Seepage Flow Research Articles

Computing of Permeability Tensor and Seepage Flow Model of Intact Malan Loess by X-ray Computed Tomography

Malan loess is an eolian sediment in arid and semi-arid areas. It is of great significance to study the pore structure of Malan loess for its evolution, strength, and mechanical properties. In order to quantitatively characterize the absolute permeability tensor of Malan loess and to simulate the seepage process of Malan loess, this study calculated the specific yield of intact Malan loess with a homemade seepage experimental device and recorded the water flow process on the surface of Malan loess during the seepage process. Modern computed tomography was used to scan the intact Malan loess samples from Jiuzhoutai, Lanzhou (western part of the Loess Plateau, China); the specific yield of the intact loess was used as the parameter value for the threshold segmentation of the scanned image for the 3D reconstruction of the connected pore space, the solver program in AVIZO software was used to solve the absolute permeability tensor of Malan loess using the volume averaging method combined with the CT scan to reconstruct the 3D pore space, and the simulation of the seepage process was carried out. The simulation results showed that Malan loess is a highly anisotropic loess; the absolute permeability in the vertical direction is 9.02 times and 3.86 times higher than the permeability in the horizontal direction. The pore spaces are well connected in the vertical direction (forming a near-vertical arrangement of pipes) and weakly connected in the horizontal direction. In the seepage simulation, it was found that the water flows first along the vertically oriented channels and then fills the horizontally oriented pores; the absolute permeability coefficient was calculated to be 0.3482 μm2. The indoor seepage experiment was consistent with the simulation experiment, which verifies the reliability of the calculated model.

Numerical investigation of solute migration and release from sediments driven by wave-induced accumulation of pore water pressure

Sediments with poor drainage conditions are prone to build-up of excess pore water pressure when exposed to dynamic wave loading. This results in accumulated seepage flow that may have a significant impact on migration of solutes in marine sediments. In this study, the complex interplay between solute transport and wave-induced seepage process is investigated through a pioneering approach that combines and synchronously solves the two-dimensional advection-dispersion equation governing nonreactive solute transport with the governing equations for wave-induced oscillatory and residual pore pressures. The simulated results have demonstrated that the accumulated seepage flow significantly contributes to the advective and dispersive fluxes of solute, where the advection leads to movement of the solute layer and the hydrodynamic dispersion primarily enlarges the thickness of solute layer. The distribution of residual pore water pressure along depth exhibits two patterns that are primarily influenced by the thickness of the seabed. When the seabed is thinner than 0.3 times the wavelength, the residual pore pressure increases monotonically with depth (Pattern I). In this situation, the solute always migrates upwards to the seabed surface. Otherwise, Pattern II depicts the distribution of residual pore pressure, where the peak value of residual pore pressure attains at a certain depth and may advance downwards with wave action time. In this case, the direction of solute migration in regions shallower than a certain depth (e.g., 0.6 times the thickness of sediment) may alternate over time but the solute can eventually be transported upwards to seabed surface. The parametric study shows that when the seabed thickness is 0.2–0.3 times the wavelength, accumulated seepage flow has less effect on solute migration, whereas decreasing relative density and shear modulus, as well as increasing soil permeability can enhance the effect of accumulated pore water pressure on solute migration.

Gravity flow in rock fractures with substrate and edge drainage

We investigate the influence of fluid rheology on flow in a finite rock fracture with vertically varying aperture and subject to competing drainage mechanisms due to a permeable substrate and a draining edge. The flow is due to the release of a finite volume of fluid, and the rheology of the fluid is either Newtonian, Ostwald–deWaele, or Herschel–Bulkley. The Hele–Shaw analogy between lubrication and seepage flows allows extending our results to a porous medium with permeability and porosity varying in the vertical direction. The general solution is numerical, except for a self-similar solution derived for Newtonian fluids in a constant aperture fracture and another for Ostwald–deWaele fluids without substrate drainage. Results for the profile of the current and the volume remaining within the fracture, or drained at the substrate and edge, depend on a dimensionless parameter λ incorporating fluid rheology, fracture geometry, and ambient depth; drainage times exhibit order of magnitude variations depending on λ. A second dimensionless parameter, λ′, intervenes for Herschel–Bulkley fluids, with λ′→∞ for Ostwald–deWaele fluids. The theoretical model is validated with a series of experiments conducted with a novel experimental apparatus, accurately reproducing the condition of substrate drainage and allowing the experimental determination of λ and λ′. The agreement between theory and experimental results for both configurations with constant and V-shaped aperture is quite good, considering model approximations and experimental uncertainties. The present analysis shows how domain anisotropy, though simply schematized, and fluid rheology are relevant for the correct estimation of all integral variables, such as the residual fluid volume in the fracture as a function of time.

