As a research hotspot, pillarless coal mining technology has a high resource recovery rate and low roadway surrounding rock stress. To grasp the three-dimensional fracture characteristics of the basic roof is the basic to reveal the strata behavior mechanism in the pillarless working face. Thus, aiming at pillarless coal mining, the analytical solution of three-dimensional fracture mechanics models of a basic roof was analyzed by elastic thin plate theory; the principal stress distribution of a basic roof being cut by continuous artificial fractures and discontinuous artificial fractures was analyzed; the fracture characteristics of the basic roof was revealed and the strata behavior mechanism was obtained. The following conclusions can be drawn: (i) an ‘O + X’ fracture occurred in the basic roof of a traditional working face, while an opposite-trapezoid-shaped or ≡-shaped fracture was generated in the pillarless working face. (ii) When the basic roof broke, the trapezoidal or rectangular hinged plate traversed the entire pillarless working face, causing the end supports to be pressured, while the trapezoidal hinged plate did not traverse the entire traditional working face and the end supports were not pressured. (iii) The break of a basic roof induced by artificial fractures in pillarless mining reduced or even eliminated the triangular hinged plate area along the goaf edges, making a roadway in the stress relief zone. (iv) Compared with the fractures in traditional roadways and in a discontinuous roof-cutting roadway, continuous fractures could minimize surrounding rock stress and make it easy to maintain a roof-cutting roadway.

The roadway of S2S2 fully mechanized caving face (FMCF) in Xiaokang Coal Mine is one of the most typical deep‐buried soft‐rock roadways in China and had been repaired several times. In order to figure out the failure reasons of the original roadway support, the geological conditions were investigated, the surrounding rock stress was monitored, the rib displacement, roof separation, and floor heave were in situ measured, and the performance of the U‐shaped steel support was simulated. The above analysis results indicated that the support failure was mainly caused by (1) the unreasonable arch roadway section, (2) the high and complex surrounding rock stress, (3) the failure control of the floor heave, and (4) the inadequate self‐supporting capacity of the surrounding rock. For optimizing, the roadway section was changed to circle and a new full‐section combined support system of “belt‐cable‐mesh‐shotcrete and U‐shaped steel‐filling behind the support” was adopted, which could specifically control the floor heave, allow the roadway deformation in control, and improve the self‐supporting ability and stress field of the surrounding rock. To determine the support parameters, the selected U‐shaped steel support was verified by simulation, and various bolt‐cable support schemes were simulated and compared. Finally, such an optimized support scheme was applied in the roadway of the next replacement FMCF. The in situ monitoring showed that the rib‐to‐rib convergence and roof‐to‐floor convergence were both controlled within 600 mm, which indicated that the roadway was effectively controlled. This case study has important reference value and guiding function for the optimal design of the soft‐rock roadway support with similar geological conditions.

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.

Guide rails’ nonlinear dynamic response to the collision process between gangues and the suspended buffer is the basis for its intensity examination and fatigue prediction. This paper established a numerical model for simulating the dynamic response of buffer’s guide rails using Pro/E and Femap based on an analysis of the basic structural components of the suspended buffer. The effects of the gangues diameter and feeding rate on the guide rails’ dynamic response were investigated, which were mainly revealed by a tension in guide rails. Simulation results showed that the tension in guide rails rapidly increased to a peak value after the suspended buffer was impacted by gangues, followed by a periodic vibration. The peak tension, maximum and minimum tensions within the periodic vibration were exponential functions of the gangues diameter. And they depended linearly on the feeding rate. The vibration frequency of the tension in guide rails was an exponential function of the gangues diameter but did not depend on the feeding rate. Based on the backfilling workface parameters used in D.Ping coal miner’s 15601 working panel, the feeding rate of 500 t/h was selected. The diameter of the crushed gangues was selected to be 50 mm based on the strength of guide rails. Their expected service life is 54.2 years. Finally, an industrial test was performed in D.Ping coal miner’s 15601 working panel and the guide rails operated steadily. The measured vibration parameters of the tension in guide rails agree well with that of numerical predictions, which verified the reliability of the numerical model to some extent.

The stability of open-pit mines under low-temperature conditions is critical for safe and efficient coal extraction. However, the mechanisms of rock damage and fracture under combined temperature and stress effects remain unclear, particularly regarding the evolution of mechanical properties under repeated freeze–thaw cycles and varying peripheral pressures. This study investigates the damage and rupture behavior of coal-bearing sandstone in cold-region open-pit mines through experimental testing and theoretical modeling. The research was conducted in three stages: (1) freeze–thaw and peripheral pressure experiments to evaluate mechanical property evolution; (2) acoustic emission monitoring to analyze internal fracture initiation, propagation, and coalescence under temperature–stress coupling; (3) development of a local deterioration model to quantify post-damage strength decay considering low-temperature erosion and freeze–thaw effects. Results show that increasing freeze–thaw cycles leads to a transition from brittle to ductile behavior, while higher peripheral pressures significantly enhance ductility. Mechanical parameters are highly sensitive to peripheral pressure but largely independent of freeze–thaw cycle count. Acoustic emission signals respond strongly to temperature, and temperature–stress coupling governs the three-stage evolution of fracture germination, extension, and penetration. The local deterioration model effectively captures post-peak residual strength and damage evolution. These findings indicate that in regions with higher microcrack density, fault propagation is driven by rapid coalescence under stress concentration, whereas in lower-density regions, it is dominated by gradual fracture growth and temperature-induced expansion. The results provide theoretical guidance for stability assessment and support design in open-pit coal mines in cold environments.