Search

The large deformation and strong rheological characteristics of the underground rock body under complex geological conditions have led to the failure of the support system and even the instability of tunnels from time to time. Based on the theory of groundwater seepage, the elastic solution of the mechanical model of the tunnel anchorage support system under seepage is solved, which reveals the influence of seepage on the peripheral rock and the support parameters of the anchorage support system; the viscoelastic solution is solved according to the corresponding principle of elasticity—viscoelasticity, which analyses the influence of seepage on the rheological process of the anchorage support system; and the model is simulated with the help of finite element software, which analyses the agreement and discrepancy of the numerical solution and the theoretical solution. The results show that the analytical and numerical solutions are basically consistent. This study can provide important guidance for controlling long-term stability of water-rich tunnel rocks. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology & Engineering Geology / Shuiwendizhi Gongchengdizhi is the property of Hydrogeology & Engineering Geology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract This study provides a general analytical approach to predict the stresses and displacements of deep noncircular tunnels excavated in saturated elastic ground, considering the hydro-mechanical coupling, the interaction between rock and liner, and arbitrary tunnel shapes. The complex variable theory is innovatively extended to solve the seepage fields for noncircular supported tunnels in both surrounding rocks and liner fields. After that, coupled hydro-mechanical solutions of stresses and displacements can be determined by considering the influence of seepage flow on the mechanical responses. Furthermore, stability analyses of supported tunnels are conducted in the hydro-mechanical coupled framework, incorporating the effect of seepage flow. As a verification, a good agreement is observed between stress and displacement fields obtained from the current analytical solutions and numerical simulations. Then, parametric analyses are performed to assess how variations in tunnel shape, liner permeability, and liner thickness influence the mechanical behaviours of supported tunnels. Meanwhile, by employing the Mohr–Coulomb strength criterion, an expression of equivalent stress is proposed to assess the potential failure behaviour of supported tunnels in the entire process of excavation and operation stages. This study provides high potential of application to a number of relevant case studies, such as tunnelling below the water table.

With the development of transportation engineering, mining engineering, underground space engineering, and long-distance water diversion projects in China, the occurrence of tunnel water inrush disasters has become increasingly frequent. Due to the limited analytical study on the flow field of circular arched tunnels, an analytical solution for the water inrush and the flow field in the surrounding rock around a deep-buried circular arched tunnel was obtained using the conformal transformation method. Then the distribution of water inrush around the tunnel circumference was explored. The results reveal that the groundwater flow field near the tunnel is significantly influenced by the tunnel shape, while its influence on the groundwater flow field further away from the tunnel can be approximated as that of a tunnel with a circular cross-section. The maximum flow velocity around the circular arched tunnel occurs near the inflection points (i.e., the corners of the tunnel bottom), while the minimum flow velocity is located at the center of the tunnel floor. The flow velocity at the corners of the tunnel bottom can exceed three times the flow velocity at the center of the tunnel floor. As the tunnel shape approaches a circle, the relative differences of flow velocities at various points around the tunnel circumference gradually decrease. This study can provide a theoretical basis for estimating the water inrush flux and characterizing the groundwater flow field in the surrounding rock around circular arched tunnels, and support for tunnel construction planning and the design for tunnel groundwater seepage/drainage.

Earth dams must be supplied with seepage control devices to prevent piping and sloughing. One such device used for this purpose is the so-called drain pipe. This study focuses on the influence of drain pipes on seepage and slope stability analysis in a zoned earth dam; here, for the specific case study of the Al-Adhaim dam, Iraq. The purpose of this study is to demonstrate the beneficial effects of drain pipes in the control of seepage and improving slope stability in zoned earth dams, thus allowing for specific recommendations for the optimal location(s) of any drain pipes. SEEP/W software was used to evaluate the steady-state seepage that occurs through and beneath the dam, and SLOPE/W software was used to analyze slope stability. In this study, two drain pipes, each with diameters of 15 cm, were used in the earth dam, with a vertical distance of 1 m between them. The effects of the drain pipes through the earth dam were investigated by varying their relative locations, specifically at X/B = 0.5, 0.6, and 0.7. The results of the study showed that the presence of the drain pipes was effective in reducing the elevation of the phreatic surface line. Additionally, the drain pipes significantly reduced the seepage flow and hydraulic exit gradient while increasing the factor of safety (FOS). Based on the findings, it was concluded that the most effective position for the drain pipes was when they were located at X/B = 0.7; in this configuration, they allowed for minimum seepage flow (70%) and hydraulic exit gradient (72%), while providing the highest FOS (17.2).