Research on Productivity Prediction Model of Three-Dimensional Directional Wells in Different Reservoirs

Productivity prediction of perforation completion is key for well optimizing completion methods and reservoir engineering research. Productivity prediction models using an additional pressure drop to represent skin factor are limited. In this study, a steady-state productivity prediction model coupled with reservoir seepage and fluid flow in the wellbore was developed. The impact of different perforation parameters on well production was studied. Considering perforation depth, perforation density, perforation diameter, phase angle, depth of contaminated zone, and pollution degree of the contaminated zone, a semi-analytical skin calculation model under different reservoir conditions and completion methods with the least-squares method combining the consideration of perforation depth, perforation density, perforation diameter, phase angle, depth of contaminated zone, and pollution degree of the contaminated zone was developed. Perforation parameters were optimized. A 3D directional well unsteady productivity prediction model was established using the finite-volume method considering the influence of conventional perforation completion parameters, gravel packing perforation completion parameters, natural fractures, reservoir heterogeneity, reservoir scale, skin factor, fluid gravity, fluid compressibility, and rock compressibility. A new method for optimizing perforation parameters and characterizing skin factors was developed, providing a theoretical basis and simulation means for deeper understanding of the development law of directional wells.

Investigating the chloride ion resistance of cracked concrete through Reverse-seepage and Saturation based Action Anti-corrosion Tech (RS-AAT): Experimental and numerical analysis

This study investigates the chloride ions transport in cracked concrete with the impact of RS-AAT (Reverse-seepage and Saturation based Action Anti-corrosion Tech) in the environment of wet-dry cycling and soaking conditions. With the effect of reverse water pressure, the chloride ions accumulation surrounding the crack on the concrete surface and the chloride ions penetration within the concrete along the cracks are demonstrated by the indoor experiments. A two-dimensional convective diffusion model of chloride ions in cracked concrete is established to simulate the correlation between crack size and the change of reverse water pressure. Four types of cracks with widths of 0 mm, 0.2 mm, 0.4 mm and 1 mm, and a depth of 20 mm were selected. Three types of water pressures with values of 0.2 MPa, 0.3 MPa and 0.4 MPa were used for the technique. The experimental results show that the anti-convection effect induced by the reverse water pressure can inhibit the accumulation of chloride ions around the cracks and effectively limit the intrusion of chloride ions into the concrete protection layer. With the increase of reverse water pressure, the inhibition effect of seepage flow on chloride ions is more obvious. The experimental findings provide valuable references for investigating marine concrete durability and resistance to chloride ion erosion.

Research on Application of Fiber Bragg Grating Seepage Pressure Sensor in Soil Test

Combined with the pressure sensitive characteristics of corrugated diaphragm and the strain sensing characteristics of fiber Bragg grating (FBG), a kind of FBG sensor is developed to measure the seepage pressure change of soil in a small range. By carrying out the soil seepage flow monitoring test and the laboratory slope model test, and comparing the theoretical and measured values of these tests, it can be found that: it is feasible to apply FBG seepage pressure sensor to the seepage pressure monitoring of soil mass. The sensor can guarantee the validity and reliability of data in the medium-term or long-term monitoring process, and shows superior performance compared with conventional seepage pressure sensor. The FBG seepage pressure sensor has the characteristics of high sensitivity, stable long-term performance, high precision and strong real-time performance. It provides a new measurement method for the seepage pressure monitoring of soil mass within the range of 0 to 100 kPa.

Experimental Investigation on Velocity Fields of Seepage Flow Inside Gravel Mount

There is little information on velocity field of seepage flows. The formation of seepage flow is significant for aquatic habitat including spawning of aquatic animals in river. To create spawning fields in river, the stability of a heaped-up gravels during floods is required for its artificial formation. The velocity measurement of seepage flows is also necessary. This paper presents velocity fields of seepage flows in a heaped-up gravels. The experimental study yields that the heaped-up gravels are stabilized by installing the consecutively assembled boulders on the gravels. Also, small mean velocity and standard deviation are recorded for different discharges. Spectrum analysis reveals that fluctuation velocity of seepage flows depends on the turbulent flow above the heaped-up gravels.

