Tao Luo

Incremental subsidence induced by sequential longwall panel extraction is associated with panel interaction and progressive instability of the disturbed rock mass. However, the governing mechanisms and the coupled effects of panel and pillar geometries remain insufficiently understood, limiting effective assessment and mitigation of cumulative ground deformation in longwall mining. This paper investigates the mechanisms and influencing factors of incremental subsidence through comprehensive approaches including field data interpretation, numerical modelling, parametric study, and sensitivity assessment. A numerical model is developed to simulate the stress and deformation response of the overburden and inter-panel pillars to sequential panel extraction under representative geological and in-situ stress conditions. The results indicate that incremental subsidence is primarily governed by stress redistribution, lateral compaction, and distance-dependent attenuation. Extraction of a subsequent panel induces secondary loading and compaction within the previously mined panel domain, thereby enhancing horizontal displacement and surface settlement, while the influence of further mining diminishes with increasing pillar width due to stress relief and reduced overburden stiffness. Parametric sensitivity assessment reveals a coupled dependence of incremental subsidence on panel and pillar widths: narrow pillars of 15 m produce up to 3 to 4 times greater incremental subsidence above the first panel compared with wide pillars of 75 m, while wider panels amplify the sensitivity of subsidence to pillar width. These findings reveal the progressive evolution of mining-induced rock mass deformation and provide quantitative guidance for optimising panel and pillar configurations to reduce cumulative subsidence and ground-instability risks.

Investigating the evolution mechanism of overlying strata fractures during mining and identifying the key factors that influence the development height of water-conducting fracture zones (WCFZs) are essential for preventing roof water inrush disasters, protecting mine water resources, and ensuring safe and sustainable mine development. To investigate the height of WCFZs and the evolution law of roof water inflow in a syncline structure working face under high-confined aquifer conditions, the 203 working face of Gaojiapu Coal Mine in Binchang Coalfield is selected as the engineering case. This paper analyzes the characteristics and control mechanisms of roof water inflow in a syncline structure mining area using UDEC 7.0 and COMSOL Multiphysics 6.0 multiphysics numerical simulation software. The results indicate that under different mining heights and advancing speeds, the height of the WCFZ in the overlying strata of a syncline structure working face continuously increases during the downward mining stage and in areas below the axis, and decreases thereafter, eventually stabilizing after reaching its maximum value at the initial stage of upward mining. When the WCFZ communicates with the strong aquifer of the Cretaceous Luohe Formation during the mining process, roof water inflow into the working face increases abruptly. The effectiveness of controlling water inflow by adjusting mining height is superior to that of controlling mining speed. Based on the response relationship between mining height, mining speed, and roof WCFZ, an on-site drainage prevention strategy was implemented involving reduced mining height and increased mining speed. Consequently, the roof water inflow at the working face has decreased from an initial rate of 950 m³/h to 360 m³/h. This study is of great significance for the safe and efficient extraction of coal seams under high-confined aquifers in the Binchang Coalfield, supporting the efficient development of coal resources while safeguarding regional water resources, thereby offering considerable engineering and practical value in promoting green mining and sustainable mining practices in large-scale coal production bases with similar geological conditions.

