Understanding and investigating the gas transport mechanisms in shale fractures is crucial for ensuring the safe operation of various underground engineering activities. In this study, experimental investigations were conducted on shale fractures with different matching degrees to examine their deformation and seepage characteristics under different confining pressures and temperatures. The results demonstrate that the permeability coefficient continuously decreases with increasing confining pressure and temperature, while the GBP shows a continuous increase. Notably, both parameters exhibit a higher rate of change during the initial stage of pressure application, which gradually slows down thereafter. Significant differences were observed in the seepage characteristics between fractures with different matching degrees. The flow rate in poorly matched fractures (S1) was approximately three times higher than that in well-matched fractures (S2), while the GBP of S1 was only about half of S2. This indicates that the matching degree not only affects the initial aperture of fractures but also influences their deformation behavior. Specifically, fractures with lower matching degrees (S1) exhibited larger initial apertures compared to well-matched fractures (S2). Under confining pressure, the primary deformation mechanism in poorly matched fractures was shear failure, whereas well-matched fractures predominantly underwent plastic deformation.

As coal mining deepens, complex geological structures and mining disturbances increasingly compromise groundwater stability; however, the associated groundwater heterogeneity and vulnerability remain insufficiently investigated in the deep mine groundwater. To address this issue, this study integrated hydrochemical parameters with mining and natural factors to evaluate the Carboniferous Limestone Aquifer (CLA) at the Xieqiao Coal Mine. Hierarchical cluster analysis, principal component analysis, Factor Analysis-CRITIC-Game Theory, and spatial autocorrelation were employed to reveal the intrinsic coupling between groundwater heterogeneity and vulnerability, thereby elucidating the driving mechanisms. Subsequently, the model's reliability was further validated through correlation analysis with three groundwater quality parameters: Total Dissolved Solids (TDS), Cl-, and the Sodium Adsorption Ratio (SAR). The results revealed significant differences in groundwater heterogeneity and vulnerability among groundwater clusters, primarily governed by geological structures and mining disturbances. Influenced by mining disturbances or faults, the aggregation patterns of multiple water-rock interactions in high-vulnerability and low-vulnerability areas of the CLA groundwater are negatively correlated, spatially manifesting as low-high or high-low aggregation. Influenced by karst collapse columns, the aggregation patterns of multiple water-rock interactions in high-vulnerability areas of the CLA groundwater exhibit a positive correlation and spatially manifest as high-high aggregation. The Factor Analysis-CRITIC-Game Theory model demonstrated stronger correlations with groundwater quality parameters than the GOD model, with the coefficients of determination increasing by 0.2718, 0.3016, and 0.0495 for TDS, Cl-, and SAR, respectively. This study offers novel insights into the evolution of deep groundwater heterogeneity and vulnerability in coal mines, providing a scientific basis for resource management.

Groundwater flow systems in coalfield aquifers are difficult to identify because diverse stratigraphic assemblages, complex geologic formations, and multilayered aquifers blur the boundaries and connectivity of groundwater flow systems. To address this challenge, this study developed an integrated methodology combining self-organizing map (SOM) hydrochemical classification, radiocarbon (14C) dating, stratigraphic-lithological analysis, and pumping test data to characterize groundwater flow systems in a structurally complex coalfield aquifer system. SOM clustering effectively identified hydrochemical characteristics and spatial heterogeneity in the bedrock aquifers, providing a systematic framework to distinguish between regional and local flow systems. Meanwhile, aquifer-specific corrections of 14C ages allowed for a more reliable determination of groundwater residence times, thereby elucidating recharge and discharge processes across different aquifers. Results indicate that water-rock interactions primarily govern the hydrochemical process, while hydrodynamic conditions control recharge pathways and flow patterns, indirectly shaping groundwater chemistry. Spatial patterns in hydrochemistry correspond to lithological assemblages, highlighting the influence of stratigraphic combinations on groundwater chemistry. SOM analysis further revealed that some Permian coal-bearing aquifer samples group with underlying aquifer samples, indicating hydrochemical convergence caused by mining-enhanced hydraulic connectivity and interlayer groundwater exchange. Pumping test analyses confirmed that major faults act as hydraulic boundaries regulating local groundwater flow systems. This study provides a robust tool for deciphering groundwater circulation in geologically complex coalfields and is broadly applicable worldwide. The findings offer valuable implications for sustainable groundwater management, mine water control, and the protection of groundwater resources in structurally disturbed environments.