Erosion mechanism for submarine pipeline on graded sediments using a coupled PORO-CFD-DEM model

To investigate the meso-mechanism of scouring process, a numerical model that couples the porous medium model, computational fluid dynamics and discrete elements method (PORO-CFD-DEM model) is established and validated. Two pipeline conditions, suspended and partially buried, are considered. The porous medium is used to replace most of the discrete elements, significantly reducing the computational requirements. Two particle generation methods, namely fictious grid method (FGM) and breath-first search method (BFM), are proposed, and three kinds of particle samples are generated with different gradations: Gaussian, gap and continuous. Detailed analyses of flow, fluid-particle interaction and sediment motion is conducted with an increasing inlet velocity. When the pipeline is suspended, the seepage flow is induced by the gap flow beneath the pipeline, with the pressure dropping along the seepage path. Around partially buried pipeline, the seepage flow is much weaker and the pressure concentration appears. The seepage force fluctuates, and the loose bed is disturbed, leading to randomly collapses. Different particle movement patterns, including the jumping, suspended transportation and the formation of sand slope, are captured during the simulations. It’s confirmed that the PORO-CFD-DEM model can capture the meso-movement of the particles and provides insights into the theory of sediment transportation.

An XFEM-based hydro-mechanical model to consider the non-Darcy flow in complex fracture networks

Geotechnical instability and failure are closely related to the hydro-mechanical coupled behavior of fractured rocks, and the existing studies often regard the fracture seepage as linear Darcy flow. Due to the neglect of non-Darcy effect caused by rough rock wall and high flow velocity, the estimated rock deformation and seepage flow can lead to incorrect assessment of geotechnical risks. Hence, this study proposed an efficient and robust hydro-mechanical (HM) coupled model to consider non-Darcy flow in complex fracture networks. The fractured rock mass's mechanical response, including the fracture surface's frictional contact, was calculated using the XFEM solver, and the widely used Forchheimer's law was adopted to describe the non-Darcy flow along the fractures. The fracture segments cut by mechanical element edges are considered one-dimensional flow elements, and the Newton-Raphson iteration method is adopted to solve the Forchheimer equation directly. To consider the influence of fracture deformation on the conductivity of fractures, the Barton-Bandis model was adopted to determine the hydraulic aperture of the fractures when the fracture was closed. Subsequently, a staggering Newton-Raphson method can be developed to decouple the fracture deformation and fluid flow process. Experimental results were adopted to validate the accuracy of the numerical model, and several numerical cases were used to illustrate the efficiency and robustness of the proposed model. The effects of inlet pressure, confining stress, and non-Darcy effect on the HM-coupled behavior of fractured rock were investigated. Numerical results suggested that the distribution of fluid pressure and failure process of rock mass based on Darcy assumption could be dramatically changed after considering the nonlinear seepage behavior.

The difference in time delay of δ18O, δ13CDIC and Mg/Ca to the hydroclimate change monitored in a subtropical cave, South China

Speleothem δ18O, δ13CDIC, and Mg/Ca are widely used to reconstruct past climatic and environmental changes. However, due to the rainfall regime and hydrological structure of caves, their application in reconstructing past hydroclimate in the East Asian monsoon region is poorly understood. In this study, we monitored two types of drip water in a subtropical cave to investigate the different responses of δ18O, δ13CDIC, and Mg/Ca to hydroclimate changes at monthly to yearly scales. Our results showed that drip rate at all drip sites responded quickly to precipitation, whereas δ18O, δ13CDIC, and Mg/Ca responded with some lag. The lag time for the parameters were in the order of δ13CDIC (lag time ranging from 1 to 2 months) < Mg/Ca ratio (lag time of 2 months) < δ18O (lag time up to 5 months), and for fissure-fed drip sites (M-5 and M-6) < seepage flow drips (M-1 and M-2), as well as single-reservoir supply (M-5) < multi-reservoirs supply (M-6). A comprehension of both fast and slow flows is crucial in order to comprehend karst reservoirs and their paths, which in turn enables the exploration of the hydrological properties of unsaturated zones under the context of Asian monsoon. We also found that the hydrological structure was crucial in generating the different response times of δ18O, δ13CDIC, and Mg/Ca in drip water. Additionally, the relationship between δ18O and δ13CDIC may be due to the different residence times in different drip sites on seasonal- to annual timescales.