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]

Using one opening (filter) within the floors of hydraulic structures is a known technique to relieve the seepage effects on their floors. In this study, a new method to control seepage flow by using two identical filters instead of one was tackled numerically. A comparative analysis of using one versus two filters was conducted for different thicknesses of the permeable stratum, apron size (b), filter length, and sheet pile wall depths. Results indicate that two filters are considerably more effective than using one where the overall uplift force, the maximum potential head, and the hydraulic exit gradient downstream of the floor are reduced to 42–56%, 42–51%, and 66–76%, respectively, compared to one filter, while slightly increasing seepage flow by 1–7%. Many reasons can lead to horizontal openings (cracks) appearing along the sheet pile walls beneath hydraulic structures. The current study tackled their effects on seepage flow for the first time and examined their impact on the floor. A crack in the upstream sheet pile wall can increase total uplift forces by up to 40%, while a crack in the downstream sheet pile wall can increase the hydraulic exit gradient by up to 230% [ABSTRACT FROM AUTHOR]

In the process of development and utilization of mine resources, the damp-heat environment has always been a difficult problem for mining. An enormous amount of research effort has gone into analyzing the underground operating environment. By summarizing the existing research theories on the damp-heat environment in the mine, this paper analyzed the influence of the wall rock, wind flow parameters, groundwater seepage, and other factors on the damp-heat environment and summarizes the determination of heat transfer coefficient (h) and mass transfer coefficient (m), which provided the theoretical basis for the improved technology of the damp-heat environment of mines. The field synergy theory (FST) reveals the essence of enhancing heat transfer performance and mass transfer performance and has been widely applied in engineering practice; based on the commonality between the research model of the FST and the damp-heat environment of the mine, we put forward a novel approach by using the FST to study the mine's damp-heat problem and gave the research models based on the FST under the form of bifurcation and turning wall rock, which can be used to guide the design and layout of the mine wind flow deflector. Finally, considering the actual economic benefits of mine engineering, the FST and ventilation system power consumption are used as comprehensive evaluation indicators to guide the design of ventilation systems, which provided fresh concepts and approaches for improving the subterranean damp-heat environment. [ABSTRACT FROM AUTHOR]

To study the stability of open-air slope with fault under seepage, this paper uses FLAC3D numerical simulation technology to establish a mechanical model of the sliding body under fault action, and deduce the expression of the stability coefficient of the longitudinal slope, to simulate the stability of the slope with fault under seepage action. The results show that the sensitivity analysis is carried out on four influencing factors such as elastic modulus of rock mass strength, cohesion, internal friction Angle, and tensile strength of rock mass. By analyzing the displacement, stress, strain and safety factor of slope under different working conditions of these four factors, the sensitivity analysis curve of each parameter is obtained. It can be seen from the sensitivity analysis curve that the cohesion of rock mass has the greatest influence on the slope stability, and the elastic modulus has the least influence on the slope stability. The main influencing factors of slope stability are different at different excavation stages. In the early stage of excavation, the main factor affecting slope stability is fault, which gradually changes to seepage in the later stage. This study provides a scientific basis for the future analysis of open-pit slope stability. [ABSTRACT FROM AUTHOR]

In this study, three machine learning models, namely, the Multilayer Perceptron Neural Networks (MLPNN), the Generalized Regression Neural Networks (GRNN) and the Radial Basis Function Neural Networks (RBFNN) were used for predicting seepage flow through an earthfill dam. Moreover, obtained results were compared with those obtained from the standard Multiple Linear Regression (MLR). The three models were developed using piezometer elevations observed at seven different piezometers, in addition to the related reservoir water level and the periodicity for a period of seven years. Obtained results indicated that the GRNN model had substantially better prediction performance than the RBFNN, MLPNN, and the standard MLR models with statistical values of coefficient of correlation R = 0.981, root mean square error RMSE = 0.386 L/s, and a mean absolute error MAE = 0.95 L/s. Moreover, including the periodicity factors improves prediction accuracy of the machine learning models.

The low permeability sandstone reservoir has poor development effect and serious gas channeling in the block W of Zhongyuan oilfield, Sinopec. In order to investigate the influence of rock surface roughness, pore distribution uniformity and homogeneity on porous media of the reservoir. Based on the theory of petro physics, fractal and seepage mechanics, laboratory experiments were carried out. Box dimensions of porous media were calculated by Frac Lab and Frac Lac software respectively, based on Gaussian distribution, Fourier analysis, power law and least square regression. The results show that the porous media of block W reservoir is of fractal characteristics, fractal dimension is about 2. 58, coarse porous media surface, complex pore structure, more micro pores, serious irregular heterogeneity and high flow resistance. The fractal dimensions obtained by Frac Lab and Frac Lac software have good consistency. The results provide strong basic support for enhancing oil recovery, oil and gas seepage law and porous transport properties, in a low permeability sandstone reservoir has excellent practical significance. [ABSTRACT FROM AUTHOR]

Using one opening (filter) within the floors of hydraulic structures is a known technique to relieve the seepage effects on their floors. In this study, a new method to control seepage flow by using two identical filters instead of one was tackled numerically. A comparative analysis of using one versus two filters was conducted for different thicknesses of the permeable stratum, apron size (b), filter length, and sheet pile wall depths. Results indicate that two filters are considerably more effective than using one where the overall uplift force, the maximum potential head, and the hydraulic exit gradient downstream of the floor are reduced to 42–56%, 42–51%, and 66–76%, respectively, compared to one filter, while slightly increasing seepage flow by 1–7%. Many reasons can lead to horizontal openings (cracks) appearing along the sheet pile walls beneath hydraulic structures. The current study tackled their effects on seepage flow for the first time and examined their impact on the floor. A crack in the upstream sheet pile wall can increase total uplift forces by up to 40%, while a crack in the downstream sheet pile wall can increase the hydraulic exit gradient by up to 230%

