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River levees are subject to bioturbation by various animals which can actively excavate into earthen structures producing an internal erosion that, during the passage of a flood, can grow in time making the levee unstable. This phenomenon can lead to river levee breaching and, as a consequence, collapse, even for relatively minor flood events. A well-known animal burrower is represented by the North American crayfish Procambarus clarkii (P. clarkii), an invasive species in Europe, mainly introduced for commercial purposes, causing a decline in biodiversity and profound habitat changes. The physical damages caused by P. clarkii on levees and banks, such as in rice fields, irrigation ditches, and small channels, have not been fully studied and behavioral components underlying this impact are mostly occasional. To understand the impact of burrowing activity on the seepage process, a field survey was done in a drainage channel in Tuscany, Italy, to evaluate the density and geometry of the internal burrows that were excavated by the crayfish. Based on these observations and some previous laboratory experiments, three dimensional (3D) numerical simulations of the seepage processes were done inside burrowed levees. Numerical results allowed the increase in the hydraulic vulnerability of levees to the process of internal seepage to be disclosed. In particular, for a given river water level, the reduction of the time scale for the phreatic line to reach the levee field side appears to be a function of a quantity here defined as the burrow hydraulic gradient. This quantity is here defined as the ratio between the hydraulic head inside the burrow and the horizontal distance from its end to the field side of the levee. Moreover, a comparison between the 3D with the analogous more common two dimensional (2D) numerical simulations illustrated the schematization which is better suited for describing the seepage processes when animal burrows, not only by crayfish, are present. [ABSTRACT FROM AUTHOR]

• Governing equations for thermal-hydro-salt-mechanical (THSM) coupling model are presented. • The THSM coupling model is used to analyze the artificial freezing process in the sand-marine clay layers under seepage flow conditions. • The average degree of artificial freezing at a given time is proposed to qualitatively analyze the effects of the artificial freezing. In this paper, the general governing equations for thermal-hydro-salt-mechanical (THSM) coupling consider the effects of adsorption salt on the surface of soil particles, the mushy zone at the phase-change interface, molecular diffusion and crystal growth, the compressibility of liquid and solid matrices, nonlinear high-salinity groundwater, non-convective flux and thermal permeability. The THSM coupling is used to analyze the artificial freezing process around freeze pipe installed in the sand-marine clay layers under seepage flow conditions. The good agreement between the calculations of the theoretical model and experiment models in the literature. Parametric studies were conducted to investigate the effects of seepage velocity and freeze pipe installation patterns on the effectiveness of artificial freezing which was evaluated using a new definition called the degree of artificial freezing. The average degree of artificial freezing DF at a given time is proposed to qualitatively analyze the effects of the artificial freezing. The lower the flow velocities of groundwater and the spacing of the freeze pipes, the more quickly the formation of the freeze curtain reaches DF =100 %. The freeze curtain with DF =100 % can be earlier formed in the sand layer with freeze pipes installed in rectangular pattern than those installed in triangular pattern. [ABSTRACT FROM AUTHOR]

Suction-induced seepage flow can significantly reduce the soil resistance during the installation of suction buckets, thereby ensuring their intended penetration depths and the designed in-service capacities. However, the lack of analytical models describing seepage flow behavior in the literature poses a significant challenge, primarily due to the complexity of seepage boundary conditions and the anisotropy and spatial variation of soil permeability. This paper addresses this gap by presenting a novel analytical solution for analyzing suction-induced seepage flow around buckets, with a particular focus on the general multilayered soil profile featuring anisotropic permeability. The method of separation of variables is used initially to derive general solutions, and the final solutions are subsequently obtained by combining continuous conditions with the orthogonality of Bessel functions. The accuracy of the solutions is confirmed through comparisons with the results obtained from finite element analysis. Furthermore, this study discusses the seepage flow behavior in several typical scenarios, including permeability anisotropy, increased permeability within the bucket, and the presence of an overlying low-permeability layer. The analytical solutions presented in this paper provide a rapid and accurate method for the analysis of suction-induced seepage flow during suction-assisted installations across a wide range of complex soil permeability conditions. [ABSTRACT FROM AUTHOR]

Understanding the pipeline scour mechanism under different conditions is essential for protection measures. The computational fluid dynamics (CFD) and discrete element method (DEM) are coupled for the simulations. To reduce the computational effort, the coarse-grained method is applied, and the Darcy-Forchheimer porous model is used to replace the far field elements. Both of the porous medium and particles-fluid interaction model are validated by comparison between simulation results and theories. The scouring simulation results show a good agreement with the experiments conducted with single-diameter spherical particles under different current-wave conditions. Further, the flow around the pipeline, the seepage in the sediment bed and the force acting on the particles are analyzed. The vortex shedding exists downstream under current but the vortex moves around under waves. The seepage depends on the pressure, influenced by the pipeline and the water depth, and the variation of the seepage is discussed. The force acting on the particles is not uniform along bed and the distribution is analyzed. This paper provides an insight into scour mechanics from the aspects including seepage and flow-particle interaction. Different methods are used for modification, giving a reference for the usage of CFD-DEM model in the analysis of scour process. [ABSTRACT FROM AUTHOR]

Maintaining the stability of the tunnel face during the construction of the submarine shield tunnel is the prerequisite for safe construction. A series of face instability model tests under saturated strata were carried out. The earth pressure, the evolution of the soil arch area and the amount of soil entering the soil groove caused by the instability of the tunnel face under different face water pressure conditions were studied. A series of numerical simulations were carried out to analyze the effects of tunnel face water pressure. The results show that the vertical earth pressure and horizontal earth pressure at different positions show a gradual decrease with the increase of the baffle backward distance, and the smaller the water pressure ratio, the more obvious this law is. According to the test results, the decrease of the water pressure ratio of the tunnel face can significantly increase the soil intake of the soil tank, which indicates that the collapse range above the tunnel face is large. The trend of instability region obtained by numerical simulation is consistent with the test monitoring results. This provides a reference for the construction of submarine shield tunnels. • Geomechanical model tests are carried out. • The pore water pressure and earth pressure are studied. • The evolution process of the soil arch area and the soil inflow volume of soil tank are investigated. • The failure areas is analyzed. [ABSTRACT FROM AUTHOR]

