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The stress change of coal body around the gas drainage borehole is one of the important factors affecting its permeability. In order to study the permeability with different degrees of fragmentation around the gas drainage boreholes, some coal particle composite samples with different range of particle diameter were prepared by the method of continuous grading, and the triaxial permeability tests with different Talbol power exponent n were carried out to analyze the influence of the effective stress on the internal structure and permeability characteristics of the fragmented coal samples. The results show that during the loading process, the axial pressure affects the permeability by changing the porosity of the broken coal, which decreases exponentially with the increase of the axial pressure. At the early stage of loading, the increase of axial pressure makes the volume of coal sample compressed, and the internal voids are closed, which causes the decrease of porosity and the weakening of permeability, resulting in the decrease of permeability. When the axial pressure is loaded with the porosity tends to 0.1, the internal compact structure of the coal sample makes a stable permeability. In the process of increasing the Talbol power exponent n of broken coal from 0.1 to 1.0, the permeability k shows three growth periods that are slow, linear and exponential stages, which are affected by the low-grade size particle, ratio of particle size and high-grade size particle respectively. The velocity of permeate is affected by the Talbol power exponent, pressure gradient, confining and axial pressure, however, the effect of pressure gradient is more significant. The larger the Talbol power exponent and pressure gradient with the smaller the confining pressure and axial pressure are, the larger the velocity of permeate is. There are the Talbol power exponent promotion effect of permeate velocity and the axial pressure and confining pressure inhibition effect of permeate velocity. The effective stress can characterize the inhibition effect of permeate velocity caused by the axial and confining pressure very well. The permeability of broken coal with different Talbol power exponents generally decays exponentially with the increase of effective stress, but the promotion effect of the Talbol power exponent on permeability gradually weakens, while the inhibition and amplitude effect of the effective stress on permeability gradually strengthen. The parameter change of the equation between the effective stress and permeability has three stages corresponding to the permeability curve. With the increase of the Talbol power exponent n, the parameter a of the equation decreases gradually, and the inhibition effect of the effective stress increases, while the increase of b, and the amplitude effect is gradually strengthened.

The coordinated arrangement of gas pre-drainage boreholes and anti-impact and pressure relief boreholes can integrate the prevention and control of mine rock burst and gas compound disasters. However, the dense arrangement of these boreholes may lead to the occurrence of phenomena such as string holes and collapse holes, which could potentially impact the efficiency of mine gas extraction. To investigate the deformation around borehole surface and the evolution of fractures during the compression failure process in the coal and rock masses with dual borehole structure, the 3D-DIC observation experiment was conducted on the coal samples containing double circular holes under uniaxial compression conditions using a digital image observation system for coal rock deformation and failure. This experiment yielded some time-series images of sample surface deformation under various stress states. The three-dimensional full-field deformation of the sample surface was calculated using the three-dimensional surface reconstruction technology and VIC3D analysis processing software. Based on the results of strain field analysis, the stress-strain curve was divided into five deformation stages using statistical index analysis methods, providing a detailed description of the deformation and fracture evolution characteristics around the borehole surface. The results show that under uniaxial compression, the grayscale of strain field in the coal samples with double circular holes shifts toward higher gray levels. The proportion of peaks in the strain field gray histogram changes slowly at first and then rapidly, with the peak stress serving as the boundary. The radial displacement curve around the sample holes presents a “从” shape, while the circumferential displacement curve presents a “人” shape. The left hole H1 always accelerates counterclockwise, while the right hole H2 always accelerates clockwise. The fractures around the holes are primarily characterized by counterclockwise dislocation, accompanied by a few instances of clockwise dislocation. The outer zone of strain localization primarily exhibits energy accumulation before the loading peak and energy release after the loading peak. This is accompanied by energy accumulation resulting from partial energy adjustment and transfer. During the loading process of the specimen, the factors such as the stress field environment, the geometry of fracture end, and the length of fracture undergo constant changes. This results in a reduction in the stress intensity factor KⅠ at the tip of the fracture, thereby impeding the expansion of the fracture.