Water inflow from roof aquifers is a critical parameter in longwall mining, which greatly affects mine safety. Existing analytical methods, such as the large well method, can only provide single-value predictions and fail to reveal the underlying mechanisms of inflow variations. To address this, a time-dependent water inflow model named ditch inflow model is proposed. The model integrates fractal theory for fracture quantification, unsteady flow theory for flow modeling, and voussoir beam theory to link inflow dynamics to strata instability. Validation with field monitoring data from the Menkeqing coal mine demonstrates that the model accurately captures the increasing trend of water inflow, and greatly outperforms the large well method. As the rock strata undergo periodic fracturing, the water inflow exhibits a stepwise increase, accompanied by fluctuations during plateau periods. The analysis reveals that more than 70

Understanding the pore structure in shale reservoirs is key to estimating the resource potential and recovery efficiency of shale gas. In this study, the probability measurement areas of the T 2 spectrum in multifractal analysis were determined and quantified, and the pore structure of shale samples was evaluated by the fractal theory using low-field nuclear magnetic resonance (LF-NMR) experiments. The results show that the shale reservoirs exhibit a complex and strongly heterogeneous pore structure, with typical single- and multifractal characteristics. The single-fractal analysis has limitations in quantifying bound fluid pores and overall pores. Subsequently, the multifractal analysis provides a robust approach for evaluating local pore heterogeneity. The multifractal parameters D -10s - D 0s exceeding D 0s - D 10s suggest that low-probability measurement areas control the heterogeneity of the pore structure. Consequently, the high- and low-probability measurement areas are identified and quantified by the calculation of local singularity strength. The two high-probability measurement areas are directly associated with the two peaks of the T 2 spectrum and mainly consist of bound fluid pores with few movable fluid pores. The range of T 2 intervals for high-probability measurement areas is greatly correlated with both the heterogeneity of the pore structure and physical properties, such as porosity. The results can provide an in-depth understanding for the characteristics of the pore structure and an effective method to correlate the multifractal analysis with specific pore size.

Investigating geothermal resources in coal mining regions constitutes an important measure for promoting the green transformation of coal industry in China. In this study, the primary genesis and evolution of geothermal water in the southern Huaibei coalfield, North China was proposed based on hydrochemistry combining with multi-isotopes. The diversity of hydrochemical types and the variance of correlation coefficients among ions signify the complexity of hydrogeochemical processes in geothermal waters. The 8D and 818O values indicate that the geothermal water originated from paleo-meteoric water during the cold period. The dissolution of carbonate and sulfate minerals is the primary cause of the observed increase in 813CDIC and 834SSO4 values with depth. Furthermore, the decrease in 87Sr/86Sr ratios with depth is jointly controlled by the composition of the recharge end-member and water-rock interactions. The maximum temperature of the geothermal reservoir calculated by silica geothermometers is 44.9 degrees C, with the corresponding circulation depth being 1282 m. The shallow cold water circulates to the depth along fissures, gets heated through thermal conduction and undergoes a series of water-rock interactions during the process, resulting in constant variations in the temperature and hydrogeochemistry. Given that deep geothermal water may ascend to the working face through fault zones and trigger water inrush disasters, it is currently managed primarily through controlled pumping and drainage. The findings of this work would provide a sound basis for the utilization of geothermal water in the Huaibei coalfield, as well as the majority of coalfields in North China.

