are present for $$J$$ ≤ 2.24 and $$J\hspace{0.17em}$$ ≥ 2.74. A sharp increase in the fine’s erosion possibility occurs for a $$J$$ value lies between 2.58 and 2.74. The erosion possibility sensibility shows an exponential relationship with $$J$$ . The model provides an effective and efficient way to investigate the process of pore blockage and internal soil erosion.

An auto-adaptive moving mesh method for the numerical simulation of piping erosion

Internal erosion caused by broken sewer pipes often leads to ground subsidence in urban area, which is a major risk to public safety and has caused substantial socioeconomic loss. In order to ensure the ground stabilization and the safety of buried pipelines, it is necessary to understand the process of internal erosion around a submerged defective pipe. In this paper, the Dynamic Fluid Mesh (DFM) is coupled with the three-dimensional discrete element method (DEM) to simulate internal erosion in gap-graded soils above a defective pipe. In this fluid-solid coupling scheme, the fluid mesh can be generated according to the soil skeleton formed by coarse particles and updated at regular intervals. Seepage forces are calculated and applied on solid particles in the DEM model. The approach accounts for permeability and porosity changes due to soil skeleton deformation and internal erosion. In this study, some gap-graded soils samples with different size ratio are established. A defective pipe is placed below the sample. After that, different hydraulic gradients are applied to the sample. Fine particles are washed away from the hole in the pipe. The results indicate that the erosion process can be divided into three stages according to changes in the erosion rate. In the initial stage, numerous fine particles are washed away, and the flow rate increases with the increase of eroded particles. Subsequently, the erosion rate decreases and the flow rate tends to reach a steady state. Finally, only a small proportion of particles fall down from the outlets and the erosion rate levels off to zero gradually. Parametric studies show that the increase of hydraulic gradient increase the eroded particle mass. The number of erosion particles from the bottom layer is much larger than those from the upper layers as more fine particles in the upper layers are locked.

Numerical simulation of solid particle erosion in pipe bends for liquid–solid flow

Simulation of wellbore erosion and sand transport in long horizontal wells producing gas at high velocities

Numerical simulations were performed in this paper to get deep insights into the drill pipe erosion phenomena. Fluid flow and particle erosion inside the drill pipe was studied numerically and validated experimentally with full-scale test samples made of aluminum. The numerical results are in good agreement with the experimental observation and conclusions can be drawn from the comparison that: (1) the static pressure of drilling fluid increases as the fluid enters the convergent section of the drill pipe, and maintains at a low level when fluid passes through the inner section of tool joint pin and increases as fluid enters the transition area of the tool joint pin and tool joint box. (2) fluid velocity of drilling fluid increases as it enters the convergent section of the drill pipe, and maintains at a high level when fluid passes through the inner section of the tool joint pin and decreases as fluid enters the transition area of tool joint pin and tool joint box. Fluid entrapment is observed near the transition area. (3) both the shear stress distribution on the inner wall of the drill pipe and the experimental observations have demonstrated that three locations, the inlet section of the tool joint pin, the inner section of the tool joint pin and the transition area of the tool joint pin and tool joint box are severely eroded and special attention should be paid to these locations.

Internal erosion, caused by seepage flow inside the soil, accelerates soil failure during a natural disaster. Numerical simulation can be an effective tool to quantitatively evaluate the relationship between internal erosion and the instability of the ground as a whole. Internal erosion and multiphase flow simulation of fluid and granular materials with a particle size distribution require coupling simulations that can represent the interaction between particles and pore water and the movement of particles. There are two main types of coupling models: "Resolved coupling model," which can calculate detailed flow and fluid forces, and "Unresolved coupling model," which is based on empirical drag and seepage flow models. Previous studies have indicated that both models should be judged appropriately based on the ratio of particle-fluid spatial resolution. However, applying a resolved coupling model to the vast number of soil particles that make up the ground is impractical from a computational cost perspective, and empirical unresolved coupling model has difficulty in representing localized failures such as internal erosion. Therefore, developing a new coupling model that satisfies both computational accuracy and efficiency is desirable. In this study, we applied ISPH (Incompressible Smoothed Particle Hydrodynamics) for fluid analysis and DEM (Discrete Element Method) for soil particles to develop a fluid-soil coupling simulation model that can directly represent the movement of soil particles during the internal erosion process. Through numerical experiments using a particle layer with the vertical upward flow, we understand the limitations of the conventional coupling model and propose a new hybrid type of semi-resolved coupling model that combines these two models appropriately.