The radial gas seepage flow regime of the coal body around borehole is one of important factors reflecting the seepage movement of extracted gas. In order to investigate the effects of different pore structures and gas pressure on the radial seepage motion of gas in the perimeter of borehole, five kinds of pore-bearing coal samples with different gradations were made, and the radial seepage test was carried out on the pore-bearing coal samples by using the self-designed gas radial seepage test system and the steady-state seepage method to analyze the changes of the Forchheimer number and non-Darcy error with the seepage velocity and gradation, and the flow velocity intervals and the Reynolds number ranges of different flow regimes were obtained by using the Hazen-Dupuit-Darcy equation and the Reynolds number theory. The results show that: ① Through the analysis of the Forchheimer number and non-Darcy error with the change curve of seepage velocity, the Forchheimer number increases with seepage velocity in a quadratic polynomial curve, while non-Darcy error increases linearly, the Forchheimer number and non-Darcy error are closely related to pore structure, and both become larger with the increase of gradation, indicating that seepage velocity and pore structure of the coal body around the pore are important factors for gas seepage deviating from linear seepage; ② The Hazen-Dupuit-Darcy equation was used to characterize and delineate the gas radial permeability flow regime. With the increase of seepage velocity, the gas radial seepage motion appears in order of pre-Darcy, Darcy and Forchheimer flow regimes. The small-graded porous specimens with n=0.2 and n=0.4 are more prone to the Darcy laminar flow, while the porous samples with n=0.6, n=0.8 and n=1.0 are more prone to the Forchheimer flow regime; ③ Through the analysis of the relative error curve of pressure gradient when Darcy’s law was applied, the relative error with the increase of seepage velocity shows the change law of decreasing, keeping stable, and then increasing, which is consistent with the change law of gas seepage flow pattern with seepage velocity; ④ In double logarithmic coordinates, the relationship between different flow regimes of gas seepage and Reynolds number was analyzed, and the Reynolds number intervals of different flow regimes were derived, and it was found that the radial seepage motion of gas conforms to the Reynolds number range of 0.0012～0.0025 for Darcy laminar flow. The results of the study can provide an important theoretical basis for the design of drilling parameters by determining the influence range of drilling extraction based on the flow regime of coal seepage movement around the borehole in coal seam gas pre-drainage work.

Abstract Faithful inheritance of parental histones is essential to maintain epigenetic information and cellular identity during cell division. Parental histones are evenly deposited onto the replicating DNA of sister chromatids in a process dependent on the MCM2 subunit of DNA helicase. However, the impact of aberrant parental histone partition on human disease such as cancer is largely unknown. In this study, we construct a model of impaired histone inheritance by introducing MCM2-2A mutation (defective in parental histone binding) in MCF-7 breast cancer cells. The resulting impaired histone inheritance reprograms the histone modification landscapes of progeny cells, especially the repressive histone mark H3K27me3. Lower H3K27me3 levels derepress the expression of genes associated with development, cell proliferation, and epithelial to mesenchymal transition. These epigenetic changes confer fitness advantages to some newly emerged subclones and consequently promote tumor growth and metastasis after orthotopic implantation. In summary, our results indicate that impaired inheritance of parental histones can drive tumor progression.

CO2 blasting has been identified as a potent method for enhancing the permeability of coal seams and improving gas drainage efficiency. This study is focused on elucidating the deformation and fracture mechanisms of coal and rock during CO2 blasting and on identifying the precursor characteristics of these processes. To this end, a CO2 blasting-induced coal rock fracture pressure model and a gas pressure distribution model were developed. The research utilized a self-developed CO2 blasting test platform along with a non-contact full-strain field measurement analysis system. Briquette samples were subjected to CO2 blasting tests under controlled experimental conditions, which included an axial pressure of 1.0 MPa and variable gas pressures of 0.5, 1.0, and 1.5 MPa. This methodology enabled the capture of the principal strain field on the surface of the samples. The Gray Level Co-occurrence Matrix (GLCM) was employed to extract and analyze the grayscale and texture features of the strain cloud maps, facilitating a quantitative assessment of their evolution. The aim was to pinpoint the precursor characteristics associated with coal rock cracking and crack propagation. The results revealed that: (1) During the cracking and subsequent propagation of samples, the strain field's grayscale histogram underwent a transformation from a "broad and low" to a "narrow and high" configuration, with a consistent increase in peak frequency. Specifically, at 3 ms, a primary crack was observed in the sample, evidenced by a grayscale peak frequency of 0.0846. By 9 ms, as the crack propagated, the grayscale peak frequency escalated to 0.1626. (2) The texture feature parameters experienced their initial abrupt change at 3ms. Correlation with the gas pressure distribution model indicated that this was the crack initiation moment in the sample. (3) A secondary abrupt shift in the texture feature parameters occurred at 9ms, in conjunction with experimental phenomena, was identified as the crack propagation phase. Monitoring the grayscale and texture features of the principal strain field on the coal rock surface proved effective in recognizing the precursor characteristics of crack initiation and propagation. This research has the potential to reduce blasting costs in coal mines, optimize blasting effects, and provided theoretical guidance for enhancing gas extraction efficiency from deep and low permeability coal seams.