Investigating geothermal resources in coal mining regions constitutes an important measure for promoting the green transformation of coal industry in China. In this study, the primary genesis and evolution of geothermal water in the southern Huaibei coalfield, North China was proposed based on hydrochemistry combining with multi-isotopes. The diversity of hydrochemical types and the variance of correlation coefficients among ions signify the complexity of hydrogeochemical processes in geothermal waters. The δD and δ18O values indicate that the geothermal water originated from paleo-meteoric water during the cold period. The dissolution of carbonate and sulfate minerals is the primary cause of the observed increase in δ13CDIC and δ34SSO4 values with depth. Furthermore, the decrease in 87Sr/86Sr ratios with depth is jointly controlled by the composition of the recharge end-member and water-rock interactions. The maximum temperature of the geothermal reservoir calculated by silica geothermometers is 44.9 °C, with the corresponding circulation depth being 1282 m. The shallow cold water circulates to the depth along fissures, gets heated through thermal conduction and undergoes a series of water-rock interactions during the process, resulting in constant variations in the temperature and hydrogeochemistry. Given that deep geothermal water may ascend to the working face through fault zones and trigger water inrush disasters, it is currently managed primarily through controlled pumping and drainage. The findings of this work would provide a sound basis for the utilization of geothermal water in the Huaibei coalfield, as well as the majority of coalfields in North China.

Rock bolting controls shear slip along rock joints, yet the deformation coordination and mechanical response during shearing are not well understood due to complex bolt-rock interaction. This study systematically conducted direct shear tests to investigate how the joint roughness coefficient (JRC), normal stress, and bolt inclination affect the shear behavior of bolted joints. A custom-designed monitoring system was employed to continuously measure the bolt axial force throughout the shearing process. Results indicate that JRC strongly influences bolt deformation and axial-force mobilization through dilatancy, thereby governing the peak and reinforced strengths of the joint. Higher normal stress suppresses joint dilatancy and reduces the bolt’s shear contribution, while bolt inclination controls the balance between axial and shear forces. 45° inclination showed the best overall shear performance. Monitoring data reveal the bolt’s axial force variation during shear displacement progresses through four stages: initial adjustment–relaxation, elastoplastic, hardening, and deformation-failure. This classification tracks how axial force evolves under compatible coordination. Correspondingly, the bolted joint’s shear process develops through elastic, plastic, failure, and residual stages, revealing the mechanical interaction mechanism between the joint surface and bolt at different stages. The study provides an experimental basis for understanding shear behavior of bolted joints and optimizing rock bolt support design.

The depletion of shallow coal resources necessitates the advancement of deep mining operations, where accurate prediction of coal–rock composite mechanical behavior is critical for disaster prevention. This study systematically develops and evaluates a machine learning (ML) framework for predicting key mechanical properties. A dataset of 162 experimental results was collected, incorporating ten input features such as densities, elastic modulus, uniaxial compressive strengths (UCSs), and key ratio parameters of coal–rock components. Five base models, namely backpropagation neural network (BPNN), extreme gradient boosting (XGBoost), support vector machine (SVM), extreme learning machine (ELM), and random forest (RF), were optimized using the sparrow search algorithm (SSA). The results show that the SSA–SVM model achieved the best prediction accuracy on test data, with determination coefficients of 0.90 for composite UCS (Urc) and 0.85 for elastic modulus (Erc). Feature importance analysis highlighted the significant influence of coal proportion (Rc) and strength ratios (Ru) on composite mechanical performance. As Rc increases, the overall composite strength decreases. Higher strength ratios also alter load-transfer efficiency between coal and rock and increase the risk of interfacial failure. This study provides data-driven insights for designing safer underground support systems in deep mines and mitigating mining disasters.

ObjectiveCurtain walls, recognized as a primary project for the prevention and control of water disasters in coal mines, will change the dynamic field of groundwater. Furthermore, their dissolution will affect the chemical field of groundwater, leading to variations in its hydrochemical composition. MethodsThis study investigated the Jurassic conglomerate aquifers in the Zhuxianzhuang Coal Mine, Huaibei coal field. Based on the statistics of conventional hydrochemical composition, Piper diagrams, ion combination proportions, and principal component analysis (PCA), this study explored the impacts of curtain walls on the hydrochemistry of the aquifers and determined the spatiotemporal hydrochemical evolutionary patterns under the influence of the curtain walls. Results and Conclusions The results indicate that the hydrochemical characteristics differ greatly between inside and outside the curtain walls, with the groundwater inside the curtain walls exhibiting elevated Ca2+ and Mg2+ concentrations compared to that outside the curtain walls. After the construction of the curtain walls, the hydrochemical processes are dominated by the dissolution of the curtain walls based on the leaching and dissolution of calcite (CaCO3) and dolomite (CaMg(CO3)2), accompanied by varying degrees of pyrite oxidation, alternating adsorption of cations, and desulfurization. Influenced by mining, the dissolution of the curtain walls produces significantly enhanced impacts on groundwater within them, with the dissolution of the northern curtain wall relatively weaker than that of the eastern counterpart. The results of this study will provide theoretical support for the monitoring and protection of curtain walls and the environmental protection of groundwater.