Mining above confined aquifers fundamentally depends on understanding the evolution of floor permeability for water hazard control and water conservation mining. A mechanical model was developed to characterize the coordinated deformation of floor aquiclude strata, accounting for non-uniform distributions of stress and water pressure. The competing mechanisms whereby neutral plane strain and flexural deflection dominantly control permeability at different dip angles were elucidated, and the influence of dip angle on the stability of the water-resistant key strata was quantified. On this basis, a quantitative method for assessing the feasibility of in situ water conservation mining above confined aquifers was developed and its effectiveness was verified through field application. The main findings are as follows: The deflection of the floor aquiclude increases with water pressure, advance distance, and panel length. Larger coal seam dip angles correspond to smaller aquiclude deflection, with a strong dependence on the water pressure treatment method. The equivalent permeability of the floor increases with water pressure, panel length, and advance distance, and its variation is most pronounced with water pressure. As the dip angle increases, the equivalent permeability exhibits a trend of first rising and then decreasing; the transition between deflection-dominated and neutral plane strain-dominated control occurs at a dip angle of 35°. Lithological assemblage is found to govern the position of the neutral plane and the bending stiffness matrix, while a soft–hard interbedded floor is effective in suppressing deformation and mitigating the increase in the equivalent permeability. For inclined aquiclude key strata, the ranking of zones most prone to failure and water inrush is as follows: lower end > upper end > coal wall position > behind the goaf. A quadratic multi-parameter response model for the mining-induced equivalent permeability at the Fenyuan Coal Mine is established, yielding the sensitivity ranking under single factor and interaction effects as follows: water pressure > panel length > advance distance > water pressure (quadratic) > water pressure × panel length interaction. The higher the water pressure, the stronger the influence of dip angle on the equivalent permeability. Groundwater ion evolution is dominated by dissolution/leaching, with sulfate (SO₄²⁻) serving as a diagnostic ion for source identification. The stepwise criteria and grouting-reinforcement parameters for in situ protection of confined aquifers are proposed. Using water quality and quantity as evaluation metrics, Working Face 5-103 at the Fenyuan Coal Mine, which is a large-inclination-angle and high-pressure working face, has achieved in situ protection of the floor water.

Coalbed methane (CBM) development involves multiple interacting physical fields, and different coupling schemes can lead to distinctly different production behaviors. A thermo-hydro-mechanical model accounting for gas–water two-phase flow and matrix dynamic diffusion (TP-D-THM) is developed and validated, achieving an error rate below 10%. By embedding the numerically estimated reservoir physical parameters of the Qinshui Basin into the numerical model, multi-field couplings during CBM production, the evolution of physical parameters, and the depth-dependent effects on production characteristics were revealed. The main findings are as follows: The inhibitory effect of water on CBM recovery consistently exceeds the promoting effect of temperature. As burial depth expands, the inhibitory effect first diminishes, then intensifies, ranging from 19.73% to 28.41%, while the thermal promotion effect exhibits a monotonically increasing trend, fluctuating between 8.55% and 16.33% and stabilizing below 1000 m. Temperature and burial depth do not alter the trend in gas production rate. For equilibrium permeability, reproducing a decrease–increase–decrease rate pattern requires explicit inclusion of water and matrix-fracture mass exchange terms, which can explain why different scholars obtained varying gas production rate trends using the THM model. Matrix adsorption-induced strain is the primary control on permeability evolution, and temperature amplifies the magnitude of permeability change. The critical depth essentially reflects the statistical characteristics of reservoir petrophysical properties. A dimensionless critical depth criterion has been proposed, which comprehensively considers reservoir pressure, permeability, and a fractional coverage index. For burial depths ranging from 650 to 1350 m, the TP-D-THM model can be simplified to the gas-mechanical model accounts for matrix dynamic diffusion (D-HM) with an error below 5%, indicating that thermal and water effects nearly cancel each other.

To unravel the permeability variation mechanism of weakly cemented rocks (WCR), the paper conducted triaxial permeability tests on weakly cemented sandstones (WCS) collected from the Jurassic formation in northwest China. The paper identified the correlation of WCS permeability versus porosity, cementation structure, and mineral composition, further developing a model to characterize the WCS stress–damage–permeability relationship. The research indicated that the WCS permeability was initially high due to the naturally high porosity, large pore diameter, and loose particle cementation, thus favoring a significant decline as pore convergence in the compaction stage. In the residual stage, kaolinite and montmorillonite minerals disintegrated into water and narrowed fractures, causing a slight permeability increase from the initial to the maximum and residual stages. The WCS matrix fracturing was phenomenologically accompanied by clay mineral disintegration. By assuming that the matrix can be compressed, jointed, and fractured, the paper defined a damage variable D and accordingly developed a stress–damage–permeability relationship model that incorporated matrix compression, jointing, and fracturing. The model can describe the WCS permeability regime regarding the high initial permeability and slight difference of the maximum and residual permeabilities versus the initial.