Abstract Particle loss is an important cause of water inrush catastrophes in collapsed columns. In order to study the relationship between the lost particles of different graded rock samples and the pore structure of the subsidence column filling, experiments were designed and the changes of the seepage parameters of graded rock samples during the particle migration process under different permeable water pressures P and axial loads F were determined. The results show that: (1) There will be obvious collapse, silting and particle loss behaviors in the sample during different loading processes, and the rock samples with gradation values of n = 0.3 and n = 0.5 are dominant; (2) The relationship between porosity φ and bearing pressure The exponential function can be used to fit the loads F well, and the porosity decreases with the increase of the bearing load. The water surging characteristics before and after 1.2 MPa are mainly in the turbulent water gushing stage, accompanied by instantaneous slurry. Possibility of splashing and indenter sliding; (3) After infiltration, the condition of the remaining skeleton rock samples in the cylinder generally shows a trend of first decreasing rapidly, then increasing slowly, and then decreasing; (4) The gradation value n of the sample and the bottom There is a good correlation between the damaged area and the mean value S of the maximum area of the top water inrush channel. The maximum area increase of the damaged area and the maximum area increase of the water inrush channel show an opposite trend. The permeable pores of the graded samples can be divided into There are three situations of digging and collapse, water inrush gap and scouring hole, and the pore seepage process can be divided into 4 stages of inoculation of water seepage, rapid adjustment, rapid scour and steady flow.

The ultrasonic characteristics of the coal and rock bodies around boreholes during failure are closely related to the crack propagation law. To investigate the ultrasonic characteristics and crack propagation law of coal and rock bodies around boreholes, different grouting samples with boreholes were taken to carry out ultrasonic test during progressive failure. The ultrasonic amplitude, velocity and attenuation coefficient of the samples were analyzed. According to the ultrasonic time difference formula, the equivalent crack width of the sample during the failure process is calculated. The influence of grouting material on the crack propagation law is quantitatively analyzed. The results show that: (1) The peak stress, elastic energy at the peak, ultrasonic parameters and crack propagation of the coal and rock bodies around boreholes show obvious differences influenced by the strength of the grouting material. (2) During the loading process, the arrival time of the first wave of the sample with holes is 5μs later than that of the grouting sample, and the ultrasonic energy attenuates fastest in the time domain, and the coda wave is not developed. (3) During the progressive failure, the ultrasonic velocity and attenuation coefficient of all show three stages of stability(0~0.6σp), slow change(0.6σp~0.8σp) and rapid change(0.8σp~1.0σp). According to the "sudden decrease" of velocity and the "sudden increase" of attenuation coefficient to judge the crack propagation of sample. (4) The equivalent crack width of the sample increases exponentially with the increase of stress level. At the time of reaching the peak stress, the equivalent crack width of SH-BH increases about 0.027mm~0.032mm, SH-PU about 0.01mm~0.014mm, and SH-CEM about 0.002mm~0.006mm.

The creep process of the coal rock around the extraction boreholes under stress-water coupling is an important factor affecting the stability of the boreholes. To study the influence of the water content of perimeter of the coal rock around the boreholes on its creep damage, a creep intrinsic model considering water damage was established by introducing the plastic element model from the Nishihara model. To study the steady-state strain and damage evolution of coal rocks containing pores, and verify the practicality of the model, a graded loading water-bearing creep test was designed to explore the role of different water-bearing conditions in the creep process. The following conclusions were obtained: 1) water has a physical erosion and softening water wedge effect on the perimeter of the coal rock around the boreholes, which affects the loading axial strain and displacement of the perforated specimens; 2) an increase in water content reduces the time taken for perforated specimens to enter the creep phase, making the accelerated creep phase come earlier; 3) the parameters of the water damage model are considered to be exponentially related with the water content. The experimental data are similar to the results of the model parameters, and the model shows some practicality; 4) the damage variables in the accelerated creep phase increase rapidly throughout the creep process, leading to local instability in the borehole. The findings of the study provide important theoretical implications for the study of instability in gas extraction boreholes.