A substantial body of research has been conducted to explore the multi-scale dynamic evolution and nonlinear coupling relationships from microstructure to macroscopic properties of carbonate rocks under reactive solute transport at the pore scale. However, these studies primarily focus on single-mineral systems, neglecting the influence of mineralogical diversity. This study examined the dissolution characteristics of calcite and dolomite under varying hydrodynamic conditions and introduced a pore-scale reaction transport model. The kinetic mechanism of mineral dissolution, microscopic pore network evolution and macroscopic seepage response were systematically analyzed. Results demonstrated that the calcite dissolution rate substantially exceeded that of dolomite, leading to heterogeneous features including discretized pore size distributions and distorted hydraulic pathways in a multi-mineral system. Low-velocity flow regimes shift the dissolution process from reaction-limited to mass-transfer-limited, further exacerbating dissolution unevenness and promoting the development of irregular pore geometries. By integrating pore-scale simulations with quantitative characterization of pore size distributions and pore shape parameters from natural carbonate rock samples, this study confirms the critical role of mineral composition and hydrodynamic conditions in governing the evolution of pore network heterogeneity. These heterogeneous features significantly impede fluid transport efficiency. Enhanced mineralogical complexity and reduced hydrodynamic conditions amplify the heterogeneity of pore structures during ongoing dissolution, consequently constraining the extent of permeability improvement. Furthermore, under low-velocity flow regimes, dissolution tends to concentrate in pore spaces that contribute less to permeability.

The trends in the key parameters (permeability coefficient and porosity) used to assess the degree of damage to the geological body are generally considered to be consistent. However, when permeability coefficient and porosity are applied as damage variables for a low-permeability geological body (i.e., underground waterproof grouting curtain wall, GCW), respectively, two different conclusions are obtained. A new layered damage evolution model of GCW under hydrodynamic-hydrochemical coupling is proposed to describe the damage evolution process of GCW. The model elucidates the mechanism of the differences in the evolution of permeability coefficients and porosity of GCW. The dissolution effect of groundwater increases the porosity of the GCW. However, the dissolution ability of groundwater in the seepage through the GCW decreases until it disappears, so that its dissolution effect does not affect the entire GCW. The model first layers the GCW based on the significant difference in dissolution effect, and then simplifies the GCW damage evolution process to an equation expressed using the hydrodynamic-hydrochemical parameters by introducing the concepts of damage thickness and dissolution porosity. The results show that the head difference, seepage velocity, saturation index (SI), and ion activity difference jointly control the damage evolution process of GCW. The area with relatively small damage thickness of the GCW has a higher maximum value of dissolution porosity and its spatial differences are higher. This study visualizes the damage evolution process of GCW using hydrodynamic-hydrochemical parameters, which provides a new method for quantitatively identifying the degree of damage in low-permeability geological bodies.

Hierarchical cluster analysis, principal component analysis, hydrochemical illustration, and objective weighting were used to study the hydrochemical characteristics and types of water–rock interaction of the groundwater in a typical North China Coalfield mine. The geological conditions and the mining disturbance were quantitatively evaluated, and mechanisms by which they affected hydrochemical evolution were elucidated. The results show that there are three types of groundwater in the coal measures: one with high Ca2+, Mg2+, and SO42−, which is oxidized disturbed water; another featuring high Na+ and HCO3−, which is reduced disturbed water; and one with low ionic content, making it undisturbed water. The coefficients of geological complexity and mining disturbance intensity exhibited spatial variability, with maximum values of 0.46 and 0.8, respectively. Less oxidation of pyrite and less dissolution of carbonate and sulphate was correlated with increased geological complexity, while enhanced cation exchange and sulphate reduction correlated with decreased geological complexity.