Study on heat-exchange efficiency and energy efficiency ratio of a deeply buried pipe energy pile group considering seepage and circulating-medium flow rate

Seepage and circulating-medium flow rate are both primary factors affecting the heat-exchange efficiency and energy efficiency ratio of underground energy structures. In this study, a thermal-seepage coupled model of a deeply buried pipe energy pile group is developed, and the effects of circulating-medium flow rate, seepage velocity, and thermal migration caused by seepage on heat-exchange efficiency and energy efficiency ratio are analyzed. The results show that increasing the circulating-medium flow rate can improve heat-exchange efficiency, but aggravate heat accumulation, resulting in energy efficiency ratio reduction. Seepage can eliminate the heat accumulation as well as improve the heat-exchange efficiency and energy efficiency ratio. The heat accumulated around upstream piles will migrate along the seepage direction, generating thermal disturbance to the downstream piles. An increase in the circulating-medium flow rate of upstream deeply buried pipe energy piles will aggravate thermal disturbance. This phenomenon is slightly retarded if seepage velocity is increased. Additionally, when the circulating-medium flow rate of the deeply buried pipe energy pile group under seepage is within the optimal range, slightly reducing the circulating-medium flow rate of the upstream deeply buried pipe energy piles can reduce thermal disturbance to the downstream piles without affecting the overall heat-exchange efficiency.

Application of 3D numerical simulations to forecast mine seepage and groundwater flow conditions with respect to progressive coal mining activity

Application of 3D numerical simulations to forecast mine seepage and groundwater flow conditions with respect to progressive coal mining activity

A Transient Productivity Prediction Model for Horizontal Wells Coupled with Oil and Gas Two-Phase Seepage and Wellbore Flow

Capacity prediction is the basis for the optimization of oil and gas well production work systems and parameter optimization design. Horizontal wells are becoming increasingly popular for oil and gas extraction. However, the seepage law of reservoirs produced with horizontal wells is more complicated than that of reservoirs produced with vertical wells, especially when the bottom hole flowing pressure or formation pressure is less than the saturation pressure of crude oil in the reservoir. Oil and gas two-phase seepage can occur in a part or all areas of the wellbore and reservoir. Because the oil and gas two-phase seepage characteristics of reservoir oil well production will be reduced—possibly greatly reduced—the formation seepage law is complex. Thus, it is very important to better predict the horizontal well capacity. To address this, a method and process of establishing a transient calculation model of two-phase flow in horizontal wells are introduced in detail from three aspects: fluid physical properties, reservoir oil and gas two-phase seepage, and the coupling model of the inflow performance and flow in the wellbore. The model is found to be reliable through verification with production data from five wells in two oilfields. The established model simplifies the reservoir model, does not involve very complex meshing, and only simulates one well. Therefore, the calculation speed will be faster than that of other reservoir numerical simulation methods under the same conditions.

Electromagnetic Waves’ Impact on Hydraulic Conductivity of Granular Soils

Electromagnetic (EM) waves, traditionally used for purposes such as geophysical characterization, impact properties to be measured. This paper describes the effects of radio frequency (RF) waves on the hydraulic conductivity of glass beads and natural sand. A series of tests was conducted using a customized, rigid-wall, cylindrical permeameter inside a resonant cavity made of Plexiglas covered with electrically conductive transparent films. Constant-head ASTM-D2434 tests were performed to measure the samples’ hydraulic conductivity. RF stimulation was performed using a magnetically coupled loop antenna at various frequencies and input RF-power levels. The hydraulic conductivity of both natural sand and glass-bead samples increased with RF stimulation. Furthermore, the measurement of the electric field component of RF waves was also performed to illustrate the pattern of the electric field, as well as evaluate RF’s impact on the hydraulic conductivity tests. The electric field was numerically simulated and validated against experimentally measured electric fields. A finite-difference numerical model was developed in MATLAB to analyze the seepage flow, which was then validated against the experimental results. An optimization scheme was then used to develop a governing equation for RF’s impact on hydraulic conductivity.