Abstract Accurate determination of the permeability of crushed coal medium is the basis for the study of their permeability characteristics. To investigate the permeability characteristics of this special porous medium composed of crushed coal particles, the permeability parameters of crushed coal specimens of different initial porosities were measured by designing a lateral-limit compression seepage test system. Parameters were determined separately for specimens of different initial porosities. (1) the Reynolds number distribution region characterising the seepage state was determined and obtained. Specimens with initial porosity distribution between 0.02 and 0.08, and seepage Reynolds number distribution in the low-permeability zone, under Darcy flow; (2) the intrinsic permeability of the crushed coal medium was obtained by using the Ergun equation. The complex inverse proportional relationship between the drag coefficient and Reynolds number was derived; (3) Through the determination of the permeability of the crushed coal medium, the mean value of βK value was obtained to be about 45.7, and the analysis of the permeability of porous medium can determine its critical permeability. The relationship between the Forchheimer number Fo and critical Reynolds number was measured. The results indicate that it conforms to a linear distribution. In-depth analysis of these two parameters can be used to explore the flow transition process between laminar, transition, and turbulent flow. This study provides insight into the permeability characteristics of the media in fractured coal bodies.

Abstract The evaluation of the coal mine gas drainage effect is affected by many factors, such as flow rate, wind speed, drainage negative pressure, concentration, and temperature. This paper starts from actual coal mine production monitoring data and based on the lasso regression algorithm, features selection of multiple parameters of the preprocessed gas concentration time series to construct gas concentration feature selection based on the algorithm. The three-time smoothing index method is used to fill in the missing values. Aiming at the problem of different dimensions in the gas concentration time series, the MinMaxScaler method is used to normalize the data. The lasso regression algorithm is used to perform feature selection on the multivariable gas concentration time series, and the gas concentration time series selected by the lasso feature and the gas concentration time series without feature selection are input. The performance of the ANN algorithm for gas concentration prediction is compared and analyzed. The optimal α value and L1 norm are selected based on the grid search method to determine the strong explanatory gas concentration time series feature set of the working face, and an experimental comparison of the gas concentration prediction results before and after the lasso feature selection is performed. We verify the effectiveness of the algorithm.

To investigate the permeability characteristics in the in-situ fractured coal body around the perimeter of gas extraction boreholes, the steady-state permeability of fractured coal bodies with different gradations was tested using the fractured rock permeability test system. By controlling the axial displacement and permeability pressure, the permeability parameters were obtained under different porosities. The interactions between the permeability parameters and the process of permeability destabilisation are discussed. The results show that the permeability characteristics of the broken coal body obey the Forchheimer relationship: As the axial displacement increases, the permeability resistance of the fluid increases and the non-Darcy property of the sample becomes more significant. With the decrease in the porosity of the sample and the increase in the power index n, the permeability k decreases and the non-Darcy factor β increases. The final fractal structure of the sample will be changed by particle fragmentation and migration during the loading process of the sample with different levels, and the internal pore structure of the sample will further affect the penetration of the penetration channel. A critical characteristic value for the seepage instability in broken coal bodies is given, and an expression for determining the seepage instability by permeability and non-Darcy factors is proposed. The results indicate that a negative non-Darcy factor is not a necessary condition for permeability instability, and the critical Reynolds number for the permeability instability in broken coal bodies was determined from the perspective of the Reynolds number. The conclusions of this study can provide theoretical support for the theoretical study of permeability and the permeability of pre-smoking coal seams.

Abstract The initiation process of the mine water inrush accident, the essence of this process is the sudden change of the seepage state of the broken coal medium under pressure and the instability of the skeleton. In order to study the re-crushing mechanism and seepage characteristics of the broken coal medium under load, a set of three-axis seepage system was designed independently. Using the steady-state infiltration method, multiple flow factors under different particle size combinations and different stress conditions of the broken coal medium were obtained. The results of the study indicate: in one hand, the reduction of the porosity of the broken coal medium will cause the flow channel to be rebuilt, and the sudden change of flow rate will directly lead to the non-Darcian flow behavior. The early stage of compaction mainly affects the permeability k value, and the later stage of compaction mainly affects the non-Darcian β value; On the other hand, the seepage throat in the broken coal medium may have a sharp increase in its flow rate, leading to a sudden change in the flow pattern. The critical Reynolds number is also used to determine whether non-Darcian flow is formed, and its value in the water inrush system is about 40–133; at the same time, the non-Darcian flow in the broken coal medium conforms to the Forchheimer-type flow law. By analyzing the dependence relationship between factors, a seepage factor representation algebraic relationship suitable for Forchheimer type non-Darcian flow of broken coal medium is given, which can be used as a calculation basis in the prevention and treatment of mine water inrush accidents.