The fault network significantly impacts the evolution of groundwater hydrochemical in coal mining regions. In this study, the spatial evolution and primary controlling mechanisms of groundwater hydrochemistry in the Carboniferous limestone aquifer of Suntuan coal mine, North China were investigated through the integration of hydrochemical correlation analysis and fault complexity evaluation model. The results show that HCO3− and Cl− are the dominant anions in the groundwater, while the cations show dispersive features. Furthermore, ion correlation analysis suggests that minerals dissolution and cation exchange between Na+ and Ca2+ are the dominant water-rock interactions. The calculation results of the fault complexity evaluation model constructed based on the AHP–entropy weight coupling method show that high values are banded along the NE direction and closely related to faults that traverse the study area, as well as at the intersection of two faults. The distribution pattern of principal component scores indicates that the dissolution of carbonate minerals decreases with the complexity of faults, while cation exchange exhibits the opposite behavior. The primary controlling mechanism of fault complexity on groundwater hydrochemical evolution mainly contributes to changes in groundwater hydrodynamic conditions, resulting in slower groundwater flow and longer contact time between ions and minerals, which inhibits the dissolution of carbonate minerals and promotes cation exchange. The findings of this work not only have important applications for the quantitative evaluation of geological structure and groundwater resource management in Suntuan coal mine, but also provide a research template for other coal mines in North China.

Coal mining in groundwater-rich coal fields will trigger failure of overlying strata, resulting in the formation of water-conducting fracture zone (WCFZ) and potentially leading to water-inrush accidents. In this study, a reliability model with consideration of spatial variability and uncertainty of strength parameters was proposed to predict the failure behaviour of overlying strata during coal mining in groundwater-rich coalfields. Rock strength parameters, including cohesion, internal friction angle, uniaxial tensile strength, and softening coefficient, are treated as random variables to determine the rock failure uncertainty. The experimental results of these geomechanical parameters at different positions are interpolated by the Kriging interpolation method. Spatially, the interpolated values are arranged as the average value of each random variable to demonstrate their autocorrelation. Furthermore, based on Mohr–Coulomb yield criterion, a performance function is deduced to calculate the failure probabilities of overburden rocks to evaluate the spatial scale of WCFZ. As a typical case, the failure features of adjacent overlying strata of No. 7121 mining face in Qidong Coal Mine is analyzed. The results show that the risks of water-inrush are high when the mining face advances to 260–380 m and 1120–1240 m, which aligns with both field monitoring results and borehole observation results. The proposed model holds significant implications for prevention of water-inrush accidents in groundwater-rich coal mines.

Systematically studying the hydrochemical evolution of bedrock groundwater in mining areas during mining process is crucial for effective groundwater resource management and coal mine production. The spatiotemporal characteristics and hydrochemical evolution patterns of the Permian fractured sandstone aquifer (PA) and the Carboniferous Taiyuan Formation limestone aquifer (CTA), both of which are directly associated with coal mining in the northern Linhuan mining area, China, were investigated using multivariate statistical analyses, hydrochemical graphical methods, ion ratio analysis, and a conceptual model. 72 groundwater samples, collected before and after mining, were classified into four groups by hierarchical cluster analysis (HCA). Principal component analysis (PCA) and ion ratio analysis indicated that water-rock interactions involve mineral dissolution (carbonates, gypsum, dolomite, silicates), cation exchange, and common ion effects. Hydrochemical evolution is influenced by bedrock paleotopography, aquifer hydraulic conductivity, and mining drainage. Paletopographic differences significantly influence water-rock interactions and spatial variability in hydrochemistry, with ion concentrations in groundwater increasing as paleotopographic elevation decreases. The pattern of hydraulic conductivity reflects the control exerted by variations in aquifer characteristics on mineral dissolution, leading to minor changes in hydrochemical characteristics. Mining activities disrupt the aquifer's reducing environment, resulting in a significant increase in groundwater SO42- concentration. These findings provide insights and a solid theoretical foundation for studying the hydrochemical variations patterns of groundwater and these control mechanisms in the hidden coal fields of North China.