In northwest China, underground mining is frequently conducted in weakly cemented rock environments, including the aquiclude that protects the aquifer from dewatering. In this context, understanding the aquiclude responses to longwall mining is significant for assessing the reliability of water-conserved mining in the weakly cemented rock environment. Taking the Jurassic and Paleogene coal measure geology in Yili Mine in Xinjiang Province, China, as a case study, the paper conducted a laboratorial three-dimensional simulation by configuring a longwall operation and induced groundwater migration. The study analysed the aquiclude depressurisation and revealed the aquiclude stability in response to longwall mining. The results indicated that the aquiclude had a significant plastic strain and self-healing ability in the ground depressurisation condition. The aquiclude experienced tension and then compression, and, accordingly, fracture initiation, propagation, and convergence, during which the aquiclude had significant bending deformation. On the aquiclude horizon, tensile fracturing dominated above the set-up and longwall stop positions. The self-healing behaviour was correlated to the high content of clay minerals and disintegration proneness. The simulation results had a good agreement with field measurements, suggesting that the aquiclude had a satisfactory water-resisting ability and that the simulation results were practically reliable.

Coal bump, a common dynamic disaster in mining of deep coal resources, its assessing and predicting is an important component in safety management. This paper presents a model to assess and predict coal bump risk based on multiparameter indices. A new energy accumulation index was proposed by considering acoustic emission and electromagnetic emission signal characteristics in mine shocks. Combined with indices (energy of microseisms) and (frequency of microseisms) of microseismic monitoring, a static and dynamic coal bump risk assessment and prediction model was established. We studied coal bump events that occurred during extraction in 311305 working face of Bayangale coal mine in Inner Mongolia, China. We obtained the acoustic emission and electromagnetic emission signal distribution and change law, using principal component analysis method and density ellipse to establish the index . A typical precursory of coal bumps is that AE and EME strength has obvious fluctuation period of 3-4 days, index showing an obvious decreasing trend, while the time-series curve of the microseismic energy is relatively stable, and the vibration frequency curve has a significant upward trend. After predict the potential coal bump risk and its area of occurrence, large diameter drilling (Φ150 mm) on-site was used to relief pressure concertation in coal seam and roof. The results demonstrate that this model based on multiparameter indices is capable of quantitatively prewarning rock burst risk.

The roof falling accident is a serious threat to the lives of miners in deep coal mining, especially when the coal mine is more than 1000 meters deep. In regard to the 5306 coalface in the Tangkou coal mine, Shandong, China, the depth of coal seam is 992.8 m and the stress concentration coefficient of the roadway surrounding rock is 3.33. This leads to a serious deformation of the roadway roof, thereby producing a high risk of the roof falling disaster. In this pursuit, based on the mechanical analysis of roadway roof subjected to a high abutment pressure, the mathematical expressions of the setting load and movable column length of supports were introduced. Furthermore, the stability control mechanism of the roadway roof was analyzed and the optimized support parameters of supports are provided. The results showed that the longtime effective support of the roadway roof required the strength and deformation coupling of supports and anchored surrounding rock. The support length of the belt roadway should be at least 57.7 m, with 0-30 m away from the coalface supported by hydraulic supports and 32-57.7 m supported by single props. In addition, the maximum setting load and movable column length of hydraulic supports were 21.67 MPa and 280.3 mm and 12.44 MPa and 177.1 mm for single props, respectively. By applying the optimized support parameters of supports to the belt roadway of the 5306 coalface, the effective control of the roadway roof and the disaster control of roof falling were realized.