The permeability of crushed coal bodies plays a bottom neck role in seepage processes, which significantly limits the coal resource utilisation. To study the permeability of crushed coal bodies under pressure, the particle size distribution of crushed coal body grains is quantitatively considered by fractal theory. In addition, the parameters of the percolation characteristics of crushed coal body grains are calculated. Moreover, the permeability of the crushed coal body during recrushing is determined by the fractal dimension and porosity. A lateral limit compression test with the crushed coal bodies was carried out to illustrate the effect of the porosity on the permeability, In addition, a compressive crushed coal body size fractal–permeability model was proposed by combination of the fractal dimension and the non-Darcy equivalent permeability. The results show (1) the migration and loss of fine particles lead to a rapid increase in the porosity of the crushed coal body. (2) Increases in the effective stress cause the porosity and permeability to decrease. When the porosity decreases to approximately 0.375, its effect is undermined. (3) The migration and loss of fine particles change the pore structure and enhance the permeability properties of the skeleton, causing sudden seepage changes. (4) At low porosity, the permeability k is slightly larger than the non-Darcy equivalent permeability ke. Thus, the experimental data show an acceptable agreement with the present model. A particle size fractal–percolation model for crushed coal bodies under pressure provides a solution for effectively determining the grain permeability of the crushed coal bodies. The research results can contribute to the formation of more fractal-seepage theoretical models in fractured lithosphere, karst column pillars and coal goaf, and provide theoretical guidance for mine water disaster prevention.

Abstract CO2 presplitting blasting is an effective method to increase coal seams permeability and improve gas drainage efficiency. During the blasting process, the empty holes in the coal and rock mass have a significant effect on crack growth. In the experiment, a sample containing empty holes was used for CO2 presplitting blasting. The VIC‐3D was used to observe the change in the surface displacement of the sample; and the amplitude of the wave during the blasting process was collected using ultrasonic waves. Here, we calculated the attenuation coefficient α, analyzed the internal crack damage of the coal and rock mass, and compared the LS‐DYNA simulation results to analyze the empty hole effect on the crack growth of the coal and rock mass. The results show that: (a) radial tensile stress is generated due to the superposition of compression waves and reflected waves during blasting, resulting in an approximately straight main crack channel between the blast hole and the empty hole; (b) When both the stress and the attenuation coefficient reach their peaks, a main crack is formed and the most severe damage occurs inside the coal and rock mass; (c) the main crack channel was formed at 0.13 seconds, and the energy consumption reached the peak at 0.18 seconds, the negative linear correlation between energy and stress was obtained. Therefore, the empty hole effect provides a good guide for the crack propagation of the coal and rock mass and provides a new experimental scheme for increasing the permeability of coal seams.

In order to investigate the compaction and re-crushing characteristics of crushed coal gangue with different gradation, the compaction fractal test was carried out for crushed coal gangue with different Talbol power index n. The compaction deformation parameters such as displacement, stress-strain were analyzed according to the test results. And according to the test results, the compaction deformation relationship of the lateral limit crushed coal rock body considering the gradation is obtained. The test results show that: the crushing of coal rock particles exists in almost the whole compaction process of the crushed coal rock body, and the crushing of coal rock particles has a non-negligible influence on the deformation of the whole crushed rock body; the structural stability of large-size coal rock particles is not as good as that of small-size coal rock particles, and the large-size coal rock is more likely to be crushed under the same stress conditions; the distribution coefficient r of the crushed coal rock body decreases with the increase of axial stress; and before the Before the axial stress reaches 8 MPa, the distribution coefficient r of crushed rock samples tends to increase with n in general, and after reaching 8 MPa and later, the distribution coefficient r of crushed rock samples tends to decrease with n in general; the difference value of particle crushing increases with the increase of axial stress, and the weight value of particle crushing decreases with the increase of axial stress, and the changes of both are non-linear; according to the stress recovery in the compaction process of crushed coal rock body The compaction deformation model of the crushed coal rock body is constructed according to the crushing characteristics of coal rock particles in the stage of compaction, which effectively combines its fine action mechanism with macroscopic physical phenomena in a simple form and has certain practical engineering significance.

The compaction and re-crushing characteristics of crushed gangue are important factors which affect the quality and effectiveness of the filling of the quarry. To study the compaction and re-crushing characteristics of the gangue particles, continuous grading and intermittent grading of two different structures were designed to study the bulk gangue particle size distribution. By conducting a side-limited uniaxial compression test on the crushed gangue, the compaction deformation parameters and particle re-crushing parameters of the samples under different axial pressure and grading conditions were calculated, the interaction between compaction and re-crushing was determined, and a compaction-re-crushing model of the crushed gangue was established. The following conclusions were obtained, (1) the axial displacement increment and fractal dimension of the graded crushed gangue are closely related to the graded structure of the skeletal particles; (2) the compaction stage of the graded crushed gangue can be divided into a fast compaction stage, a slow compaction stage, and a stable compaction stage—the fast compaction stage is significantly elastic, the slow compaction stage is more plastic, and the stable stage behavior approaches that of the original rock body; (3) the degree of crushing of the graded crushed gangue increases with an increase in axial stress, and the re-crushing of the specimen mainly occurs in the slow compaction stage; (4) the compaction-crushing-fractal evolution of the graded crushed gangue in the lateral limit compression process is established as the line of questioning. The physical significance of the parameters in the equation is discussed in this paper. The study can provide theoretical support and engineering guidance for the precise filling of a quarry and the prevention of later collapse.

