Seepage Coupling Research Articles

Internal erosion of debris-flow deposits triggered by seepage

Debris flows can be triggered by runoffs at considerably steep natural channels and streams. Specifically, runoff-generated debris-flow deposits are loose mixtures, comprising coarse and fine particles. Owing to seeping water, these fine particles are eroded and transported through the skeleton formed by the coarse particles. Such erosion can modify the porosity of deposits and influence their mechanical characteristics, which can be non-negligible for geotechnical and geological engineering. In this study, seven groups of seepage tests on gravel–sand–clay mixtures with different coarse particle content proportions (48%, 52%, 60%, 70%, 80%, 90%, and 100%) were conducted to investigate the erosion characteristics of debris-flow deposits triggered by seepage flows. In particular, concentrated leak erosion, internal instability erosion, and piping were noted in the soil with a coarse particle content of 48%–80%. Further, when the coarse particle content exceeds 80%, the soil does not disintegrate. A model coupling seepage and internal erosion was also developed to characterise internal erosion. For this model, mass conservation equations were reformulated for different types of internal erosion, based on the assumptions for the pore channel erosion of suspended materials and general erosion. Moreover, an equation based on the internal erosion rate, considering the pore size distribution and hydraulic gradient, was firstly introduced for concentrated leak and internal instability erosion. This equation could efficiently evaluate the mass of particles eroded from the soil. Lastly, the model was calibrated based on experimental data; the corresponding results are discussed herein.

Experimental method and application of the slurry “diffusion-bleeding-seepage” of isolated overburden grout injection

Isolated overburden grout injection (IOGI) is a green mining method to control surface subsidence. Slurry water significantly influences grouting effectiveness and mining safety. This study establishes a three-dimensional visualization experimental system for slurry “diffusion-bleeding-seepage” to investigate the seepage law of slurry water. The system is composed primarily of a transparent box (1.2 m × 0.5 m × 0.25 m) and support, with the solid–liquid coupling seepage similar material and modules for mining, grouting injection, slurry pressure and displacement monitoring, overburden saturation monitoring, and water leakage monitoring of the working face. A similar material with good permeability and non-disintegration is obtained by hydrophilic, water absorption, and permeability tests. Grouting and mining are simulated by pulling acrylic sheets and pumping slurry. With the fly ash slurry entering the injection layer, the slurry undergoes water–cement separation, and the water bleeding is formed to seep into the similar material. The volumetric water content of the similar material is obtained by arranging multiple groups of volumetric water content sensors into the similar material. The corresponding saturation is obtained by theoretical calculation. The experimental system is used to simulate the seepage of slurry water in a high initial saturation overburden, and the characteristics of injection slurry diffusion and water bleeding are obtained. The profile distribution of seepage of slurry water is found to possess a semi-elliptical shape. Under the condition of high initial saturation, slurry water appears in the working face. The system provides a convenient method for further research of IOGI slurry water seepage.

Research on the thermo-hydraulic response characteristics of pore-fissure media using mixed finite volume method

After lengthy diagenesis and tectonic movement, a rock mass inevitably develops many pores and micro-fissures. A numerical simulation method was employed to study the thermal response characteristics of the rock mass under temperature seepage coupling by treating it as a pore-fissure medium and considering its anisotropic properties. Based on the mixed finite volume method (FVM), a numerical scheme of the governing equation for the temperature seepage coupling of the pore-fissure medium is derived, with the program solution module independently written in C++. On this basis, a numerical test model of the fissured mudstone is established to analyze the distribution of the rock mass temperature field under various thermal conductivities and the influence of fissure permeability on the seepage field. The mixed FVM results revealed that the temperature and water pressure distributions near the fissure were closely related to the directionality of thermal conductivity in the rock mass, as well as the thermal conductivity and permeability coefficient, respectively, of the fissure itself. Comparison with results from the finite element software ABAQUS demonstrated significant advantages of the proposed method when solving temperature and seepage problems in discontinuous geological bodies containing hiatuses, mutations, and fissures.