The inrush of groundwater impairs heating efficiency during oil shale in situ pyrolysis mining, and it also increases oily waste-water production. Artificial ground freezing (AGF) is an ideal method to block the adverse groundwater infiltration, while the poor freezing performance and high energy consumption of the current AGF pattern are the biggest obstacles, even failing at high-velocity seepage flow. This study proposed and investigated a novel pattern of AGF through cold gas convection (GC) for oil shale in situ reservoir, this pattern have the potential to enhance the freezing performances, especially when encounters the high-velocity seepage flow. In this study, a coupled hydro-thermal-solid model was developed and numerical simulations were performed, the enhancement mechanism of freezing performances and energy conversion have been analyzed to reveal the superiority of the GC-AGF. The results indicated that the maximum freezing rates were twice the current AGF. With seepage flow, the shape of the frozen zone developed elliptically perpendicular to the seepage flow direction, and the effective radius of the frozen zone formed by GC-AGF decreased only by 10%–20 %, even at a higher-velocity seepage flow. The analysis showed that the gas-water two-phase zone was a barrier to the direct heat exchange between the infiltrated groundwater and the frozen zone, which was the enhancement mechanism of GC-AGF. Correspondingly, the specific energy consumption reduced from 8.0 × 107 to 3.8 × 107 J/m at a higher-velocity seepage flow. The results showed that the proposed GC-AGF method significantly enhanced the freezing performance with low energy consumption. [ABSTRACT FROM AUTHOR]

The method of smoothed particle hydrodynamics (SPH) has been recently developed to study the coupled flow-deformation problems in porous material and considerable success has been achieved comparing to traditional mesh-based method, especially for treating large deformation and post-failure. However, computational challenges remain for the hydro-mechanical boundary treatment as well as the accuracy and stability of the numerical scheme. It is shown that the use of conventional SPH operator for the solution of the coupled problem can lead to several issues including numerical instabilities, inaccuracies and unphysical particle clumping as well as particle disorders near the boundary. To address these issues, a general SPH scheme with enhanced accuracy for saturated/unsaturated porous material is proposed in this paper. An improved SPH formulation for seepage analysis is proposed to allow an accurate prediction of liquid flow in porous material. A new stabilisation technique that combines the use of a density diffusion term, a modified particle shifting algorithm, and a new viscous damping term is developed to further improve the accuracy, stability and robustness of the proposed method. The implementations of stress boundary conditions and hydraulic boundary conditions in SPH, such as confining stress, hydraulic head, infiltration/evaporation, and potential seepage face, using either wall boundary particles or free-surface domain particles, are discussed in detail. A range of benchmark examples is adopted to verify the validity of the present coupled framework. The proposed model is finally applied to simulate the failure process of embankment dam due to rapid drawdown. Results indicate that the methodology proposed herein can be a promising tool for the analysis of the coupled hydro-mechanical process in porous material involving large deformations. [ABSTRACT FROM AUTHOR]

• The newly developed Lagrange-Lagrange coupling model allows simulating sediment transport under complex moving boundary conditions. • A seepage effect on sediment transport is particularly found around the tip of uprush /backwash waves. • An important role of the DEM-base granular model to evaluation of the bottom shear stress is indicated. Interactions between the uprush and backwash waves around a swash zone cause a complex water surface with wave breaking. Infiltration and exfiltration on a permeable beach face produce significant effects on the bottom shear stress. Abrupt changes of the bottom shear stress induced by uprush waves onto a dry bed have a significant impact on the estimation of sediment flux. In order to simulate, with a high degree of accuracy, a violent flow with wave breaking and complex moving bed boundaries along the on-off shore direction, wave motions are solved by using an enhanced particle method based on the MPS (Moving Particle Semi-implicit) method, while the DEM (Discrete Element Method) is used for a movable bed simulation. Consequently, the high potential of a MPS-DEM coupling model to simulate the swash beach process is clearly demonstrated by comparison with previous experimental results. Furthermore, the significance of the seepage flow in the swash beach process is shown with referring the Nielsen's modified Shields number. [ABSTRACT FROM AUTHOR]

Abstract In this study, a new shape-dependent fluid-particle drag model for irregularly shaped particles is integrated into the fluid dynamic program CFD-DEM and used to analyse the behaviour of calcareous sand particles in liquids. The new drag model had been correlated by pervious settling experiments of calcareous sand particles in a static Newtonian Liquid. The new drag model defines the particle-fluid drag coefficient as a function of both the fluid regime and particle shape characteristics which can evaluate how the particle shape deviates from a regular sphere. This study is a follow-up work of the authors' previous experimental research, focusing on the numerical modelling of sand particle-fluid interaction. To validate the integration of the new drag model in program CFD-DEM, the code has been used to reproduce the calcareous sand particle settling and seepage experiments. The comparison with simulations using the existing drag models without considering particle shape effect demonstrates that, by means of the new drag model, a significant improvement in the capability of CFD-DEM program to predict the terminal falling velocity of irregularly shaped particles is obtained. With this implementation, CFD-DEM program is used to simulate seepage flows within calcareous sand sample in which particles are significantly different from regular spheres, as is usually the case of environmental and geological fluid-particle flows. Graphical abstract It presents the images of settling of a typical calcareous sand particle taken from the experiment and numerical simulations together with the numerical predictions of terminal fall velocity by new drag model; and the numerical model of seepage flow in cylindrical calcareous sand sample and the relationship between flow velocity and hydraulic gradient obtained by the experiment and numerical simulations. Unlabelled Image Highlights • New shape-dependent drag law for irregular particle is implemented in CFD-DEM model. • The CFD-DEM model predicts the settling of calcareous sand particle in liquid well. • The seepage flow in calcareous sand sample is accurately simulated by CFD-DEM model. • The model with new drag law is useful for hydro-mechanical analysis of natural particles. [ABSTRACT FROM AUTHOR]

• Fracture-matrix model considering free/seepage flow and roughness effects. • Non-Darcy coefficient is obtained from 284 seepage tests. • Porosity, permeability, aperture, and roughness are the main factors. • Friction factor reveals critical flow regimes and Reynolds number. The friction factor plays a crucial role in evaluating pressure gradient loss for water flow through fracture-matrix systems (FMS). This study presents a theoretical model for the FMS friction factor, incorporating viscous and inertial terms based on Forchheimer's law. The model considers the coupled effects of free flow, seepage flow, and roughness. The non-Darcy coefficient in the inertial term is determined by fitting 284 sets of FMS seepage test data. To validate the derived friction factor, COMSOL simulations are conducted using the coupled free and porous media flow module, considering two relative roughness values. The proposed model demonstrates higher accuracy compared to existing models and experimental data, with 101 fewer missed prediction points and a 21.4% improvement in accuracy. Additionally, this study examines fluid flow regimes and critical Reynolds numbers for various matrix porosities, permeabilities, fracture apertures, and relative roughness values. The findings reveal that FMS with low matrix permeability, high roughness, and small apertures exhibit larger friction factors and are more prone to nonlinear deviations from Darcy flow. [ABSTRACT FROM AUTHOR]

