Surface subsidence caused by underground coal mining has received wide attention due to its impact on the ecological environment. To obtain first-hand data on mining subsidence, we arranged line measurement stations in the mining area of the Weiqiang coalfield and implemented surface movement observation at its first mining working face and obtained the dynamic subsidence curve. The subsidence curves reflected the initial, active and declining stages of subsidence at each measurement point at a basic level, and were consistent with the general rule of surface subsidence. To accurately analyze the surface movement caused by coal mining, based on the probability integral method and considering the actual advancement progress of the working face, a new three-dimensional dynamic prediction model, namely the strip unit mining model, was proposed. The core assumption of this model was that the longwall mining is regarded as the result of superposition of many units of mining. Considering the influence of different mining times and periods after mining, the subsidence time function of two-time factors was introduced into the strip unit mining model, and the final formulation of the dynamic subsidence prediction of the three-dimensional surface is derived by considering the time factor. Based on the analysis of the measured data of the Weiqiang coalfield, the prediction parameters of surface movement were obtained, and the surface movement and deformation are predicted via the probability integral method. Finally, the measured surface subsidence was compared with the theoretically-predicted one. The good match showed that the parameters of the probability integral method, determined according to the measured data, meet the requirements of geological conditions and mining settings in the mining area, and the predicted subsidence curves agreed well with the field measurements, demonstrating the effectiveness of the newly-developed strip unit mining model.

In order to investigate the impact of a crushed rock shape on the storage coefficient of underground reservoirs in coal mines, statistical analysis of the shape characteristics of crushed rocks was conducted, which was followed by numerical packing tests using the rigid block model. These tests aimed to investigate the spatial structure characteristics of underground reservoir water storage space in coal mines under the influence of different shapes of crushed rock. The results demonstrated the following: (1) Crushed rock exhibits a lognormal distribution in its shape characteristic parameters at different scales with a predominant discoid shape. The shape coefficient M can be utilized as a comprehensive indicator to characterize the shape characteristics of crushed rock. (2) The average storage coefficient of crushed rock increases exponentially as the shape coefficient M increases. There is a 50.1% increase in the storage coefficient from M = 1 to 3.5. (3) The spatial structure of the water storage space exhibits self-similarity, and both the void fractal dimension and the void boundary fractal dimension increase with an increase in the shape coefficient M. (4) When comparing the non-spherical particle system with the spherical particle system, it is observed that the spherical particle system has smaller water storage space, lower connectivity among voids, and more irregular void space. In the non-spherical particle system, the water storage space becomes larger as the shape of crushed rock becomes more irregular, resulting in more irregular void space. However, there is no significant effect on void connectivity.

Coal mining is often associated with groundwater pollution and loss, and coal–water conflicts are becoming increasingly prominent in Western China. As a new way to protect mine water, coal mine underground reservoirs (CMURs) have effectively alleviated the water shortage problem in Western China. The CMURs have been in existence for 25 years, but field-monitoring studies on their long-term stability are rare. In this paper, we take the Shigetai coal mine in the Shendong mining area as the research background. Long-term observation of stress, deformation, seepage pressure, and other parameters of 22 dams in five goaves (31201–31205) of the Shigetai coal mine for the whole year of 2022 has been pioneeringly carried out. A novel early-warning model, which incorporates expert evaluations and real-time indicator fluctuations, is proposed to assess the stability of CMURs. The stability characteristics of coal pillar dams (CPDs) and artificial dams (ADs) of CMURs are evaluated by this model, proving the validity and applicability of this model. This model provides theoretical and methodological guidance for long-term monitoring and early-warning systems for CMURs in the Shendong mining area.

Addressing the challenge of efficient gas control in high-gas coal mines with ultra-long panels, this study focuses on the No. 8 coal seam in the Baode Mine. A multi-parameter integrated methodology was developed to establish a hierarchical classification system of Gas Geological Units (GGUs), aiming to identify regions suitable for large-scale gas extraction. The results indicate that the overall structure of the No. 8 coal seam is a simple monocline. Both gas content (ranging from 2.0 to 7.0 m³/t) and gas pressure (ranging from 0.2 to 0.65 MPa) generally increase with burial depth. However, local anomalies in these parameters, caused by geological structures and hydrogeological conditions, significantly limit the effectiveness of large-scale drainage using ultra-long boreholes. Based on key criteria, the seam was classified into three Grade I and ten Grade II GGUs, distinguishing anomalous zones from homogeneous units. Among the Grade II units, eight (II-i to II-viii) were identified as anomalous zones with distinct geological constraints, while two (II-ix and II-x) exhibited homogeneous gas geological parameters. Practical implementation of large-scale gas extraction strategies—including underground ultra-long boreholes and a U-shaped surface well—within the homogeneous Unit II-x demonstrated significantly improved gas drainage performance, characterized by higher methane concentration, greater flow rate, enhanced temporal stability, and more favorable decay characteristics compared to conventional boreholes. These findings confirm the critical role of GGU delineation in guiding efficient regional gas control and ensuring safe production in similar high-gas coal mines.

Coal pillar dams are affected by mining disturbance, which threatens the efficient operation of the underground reservoir. To study the deformation behaviors and failure mechanism of coal pillars under mining disturbance, an acoustic emission (AE) system and a deformation field system were applied to conduct uniaxial compression tests at various displacement rates. The AE characteristics and deformation field evolution of coal were investigated, and the microfailure mechanism was identified. The result shows that the deformation field evolutions are the same under various displacement rates. The increment of accumulated absolute energy near the peak stress rises with the displacement rates. The increase rate of the mean vertical displacement is positively correlated with the displacement rate. The coefficient of variation (C_V) of the deformation field can be applied to identify the deformation behaviors of coal and shows the fluctuate–slow increase–rapid increase trend. The distribution ranges of AF (count/duration) and RA (rise time/amplitude) are mainly 0–750 kHz and 0–700 μs/dB. The microfailure mechanism is mainly tensile failure and is accompanied by some shear failure. The percentage of shear failure increases with the increase in the displacement rate. The result provides a reference for the design and stability evaluation of the underground reservoir.

High-performance alkali-free accelerators require a mechanistic understanding of interactions between inorganic accelerants and organic modifiers. Although aluminum sulfate (AS) promotes rapid ettringite (AFt) formation, uncontrolled crystallization leads to coarse microstructures and instability from AFt-to-AFm conversion. Here, a molecular-scale synergistic mechanism is identified in which an amide regulates AS-driven hydration. The amide controls nucleation and growth of AFt and C–S–H via chemisorption on C₃A/C₃S and complexation with Ca²⁺. Within the tested mixing proportions, the high-aluminum-sulfate and moderate-amide combination achieves the highest early strength (17.05 MPa at 1 day) via constructing an interlocked AFt/C–S–H skeleton, whereas excessive amide suppresses crystallization and low AS accelerates AFt-to-AFm conversion, reducing long-term performance. In-situ XRD, thermal analysis, and microscopy confirm a denser, more stable microstructure (27.37 MPa at 10 days) with minimal 28-day strength loss (17.38 MPa). Density functional theory shows an adsorption hierarchy of amide > AS species > H₂O, explaining its dominant surface-modifying role. This study provides a framework for designing cement accelerators with balanced early strength and durability.