Exploring the evolution characteristics of gas seepage between boreholes during the drainage process is critical for the borehole’s layout and high-efficiency gas drainage. Based on the dual-porous medium assumption and considering the effect of stress redistribution on coal seam gas seepage characteristics, a coal seam gas seepage model with a three-dimensional roadway and borehole crossing structure has been established and numerically calculated, concluding that the coal seam is between the drainage boreholes. The temporal and spatial evolution characteristics of gas pressure and permeability help elucidate the gas seepage law of the nearly flat coal seam associated with the deep soft rock roadway and borehole intersection model. The results indicate that: (1) The roadway excavation results in localized stress in some areas of the surrounding rock, reducing the strength of the coal body, increasing the expansion stress, and increasing the adsorption of gas by the coal body. (2) Along the direction of the coal seam, the permeability decreases initially and then increases. The gas pressure in the coal seam area in the middle of the borehole is higher than the pressure in the coal seam around the borehole, and the expansion stress and deformation increase, reducing the permeability of the coal body; when near the next borehole, the greater the negative pressure, the faster the desorption of the gas attracts the matrix shrinkage effect and causes the coal seam permeability rate to keep increasing. (3) The improvement of gas drainage with the overlapping arrangement of two boreholes firstly increases and then decreases as time goes on. (4) When the field test results and numerical simulation of the effective area of gas extraction are compared, the effectiveness of the model is verified. Taking the change of the porosity and the permeability into the model, it is able to calculate the radius of gas drainage more accurately.

The accurate determination of permeability is one of the parameters essential for the study of fluid flow and transport state. However, a large number of fractured coal bodies are faced during the production of coal mines. The study of permeability of these special media composed of grains of a certain size, whose structure is different from that of raw coal, has been in the exploratory stage. In this paper, inspired by the calculation method of median particle size and the calculation principle of KC's equation, we calculate the permeability parameters of broken coal particles. It is considered that its permeability is closely related to the compaction and re-crushing process of skeletal grains. The lateral limit compression test of the crushed coal body was designed, and the pore-dominated permeability calculation method was given to reveal the mechanism of the action of the effective stress. The dependence relationship between the effective stress and the pore-correlation permeability is obtained by data analysis, and the force and deformation process of the crushed coal grain media is described. In contrast to the conventional Darcy series of permeability discussions, our approach excludes the influence of fluid factors on the permeability of porous media. The permeability of porous media is considered to be determined only by its own pore structure.

Stress is one of the main factors influencing coal and gas outbursts. The apparent effects of the crustal stress, the structural stress, and the mining-induced stress increase as the depth of mining increases. At present, there have been few studies of the relationship between the comprehensive analyses of the crustal stress, mining-induced stress, and coal gas. The in situ measurement of the relationship between stress-related behaviors and coal gas under the influence of mining was conducted through experimental analysis of surrounding rock support and coal and gas outburst control and optimization of surrounding rock support materials and system construction. The results showed that the mining-induced stress first increased to a peak value, then gradually decreased, and tended to stabilize as the footage progresses. Stress appears at 96 m ahead due to mining; after 57 m of advancing, there is a large increase until it passes through this area. The stress in front of the working face increases linearly, and the increase range is obviously larger than that of the coal body in a certain range on both sides. The support anchoring force gradually decreased and tended to be stable after rapidly increasing to a maximum value. The deep displacement of the roof increased linearly and tended to be stable after reaching an accumulated displacement which can reach 16-28 mm. The residual gas pressure in front of mining operations decreased rapidly, and beyond 15 m on each side of the roadway, it decreased significantly. The residual gas pressure and gas content were consistent with the gas desorption index of drill cuttings due to the influences of gas predrainage and mining. The stress along the direction of the roadway and the residual gas content, the residual gas pressure, and the gas desorption index of drill cuttings conform to the logarithmic functional relationship. The research results provide a basis for the comprehensive prevention and control of coal and gas outbursts from multiple angles considering stress, coal, and gas.