The early stages of particle‐scale filtration in idealised granular soils were investigated using coupled Computational Fluid Dynamics and Discrete Element Method. Filtration simulations were conducted for assemblies of finer base particles underlying coarser filter particles with upward seepage flow perpendicular to the base‐filter interface. A wide range of size ratios that covered the complete spectrum of filtration behaviours were considered, along with different ramping accelerations for seepage flow to investigate the combined influence of geometric characteristics and hydraulic loading. The influence of flow conditions and size ratios on the time‐dependent infiltration depth of transported base particles was observed to be universal with respect to a newly proposed dimensionless time parameter. The susceptibility to filtration during the early stages was quantitatively investigated with the number of infiltrating base particles and the filling degree of pores within the filter. The susceptibility during the early stages was shown to have a strong correlation with pore space geometry at the filter boundary, which was also reflected by the maximum pore filling degree of the filter. While filter susceptibility has been conventionally evaluated by the size ratio of the assembly, the consideration of the pore space geometry at the filter boundary provided an alternate approach of evaluating local filter susceptibility. [ABSTRACT FROM AUTHOR]

This paper focuses on the influence of permeability anisotropy of seepage flow on the face stability for a shied tunnel. An analytical model has been proposed to present the hydraulic head distribution around the tunnel face in the anisotropic ground, considering the difference of permeability coefficient in the horizontal direction and the vertical direction. The rationality of the proposed model is verified by a series of numerical simulations. Then, an analytical model of face stability for a tunnel under the anisotropic seepage has been established based on the limit analysis upper bound method. Comparisons of the analytical solutions and the numerical simulations are conducted, and the limit support pressure of the two methods is consistent. The effect of permeability anisotropy and water pressure on the stability of the tunnel face is analyzed through the three-dimensional analytical solution. Anisotropy of permeability has a significant impact on the stability of the tunnel face, and its impact gradually decreases. It can also be found that the water pressure coefficient of the tunnel face has a significant effect on the limit support pressure and the failure area when the ratio of the horizontal permeability to the vertical permeability is large.

Copyright of Railway Construction Technology is the property of Railway Construction Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To evaluate hydraulic head distribution in front of a shield tunnel in a saturated soil layer, theoretical analysis and numerical simulations are carried out in this study. Based on the partial differential equilibrium equation of seepage flow, a three-dimensional (3D) theoretical analytical model of the shield tunnel face and the seepage field in front of it is established using the eigenfunction and the Fourier series expansion methods, and the hydraulic head calculation formula is derived. Combined with engineering cases, the theoretical analysis results and the 3D numerical simulation results are compared and analyzed. The effect of the water pressure of the tunnel face on the hydraulic head distribution is also analyzed. The results of the proposed analytical solution are in agreement with those of the numerical simulation solutions; moreover, the proposed analytical solution requires less time to calculate the seepage hydraulic head than the numerical simulation. The ratio of the initial water table to the diameter (D) of tunnel face has a more significant impact on the hydraulic head distribution at a position 0.5D above the tunnel vault. When the water pressure on the tunnel face is not considered, the values of the hydraulic head are significantly underestimated.

The occurrence of water inrush accidents in most mines is related to geological structures, especially faults. The influence of mining and confined water on floor fault activation and aquitard stability was analyzed theoretically using mechanical models to study the mechanism of water inrushes caused by mining above confined water under a fault structure. In addition, the stress distribution and seepage characteristics of the floor during mining were simulated and studied by COMSOL Multiphysics. We found that a fault is easier to activate when its dip angle is closer to 45° plus half of the fault's internal friction angle. Fault activation becomes more likely with decreased fault cohesion, friction angle, and minimal principal stress. The instability and failure of the key aquitard occur when: the maximum failure depth of the floor exceeds the distance to the aquitard, and the actual confined water pressure exceeds the critical water inrush pressure. A water inrush point occurred at the floor of the working face 35 m from the fault during mining, where the peak seepage velocity reached 0.22 m/s. The seepage velocity within the fault positively correlated with the initial confined water pressure. This study provides a criterion for fault activation and aquitard failure and improves our ability to predict fault-induced mine water inrushes. [ABSTRACT FROM AUTHOR]