Numerical simulation and protection of the dynamic change of Jinan karst spring based on coupling of seepage and conduit flow

The objective of this study was to predict the dynamic change in the spring water level more precisely, to provide timely solutions for karst spring protection. Using the Jinan spring region as a case study, this study established a numerical model of a karst groundwater system, and optimized the mining layout. The calculated maximum extraction volume following the optimized exploitation layout was 0.69 m3/s, in order to ensure the continuous flow of spring water in the median water year. A coupled karst groundwater numerical model with dual structure was developed using the MODFLOW-Conduit Flow Process (CFP), which simulates and then precisely predicts changes in the water level of the karst springs. Here, the plane extension direction of the karst conduit was determined by a tracer test and correlation analysis of the spring water levels and groundwater levels of the observation wells. Meanwhile, the vertical location of the karst conduit was determined by layered monitoring of the groundwater temperature and conductivity. Based on this, a coupling model of seepage and conduit flow was created to simulate the dynamic change in the spring water level, and the dual-media coupling model improved the simulation accuracy of the spring water level. The current study confirmed that, compared to the porous media seepage model, the dual-media coupling model can simulate the groundwater level dynamic change more accurately in a heterogeneous karst aquifer in northern China. The coupling model was used to analyze the effect of supplementation and optimize mining, to ensure that spring water continues to flow during the dry season while supplying the mining demand.

Coupled Seepage Mechanics Model of Coal Containing Methane Based on Pore Structure Fractal Features

The paper applies fractal theory to the structure of fractal coal pores and calculates the fractal dimension and integrated fractal dimension for each pore section >100 nm, 100 nm > d > 5.25 nm, and <2 nm. In the experiment, we performed the full stress–strain-seepage experiment of methane-bearing coal, revealed the deformation–seepage characteristics of methane-bearing coal under load, and deduced the dynamic prediction mechanical model of methane-bearing coal permeability based on pore heterogeneity, followed by practical verification. The results show that the permeability change in methane-bearing coal is an external manifestation of coal pore deformation, and the two are closely related and affected by changes in the effective stress coefficient. The derived fractal-deformation-coupled methane permeability mechanics model based on coal pore heterogeneity has high accuracy, a general expression for the stress–strain-permeability model based on coal heterogeneity is given, and the fractal Langmuir model is verified to be highly accurate (>0.9) and can be used for coal reservoir permeability prediction.

A Numerical Analysis of the Leakage Characteristics of an Embankment Dam Slope With Internal Erosion

Leakage is a common defect of embankment dam slopes, and is usually accompanied by internal erosion. This study establishes a mathematical two-phase seepage coupling model that explicitly considers the effects of internal erosion. With the help of finite element software COMSOL Multiphysics®, we use this model to study the characteristics of fluid seepage, the fraction of leakage volume that is made up of migrated fine particles (migrated fine particles volume fraction), porosity, permeability, and displacement in the leakage process of a three-dimensional embankment dam slope, as well as to study the influence of the water level and leakage outlet size on the aforementioned features. Our results show that water seepage velocity gradually increases with time, especially at the downstream leakage outlet. Therefore, the erosion and migration of fine particles occur primarily at the downstream leakage outlet, resulting in a significant increase in the migrated fine particles volume fraction, porosity, and permeability. In addition, the maximum migrated fine particles volume fraction, the maximum porosity, and the maximum permeability in the slope increase nonlinearly with time. Curves for maximum displacement with a strength reduction factor can be divided into three stages: the early stable stage, the midterm nonlinear growth stage (creeping state), and the later rapid growth stage (instability state). We also find that the rise of the water level promotes the erosion and migration of fine particles on the slope and that the maximum migrated fine particles volume fraction and the maximum porosity increase with the water level. The values of the strength reduction factor for the creeping state decrease as the water level rises. Furthermore, the larger the size of the downstream leakage outlet, the larger the maximum migrated fine particles volume fraction and maximum porosity. However, the relationship between maximum displacement and strength reduction factor is nearly unaffected by the size of the leakage outlet.

Analysis of Coupled Seepage and Temperature Fields of Fractured Porous Rock Mass under Brine–Liquid Nitrogen Freezing

The existence of fracture flow has an undesirable effect on the creation of the frozen wall. Brine and liquid nitrogen combined freezing technology can ensure the safety of freezing engineering, reduce the construction period and save cost. Considering the permeability of the rock matrix, fluid exchange and Darcy–Stokes coupling effect between the rock matrix and fracture, a thermo-hydraulic model of the fractured porous rock mass under water seepage is herein established. The interfacial seepage field characteristics of fractured rock mass under different fluid flow models and interface conditions are compared. The numerical simulations of the initial brine freezing and liquid nitrogen reinforcement freezing are carried out. The results show that the overall permeability of fractured rock mass computed by free flow considering the Darcy–Stokes effect is greater than that computed by the Cubic law. The limit seepage velocity of the intact rock mass in brine freezing is 2.5 m/d, and that of fractured rock mass decreases to 1 m/d. The fracture aperture and groundwater seepage velocity are directly proportional to the closure time of the frozen wall. Liquid nitrogen freezing can seal water quickly and shorten the closure time of the frozen wall when the seepage velocity of the fractured rock mass is greater than the limit seepage velocity, and the rapid cooling of the upstream region plays an important role in the formation of the frozen wall in fractured rock mass.