The karst collapse pillar (KCP) is a common geological structure in the coal mines of northern China. KCPs contain many fractured coal rocks, which can easily migrate under the action of high-pressure water. The destruction or instability of the cementation structure between the rocks can directly induce coalmine water-inrush accidents. To study the seepage stability of cemented and fractured coal rock under triaxial pressures, a self-designed triaxial seepage testing system was used and the permeability k and non-Darcy factor β of the cemented and fractured coal rock were tested. Furthermore, the 1D non-Darcy seepage equations were used to calculate the evolution criteria of the seepage loss stability. The results show the following: (1) The cemented structure in the KCP under the triaxial pressures can be easily destroyed. The damaged coal and rock body mainly exists in bulk form, and the permeability depends mainly on the effective stress of the particles. (2) The seepage process in the KCP structure is a combination of pore flow, fracture flow, and pipe flow, and the transition of the seepage state is closely related to the change in the magnitude of β. (3) Under the long-term effect of confined underground water, the migration of small fractured particles in the KCP will increase the structural porosity. If the parameter βk2 reaches the threshold value, the seepage system will evolve into a pipeline flow state, eventually causing a water-inrush accident.

Abstract Taking advantage of the synergetic effect of confined ultrasmall metal clusters and zeolite frameworks is an efficient strategy for improving the catalytic performance of metal nanocatalysts. Herein, it is demonstrated that the synergetic effect of ultrasmall ruthenium (Ru) clusters and intrinsic Brønsted acidity of zeolite frameworks can significantly promote the hydrogen generation of ammonia borane (AB) hydrolysis. Ultrasmall Ru clusters are embedded onto the silicoaluminophosphate SAPO‐34 (CHA) and various aluminosilicate zeolites (MFI, *BEA, and FAU) with tunable acidities by a facile incipient wetness impregnation method. Evidenced by high‐resolution scanning transmission electron microscopy, the sub‐nanometric Ru clusters are uniformly distributed throughout the zeolite crystals. The X‐ray absorption spectroscopy measurements reveal the existence of Ru‐H species between Ru clusters and adjacent Brønsted acid sites of zeolites, which could synergistically activate AB and water molecules, significantly enhancing the hydrogen evolution rate of AB hydrolysis. Notably, the Ru/SAPO‐34‐0.8Si (Si/Al = 0.8) and Ru/FAU (Si/Al = 30) catalysts with strong acidities afford high turnover frequency values up to 490 and 627 min−1, respectively. These values are more than a 13‐fold enhancement than that of the commercial Ru/C catalyst, and among the top level over other heterogeneous catalysts tested under similar conditions.

Water content is an important factor in the deformation-destruction process of coal bodies. To analyze the influence of water on the creep acoustic emission (AE) characteristics of coal rock surrounding a borehole, we conducted graded loading creep AE tests of single-hole specimens with different water contents (0%, 4%, 8% and water-saturation) under uniaxial loading. The findings include the following: the water content affects the creep mechanical properties of the coal body around a borehole. The creep transient strain and steady-state strain increased exponentially with rising water content; the saturated specimen showed the highest increase, reaching 44.5% and 28.6%, respectively. The specimen water content affected the cumulative ringing count (CRC) and the axial strain during creep. The axial strain increased with rising water content, the CRC increased linearly with rising axial strain. The higher the water content, the greater the CRC rise. At different stress levels, the CRC in the 4%, 8% and saturated water content specimens changed by 43%, 53% and 74%, respectively. The AE ringing rate showed a pattern of grow–decline–stabilize at each creep stage. The AEs decreased significantly with the rising water content and the creep curve lagged behind the AE data. This paper provides guidelines for gas extraction, borehole maintenance and AE detection.

The effective prediction of gas concentration and the reasonable formulation of corresponding safety measures have important significance for improving the level of coal mine safety. To improve the accuracy of gas concentration prediction and enhance the applicability of the models, this paper starts with actual coal mine production monitoring data, improves the accuracy of gas concentration prediction through multi-parameter fusion prediction, and constructs a recurrent neural network (RNN)-based multi-parameter fusion prediction of coal face gas concentration. We determined the performance evaluation index of the model’s prediction method; used the grid search method to optimize the hyperparameters of the batch size; and used the number of neurons, the learning rate, the discard ratio, the network depth, and the early stopping method to prevent overfitting. The gas concentration prediction models—based on RNN and PSO-SVR and PSO-Adam-BP neural networks—were compared and analyzed experimentally with the mean absolute percentage error (MAPE) as the performance evaluation index. The result show that using the grid search method to adjust the batch size, the number of neurons, the learning rate, the discard ratio, and the network depth can effectively find the optimal hyperparameter combination. The training error can be reduced to 0.0195. Therefore, Adam’s optimized RNN gas concentration prediction model had higher accuracy and stability than the BP neural network and SVR. During training, the mean absolute error (MAE) could be reduced to 0.0573, and the root mean squared error (RMSE) could be reduced to 0.0167; however, the MAPE could be reduced to 0.3384% during prediction. The RNN gas concentration prediction model and parameter optimization method based on Adam optimization can effectively predict gas concentration. This method shows high accuracy in the prediction of gas concentration time series and can be used as a reference model for predicting mine gas concentration.