Sediment incipient motion is the first step in sediment resuspension. Previous studies ignored the effect of seepage flow on the mobility of sediment particles and simplified the seabed surface as a rigid boundary. A flume experiment was designed to innovatively divide the seabed into two parts to control the dynamic response of the seabed and control the seepage conditions. In the experiment, the seabed sediments and the amplitude of internal solitary waves (ISWs) were changed to compare and analyze the impact of seepage flow on the sediment resuspension by shoaling ISWs. Moreover, parametric research and verification were carried out. Results indicate that seepage flow can greatly influence fine sand, promote sediment resuspension, and increase the amount of suspension by two times on average. However, seepage flow had a little effect on the suspension of clayey silt and sandy silt. Besides, seepage force was added to the traditional gravity, drag force, and uplift force, and the parameterization of threshold starting shear stress of coarse-grained sediments was developed. The results of this parameterization were verified, and seepage force was critical to parameterization. The threshold starting shear stress was reduced by 54.6% after increasing the seepage force. The physical mechanism of this process corresponded to the vertical reciprocating transient seepage in and out the seabed interface caused by the wave-induced transient excess pore water pressure. This quantitative study on seepage flow for shear stress of coarse-grained sediments induced by ISWs is critical to geohazard assessment. [ABSTRACT FROM AUTHOR]

Tidal channels migrate frequently under the combined actions of coastal dynamics and bank collapse, significantly affecting the stability of tidal network systems. However, existing studies mainly focus on in-channel flow erosion during flood tides, while less efforts are devoted to bank retreat driven by seepage erosion during the ebb tides. It is thus urgent to understand the underlying mechanism of bank collapse that driven by seepage. This study investigates the impact of seepage head height on bank collapse through physical experiments, including bank collapse modes, bank line variations and bank retreat rate. Results show that the process of bank collapse is related to seepage head height. We observe a transition of bank collapse mode from cantilever failure to tension failure, with increased seepage head height. A positive correlation between bank retreat rate and seepage head height is found. Overall, this research reveals the mechanism of bank collapse driven by seepage, and explains the distinct failure process of bank collapse over ebb tides, which is of great significance to the study of tidal channel evolution. [ABSTRACT FROM AUTHOR]

In the present study, three machine learning methods were applied for predicting seepage flow through embankment dams, namely (i) support vector regression (SVR), relevance vector machine (RVM), and Gaussian process regression (GPR). The three models were developed using seepage flow (Q: L/mn) and piezometer level (Z:m) measured at several piezometers placed in the corps body of the dam. The proposed models were calibrated and validated using a separate subset. Models evaluation and comparison was successfully achieved using various performances metrics, i.e., coefficient of correlation (R), Nash-Sutcliffe efficiency (NSE), root mean square error (RMSE), and mean absolute error (MAE). Experimental results showed that the proposed models are a good alternative to the in situ measured and contributed significantly in overcoming the case of missing measured seepage flow. The best performances were obtained using the RVM model with R and NSE values of ≈0.909 and ≈0.823, followed by the GPR model with R and NSE values of ≈0.891 and ≈0.767, while the SVR model was ranked as the poorest one exhibiting R and NSE values of ≈0.780 and ≈0.600, respectively. While, a growing number of investigations have focused on testing machine learning in terms of their feasibilities to accurately describe seepage flow, as well as providing important support to our understanding of the factors affecting its fluctuation, the present work was demonstrated that the combination of a wide range of variables can help in simulating seepage flow, and enhance their sensitivity which has help in developing new algorithms. [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]

The analysis of water seepage below the model's foundation of hydrotechnical object is conducted in the paper. A physical model of gravitational dam is made with the aim to visualize seepage through the ground below the dam. The model is made at the laboratory of the Faculty of Civil Engineering and Architecture in Osijek. The aim of the paper is to analyze the influence of the hydraulic gradient on seepage domain deformation, as well as to study the effect of different engineering measures on the decrease of hydraulic gradient. Four measurements were conducted which were mutually distinguished by the shape of the dam model, i.e. the foundation sheet. The first part of the paper is based on the assessment of measurement variants, i.e. engineering solutions used for the reduction of the seepage part of the buoyancy and seepage flow. The second part of the paper is dedicated to adoption of different models in the analysis of groundwater seepage below the object. Values related to seepage flow as well as buoyancy and pressure distribution below the foundation sheet were analyzed. Graphical, numerical, and approximate methods of analysis were used. [ABSTRACT FROM AUTHOR]

Copyright of Tunnel Construction / Suidao Jianshe (Zhong-Yingwen Ban) is the property of Tunnel Construction Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This work is motivated to study the face stability of earth pressure balance shield tunnels excavated in the semi-open mode and supported by non-uniform chamber pressure under seepage conditions. Within the kinematic approach of limit analysis, an analytical framework incorporating the seepage effect and linear chamber pressure distribution is developed. The pore pressure distributions are numerically simulated and imported into the three-dimensional (3D) discrete rotational failure mechanism. The work rates caused by the pore pressure and non-uniform support in the semi-open mode are introduced into the work rate balance equation to optimize the critical support pressure. Then, a parametric analysis of three typical soils, including the sand, silt, and clay, is performed to investigate the difference between the semi-open mode and closed mode under seepage conditions. The effects of the muck height and pressure gradient in the chamber, the groundwater levels, and anisotropic permeability are also studied. Finally, several design charts of the normalized critical support are presented. The results show that the difference between considering a linear pressure distribution and a uniform distribution in the semi-open mode is small, with a maximum difference of 3%. Compared to the closed mode, the instability of the tunnel face is significantly higher in the semi-open mode under seepage conditions. [ABSTRACT FROM AUTHOR]