Face failure analysis of a shield tunnel with slurry penetration into the ground

This paper focuses on the face stability analysis of a tunnel driven by a slurry shield machine in the water-bearing ground. A multifield model coupling seepage flow and face stability of the tunnel is developed. The slurry-soil interaction in the ground is considered as a multiphase flow process in porous media. The kinematic approach of limit analysis is used to assess the tunnel face failure. The pressure transfer mechanism of the bentonite suspension is time-dependent and shows good agreement with the field measurement. This model allows the consideration of the slurry support efficiency and its influence on the failure shape through the discretization technique. The results obtained indicate that the support effectiveness decreases with the slurry penetration into the ground, and the traditional membrane model leads to an overestimation of the face stability. Several charts are provided for parametric analysis to discuss the influence of the hydrogeological and slurry properties.

Mathematical Model and Numerical Simulation of Coalbed Methane Migration Considering the Adsorption Expansion Effect

The influence of gas adsorption and desorption on the volumetric strain of coal was measured by a self-designed, fluid–solid coupling triaxial coal adsorption deformation experimental system. The experimental results show that coal deformation has a threshold value with an increase in gas content. Before the gas content reaches the threshold value, coal deformation is not obvious. When the gas content reaches the threshold value, the deformation will increase sharply. At the same time, coal volume strain changes with coal gas content in accordance with exponential law ε = ε0(eϒc-1). Based on the experimental results, considering the coupling effects of heat transfer, water seepage, coal and rock mass deformation, and coalbed methane desorption and seepage, a mathematical model of heat transfer–deformation–seepage coupling coalbed methane migration was established, and a numerical simulation study was carried out on the heat injection-enhanced coalbed methane mining project. The results show that (1) With continuous heat injection, the gas in the coal seam is rapidly desorbed, and the adsorbed gas content forms an elliptical funnel that extends from the extraction hole to the deep part of the coal body and takes the fracturing crack as the center to the upper and lower boundaries of the coal seam. At day 30, the adsorbed gas content in the whole drainage area has decreased to 0.1 m3/t within 2m from the fracture zone. (2) On the basis of considering the gas adsorption expansion effect, the strain of the coal body decreases from roof to floor. With the increase in the heat injection time, the strain value will also increase, and the strain increase will decrease. When the heat injection is 30 days, the maximum strain at the roof is 0.015. The research results have important guiding significance for predicting coal rock deformation and determining gas extraction efficiency in the process of heat injection-enhanced coalbed methane extraction.

True triaxial experimental study on fluid flow in single fracture with different dip angles under three-dimensional stress at different depths

The shape of ore body in deep underground engineering is complex, and its fracture development degree is affected by water abundance, fracture zone, fault and other factors. With the deepening of depth, the vertical and horizontal stress changes significantly, which has a great impact on the fracture opening. Therefore, the fracture dip angle and its three-dimensional stress state are the main factors affecting the fluid flow of fractures in a large area of ore body and its hanging and footwall rock mass. In this study, firstly, the three-dimensional fractal dimension of a single-fracture specimen was obtained by using CT (Computer Tomography) scanning technology and the single-fracture specimen with a similar three-dimensional fractal dimension was selected for testing. Then, the self-developed single fracture stress seepage coupling true triaxial test system is applied to test the seepage of single fracture samples with six different fracture dip angles under different stress states of underground depth. The experimental results show that the fluid flow and strain of fractured rock mass are comprehensively affected by the fracture dip angle and the stress state of the underground depth, and the influence degree of the fracture dip angle changes with the deepening of the underground depth. The above conclusions can be mutually verified in the aspects of stress-strain, water pressure and permeability coefficient. Furthermore, the relationship between the minimum injectable water pressure (MIWP) of fractured rock mass with different dip angles and underground depth is obtained, the expression of seepage coefficient of single fracture specimen with different dip angles and underground depth under three-dimensional stress is summarized, and the relationship between eh and em of single fracture specimen with different fracture dip angles is determined. This study provides a basic reference for the design scheme of hydraulic conductivity of fractured zone or fractured rock mass with different underground depths.