Effective prediction of gas concentrations and reasonable development of corresponding safety measures have important guiding significance for improving coal mine safety management. In order to improve the accuracy of gas concentration prediction and enhance the applicability of the model, this paper proposes a long short-term memory (LSTM) cyclic neural network prediction method based on actual coal mine production monitoring data to select gas concentration time series with larger samples and longer time spans, including model structural design, model training, model prediction, and model optimization to implement the prediction algorithm. By using the minimum objective function as the optimization goal, the Adam optimization algorithm is used to continuously update the weight of the neural network, and the network layer and batch size are tuned to select the optimal one. The number of layers and batch size are used as parameters of the coal mine gas concentration prediction model. Finally, the optimized LSTM prediction model is called to predict the gas concentration in the next time period. The experiment proves the following: The LSTM gas concentration prediction model uses large data volume sample prediction, more accurate than the bidirectional recurrent neural network (BidirectionRNN) model and the gated recurrent unit (GRU) model. The average mean square error of the prediction model can be reduced to 0.003 and the predicted mean square error can be reduced to 0.015, which has higher reliability in gas concentration time series prediction. The prediction error range is 0.0005–0.04, which has better robustness in gas concentration time series prediction. When predicting the trend of gas concentration time series, the gas concentration at the time inflection point can be better predicted and the mean square error at the inflection point can be reduced to 0.014, which has higher applicability in gas concentration time series prediction.

For studying the law of crack propagation around a gas drilling borehole, an experimental study about coal with a cavity under uniaxial compression was carried out, with the digital speckle correlation method capturing the images of coal failure. A sequence of coal failure images and the full-field strain of failure were obtained. The strain softening characteristic was shown by the curve. A method of curve dividing—named fitting-damaging—was proposed, combining the least square fitting residual norm and damage fraction. By this method, the five stages and four key points of a stress-strain curve were defined. Then, the full-field stress was inverted by means of the theory of elasticity and the adjacent element weight sharing model. The results show that σci was 30.28–41.71 percent of σf and σcd was 83.08–87.34 percent of σf, calculated by the fitting-damaging method, agreeing with former research. The results of stress inversion showed that under a low stress level (0.15 σf < σ < 0.5 σf), microdamage evolving into plastic failure later was formed around the cavity. Under a high stress level (0.5 σf < σ < 0.85 σf), the region of stress concentration suddenly crazed and formed a brittle crack. When σ ≥ 0.85 σf, the crack was developing, crack lines were connecting with each other, and the coal finally failed. The outcome of the stress inversion was completely concomitant with the images of crack propagation. Additionally, the stress around the cavity was able to be calculated accurately.

Coal elasticity and gas expansion are important factors for coal and gas outburst. During the outburst process, the elastic strain energy of coal is mainly released from the stress region, and the gas expansion energy near the working face is larger, and it is not a continuous release process. To reveal the mechanical characteristics and energy evolution of outburst coal seam, uniaxial and triaxial compression tests were carried out on outburst coal seam samples under different loading methods. The experimental results show that the elastic characteristics become more obvious with the increase of loading rate, the peak strain increases, the elastic modulus is linearly related with the loading rate，and the overall degree of fragmentation increases with the increase of loading rate, which is consistent with the severity of macroscopic coal failure. The failure mode of coal under uniaxial compression conditions is often manifest as brittle failure. The strength characteristics of coal under different loading rates comply with the Mohr‐Coulomb criterion, and the peak strength is linearly related to the failure time and loading rate. With the increasing confining pressure causes the failure of coal samples to transition from ductile to brittle, and the failure mode develops from local shear to overall splitting. The elastic energy evolution curve is consistent with its stress‐strain curve. With the increase of confining pressure, the limiting elastic energy and peak total energy increase in a quasi‐linear manner. The accumulated limit elastic energy plays an important role in the failure of coal samples, and the macroscopic manifestation thereof is that the coal samples fail more severely under high confining pressure conditions than under low confining pressure conditions. The research results are of great significance for the comprehensive prevention and control of coal and gas outburst. [ABSTRACT FROM AUTHOR]