Abstract It is known that the seepage force has a significant impact on the mobility of bed particles. To assess the effect of seepage force on the sediment transport around a suspended pipeline, a series of numerical tests have been carried out utilising the commercial software Comsol. In the simulation, the shear-stress transport turbulence model was used to simulate the upper turbulence flow field and the porous medium model was adopted to describe the dynamic response of the underlying seabed. Both the fluid flow and the seepage flow within the seabed were modelled. The effect of the vertical seepage force on the Shields number was investigated. The simulation results indicate that seepage plays a vital role in the process of tunnel scour, but becomes quite weak with the form of a scour hole beneath the pipeline. With an increase in scour depth, vortices shed from the pipe lead to a fluctuating fluid pressure, inducing significant upward seepage, and thus influencing the stability of bed particles. If sagging of the pipeline appears, the fluctuation of fluid pressure becomes weak and the seepage effect is minor. Highlights • The seepage effect on the Shields number is studied through numerical simulation. • The vortex shed onto the seabed can induce upward seepage flow due to the negative pressure inside it, which will promote the sediments scour. • Study seepage effect on shields number around fixed and sagging pipeline by coupling numerical simulations with experiments. [ABSTRACT FROM AUTHOR]

Abstract Sediment incipient motion is the first step of the whole process of sediment transport. However, previous numerical works simplified the seabed surface as a type of impermeable and rigid boundary, and ignored the effect of seepage flow on the mobility of bed particles. In this paper, to reveal the physics behind sediment incipient motion around a free spanning pipeline, an integrated numerical model, coupling the SST (Shear-Stress Transport) turbulence model with the porous seabed model, was proposed. Numerical studies showed that with the periodic formation and shedding of vortices around the pipeline, both the oscillatory and residual excess pore-pressures developed within the seabed. In some cases, the vertical gradient of excess pore-pressure (seepage force) had a significant impact on the mobility of bed particles around the pipeline. It was found that lower saturation degree and seabed permeability would remarkably increase both the oscillatory and residual seepage forces, and thus enhance bed particle mobility. While for a sandy seabed with smaller soil shear modulus, the oscillatory seepage force was only slightly reduced, but a high residual seepage force would be generated with time. This could lead to obvious decrease in the submerged weight of bed particles, making them more easily dragged away from the seabed. Highlights • Propose an integrated numerical model to couple the turbulent flow and porous seabed models. • Study the excess pore-pressure responses in the seabed beneath the suspended pipeline. • Quantify the effect of seepage flow on the mobility of bed particles. • Study the effects of seabed parameters on the flow-induced seepage force. [ABSTRACT FROM AUTHOR]

This paper presents the case study of a collapsed riverbank protection structure, located in the curvature of the watershed along the Pasak river in Saraburi province, Thailand. Although efforts have been made to twice rehabilitate this collapsed structure, the rebuilt protection structures were unstable to prevent progressive collapse damage and the causes of their failure remained elusive. The project team was engaged to carried out the site investigation and finite element analysis prior to providing the remedial approach on the collapsed structure. The outcome from this study reveals that the natural disaster events were the main causes of the structure failure. During the rainy season, water flowed into the river from upstream farmlands by crossing the backfill of the riverbank protection structure. Seepage forces were thus developed in the direction of inflows, which resulted in reduced stability of the riverbank protection structure. Furthermore, the strong currents in the river continuously scoured the banks, undermining the natural slope in front of the riverbank protection structure, resulting in soil erosion in the passive zone and instability of the protection structure. Based on these two causes of failure, a remedial solution was devised using a new bored pile riverbank protection structure with the usage of geocomposites and ripraps. Geocomposites and ripraps were installed at the back and front of the bored pile walls to relieve the structure from seepage forces and to prevent soil erosion, respectively. An adequate factor of safety against the external and internal failure of the new riverbank protection structure was verified by finite element modeling and the results confirmed that the structure was safe. [ABSTRACT FROM AUTHOR]

Extreme weather events, such as floods, are becoming more frequent in future with all consequences concerning the safety especially of water retaining structures, in particular, levees used as technical flood protection. The knowledge and correct consideration of coupled hydro-mechanical processes influencing the failure and post-failure behaviour of water saturated soils are of paramount significance for the assessment of hydraulically loaded geotechnical structures. This study focuses on the modelling of the processes governing the behaviour of water saturated soils using Smoothed Particle Hydrodynamics (SPH) on the example of a homogeneous embankment under different loading conditions. This paper aims to improve available SPH framework in order to enhance soil-water interaction in this method for geotechnical engineering investigations. To achieve this goal, the suggested approach is validated intensively by various well-known problems. Finally, the verified tool is used to investigate the hydro-mechanical behaviour of homogeneous embankments under simultaneous hydraulic and mechanical loading. The simulation results prove that the suggested approach is capable of simulating relevant hydraulic and mechanical processes governing the deformation behaviour of hydraulically loaded structures beyond the failure point allowing the detailed analysis of the post-failure behaviour characterised by large deformations. [ABSTRACT FROM AUTHOR]

• A new method was proposed for determining the maximum paste coating thickness. • Digital models of pervious concrete were created. • Influence of maximum paste coating thicknesses on the pore characteristics and seepage flow was investigated. • An empirical formula was proposed to determine the Kozeny–Carman constant. The determination of the maximum paste coating thickness on aggregate (MPCT) without void clogging is essential for effectively controlling the permeability of a pervious concrete (PC). The main objective of this study is to investigate the influence of varying MPCTs on the pore characteristics and seepage flow of PC. A new method was proposed for determining the MPCT of PC, and the relationships between the MPCT and the rheological properties of cement paste were established. Subsequently, digital models of PC with varying MPCTs were created, and the connected pore was extracted for analysis of pore characteristics. Seepage flow simulations were conducted to analyze the permeability characteristics of PCs under varying MPCTs. The results indicate that the pore characteristics are directly influenced by the MPCT, in which the effective porosity, specific surface, and tortuosity show linear correlations with the MPCT. When the MPCT ranges from 0.44 to 0.99 mm, the pore size of the PCs exhibits a single-peak distribution ranging from 1.4 to 13.5 mm, while the coordination number of the pores is distributed within the range of 1 to 14. Additionally, the permeability coefficient of PC decreases as the MPCT increases. When the MPCT exceeds 0.85 mm, the permeability coefficient drops to less than 1 mm/s, and the rate of decrease slows down. An empirical formula was proposed to determine the Kozeny–Carman (KC) constant, which improves the accuracy of the KC equation in predicting the permeability of PC. The findings presented in this study serve as a reference for the design of mixture proportions and the optimization of permeability in PC. [ABSTRACT FROM AUTHOR]