In open channel flow, the velocity distribution is required to analyze the flow parameters such as discharge, energy and momentum correction factors, and scour depth. Though the existing technique can simulate the velocity distribution practically sound, the hypothesis on the cumulative distribution function of velocity is difficult to track and restricted by several factors that it holds. The paper aims to extend the entropy-based 1-D velocity distribution to rectangular seepage channels, considering the cumulative distribution function based on channel geometry. The present work developed a Tsallis and Shannon entropy-based model for proposing 1-D velocity distributions in seepage-affected alluvial channels. The velocity distributions were evaluated with laboratory observations and were compared with Shannon and Tsallis entropy-based velocity distributions equation. The Shannon and Tsallis entropy-based 1D velocity distributions agreed with experimental data satisfactorily and compared well. However, based on the regression analysis, Tsallis-based velocity distribution performed better than the Shannon-based entropy model. [ABSTRACT FROM AUTHOR]

This paper presents a unified semi-analytical solution to investigate the passive earth resistance of unsaturated soils retained by a rigid wall in the framework of limit-equilibrium approach based on a rotational log-spiral failure mechanism. Coupled influences of unit weight and suction stress changes in unsaturated soils under different steady vertical flow conditions have been considered to provide a more realistic solution. The impact of different parameters such as effective internal friction angle soil, inclination of backfill surface and wall back face, surcharge pressure, height of wall, location of water table, and soil–wall interface friction has been explored by performing a parametric study. It has been found that the changes in the suction stress and unit weight of unsaturated soils under different input parameters have a greater effect on modifying the critical slip surface, and magnitude and point of application of passive earth resistance on the retaining walls. The results obtained from the present study compare reasonably well with the solutions in the literature. [ABSTRACT FROM AUTHOR]

The permeability prediction for fractured rock mass is the basis for analyzing permeability problems such as oil and gas exploitation, pollutant migration, and so on. In this paper, the in-house sub-element program was used to solve the steady-state Navier-Stokes equation for incompressible viscous flow. The periodic boundary conditions (PBC) were introduced to eliminate the error induced by choosing only a small section of fracture and ignoring the extension length of fracture in the previous numerical simulation. This method was applied to explore the effects of joint roughness coefficient (JRC), fracture width and mutual dislocation of two surfaces of fracture on permeability. The results show that the influence of JRC value on permeability decreases as the fracture width grows; the permeability of fractures cannot be accurately evaluated by using JRC values only. [ABSTRACT FROM AUTHOR]

The roughness and tortuosity of fractures are essential parameters affecting the fluid flow in a jointed rock mass. This paper investigates the influence of fracture roughness and tortuosity on fluid seepage behavior. A rough fracture surface was characterized by means of three-dimensional scanning and three-reconstruction technology, and the roughness and tortuosity of rock fractures were calculated. Hydraulic tests were conducted on deformed sandstone fractures with a self-made fracture seepage device, and the variation in the seepage flow was analyzed in rough fractures. The experimental results showed that the seepage flow of fluid decreased non-linearly with the increase in fracture roughness. Under different normal pressures, the friction resistance coefficient and tortuous resistance coefficient decreased with the increase in the Reynolds number. The friction resistance coefficient model and tortuous resistance coefficient model were used to quantitatively analyze the influence of fracture tortuosity and roughness on fluid flow, respectively. A modified model of the frictional resistance coefficient, considering fracture tortuosity and roughness, was established, which clearly expresses the law that with the increase in fracture tortuosity and roughness, the seepage flow of fluid decreases, and the head loss increases. The results of this research can provide a theoretical and experimental basis for studying fluid seepage behavior in deformed sandstone fractures. [ABSTRACT FROM AUTHOR]

Assuming time-averaged normalized velocity as a random variable, the present work developed a Renyi entropy-based model for deriving one-dimensional and two-dimensional velocity distributions in seepage-affected alluvial channels. The model requires the maximization of Renyi entropy using the principle of maximum entropy, subject to specified constraints. The derived velocity distributions can have maximum velocity on or below the free surface. The velocity distributions were evaluated with laboratory observations and were also compared with theoretical velocity distributions reported in the literature. The Renyi entropy-based 2D velocity distributions satisfactorily agreed with experimental data, and compared well with reported distributions. Also, the Renyi entropy provided more accurate 2D velocity distribution in the near-bed flow of seepage experiments than the other technique. The present paper concluded that the Renyi entropy model can be used to predict the velocity distribution in seepage flows. [ABSTRACT FROM AUTHOR]

