Yachao Guo

To address the high-stress problem in underlying roadways caused by the combined effects of concentrated loads from residual coal pillars and suspended-load-bearing behavior of thick and hard interburden strata during downward mining of closely spaced coal seams, a dual-location synergistic fracturing method for pressure relief was proposed based on the 221001 working face of a coal mine. 3DEC numerical simulations were used to investigate the effects of fracturing location, height, and angle on surrounding-rock stress and coal-pillar deformation, and the optimized scheme was further verified through physical similarity simulation and field tests. The results show that synergistic fracturing provides a better pressure-relief effect than single-location fracturing. The stress in the middle of the interburden strata decreases by 45.54%, and the deformation of the sectional coal pillar decreases by 90.69%. The reasonable fracturing height and angle are 22 m and 70°, respectively. The physical similarity simulation shows that the target strata can progressively fracture along the weakened zone. Field tests show that roof-to-floor and rib-to-rib convergence decrease by 58.82% and 54.39%, respectively; the average support working resistance decreases by 34.58%; and the peak coal stress at a depth of 6 m from the roadway rib decreases by 37.62%. The results indicate that the synergistic fracturing scheme with an interburden fracturing height of 22 m and an inclination angle of 70° can effectively mitigate stress concentration and improve roadway stability, providing a practical reference for pressure-relief control under similar closely spaced coal-seam mining conditions.

To address the engineering challenges associated with the high brittleness and poor crack resistance of coal-based solid waste grouting materials, this study systematically investigates the flexural performance and damage evolution characteristics of the material by incorporating various types and amounts of fibers into a matrix composed of coal gangue, fly ash, Portland cement, and sulfoaluminate cement. Macroscopic mechanical testing, digital image correlation (DIC) technology, and scanning electron microscopy (SEM) are employed to reveal the mechanisms by which fibers influence the grouting material. The results demonstrate that fiber type and dosage significantly affect the flexural strength and damage evolution behavior of the material. Among them, basalt fiber exhibits the most pronounced improvement in flexural strength at a dosage of 0.4%, achieving a 28-day flexural strength of 6.33 MPa, which is 73.9% higher than that of the control group. Similarly, glass fiber shows a flexural strength increase of 63.18% at a dosage of 0.8%. The fibers enhance the material’s ductility and promote the uniformity of the failure process through mechanisms such as crack bridging, energy dissipation, and optimized interfacial structure. Furthermore, joint analysis using DIC and acoustic emission (AE) techniques reveals that when the fiber dosage reaches 0.6%, the proportion of shear cracks during material failure significantly increases (12.78–16.13%), indicating that fibers improve the uniformity of strain distribution under loading, delay the propagation of the main crack, and thereby enhance the overall crack resistance of the material. These findings provide theoretical and technical support for the development of high-toughness and high-performance coal-based solid waste grouting materials.

Grouting technology can be employed to repair cracks in an aquifer to maintain its stability; however, existing grouting materials tend to come with problems such as low flexural strength, poor cracking resistance, and the coupled effects of fiber reinforcement and sulfoaluminate cement (SAC) addition on hydrate evolution, and pore-refinement and crack-resistance mechanisms in coal-based solid-waste cementitious grouts remain insufficiently understood. In this paper, fiber-modified coal-based solid-waste grouting (F-CWG) materials were prepared by mixing different contents of sulfoaluminate cement (SAC) and different fibers. The mechanical strength, microstructure, hydration products, and pore evolution characteristics were analyzed by means of mechanical property tests, energy-dispersive X-ray spectroscopy (SEM/EDS), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and nuclear magnetic resonance (NMR). The results show that the mechanical strength decreases at first due to insufficient early-stage hydration products. Specifically, the 28 d compressive and flexural strengths decrease from 15.34 MPa and 4.55 MPa at 0% SAC to 8.18 MPa and 2.99 MPa at 40% SAC but increase again to 13.36 MPa and 3.79 MPa at 60% SAC as the formation of ettringite (AFt) and C–S–H is promoted with higher SAC content. Among the tested fibers, a dosage of 0.6% generally improves mechanical strength and refines pore structure, with PVA and steel fibers showing the most pronounced effects. Our results reveal the mechanism behind the enhancement of cracking resistance in F-CWG materials, providing a scientific basis for grouting and water-preservation mining, and are of great significance in improving the utilization rate of coal-based solid waste.

The excessive consumption of resources and the destruction of ecological environment in mining areas have severely restricted coal mining, and the research on resource and environmental carrying capacity (RECC) of mining areas is of great significance in reconciling coal mining and resource environmental protection. To review the existing research on the RECC of mining areas, the concepts of the RECC were elaborated, and then the development process and application areas of both resource carrying capacity (RCC) and environmental carrying capacity (ECC) were studied. The main methods and models involved in the RECC study were counted. The results showed that the research on the RECC of mining areas has not attracted sufficient attention, and the relevant literature is relatively few. The existing research on RECC in mining areas mainly adopts single-factor analysis, which makes it difficult to comprehensively evaluate the overall situation of RECC in mining areas. Thus, a comprehensive evaluation of the RECC of mining areas by scientific evaluation methods is required to ensure the coordinated development of coal production, resources and environment of mining areas. This review provides an important reference and guidance for the necessity and thinking of the comprehensive study of resources and environment carrying capacity in mining areas.

With the increase of mining depth in underground engineering, deep ground pressure has an extremely unfavorable impact on safety production and the economic benefits of coal mines and the control of the roadway stability in deep mines are gradually highlighted. In this study, the working face 14203 of the Zaoquan coal mine was taken as the engineering background, the deformation mechanism of surrounding rock in the deep‐buried high‐stress roadway was analyzed, and the hydraulic fracturing pressure relief technology in the advanced roadway was proposed for surrounding rock control. Finally, the numerical simulation and field tests were used to validate the comprehensive effect of the proposed technology. Without damaging the roadway stability in the working face, the hydraulic fracturing pressure relief technology can optimize the stress environment and stability of the roadway through the artificial control of the roof fracture position. The numerical simulation shows that under the action of hydraulic fracturing, the cutting slot is formed, the deformation and failure mode of the roof are changed, the stress of surrounding rock is reduced, and the development of the plastic zone of surrounding rock is limited. As a result, the stability of surrounding rock in the roadway is effectively protected. The field test shows that after the adoption of hydraulic fracturing pressure relief technology, the roof subsidence, floor separation, bolt stress, and cable stress decrease, and the deformation of surrounding rock is reduced significantly. Therefore, hydraulic fracturing pressure relief technology is verified as an effective method to control the large deformation of the surrounding rock in the deep‐buried roadway.