The artificial freezing in the clay-sand stratum under seepage flow conditions involves the hydro-ice-salt-crystalline-thermal-mechanical coupling process. A theoretical model is derived to investigate the influences of water seepage on the freezing process in the clay-sand stratum. The good agreements between the results from the theoretical model and laboratory tests in the literature verified the accuracy of the proposed model. Parametric studies are conducted to investigate the influences of the seepage velocities and temperature gradients on the spatial distributions. It is found that the ice contents, crystalline salt contents and adsorbed salt contents distribution profiles in the clay-sand stratum are nonlinearly distributed with a cliff distribution curve existing on their interface. The crystalline salt contents in the clay layer are higher than those in the sand layer due to the influence of water seepage and heat transfer. The adsorbed salt contents in the frozen area account for 2% of the total salt contents, but those in the unfrozen area account for 8% of the total salt contents. Due to the volume expansion caused by the soil skeleton deformation, thickness of fractional ice, ice frost heave deformation and salt swelling deformation, the soil deformation distribution curves in the clay-sand stratum are in a bilinear shape. • Theoretical model is derived to investigate the influences of water seepage on artificial freezing along clay-sand interface. • The components spatial distributions under different seepage velocities and temperature gradients in the clay-sand stratum are analyzed. • The proposed model is capable to calculate the artificial and seasonal frozen in the non-uniform soil stratum. [ABSTRACT FROM AUTHOR]

Interfacial seepage on soil-structure interface is common in water-related engineering, such as dam, culvert, water tunnel, foundation pit, etc. As a weak part in the project, seepage failure on soil-structure interface has caused many project accidents. However, there are few studies on the seepage mechanism analysis of soil-structure interface. In this paper, a series of numerical tests of interfacial seepage are carried out using CFD-DEM coupling method. The seepage mechanism and characteristics of different soil layers in the seepage device are analyzed and a formula for calculating the critical hydraulic gradient of the interface is discussed. The main conclusions are as follows: (1) The seepage flow on soil-structure interface will go through three stages: stability stage, transition stage and particle erosion stage; (2) The porosity and flow velocity of soil on the interface are greater than those in the far-field soil at the beginning of seepage flow; (3) The particle erosion on the soil-structure interface occurs earlier and the erosion degree is more serious than that of the far-field soil; (4) The critical hydraulic gradient of the interface rises nonlinearly with the increase of the degree of soil compaction; (5) The formula for calculating the critical hydraulic gradient of the interface could predict the numerical test results well. [ABSTRACT FROM AUTHOR]

Most of the current studies on the bearing capacity of rock foundations follow the Hoek-Brown (HB) criterion, but all adopt the generalized tangent technique or the multi-tangent approach, which does not reflect the essence of the nonlinear dependence of the Hoek-Brown criterion. Therefore, a modified unilateral failure mechanism is proposed in the paper, using which the bearing capacity of shallow strip footings considering seepage and seismic forces is evaluated. Use of a statics-like approach for seepage condition and a modified pseudo-dynamic method for seismic condition. The comparison with the results of other literature confirms the feasibility and effectiveness of the study in the paper, while the parametric analysis shows that a smaller upper bound solution is yielded based on the failure mechanism proposed in this paper, and the horizontal gradient ratio, the horizontal factor of seismic acceleration, the normalized frequency, the geological strength index, the disturbance coefficient, and the rock type-dependent parameter all have significant effects on the bearing capacity of rock foundations. In addition, the analysis of the working conditions considering both seepage and seismic forces confirmed the dominance of seismic forces. The results of the superposition treatment between different working conditions are inaccurate, which will underestimate the foundation bearing capacity and cause a waste of cost. This paper develops a more accurate method of assessing the bearing capacity of rock foundations and gives a table of coefficients that can be adopted in engineering practice. [ABSTRACT FROM AUTHOR]

• A widely used mapping in water waves problems is newly applied to seepage flows. • The proposed σ -mapping transforms the time-dependent water table into a fixed boundary. • Steady and unsteady seepage problems are analyzed, with and without recharge. • The method is in excellent agreement with the exact Polubarinova-Kochina solution for the dam problem, and with other solutions in the literature. Regional groundwater flow forecasting is frequently accomplished using model equations based on Darcy's law, the continuity equation, and kinematic and dynamic boundary conditions for a time-dependent water table, to predict hydraulic heads and fluxes. For homogeneous and isotropic aquifers, the model reduces to Laplace's equation for the hydraulic head and a transient non-linear free surface boundary condition. These equations are solved in the literature and in computer packages by a variety of numerical methods, including finite difference, finite element, and boundary element methods. The solution of this model is not simple and subject to instability problems. Computations in a vertical plane using finite-difference methods are not easy due to the irregular mesh needed near a highly curved water table, frequently involving smoothing of the numerical results to ensure stability. A technique to avoid the complications related to mesh generation near a curved boundary and its tracking entails using mappings to produce transformed domains. However, this is not so frequent to compute unsteady seepages. In particular, the so-called sigma mapping is widely used to model irrotational water waves; it applies to any flow involving a time-dependent free surface boundary. This mapping transforms the domain into a rectangle, so that the free surface becomes static in the transformed plane. There is close similarity between the mathematical model describing irrotational water waves and that of unsteady seepage flow, e.g., both are governed by Laplace's equation involving relevant boundary conditions at the moving boundary. Both moving free surfaces are different in character, e.g., the seepage is dissipative whereas the water wave is dispersive. However, it is possible to transfer mathematical approximations between both fields of research. This transfer is exploited in this work and the sigma mapping is newly and successfully applied to seepage flows involving both a steady and unsteady water table either receiving, or not, a recharge from rainfall or an artificial source. [ABSTRACT FROM AUTHOR]

• A physical model test based on cross passage freezing was conducted. • A hydro-thermal coupling model of AGF was proposed. • The effect of four indicators on formation of frozen wall was investigated. Artificial ground freezing is an environmentally friendly and reliable method for ground improvement during subway cross passage construction under variable hydrological conditions. However, natural or induced seepage flow influences significantly the closure of frozen wall, as it supplies a substantial source of heat. In this study, a physical model test was conducted based on the freezing project of a subway cross passage in Beijing Subway Line 19. A series of thermistors were installed in some representative locations to measure the temperature distribution and further calculate power demand. Besides, a hydro-thermal coupling model of freezing process under seepage conditions was derived to consider the variations of physical and thermodynamic parameters of the porous media and the latent heat of ice/water phase transition. The numerical approach was validated by the experimental results. Furthermore, four crucial indicators affecting the closure time during AGF process were quantitatively evaluated. The results showed that the closure time at seepage velocities of 0, 25.6 and 51.2 m/d were respectively 60, 110 and 441 min. Nevertheless, it was impossible to form continuous frozen bodies at 76.8 m/d. Among these indicators, the seepage velocity had the greatest effect on the thickness and shape of frozen body, while seepage temperature had the least impact. [ABSTRACT FROM AUTHOR]