Seepage analysis plays a key role in geotechnical engineering and contributes significantly to the success of its infrastructure projects. Several engineers consider the Finite element (FE) method basics when executing calculations for designing hydraulic structures and dams. Numerical methods are used herein to solve the problem of seepage flow of water under concrete dams. The FE method is applied to model the dam structure and water level. The seepage velocity distribution in the porous soil is determined, and the effects of varying multiple parameters on the velocity are studied. The different parameters investigated are the dam dimensions (i.e., width (4,8,10,15 m) and depth (0,2,4,8 m)), upstream water head level (10, 15, 20 m), soil permeability (10, 15, 20 m day−1) and ambient temperature (5 °C and 50 °C). The developed FE models were validated by carrying out comparisons with analytical solutions that showed that they were in good agreement. It was found that the dam width is inversely proportional to the seepage rate and is independent of the water head level where increasing the dam by 1 unit width drops the seepage by 3.7% regardless of the water head levels. The depth of the dam is exponentially related to the distance away from the toe and independent of both the dam's width and water head level. Increasing the dam depth reduces the seepage flow by 73% at shallower depths and the effect minimizes as we increase the depth to 1% reduction in seepage simulating an exponential behavior. Such behavior is typical for the dam depth factor regardless of the dam width and water head level variations used in the study. The water head level was also found to be linearly proportional to the seepage flow rate with an increased effect of about 10% per additional 1-m head level. In addition, the soil permeability is linearly proportional to the seepage rate, and the same increment is obtained regardless of the dam's dimensions and water head level. The effects of ambient temperature on the seepage flow were introduced in this paper and will be further studied in detail in our future simulations. Our study concludes that the developed FE model can predict the seepage flow of water under concrete dams with a reasonable level of accuracy. [ABSTRACT FROM AUTHOR]

In order to explore the seepage characteristics of coal seam pressure water injection under different permeability and fracture conditions, CT scanning technology was used to scan coal samples and obtain the original image. The noise points are filtered by using the median filter function of MATLAB software, and then the original binary image is obtained. Finally, the two-dimensional model of coal body is reconstructed by using the interpolation function in COMSOL numerical analysis software, and the fluid-solid coupling model of coal body seepage process is established, and the seepage evolution process of pressure water is analyzed by numerical simulation. The results show that the pore structure of coal can be accurately described by processing CT scanning images with MATLAB analysis software; the two-dimensional model of coal can be finely characterized by COMSOL interpolation function; the flow of water in coal is mainly affected by pore structure, and the flow attenuation rate of main fissure water is very small, while in the coal matrix and sub-fissure inclusion area, the flow is basically not in the matrix part flow.

This paper proposed a calculation method for bolts reinforcement of tunnel face under the seepage condition. The existence of seepage in tunnel engineering may greatly reduce the stability of tunnel face, and bolts reinforcement technology is widely used in traditional tunnel engineering. In this paper, a 3D rotational failure mechanism is proposed by the kinematics method combined with the discretization technique. The pore water pressure was added in the energy calculation based on the empirical distribution formula of water head. The interaction between soil and bolts is simulated by using a finite thickness interaction region. The method was compared with the published works in order to verify the effectiveness. The influence of the bolt length, the bolt strength, the hydraulic head size, the face height and the soil parameters are given in the form of some graph. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Applied Ecology / Yingyong Shengtai Xuebao is the property of Chinese Journal of Applied Ecology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Mammal bioerosion is an emergent threat to the functionality of levees. In the present paper, the problem of assessing the failure probability of levees affected by mammal bioerosion is addressed. A fully bivariate description of peak flow discharge and flood duration is combined with a deterministic unsteady seepage flow model to obtain a suitable model of variably disturbed levee response to the observed natural variability of floods. Monte Carlo analysis is also implemented to evaluate the epistemic uncertainty connected to the description of the river system. The obtained model is tested with respect to a real‐world levee located along the Secchia River in northern Italy, which underwent a disastrous failure caused by mammal bioerosion in 2014. The convex linear combination of two Archimedean copulas is found to fit the empirical dependence structure between peak flow discharge and flood duration. The reliability of the unsteady seepage flow model is tested against detailed numerical simulations of the seepage occurring through the levee body. A limit state function is obtained by comparing the maximum extent of the seepage front to the distance between the den end and the riverside levee slope, and the corresponding levee safety and failure regions are delimited. Results obtained from the developed model reveal a significant impact of mammal dens located near the levee crest in terms of failure probability and related return period. This impact is consistent with failures observed in the study area. Plain Language Summary: Burrowing mammals often find in levees a suitable habitat. Unfortunately, mammal dens can significantly compromise the functionality of levees by creating preferential flow paths for flood water seeping through the levee bodies, and by causing ultimately levee failures due to excessive seepage and internal erosion. In fact, many levee failures have been connected to the levee weakening caused by mammal dens. Mammal bioerosion significantly increases the failure probability of levees and the related flood risk in densely populated floodplains. Estimating the failure probability of levees affected by mammal bioerosion is therefore a relevant societal need. In the present study levee, safety and failure conditions are estimated by combining a fully bivariate statistical description of peak flow discharge and flood duration with a computationally efficient unsteady seepage flow model. The resulting modeling framework incorporates the natural variability of floods and the essential hydraulic properties of disturbed/undisturbed levees. Model results reveal that the return period of levee failure due to excessive seepage reduces from 100 to 9 years, namely of −91%, when the mammal den extends for 84% of levee thickness. These results can be used to inform levee design and maintenance programs for the safety of societies living in floodplains worldwide. Key Points: Fully bivariate analysis of peak flow discharge and flood duration is used to describe the hydrologic forcing to leveesVorogushyn et al.'s unsteady seepage flow model is extended to derive the failure probability of variably disturbed leveesReturn period of levee failure due to excessive seepage reduces from 100 to 9 years when the mammal den extends for 84% of levee thickness [ABSTRACT FROM AUTHOR]