A novel approach to investigating the mechanism of permeability-induced borehole breathing in deepwater shallow formations

Due to the uniqueness of deep-water shallow formations, there is no fracture system around the wellbore when borehole breathing is observed in this part of the formation. Therefore, the inducing mechanism of the opening/closing of the fracture network cannot reasonably explain this type of borehole breathing. In this study, a new mechanism of permeability-induced is proposed to explain borehole breathing, based on the fact that there is no fracture system around the well and the formation has the characteristics of high permeability and porosity. By using the stress and seepage coupling method in the porous elastic medium, a new model is established to simulate and describe permeability-induced borehole breathing. Through comparison with actual cases, this model can effectively simulate the typical characteristics of fluid loss-flow back in borehole breathing. This study also analyzed the influence of factors such as formation parameters and mud rheological parameters on the borehole breathing caused by permeability. According to the results of the study, the use of a smaller diameter wellbore and agents that can adjust related parameters (such as loss-reducing circulating material) can effectively inhibit wellbore breathing while drilling.

Studies on Gas Seepage Characteristics in Different Stress Zones of Bottom Coal in Steeply Inclined and Extra-Thick Coal Seams under Mining Action.

The gas released from the bottom coal of the horizontal slicing mining face in steeply inclined and extra-thick coal seams seriously threatens the safety of the upper slicing mining face. To explore the seepage characteristics of bottom coal gas, the coal deformation and gas permeability evolution law of four coal samples in different stress zones of bottom coal in the working face were analyzed through true triaxial fluid–solid coupling seepage experiments. At the same time, the seepage capacity of bottom coal gas was partitioned according to the field test. The results show the following: (1) The gas permeability of the bottom coal stress concentration zone first decreased and then increased with axial pressure loading and confining pressure unloading. The gas permeability of the bottom coal stress relief zone increased rapidly with decreasing axial pressure and confining pressure. The gas permeability of the bottom coal stress recovery zone gradually decreased with the cyclic loading and unloading of axial pressure and tended to be stabilized. (2) The evolution law of gas permeability in the bottom coal was closely related to the damage and deformation of coal. (3) From the original stress zone to the stress recovery zone, the gas seepage capacity of bottom coal can be divided into four zones, namely, the original seepage zone, the seepage reduction zone, the seepage sharp increase zone, and the seepage reduction zone. The gas seepage capacity in the stress concentration zone was more substantial than that of the stress recovery zone. The results of this study are of great significance for strengthening the dynamic disaster prevention and control of bottom coal gas in the horizontal slicing mining face of steeply inclined and extra-thick coal seams.

Development and application of triaxial rock shear - self-supporting fracture conductivity experiment system

The structure and function of shear - self-supporting fracture conductivity test device in great detail were presented. This device system consists of five parts: vertical loading system, horizontal shear loading system, the servo control system, power system, shear box and its sealing system, digital control and acquisition system. It can provide vertical force up to 2000KN, shear force 500KN, lateral stress 50MPa and hydraulic pressure 40 MPa. Characteristics of the system are illustrated as follows. (1) The experimental research of rock shear failure can be performed under three axial stress conditions, the lateral stress is loaded by hydraulic oil and the vertical stress is loaded by pressing machine. (2) True triaxial and quasi-triaxial loading modes can be switched by using different sealing sleeves. (3) The shear seepage coupling and self-supporting fracture conductivity tests could be conducted under three axial stress conditions. (4) The stress and displacement loading modes under different loading rate can be realized by servo system. Based on this experimental system, shear - fracture conductivity test under three axial stress conditions was performed on shale specimen and its reliability was verified. The experimental system can be used to provide theoretical basis for the shear destruction mechanism and Self-supporting shear fracture conductivity test under true triaxial stress conditions. The research has an important guiding significance on the formation mechanism of unconventional reservoir shear fracture and the flow capacity of self-supporting shear fracture and its influencing factors.

A well test analysis model of generalized tube flow and seepage coupling

“Generalized mobility” is used to realize the unification of tube flow and seepage in form and the unification of commonly used linear and nonlinear flow laws in form, which makes it possible to use the same form of motion equations to construct unified governing equations for reservoirs of different scales in different regions. Firstly, by defining the generalized mobility under different flow conditions, the basic equation governing fluid flow in reservoir coupling generalized tube flow and seepage is established. Secondly, two typical well test analysis models for coupling tube flow and seepage flow are given, namely, pipe-shaped composite reservoir model and partially open cylindrical reservoir model. The log-log pressure draw-down type-curve of composite pipe-shaped reservoir model can show characteristics of two sets of linear flow. The log-log pressure drawdown plot of partially opened cylindrical reservoir model can show the characteristics of spherical flow and linear flow, as well as spherical flow and radial flow. The pressure build-up derivative curves of the two models basically coincide with their respective pressure drawdown derivative curves in the early stage, pulling down features in the late stage, and the shorter the production time is, the earlier the pulling down feature appears. Finally, the practicability and reliability of the models presented in this paper are verified by three application examples.