Artificial ground freezing is an environmentally friendly technique to provide temporary excavation support and groundwater control during tunnel construction under difficult geological and hydrological ground conditions. Evidently, groundwater flow has a considerable influence on the freezing process. Large seepage flow may lead to large freezing times or even may prevent the formation of a closed frozen soil body. For safe and economic design of freezing operations, this paper presents a coupled thermo-hydraulic finite element model for freezing soils integrated within an optimization algorithm using the Ant Colony Optimization (ACO) technique to optimize ground freezing in tunneling by finding the optimal positions of the freeze pipe, considering seepage flow. The simulation model considers solid particles, liquid water and crystal ice as separate phases, and the mixture temperature and liquid pressure as primary field variables. Through two fundamental physical laws and corresponding state equations, the model captures the most relevant couplings between the phase transition associated with latent heat effect, and the liquid transport within the pores. The numerical model is validated by means of laboratory results considering different scenarios for seepage flow. As demonstrated in numerical simulations of ground freezing in tunneling in the presence of seepage flow connected with the ACO optimization algorithm, the optimized arrangement of the freeze pipes may lead to a substantial reduction of the freezing time and of energy costs. [ABSTRACT FROM AUTHOR]

• Stability of non-circular tunnel face reinforced by bolts under seepage is assessed. • Upper-bound estimations to the safety factor of tunnel faces are provided. • Pore pressures considerably influence the required bolt layouts. This paper aims to develop a three-dimensional (3D) analytical framework to assess the safety factors of realistic non-circular tunnel faces reinforced by longitudinal bolts under seepage conditions from a discretization-based perspective. The axial failure mode of bolts (including the tensile failure of the bolt and the pull-out failure at the bolt-soil interface) paired with the introduction of the interaction zone is employed to describe the reinforcement effect of bolts. A numerical fluid calculation is performed to simulate the 3D seepage towards the non-circular tunnel face, and the resulting pore pressure distribution is extracted and further interpolated to determine the pore pressure of each discrete point on the 3D discretization-based failure mechanism. Within the kinematical approach of limit analysis, the work rate balance equation incorporating the role of the axial force along the interaction zone and the pore pressure due to the 3D seepage is established based on the discretization-based failure mechanism. Afterward, combining the strength reduction method with the dichotomy, the upper-bound estimations of safety factors can be obtained by an optimization process. The developed framework is compared with numerical fluid-mechanical calculations and other analytical methods with respect to an actual horseshoe tunnel, which proves that the developed framework is effective in providing fast and reasonable estimates of reinforced tunnel face under seepage conditions. Parametric analyses are performed to investigate the effect of bolt layouts (including the length and density of bolts) and seepage conditions (including the groundwater level and permeability anisotropy). Finally, a series of design nomograms for various water levels and soil strength parameters are provided for reference. [ABSTRACT FROM AUTHOR]

Based on the three-dimensional hydraulic head distribution model and the upper bound theorem of the limit analysis, a new model was established to calculate the limit support pressure in shield tunnel faces. A series of numerical simulations were conducted to evaluate the accuracy of the proposed model and the obtained results were compared with those of other classical analytical methods. It is found that the obtained analytical solutions are in good agreement with the numerical simulations and the proposed method outperforms other methods in terms of accuracy. In the present study, the influence of the water level, internal friction angle, burial depth, and water pressure on the stability of the tunnel face is analyzed. The performed analyses reveal that the limit support pressure is negatively correlated with the internal friction angle, while the burial depth does not affect the limit support pressure of the shield tunnel face in subsea tunnels (C/D ≥ 1). Meanwhile, it is found that as the water level and the water pressure on the tunnel face increase, the limit support pressure increases linearly, and the failure area extends to the front of the tunnel face and decreases in height. • A calculation formula is derived to analyze the stability of tunnel face in saturated soil. • The analytical solutions proposed in this paper excels the solutions of other existing methods. • The influence of water level, C/D and internal friction angle on the stability of the tunnel face is investigated. • The effect of the water pressure of the tunnel face on the stability of the tunnel face is explored. [ABSTRACT FROM AUTHOR]

Seepage-induced internal erosion and failure in unsaturated/saturated porous media is challenging for computational simulations as they involve the behaviour, interactions (solid, air, water) and transformation (fluidisation and deposition of fines grains) of different phases. Tackling this challenging problem requires correct mathematical descriptions of phase interactions and transformation together with a robust computational framework, both of which are addressed in this paper. The new mathematical model and coupled governing equations based on the continuum mixture theory enable the use of a single set of SPH particles for the descriptions of behaviour, interactions and phase transformation of all five phases of the porous media (soil skeleton, erodible fines particles, fluidised particles, water, and air), including the effect of both saturation and erosion on the shear strength of porous media. A fully explicit and stabilised SPH framework that allows accurate SPH approximations of spatial gradients is proposed for the numerical solutions of coupled governing equations. The proposed computational framework performs well in benchmark tests against available analytical and numerical solutions and achieved reasonable agreements with experiments. Numerical results obtained from the predictions of seepage-induced erosion and failure demonstrate that the proposed computational framework is efficient for addressing challenging problems involving coupled flow-deformation, seepage-induced internal erosions, and large deformation failures of unsaturated/saturated porous media. • A five-phase mathematical model for internal erosion in porous media is developed. • A robust constitutive model considering erosion on soil's shear strength is proposed. • A stabilised fully coupled flow deformation SPH erosion framework is proposed. • The new SPH framework can handle seepage erosion-induced failure of porous media [ABSTRACT FROM AUTHOR]

Located in the middle reach of Yalong River in China, the Jinping-I Hydropower Station consists of a large-scale cavern system for water conveyance and power generation. Compared to other typical large-scale underground powerhouse cavern systems in Southwestern China, the construction site is characteristic of higher in situ geostresses, lower uniaxial compressive strength (UCS) and poorer quality of the surrounding rocks, resulting in greater depth of the disturbed zone. In this study, the excavation-induced relaxation effects and their impacts on the hydraulic conductivity variations and seepage behaviors in the surrounding rocks of the Jinping-I underground powerhouse caverns were assessed with site characterization data and numerical simulations. The excavation-induced disturbance zones around the caverns were modeled using the plastic yield zone predicted with an equivalent elasto-plastic model and a constant deviatoric stress criterion based on the Hoek–Brown parameters of the surrounding rocks, respectively. The predicted results agree rather well with the disturbed zones detected by the in situ acoustic wave velocity measurements and borehole TV images. The excavation-induced permeability changes in the surrounding rocks were characterized with a strain-dependent hydraulic conductivity model that accounts for the development patterns and deformation behaviors of the critically-oriented fractures. The seepage behaviors with consideration of the permeability changes in the surrounding rocks were modeled with a variational inequality method at a steady state, and the numerical results imply the significance of proper characterizations of the excavation-induced disturbance effects and permeability changes in better understanding the groundwater flow and its controlled effect in the surrounding rocks. [ABSTRACT FROM AUTHOR]

The bottom friction beneath random waves is predicted taking into account the effect of seepage flow. This is achieved by using wave friction factors for rough turbulent, smooth turbulent and laminar flow valid for regular waves together with a modified Shields parameter which includes the effect of seepage flow. Examples using data typical to field conditions are included to illustrate the approach. The analytical results can be used to make assessment of seepage effects on the bottom friction based on available wave statistics. Generally, it is recommended that a stochastic approach should be used rather than using the rms values in an otherwise deterministic approach. [ABSTRACT FROM AUTHOR]