This paper aims to analyze the turbulent structure of flows over beds undergoing downward seepage under clear-water conditions. Laboratory experiments in this regard were carried out in a straight rectangular channel that was 17.20 m long and 1.00 m wide. A sandy bed with median grain size d50 = 0.50 mm and sediment gradation σg = 1.65 (i.e., slightly non-uniform sediment) was used for the channel bed. The 3D instantaneous velocities of water were measured with an Acoustic Doppler Velocimeter (ADV) at the working test section. In the vicinity of the bed surface with seepage, measurements revealed that the flow longitudinal velocities (i.e., velocities in x direction) were higher than those in the case of a bed without seepage. Moreover, the variations inthe Reynolds shear stresses increased for the bed with seepage, indicating a higher exchange of flow energy towards the boundary and vice versa. Therefore, it was found that seepage processes influence the turbulence intensity, with a prominent magnitude in the streamwise and vertical directions. The paper also focuses on the third-order moment (skewness) and the kurtosis of velocity fluctuations and the governance of sweep events within the near-bed flow in cases where seepage was observed. [ABSTRACT FROM AUTHOR]

Silty sand slopes are prone to damage due to seepage or rainfall. A partial reinforcement method using short polypropylene fiber and sand mixtures was proposed to protect silty sand slopes from seepage flow failure. The effects and the reinforcement mechanism were explored. First, triaxial tests were performed on sand samples reinforced with fiber lengths (6 and 12 mm) and contents (0.25 and 0.50%) to verify the reinforcement effect. Then, model tests were conducted on sand slopes under lateral seepage flow and the failure mode with different fiber contents and reinforcement method were examined. The results showed that the cohesion and shear strength of sand were significantly improved with the increase of fiber content and length. The suction of unsaturated sand was also enhanced by the fibers. The change in stress-strain behavior from strain softening to strain hardening indicated that static liquefaction could be effectively prevented. The failure mode and extent of slope damage depended on the fiber content. However, it was noted that the slope surface with small reinforcement range performed similarly to that with large reinforcement range. In conclusion, the partial reinforcement method with short discrete synthetic fibers can be used as an effective alternative for slope reinforcement. [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]

Artificial ground freezing (AGF) technology has been commonly applied in tunnel construction. Its primary goal is to create a frozen wall around the tunnel profile as a hydraulic barrier and temporary support, but it is inevitably affected by two natural factors. Firstly, seepage flows provide large and continuous heat energy to prevent the soil from freezing. Secondly, as a key soil parameter in heat transfer, the soil thermal conductivity shows inherent spatial variability, binging uncertainties in freezing effects and efficiency. However, few studies have explored the influence of spatially varied soil thermal conductivity on AGF. In this study, a coupled hydro-thermal numerical model was developed to examine the effects of seepage on the formation of frozen wall. The soil thermal conductivity is simulated as a lognormal random field and analyzed by groups of Monte-Carlo simulations. The results confirmed the adverse effect of groundwater flow on the formation of frozen wall, including the uneven development of frozen body towards the downstream side and the higher risk of water leakage on the upstream face of the tunnel. Based on random finite element analysis, this study quantitively tabulated the required additional freezing time above the deterministic scenario. Two levels of the additional freezing time are provided, namely the average level and conservative level, which aim to facilitate practitioners in making a rule-of-thumb estimation in the design of comparable situations. The findings can offer practitioners a rule of thumb for estimating the additional freezing times needed in artificial ground freezing, accounting for the seepage flow and spatial variation in soil thermal conductivity. [ABSTRACT FROM AUTHOR]

In recent years, sediment disaster has frequently been caused by heavy rainfall and has cost many human lives and great property losses. To estimate such risks, Wakai et al. [1] proposed a simplified prediction method to calculate the variation of groundwater levels in natural slopes both at the time of rainfall in wide areas and in real time. To calculate the variation of groundwater levels using this method, the slope conditions (such as material constant and initial conditions) must be determined in advance. This study takes the 2017 heavy rainfall in Northern Kyushu as an example to analyze surface layer thickness, one of the slope conditions that most significantly influences slope stability, over wide areas. The findings reveal that the prediction of slope failure distribution differs depending on how the surface layer thickness and sliding surface are determined. [ABSTRACT FROM AUTHOR]