Rock mechanics and wellbore stability of deep shale during drilling and completion processes

The seepage coupling effect between the borehole rock mass and borehole fluid and the effective stress field distribution around the wellbore are obviously different under different working conditions of drilling, fracturing and completion, which affect the stability of horizontal borehole of shale gas reservoir. The physical, chemical, and mechanical properties of the shale in Longmaxi formations in a block of China immersed with different working fluids were tested experimentally. Combined with the experimental data, a theoretical model was established to evaluate and analyze the wellbore stability of Longmaxi formations shale under different working conditions of drilling, fracturing and completion. The results show that the shale of the Longmaxi Formation is a typical hard and brittle shale, the bedrock is dense, with high mechanical strength and weak hydration and expansion ability. The immersion effect of different working fluids has little influence on the expansion and mechanical properties of shale bedrock. However, the mechanical strength of shale with relatively developed bedding fractures is low, and the immersion effect of different drilling fluid further weakens the mechanical strength, resulting in obvious anisotropy of mechanical strength of underground rock. The coupling effect of seepage between wellbore and formation has obvious influence on the dynamic distribution of borehole pore pressure and wellbore stability under different working conditions. The effective fluid column pressure at the bottom of the hole is the highest during the fracturing process, which leads to the increase of pore pressure near the wellbore, and then to the increase of collapse pressure around the borehole wall. The equivalent density of collapse pressure rises to the maximum of 1.93 g/cm3, and the wellbore stability is the worst in the fracturing process. The wellbore stability is secondary in the drilling process, and the wellbore stability is good when drilling along the direction of the maximum horizontal principal stress, and the equivalent density of collapse pressure is 1.69 g/cm3. During the completion process, the formation fluid flows into the wellbore, the pore pressure in the borehole is relieved, and the equivalent density of the collapse pressure is reduced to approximately 1.35 g/cm3, the wellbore stability is the best and open hole completion can be attempted in the horizontal well section. The results provide a certain theoretical reference for the selection of the drilling and completion schemes in shale formation.

Deformation control method of a large cross-section tunnel overlaid by a soft-plastic loess layer: a case study

This paper presents a case study of a large cross-section high-speed railway tunnel overlaid by a Q2 soft-plastic loess layer. Due to poor engineering properties of the soft-plastic loess, two unexpected collapses occurred. This indicates that there is great difficulty and risk during tunneling. In this paper, the deformation control methods are studied by carrying out a series of numerical simulations and then validating via field tests. The stress and seepage coupling equations are deducted to embed into a 3D fluid-mechanical coupled numerical analysis. The results show that the curtain grouting scheme can effectively control the deformation of surrounding rock, and the real field data of settlement and horizontal convergence are 152 mm and 37 mm, respectively. However, the tunneling advance rate is slow (0.6 m/day) in trial sections because of the mutual interference between construction procedures. It can be used as an alternative scheme for lager deformation. The advanced drainage scheme can lower the ground water table below the excavation outline. The average water content of soft-plastic loess decreases from 26 to 22%, and the state of surrounding rock changes from soft plastic to hard plastic. The in situ settlement and horizontal convergence are 165 mm and 51 mm, respectively. Finally, it is proposed to use advanced drainage in combination with advanced small pipe grouting as a follow-up construction scheme. The successful completion of the whole tunnel proved the effectiveness of the proposed method.