Abstract: The mean net bedload sediment transport rate beneath random waves is predicted taking into account the effect of seepage flow. This is achieved by using wave half-cycle bedload sediment transport formulas valid for regular waves together with a modified Shields parameter including the effect of seepage flow. The Madsen and Grant (1976) bedload sediment transport formula is used to demonstrate the method. An example using data typical to field conditions is included to illustrate the approach. The analytical results can be used to make an assessment of seepage effects on the mean net bedload sediment transport based on available wave statistics. Generally, it is recommended that a stochastic approach should be used rather than using the rms values in an otherwise deterministic approach. [Copyright &y& Elsevier]

• 3D tunnel face stability is assessed under three slurry pressure transfer mechanisms. • Upper-bound estimations to the face stability of slurry-shield tunnels are provided. • Excess pore pressures considerably reduce the slurry pressure transfer efficiency. In slurry-shield tunneling, the bentonite slurry tends to infiltrate into the soil skeleton ahead of the tunnel face, causing a forward seepage flow associated with excess pore pressures in the ground. Both the slurry infiltration and the forward seepage flow significantly impact the tunnel face stability. In the present paper, a kinematic approach of limit analysis with the classical three-dimensional discretized rotational failure mechanism is employed to assess the face stability of a slurry-shield-driven tunnel. Three situations of slurry infiltrations that influence the face pressure transfer mechanisms were considered: a full filter cake, a penetration zone, and pure groundwater flow without a filter cake or a penetration zone. The pore pressure distributions surrounding the tunnel face were firstly obtained using numerical calculations. Afterward, the incorporation of numerically obtained pore pressure distributions into the work rate calculations allows considering a three-dimensional forward seepage flow ahead of the tunnel face, which provides a rigorous upper-bound estimation to the tunnel face safety factor determined by the strength reduction technique. The proposed method is validated by comparing the calculated results with those provided by previously published literature. The effects of excess slurry pressures, hydraulic conditions, pressure drop coefficients, and soil shear strength were investigated. Several design charts are given for practical application. [ABSTRACT FROM AUTHOR]

• Groundwater-surface water interactions are studied in two shallow aquifers. • A combination of hillslope processes shapes the catchment-scale streamflows. • Low-conductive hillslopes enhance overland flows and sustain late recessions. • High-diffusive hillslopes shape the event- and seasonal-scale recessions. • Hydraulic properties are significantly heterogeneous at the catchment scale. Surface and subsurface flows interact at different spatial and temporal scales through the development of saturated areas occurring when the aquifer reaches the surface. While this interaction exerts a strong control in the partitioning of water between base flow, seepage flow and overland flow, its quantification remains a challenge. Here, we propose a novel modeling approach based on two equivalent hillslopes to capture spatial and temporal variabilities of the main processes. We calibrate their subsurface hydraulic properties based on the temporal dynamics of stream discharge. The model is tested on two pilot catchments located in Brittany (France). For both catchments, the model is successfully calibrated on 40 years of stream discharge data. The results demonstrate that contrasted hydraulic properties are required, with: (1) a relatively low conductive hillslope (conductivities between 3x10–8 m/s and 2x10–6 m/s) enhancing overland flows during recharge periods while also sustaining low flows in the late recession period through slow aquifer discharge, and (2) a highly diffusive hillslope (diffusivity between 5x10–3 m2/s and 3x10–1 m2/s) dominantly shaping the event- to seasonal-scale streamflow recession behavior. The strong contrast of the two hillslopes reveals the fundamental role of heterogeneity in controlling groundwater storage-discharge functions, ruling out any homogeneous equivalent at the catchment scale. Low flows appear to be a non-obvious combination of the contributions of the two hillslopes, the less diffusive hillslope catching up to the more conductive one by the end of the low flow period. Catchment-scale responses integrate complex interactions between recharge, groundwater and overland flows through the volume of subsurface storage and the extent of the saturated area. [ABSTRACT FROM AUTHOR]

Abstract: Foam flooding has become one of the most effective methods to improve oil recovery in high water-cut oilfields. In order to obtain images of the texture of foam in the cores under high pressure, this paper developed an experimental real-time image acquisition device for detecting the foam's texture as the bubbles flowed in the porous media. Image processing and statistic analysis methods for describing the foam's texture were also established. Experimental results showed that the bubble distribution became homogeneous and stabilized, and the pressure difference between two ends of the core increased gradually during the process of foam flooding. In the initial stage, the bubbles presented a flake-like distribution. The liquid phase flowed continuously, as did the gas phase. As the displacement continued, the volume of a single bubble lessened, while the number of bubbles increased. When the bubbles reached a steady state, the pressure difference between the two ends of the core was stable, and the bubbles presented a uniform distribution. A larger injection rate, a higher core permeability and a larger gas–liquid ratio all can cause a larger-than-average bubble diameter, poor stability and a decreased degree of homogeneity. [Copyright &y& Elsevier]

Abstract: Groundwater inrush has an impartible relationship with geological structures such as karst collapse pillars (KCPs), which are widely distributed in North China. In order to study the mechanism of groundwater inrush from coal seam floor, the variable mass dynamics and nonlinear dynamics were introduced. A mechanical model–plug model is established to describe the behavior of water seepage flow in coal-seam-floor containing KCP. The study shows that: (1) If the mass of the KCP keeps steady, the water seepage velocity in the KCP and the surrounding rocks will reach a constant value soon; (2) if the mass of the KCP and the surrounding rocks increases by grouting, etc, the seepage velocity in the KCP and the surrounding rocks will reach its minimum value gradually, and (3) if the mass of the KCP and the surrounding rocks decreases by scouring, the flow velocity in the KCP and the surrounding rocks shows a monotone increase, the water flow may change into pipe flow, especially when a large number of the mass of the KCP and the surrounding rocks enters into goaf road, which may lead to instable flow and cause groundwater inrush. [Copyright &y& Elsevier]

Abstract: Through the determination test for the quantity of gas adsorption and desorption under different temperature conditions, the law of influence of the temperature change on the adsorption and desorption of coal and methane in constant pressure condition was researched. The paradoxical law highly emphasizes that the increase of gas desorption quantity due to temperature rise and part of water adsorbing coal under the effect of high pressure water together affect the quantity of gas adsorption and desorption. In the end, we can obtain the law of desorption seepage of the coal seam gas when the coal was placed under different water contents and different temperature. Making use of the adsorption and desorption experiment system of the coal under constant pressure, the temperature control module was added to the osmoscope, thus, the desorption quantity of the coal sample in different temperature and high pressure water was measured. The result shows that, when the adsorption tank is under the same pressure, desorption quantity of the coal will increase with the temperature; if the same coal sample adsorbs twice, the adsorption quantity is bigger than the former. When it is affected by high pressure water, the adsorption rate of the coal to the gas will reduce. If the same coal sample experiences high pressure water twice, the water quantity injected in the second time is larger; and the adsorption and desorption quantity is different, the second one is a little larger than the first one. The initial temperature is also higher when it begins to desorb. When the coal is affected by high pressure water, the water adsorbed influences the gas desorption and seepage. [Copyright &y& Elsevier]