Identification and evaluation of bed separation induced by mining in the overburden is critical to prevent secondary disasters during coal mining. Traditional theoretical methods ignore the effect of horizontal stress in bed separation and fail to accurately identify bed separation and evaluate its dynamic evolution process. In this study, based on the beam-column theory, the deflection of composite beam is determined, in which the horizontal stress is considered. On this basis, by combining beam-column and stress-balanced arch theory (BS theory), the BS model is proposed for identification and evaluation. The identification results from the BS model agree well with the field measurement results with a high accuracy rate of 88.9%. Furthermore, one working face in a coal mine is selected to evaluate the dynamic evolution process of bed separation by the numerical simulation and the BS model. It is found that the bed separation shows evident stages of growth and extinction during mining. The BS model has a wide range of applications for the identification and evaluation of bed separation induced by mining and can be used to ensure the safety of mining operations.

Determining the hydrochemical variations and groundwater mixing is crucial for mining safety and water resource management in the Sulin mining area in North China, especially after mining activities. In this study, 94 groundwater samples were collected from the main aquifers in the Sulin mining area during the early and late stages of mining. Water-rock interactions, spatiotemporal variations in hydrochemistry, and groundwater level characteristics during the early and late stages of mining were determined by analyzing data on major ions, hydrogen and oxygen isotopes, and groundwater level. Analytical methods included Piper diagram, principal component analysis, ionic ratio analysis, and Kriging interpolation. A comprehensive conceptual model was proposed to describe the spatiotemporal variations and mixed patterns of the multi-aquifer systems. Results showed that groundwater level in the study area remained relatively consistent before and after mining, with no significant changes observed. The distribution of regional geological structures significantly affects on the groundwater distribution characteristics, which, in turn, determines the spatial variations in groundwater hydrogeochemistry and mixing patterns of groundwater under natural conditions. Moreover, there was significant temporal variation in hydrochemistry in areas of strong drainage. Mining activities led to a decrease in groundwater level, resulting in regional differences in water-rock interactions and groundwater mixing patterns. The Bayesian isotope mixing model (MixSIAR) and the hydrogeological conceptual model can be applied to quantitatively verify the groundwater mixing and the hydrogeochemical process. The study offers insights into the spatiotemporal variations and mixing patterns of groundwater under the impact of exploitation.

华北型煤田是我国重要的煤炭基地,水文地球化学勘探是解决煤田开采过程中一系列水文地质问题的重要手段.在概化华北型煤田典型水文地质结构的基础上,分析采动影响下典型水文地质问题,揭示了华北型煤田地下水多场耦合关系与水文地球化学勘探作用机制及其测试分析处理技术;通过回顾水文地球化学理论发展历史,明确华北型煤田水文地球化学勘探技术的可靠性;汇总地下水常用的水文地球化学组分及其测试仪器,并从图解法、数理统计法、物理模拟和数值模拟等方面阐述水文地球化学勘探的技术手段;在此基础上,从地下水资源评价、突水水源动态识别、水文地球化学时空演化、地下水动力异常反演、地质结构异常反演、地下水混合模式构建及水热资源勘察等角度综述了多场耦合下华北型煤田水文地球化学勘探关键技术的应用研究进展,明确了水文地球化学勘探的优越性与可操作性.结合华北型煤田水文地质条件,提出华北型煤田水文地球化学勘探典型技术核心及其存在的问题,指明了水文地球化学勘探技术研究的努力方向.

To prevent water inrush hazards of mining under the Quaternary unconsolidated confined aquifer in North China coalfield, it is necessary to build a water inrush prediction model to guarantee coal safety production. The current method of evaluating mining hazards under unconsolidated confined aquifers is easy to fall into the problems of simple superposition of evaluation factors, large subjectivity of the factor selection, and low accuracy of prediction results. In this paper, an analytic hierarchy process (AHP) is improved according to contribution of information value method (IVM) to analyze the impact of water inrush factors. The factor weight values are considered in calculating the total information value of IVM to build a coupled AHP-IVM model. The information value of each factor is calculated through IVM, and area under curve (AUC) value is used to rank the factors, to exclude the subjective judgment of the importance of each factor. The geological and hydrogeological data of Qinan coal mine in Huaibei coalfield are analyzed and organized. The results suggest that the coupled AHP-IVM model has an AUC value of 0.8309, indicating its great potential and practical significance for future mining operations.