Tightness and stability evaluation of salt cavern underground storage with a new fluid–solid coupling seepage model

The effects of operating pressure and ground stress on the seepage parameters (permeability and porosity) of surrounding rock and stability and tightness of salt cavern have been investigated, and a method is proposed for safe operating pressure classification. In previous works, the analysis of stability and tightness of salt caverns were mostly carried out independently, and few studies have considered the interaction between them. However, when used as a storage space for natural gas, petroleum and brine, there are many fluid–solid coupling problems in salt cavern underground storages. To address these problems, we establish a fluid–solid coupling seepage model based on the relationships between pressure, rock deformation and seepage parameters, and apply it to actual engineering. The coupling analysis results show that the relationship between shrinkage displacement of salt cavern and operating pressure is an exponential function with negative correlation, while the relationship between seepage range of a salt cavern and the operating pressure is a power function with positive correlation. Therefore, the effects of operating pressure on the stability and tightness of salt caverns are diametrically opposite. The seepage range of gas in surrounding formations gradually increases with time, and eventually tends to become stable. Under an operating pressure of 12 MPa and after operating for 30 years, the maximum seepage range and shrinkage displacement of the studied salt cavern are 99.72 m and 1.86 m, respectively. Hence the stability and tightness of this salt cavern meet the requirements of the regulations in China, and a gas leakage accident will not occur in this storage during operation. The seepage parameters of the surrounding formation increase with operating time of gas storage, and the increase in permeability is larger than that of porosity. The research results can provide reference and guidance for safe operation and parameter design of salt cavern underground storage.

Study on the Proportion of Conglomerate Similar Materials Based on the Orthogonal Test

Similarity model test is one of the important methods to study the properties of rock engineering. In this paper, quartz sand, 42.5 ordinary Portland cement, and tap water are used as the similar test materials to simulate the properties of conglomerate. The three control factors are cement‐to‐water ratio, cement‐to‐sand ratio, and quartz sand particle size, and orthogonal tests are set at four levels. The permeability coefficient, compressive strength, elastic modulus, density, and Poisson’s ratio are tested on specimens of similar materials of conglomerate, and the corresponding physical and mechanical indexes are obtained. The range analysis method is used to analyse the influence of various factors on the mechanical properties. The results show that (1) the physical and mechanical parameters of similar materials have a certain degree of dispersion under different proportions; (2) the proportion of similar conglomerate materials is cement : sand : water : water reducer = 1 : 2 : 0.4 : 0.6%; and (3) multiple linear regression analysis is carried out on the control factors and mechanical parameters to obtain the regression equation of the proportion of similar materials, which proves that the equation could be used to make the study of conglomerate similar materials under the stress coupling of seepage.

Coupled Hydraulic-Thermal Modelling and Related Numerical Analysis on Rock Fractures

Hydraulic-thermal coupling is a key problem in rock mass engineering, especially in the disposal of nuclear wastes in deep rock mass. To accurately describe the coupling action of rock mass when under the interaction of hydraulic stress and thermal, the hydraulic-thermal coupling solving methods were proposed in this paper; in addition, the corresponding hydraulic-thermal coupling program FRHT3D was complied. Consequently, the numerical simulation was performed, it can be concluded that the flow speed is faster when the coupling effect is considered at the unstable seepage stage, and the seepage coupling solution is larger than that of uncoupling. Furthermore, when the coupling effects are considered, the permeable water head solution is much larger than that of the uncoupling solution at the unstable seepage stage. The proposed hydraulic-thermal coupling solving methods and programs can be applied to rock mass engineering practice.

Gas Flow Characteristics and Optimization of Gas Drainage Borehole Layout in Protective Coal Seam Mining: A Case Study from the Shaqu Coal Mine, Shanxi Province, China

With increasing demands for coal resources, coal has been gradually mined in deep coal seams. Due to high gas content, pressure and in situ stress, deep coal seams show great risks of coal and gas outburst. Protective coal seam mining, as a safe and effective method for gas control, has been widely used in major coal-producing countries in the world. However, at present, the relevant problems, such as gas seepage characteristics and optimization of gas drainage borehole layout in protective coal seam mining have been rarely studied. Firstly, by combining with formulas for measuring and testing permeability of coal and rock mass in different stress regimes and failure modes in the laboratory, this study investigated stress–seepage coupling laws by using built-in language Fish of numerical simulation software FLAC3D. In addition, this research analyzed distribution characteristics of permeability in a protected coal seam in the process of protective coal seam mining. Secondly, the protected coal seam was divided into a zone with initial permeability, a zone with decreasing permeability, and permeability increasing zones 1 and 2 according to the changes of permeability. In these zones, permeability rises the most in the permeability increasing zone 2. Moreover, by taking Shaqu Coal Mine, Shanxi Province, China as an example, layout of gas drainage boreholes in the protected coal seam was optimized based on the above permeability-based zoning. Finally, numerical simulation and field application showed that gas drainage volume and concentration rise significantly after optimizing borehole layout. Therefore, when gas is drained through boreholes crossing coal seams during the protective coal seam mining in other coal mines, optimization of borehole layout in Shaqu Coal Mine has certain reference values.