Abstract: Hydrodynamic forces exerting on a pipeline partially buried in a permeable seabed subjected to combined oscillatory flow and steady current are investigated numerically. Two-dimensional Reynolds-Averaged Navier–Stokes equations with a k−ω turbulent model closure are solved to simulate the flow around the pipeline. The Laplace equation is solved to calculate the pore pressure below the seabed with the simulated seabed hydrodynamic pressure as boundary conditions. The numerical model is validated against the experimental data of a fully exposed pipeline resting on a plane boundary under various flow conditions. Then the flow with different embedment depths, steady current ratios and KC numbers is simulated. The amplitude of seepage velocity is much smaller than the amplitude of free stream velocity as expected. The normalized Morison inertia, drag and lift coefficients based on the corresponding force coefficients of a fully exposed pipeline are investigated. The normalized Morison force coefficients reduce almost linearly with the increase of embedment depth and that the KC only has minor effect on the normalized Morison coefficients. It is also found that the permeable seabed condition causes a slight increase on the inline force and has a little effect on the lift force, compared with corresponding conditions in an impermeable bed. [Copyright &y& Elsevier]

Abstract: The composite element method (CEM) is formulated for the seepage analysis of rock masses containing fractures and drainage holes. Each fracture or drainage segment is treated as a special sub-element having definite seepage characteristics, and is located explicitly within the composite element. The governing equation for the composite element containing both fractures and drainage holes is established using the variational principle. By the CEM developed in this paper, the fractures and drainage holes can be simulated explicitly but do not intervene in the discrete of the calculation domain concerned, in this way the generation of the computation mesh is not restricted strongly by the position and the orientation of the fractures and drainage holes, which is important in the optimal design of seepage control system. If there are no fractures and drainage holes, the CEM will automatically be degenerated to the conventional finite element method (FEM). The validity and reliability of the CEM is verified by a numerical example. The application and comparative study for the Baozhusi dam foundation is presented. [Copyright &y& Elsevier]

Abstract: A numerical model is developed to predict the onset of local scour below offshore pipelines in steady currents and waves. The scour is assumed to start when the pressure gradient underneath the pipeline exceeds the floatation gradient of the sediments. In this model, the water flow field above the bed is determined by solving the two-dimensional (2-D) Reynolds-averaged Navier–Stokes equations with a k-ω turbulence closure. The seepage flow below the seabed is calculated by solving the Darcy''s law (Laplace''s equation) with known pressure distribution along the common boundaries of the flow domains-seabed. The numerical method used for both the turbulent flow around the pipeline and Darcy''s flow in the seabed is a fractional finite element method. The average pressure gradient along the buried pipe surface is employed in the evaluation of onset condition with a calibration coefficient. The numerical model is validated against experimental data available in literature. A unified onset condition for steady currents and waves is proposed. Influences of flow parameters, including water depth, embedment depth, boundary layer thickness, Reynolds number (Re) and Keuleagan–Carpenter (KC) number, on the pressure drop coefficient over the pipeline are studied systematically. [Copyright &y& Elsevier]

• The pore clogging is concentrated in the upper layer, and is lesser in the lower layer. • The particle gradation of clogging substances has a great influence on pore clogging. • The clogging of lower layer is greatly affected by the combination of layer thickness. • The pore clogging of upper and lower layers is affected by void volume combination. • Seepage flow has a great effect on clogging substances with particle size less 0.6 mm. To understand the pore clogging mechanism and the distribution regularity of pore clogging substances in double-layer drainage asphalt pavement, the discrete element method (DEM) and computational fluid dynamics (CFD)-DEM were used to discuss the clogging substance distributions and clogging depth development in upper and lower layers under natural deposition and seepage flow. Results indicate that the pore clogging of double-layer drainage asphalt pavement is mainly attributed to the accumulation of small-sized clogging substances centered on the large-sized ones, the agglomeration of various particle-sized clogging substances, and the interference between the sizes of clogging substances and pavement pores. Also, the particle gradation of clogging substance shows a significant effect on its distribution and deposition depth in upper or lower layer under natural deposition and seepage flow. Additionally, the void volume combination and thickness combination between upper and lower layers obviously affect the distribution regularity of clogging substances under natural deposition. The clogging depth of each particle-sized clogging substance is directly proportional to void volume and inversely proportional to thickness of upper layer under seepage flow. Finally, the main clogging substances are mainly concentrated in upper layer under natural deposition and seepage flow, and only fewer small-sized clogging substances are distributed in lower layer. Some small-sized clogging substances are flowed out of the pavement pore under seepage flow, which is difficult to cause the pore clogging. This study provides a reference for the optimization design and maintenance of double-layer drainage asphalt pavement. [ABSTRACT FROM AUTHOR]

• Shield face stability model is proposed for layered ground with seepage flow. • Collapse mechanism includes wedge with inclined angle varying between soil layers. • Limit equilibrium is established by method of slices and considering seepage force. • Stability model is validated by 3D stress-seepage coupled FEM. This paper presents a limit equilibrium model for the shield face stability with special emphasis on the effects of ground heterogeneity and seepage flow. The model considers a new wedge mechanism whose inclination is capable of changing across soil layers to account for the spatial variation of soil mechanical properties. The limit equilibrium of the mechanism is established by using the method of slices, which considers horizontal arching without the need for arbitrary assumptions on soil stress distribution. The deterioration effects of groundwater flow are included by evaluating seepage force in the limit equilibrium based on an analytical hydraulic head field. To assess the proposed model, three-dimensional coupled pore fluid flow and stress finite element simulations are conducted. The above two methods are compared under different combinations of ground profiles, soil parameters, and hydrogeological conditions. These comparative analyses show the suitability of the limit equilibrium model. The influences of how horizontal arching is considered on the computed necessary face pressures under complex geological and hydrogeological conditions are explored. [ABSTRACT FROM AUTHOR]

• A closed-form analytical solution for the hydraulic head distribution is proposed. • 3D rotational collapse mechanism is extended to consider the effect of seepage flow. • Analytical head solution with anisotropic permeability is presented and discussed. • Presented method agrees well with the numerical analysis and other existing studies. To assess the face stability of a shield tunnel excavated in saturated soils under steady seepage flow condition, both numerical simulation and theoretical analysis are carried out. Based on the characteristics of the hydraulic head distribution, an analytical solution for the hydraulic head distribution ahead of tunnel face in the homogeneous and isotropic ground is proposed. And based on the upper bound theorem of the limit analysis, the analytical head equation is introduced into the 3D rotational rigid block collapse mechanism to take into account of the effect of the seepage flow. The comparisons show that the presented method agrees well with the numerical analysis and other existing studies. Finally, an analytical solution for the hydraulic head distribution ahead of tunnel face considering the permeability anisotropy is also presented and discussed. It is suggested that the neglect on the permeability anisotropy of soils may lead to an overestimate on the required face pressure. [ABSTRACT FROM AUTHOR]