Experimental study on the evolution of rock microstructure under dynamic water pressure

The pore structure of rocks has an important influence on their mechanical strength and permeability. In this experiment, the evolution of the internal multiscale structure of rocks under the action of seepage flow is investigated. The results show that progressive damage occurs inside the rock at the early stage of osmotic pressure action, and the expansion and connectivity of pores form a damage mutation at a certain moment, which triggers rock damage destabilization. In addition, a damage evolution equation based on NMR test values is established to obtain the threshold of damage mutation in rocks; It is also found that rock permeability is mainly affected by pore connectivity, and the effect of porosity on rock permeability is relatively small.

Effect of initial failure geometry on the progress of a retrogressive seepage-induced landslide

Natural and man-made slopes can undergo a retrogressive landslide when subjected to seepage. Studying the mechanism of retrogressive landslides contributes greatly to the employment of effective mitigation approaches. A multi-stage limit equilibrium-based study was performed to explore how the geometry of initial failure affects the progress of a retrogressive, multiple-rotational landslide caused by seepage flow. Seepage-stability analyses were carried out on two silty sand slopes which were previously found to experience successive rotational failures upon raising the water table in centrifuge tests. Analyzed in prototype dimensions were the slope models with the height of 24 cm and inclinations of 45° (1V:1H) and 63.4° (2V:1H) tested at different centrifugal accelerations. According to the tests, the initial shallow failures were assumed to be circular initiating from the face and emerging from the toe of the slopes in the stability analyses. The impact of curvature and length of the initial failure surface (referred to as IFS) as well as the height of the scarp shaped at each failure episode were investigated. The results show that the landslide continues until the slope profile finds a stable curvature. For the landslides that occur in the 45° inclined slope, when the initial failure initiates at a higher elevation on the slope face, the landslide retrogresses further. In addition, with an increase in the length or curvature of IFS, the final retrogression distance decreases. Further, it was observed that the progress of landslides depends on the height of the scarp exposed at each failure episode.

Stability of complex rock tunnel face under seepage flow conditions using a novel equivalent analytical model

The longitudinally inclined layered rock masses under seepage flow conditions have an important impact on tunnel face stability. To solve this issue, a novel equivalent analytical model is proposed in this paper. This model settles the puzzle that the traditional model of limit analysis cannot directly determine the hydraulic head by treating the distribution hydraulic head at the anterior aspect of the tunnel face with the equivalent method, that is, without the tedious calculation by the numerical software. The seepage force is directly considered as a body force in this analytical model. Then, combined with the mirror-image method, layered discretization technique, limit analysis method, and Hoek-Brown yield criterion, an analytical expression for stability determination can be derived. The main factors affecting the stability of tunnel face are analyzed, such as the inclination angle of the flow line, the inclination angle of the rock layer, hydraulic conductivity, rock quality, excavation disturbed zone (EDZ), and the groundwater table height. The calculated diagrams have a certain guiding effects for tunnel construction.

An exact analytical approach for determining the seepage field around underwater twin tunnels with linings

A reasonable prediction of the seepage field around twin tunnels is important in tunnel design. In this paper, a new alternating analytical approach is proposed to obtain the exact solution of the steady-state seepage field around underwater twin tunnels in semi-infinite saturated aquifers, precisely taking into account the effect of linings or grouting regions, as well as the tunnels’ seepage flow interactions. This study is an extension of analytical research on seepage around tunnels, and rapid estimations of hydraulic heads, pore pressure and water inflows into tunnels can be gained by the proposed approach and solutions.By extending the Schwartz alternating method to problems with multi-connected domains and multiple regions, a new and relatively simple analytical approach is provided to obtain the seepage field (e.g., hydraulic head, pressure) around twin circular tunnels with linings/grouting regions. Employing conformal mapping, a single tunnel with a lining subjected to the reverse redundant hydraulic head generated in the previous step, and another lining under continuity conditions with the rock, are successively analysed in each iteration step. Only after two to three iterations can an exact solution with high precision be obtained by superposing all the solutions in the alternating steps, and good agreements are shown between the analytical solutions and the numerical results both in the surrounding rock and linings. Through a case study, the applicability of the analytical solution is validated. The functional relation between the hydraulic head and some parameters is discussed based on the proposed analytical solution, and a parametric study is conducted to investigate the influence of key parameters on the water inflow into tunnels and the water pressure outside the linings.

Influence of maximum paste coating thickness without void clogging on the pore characteristics and seepage flow of pervious concrete

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.

Influence of hydraulic and geometric conditions on the early stages of the filtration process in idealised granular soils comprising spherical particles

AbstractThe 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.