Suction buckets are a promising concept for the foundations of offshore wind turbines. During the installation process of a suction bucket, localized fluidization of the granular soil, so-called piping erosion, may lead to installation failure. A 3D fluid-solid coupled micromechanical simulation is presented to study the occurrence of piping. An Euler-Lagrangian coupling employs momentum exchange between the fluid phase and the geometrically resolved particles. We investigate the behavior of the soil for three cases with varying prescribed suction velocities. We observe piping in the case with the highest suction velocity by analyzing the deformation of the granular fabric and monitoring the differential pressure. The grains under the bucket wall-tip show the highest hydraulic gradients and forces at the onset of piping. This approach permits a detailed analysis of piping phenomena and brings novel insights on the triggering conditions for piping failure of suction-aided foundations.

Accurately assessing the erodibility of geomaterials is of great significance for the design of earthen structures and the prevention of the associated failure induced by seepage force. Recently, the un-resolved Computational Fluid Dynamics–Discrete Element Method (CFD–DEM) has been widely used to investigate internal erosion. However, due to the use of wall boundary and the fact that the fixed CFD domain cannot be changed with the soil sample’s volume contraction during the erosion test, a larger porosity at the boundary of the CFD domain is commonly formed, resulting in sidewall preferential flow (i.e., relatively more fine particles migrate along the boundary of the DEM domain) and thereby overestimating the soil erodibility. In this study, a new method based on particle boundary is developed to tackle this problem. The newly proposed particle boundary can prevent its particles from erosion via inter-particle bonding and transfer stress from servo walls to the simulated sample. An optimal particle boundary thickness is determined by considering sample contraction and computational efficiency. The performance of the new method was compared with the conventional method and also verified using experimental results. The results show that the newly proposed method has significantly improved the uniformity of fluid velocity distribution. Furthermore, the cumulative eroded mass of fine particles in the new model is approximately 15% lower than in the conventional model. It is convincingly demonstrated that the new method can simulate internal erosion better and give a more accurate assessment of geomaterial erodibility.

The work detailed here is part of an international initiative on the evaluation of dam safety simulation software for internal erosion performance and best practices. The primary experiments involve simulating uncertainty in the failure events of two dams with two different models: DLBreach and WinDAM C. DLBreach is a physically-based dam/levee breach model developed by Wu. WinDAM C is also a physically based dam breach model capable of analyzing both dam overtopping and internal erosion. The dams selected for the analysis include a 1.3 m high dam tested in the lab and a larger 15.56 m high dam, which suffered a failure in the field. The findings from these experiments are extended with a further analysis on variance, sensitivity, and optimization. Finally, a regression model is trained using the results of these simulators as an inquiry into how well such a system can be captured using machine learning techniques. The results of these experiments, together with the results of the other members of the initiative, improve our understanding of the influences that users bring to using these tools.

Rainfall is the main cause of erosion damage in loose slope deposits. During rainfall infiltration, fine particles in the soil mass will move with water infiltration, thus changing the localized particle distribution of the soil mass, which, in turn, causes changes in the pore water pressure and volumetric water content within the slope and ultimately affects slope stability. In order to develop advanced soil and water conservation programs to prevent slope damage, it is crucial to understand and accurately reproduce the particle migration and aggregation characteristics of soils under different rainfall conditions. Therefore, this paper systematically investigates the soil particle migration characteristics of the soil body under rainfall conditions by simulating the internal erosion of the lateritic soil slope body under rainfall conditions via slope internal erosion simulation experiments and experimentally analyzing the migration and aggregation of fine particles in the slope body, as well as the changed rules regarding pore water pressure and volumetric water content at different locations of the slope body with rainfall. The results of this study show that (1) with the infiltration of rainfall, the fine particles in the slope body mainly infiltrate in the vertical direction in an early stage of rainfall; in a later stage, there is vertical downward and down-slope seepage. Therefore, fine particles always gather at the toe of the slope, which leads to relatively high water content and pore water pressure at the toe of the slope, and thus, the slope is always damaged from the toe of the slope. (2) Inside the slope, the fine particles always gather at the smallest pore diameter. With the enhancement of hydrodynamic force, they will be lost again, which leads to a sudden decrease in the local volumetric water content of the slope, and the pore space increases. Then, it is filled with seepage water, which makes the pore water pressure fluctuate or increase. (3) Based on the particle distribution parameter, the present study produced a distribution map of the fine particle content of the slope body under different rainfall intensities and established a model of the dynamic change of fine particles, which improves the understanding of the effect of the change in the fine particle composition of the slope body on the water content and the pore water pressure and may be helpful for the assessment of the initiation of the mudslides.