• Accurate estimation of seepage flow through embankment dam using Extended Kalman Filter based neural network approach. • Validation of the EKF-ANN paradigm using the MLP, RBF-NN, and RF approaches. • Assessment of four efficient scenarios based on 10 input variables for predicting the seepage flow. • Outlier analysis to specify the applicability domains of the provided models. Seepage flow through embankment dam is one of the most influential factors in failures of them. Thus, the monitoring and accurate measuring of seepage are crucial for the safety and construction cost of an embankment dam. In this study, an efficient data-intelligence paradigm comprised of Extended Kalman Filter integrated with the Feed Forward type Artificial Neural Network (EKF-ANN) scheme, as the main novelty, was developed for precise estimation of the daily seepage flow through embankment dam in Fontaine Gazelles Dam in Algeria. Here, three robust machine learning approaches, namely the Multilayer Perceptron (MLP) Neural Networks, Radial Basis Function-Neural Networks (RBF-NN), and Random Forest (RF), were examined for evaluating the capability of the EKF-ANN in the prediction of seepage flow. According to the obtained results, the EKF-ANN paradigm outperformed the MLP, RF, and RBF-NN, respectively. Besides, the leverage approach was applied to report the applicability domain of provided models. [ABSTRACT FROM AUTHOR]

• Capture the global and localized characteristics of seepage flow in porous media using visualization seepage technology. • Investigate the connection of macro and mesoscopic characteristics of seepage flow in porous media. • Reveal the reason why the global and localized seepage regions are different. Aiming to investigate the macro-mesoscopic characteristics of seepage flow in porous media, flume experiments have been conducted with the visualization technology. As comparisons, a series of numerical simulations were performed. The results show that the local flow regime of seepage in porous media can be different from the global flow regime. It is found that the seepage velocity in the middle region is lower than that near the wall of flume. This phenomenon is more obvious in the upper part of the porous media. It is proved by both numerical simulations and experiments that the small deviations in the size and position of internal pores are the reason for different flow characteristics between the local and global seepage fields. [ABSTRACT FROM AUTHOR]

Progressive failure, which begins in the downstream slopes of dams, is one of the main failure modes for natural dams in the field. However, this failure mode lacks attention in the scientific literature, especially regarding its formation mechanism. In this paper, flume tests were conducted to simulate the progressive failure of a natural dam. The results show that the progressive failure process is induced by seepage water discharging on the downstream slope, including the erosion of individual soil particles, repeated minor slip failures, upward head-cutting erosion of the dam crest, and finally the collapse of the dam when the processes have evolved sufficiently. This study focuses on analyzing the initiation mechanism of soil particle migration. The influence of seepage and interflow stresses on the incipient erosion of soil particles is analyzed. In addition, the buoyancy of soil particles on the downstream slope surface is not considered in the vertical direction in this paper but in the direction perpendicular to the downstream slope surface. The paper also discusses how to estimate the occurrence of the progressive failure of a natural dam. In the estimation method, the stress of the interfacial flow, the seepage flow stress, and the friction stress of the soil particles are considered when the phreatic line reaches the downstream slope surface. • The characteristics of progressive failure of non-cohesive natural dams were studied by laboratory tests. • The mechanism of progressive failure of non-cohesive natural dams was analyzed based on soil particles' initiation condition. • A new method was developed to estimate the occurrence of progressive failure of a natural dam. [ABSTRACT FROM AUTHOR]

• Incipient motion of cohesionless soil particles due to injection is experimentally studied. • The change of dimensionless critical shear stress of soil bed due to injection is determined. • A range of critical shear stress is proposed for incipient motion of soil bed particles with injection. • The experimental results support the theoretical estimation of critical shear stress. Understanding the interaction of the groundwater seepage flow and sediment transport along permeable boundaries is essential for managing soil beds and bank erosion. A significant bank failure may occur due to sediment transport under the boiling condition. In the present study, an experiment is conducted to investigate the effects of injection or upward seepage on the critical shear stress of a cohesionless soil bed subjected to surface flow. The upward seepage force acting on the soil bed particles may reduce the virtual weight of the particles. In turn, it may also reduce the critical shear stress acting on the particles. A theoretical analysis examines how the upward seepage force acts to modify the critical shear stress for the sediment entrainment due to the increase in the hydraulic gradient of the seepage flow. A force analysis reveals that the ratio of the critical shear stress with seepage to that without seepage is dependent on the ratio of the hydraulic gradient of seepage to its value at the quicksand condition. A test apparatus was built, and the effects of injection on the critical shear stress of cohesionless soil bed particles were measured. An acrylic channel with a rectangular cross section was prepared, and a section of a cohesionless soil bed subjected to an upward seepage flow was installed at the bottom of the channel. The experiment demonstrates that the induced seepage affects the dynamics of the channel flow, even though the magnitude of the seepage flow velocity is significantly smaller than that of the free surface water flow. The test results show that the dimensionless critical shear stress of the cohesionless soil bed particles decreases slightly as the hydraulic gradient of the seepage flow is increased when critical shear stress is determined at the upstream edge of the seepage zone. Furthermore, the dimensionless critical shear stress decreases sharply with the increment of the hydraulic gradient of the seepage flow when critical shear stress is determined in the seepage zone. However, it does not decrease in either case, as was theoretically assumed, even when the hydraulic gradient approaches to the critical hydraulic gradient or the quicksand condition. [ABSTRACT FROM AUTHOR]

• A moisture-heat coupling model for artificial ground freezing was proposed. • The model was to quantify the temperature field under various seepage conditions. • The predicted results were in agreement with the monitored results. • An increase in seepage velocity increases the time for freezing curtain formation. Artificial ground freezing (AGF) is a reliable technique for ground improvement to address adverse geotechnical engineering conditions. The formation of a freezing curtain during the AGF process is crucial as it serves to control groundwater flow and enhances the strength of the soil. However, groundwater flow has a considerable influence on the formation of the freezing curtain because it provides a continuous source of heat. Thus, to investigate the influence of water flow on the freezing process during AGF, a moisture–heat coupling model was proposed considering ice/water phase transition to quantify the temperature distribution in soil during the freezing process. The proposed numerical model was further validated using thorough laboratory tests under various seepage flow conditions. Finally, a numerical simulation of AGF was conducted for the end well of the Harbin metro station in China. Five representative monitoring points on the end well were selected and continuously monitored for 30 days to predict the formation of a freezing curtain. It was observed that the temperature results obtained using the proposed model are consistent with actual field monitoring data. [ABSTRACT FROM AUTHOR]