Suffusion is a grave threat leading to accidents in embankment dams across the world. The process has been widely studied experimentally and numerically with gap‐grading cohesionless soil. One of the direct observations in the studies is the finer particle loss of the soil. However, the movement of the finer particles in the numerical models is commonly predicted with an empirical law. This paper proposes a theoretical particle movement model based on the force balance of soil particles and a probability distribution of the soil pores under one‐dimensional upward seepage flow. In the proposed model, the velocity and the critical movement state of soil particles were deduced, and a method to predict the critical hydraulic gradient was established. The finer particle movement rate was estimated theoretically using the particle movement velocity and probability. The model was verified with several experiments and showed a good consistency in the critical hydraulic gradient, seepage velocity, finer particle loss and hydraulic conductivity. Finally, the changes in the soil parameter during the suffusion process, the effects of the hydraulic gradient and initial porosity and the model applicability are discussed quantitatively. The results indicate that the modelled soil parameter changes match well with the movement characteristics of the finer particles observed in the experiment. The particle movement process is very sensitive to changes in the hydraulic gradient and soil initial porosity. The theoretical model provides a new method to assess the suffusion process for internal unstable cohesionless sand soil. Highlights: A evaluation model of the suffusion‐induced soil particle movement was proposedThe model was established based on force equilibrium of soil particlesThe model was credible in varied factors based on experiment dataThe model evaluated suffusion process, variables affects and model applicability were discussed [ABSTRACT FROM AUTHOR]

The roughness and tortuosity of fractures are essential parameters affecting the fluid flow in a jointed rock mass. This paper investigates the influence of fracture roughness and tortuosity on fluid seepage behavior. A rough fracture surface was characterized by means of three-dimensional scanning and three-reconstruction technology, and the roughness and tortuosity of rock fractures were calculated. Hydraulic tests were conducted on deformed sandstone fractures with a self-made fracture seepage device, and the variation in the seepage flow was analyzed in rough fractures. The experimental results showed that the seepage flow of fluid decreased non-linearly with the increase in fracture roughness. Under different normal pressures, the friction resistance coefficient and tortuous resistance coefficient decreased with the increase in the Reynolds number. The friction resistance coefficient model and tortuous resistance coefficient model were used to quantitatively analyze the influence of fracture tortuosity and roughness on fluid flow, respectively. A modified model of the frictional resistance coefficient, considering fracture tortuosity and roughness, was established, which clearly expresses the law that with the increase in fracture tortuosity and roughness, the seepage flow of fluid decreases, and the head loss increases. The results of this research can provide a theoretical and experimental basis for studying fluid seepage behavior in deformed sandstone fractures.

The paper is devoted to the simulation of oil displacement by water and the formation of the Saffman–Taylor instability. The problem is solved in two-dimensional formulation. A circular domain with one injection well and eight production wells located along the contour around the injection well is considered as geometry. To study the patterns of oil displacement by water, hydrostatic pressure, oil and water seepage rates, and oil saturation are calculated. The graphical analysis considers mainly the oil saturation field. The hydrostatic pressure field is calculated by solving the steady-state piezoconductivity equation; the field of the oil-water seepage rate is calculated using the linear Darcy filtration law; and the oil saturation field is calculated from the solution of the advection transport equation. The two-phase nature of the flow considered in the problem lies in the fact that the oil and water phases have their own relative phase permeabilities calculated using the Brooks–Corey model. The equations are solved numerically using the finite volume method. An irregular triangular grid is used to discretize the computational domain. As a result of the simulation, it is established that the type of the Saffman–Taylor instability, due to its randomness, strongly depends on the computational grid. After the production wells are flooded, the displacement front stabilizes. The instability increases as the ratio of dynamic viscosities of oil and water increases. [ABSTRACT FROM AUTHOR]

A tractable analytical solution for steady-state two-dimensional seepage from a trapezoidal channel in a homogeneous, isotropic porous medium of considerable depth is presented. The analysis is performed by applying the method of inversion and the Schwarz-Christoffel transformation accounting for the capillary action. Because the right half-seepage domain is a mirror image of the left half-seepage domain about the vertical axis (on either side of the channel central plane) owing to the axisymmetric channel, a solution is sought for the right half-seepage domain. The results show that an increase in channel bottom width boosts seepage flux. On the other hand, an increase in channel side slope also amplifies seepage flux. In addition, capillarity plays a subtle role in augmenting the seepage flux from a channel. The analysis suggests that the dynamic capillary rise (i.e., the vertical rise of seepage water along the side slope owing to capillary action) is always less than the static capillary rise. The analysis also presents the relation for the seepage velocity distribution along a channel perimeter. The equations of seepage line coordinates yield the seepage line initially curving downward with a significant lateral shift and eventually becoming vertical at a great depth. Particular solutions for the triangular and rectangular channels and the vertical slit, which is a channel with vertical sides and negligible top width, can be obtained from the generalized solution for the trapezoidal channel. Therefore, this study provides insight into the hydraulics of seepage from a trapezoidal channel, including its particular cases, revealing some new features. [ABSTRACT FROM AUTHOR]