Internal erosion is the loosening, detachment and transport of fine particles through the pore structure of a coarse material due to a seepage flow. Once erosion is initiated and fine particles are not blocked within the coarse material, particles can be washed out leading to larger scale deformations. This phenomenon can be frequently seen in water retaining structures like dams, levees and embankments. This kind of hydraulically induced erosion processes caused enormous damage to infrastructure and buildings as well as loss of human lives. Prevention of these catastrophic events includes a better understanding of the initiation of this process. Although an extensive number of studies have been carried out on this topic, the hydro-mechanical mechanisms of the onset of erosion at micro scale are still poorly understood. In the presented thesis, contact erosion induced by hydraulic flow perpendicular to the interface was studied. Base material can be dislodged and transported into the filter material due to upward water flow. The study focuses on the hydraulic changes happening at the interface between fine and coarse layer and the conditions leading to first detachment of fine particles. In the sequence of processes leading to erosion and as consequence the failure of the structure, it is the onset of erosion indicating the initiation of the process, which is of interest in this research. Initiation of contact erosion process takes place locally at the pore scale and therefore, measurements of the pore scale parameters are necessary. The major difficulty of a micro-scale experiment is the optical opaque nature of real samples that do not allow observations inside of samples. Due to this limitation, most of the studies have been carried out based on the observations at the wall of the test cell, measurements of the outflow turbidity, settlement of the sample at the wall of the sample cell. To overcome this problem, transparent soil has been introduced for our lab-scaled experiments using Refractive Index Matched (RIM) media technique. RIM medium was obtained by using the same refractive index for both fluid phase and solid phase. Hydro-gel beads were used for the soil matrix, and pure water was used for the fluid phase which creates a transparent medium. Visualization of the local flow field inside the transparent soil was done by Particle Image Velocimetry (PIV) technique. Rather than using an expensive laser systems, Light Emitting Diode (LED) based light sheet was used for the illumination. This developed experimental apparatus was first used to identify the porous flow characteristics inside a mono-dispersed packing. Results were successfully compared with the available literature data on porous flow studies. Formation of preferential flow channels, flow characteristics for different pore geometries, pore scale measurements for the deviation of laminar flow were identified. Finally, experimental results for the layered porous medium was used to validate a numerical model which was developed using an existing code to simulate contact erosion models as same as in the experimental conditions. Discrete Element Method (DEM) was used to model the solid phase while Lattice Boltzmann Method (LBM) was used for the fluid phase. First, a simple fluidized bed problem was developed and identified the mechanism for particle dislodgement and transportation due to an applied upward flow. Then contact erosion was simulated for several particle size combinations where erosion is geometrically possible. Local flow behaviour of different pore shapes at the contact zone was studied and their influence for the contact erosion was quantified. Main outcomes of the study were presented through three journal papers and one conference paper which form the core of this thesis. Key findings can be summarized as: 1. Development of an experimental method for measuring pore scale flow characteristics inside the porous medium 2. Identification of preferential flow channels and flow characteristics for different pore geometries 3. Modification of an existing numerical code for contact erosion simulations and validation of it through experimental results 4. Quantification of hydro-geometrical influence for onset of contact erosion

Numerical Simulation of Erosion in Different Diameter Ratio Sudden Contraction Pipe

The present study discusses the erosion of aluminium pipe using nano and micro particles. The Computational Fluid Dynamics (CFD) analysis using ANSYS-fluent is done for the prediction of the erosion. DPM model is used in CFD for erosion simulation. The analysis is done for the pipe bend angle in the range of 30–150° and the radius of curvature from 25 to 100 mm for both nano and micro particles. The test combinations and related CFD results are processed through Design of Experiments (DOE) – Response Surface Methodology (RSM) using Minitab tool. The micro particles show higher erosion compared to nano particles. Also it has been observed that, erosion depends mainly on Particle impact angle, Turbulence – secondary flow. The correlation is developed for the prediction of erosion at the given range.