Chaowen Hu

Gob-side entry retaining by roof cutting and pressure relief (CRRE) eliminates coal pillar waste and mitigates mining-induced stress concentration. Although widely applied in mines shallower than 1000 m, systematic research on asymmetric deformation mechanisms and matched control technologies under ultra-deep conditions (>1000 m, σH > 60 MPa) remains limited. This study investigates the 5307 working face of Anju Coal Mine (burial depth: 1127–1195 m) using theoretical analysis, FLAC3D numerical simulation, and 480 m of field monitoring. The stress evolution, deviatoric stress field response, and asymmetric deformation mechanisms of the surrounding rock under ultra-deep mining conditions are systematically analyzed, based on which a targeted collaborative control technology is proposed. The key findings indicate that (1) CRRE significantly attenuates advanced abutment pressure compared with conventional pillar retention, with an average stress reduction of 20.1 ± 1.2% (95% CI: 17.8–22.4%, p < 0.01). (2) During the advanced mining stage, the second invariant of deviatoric stress exhibits a saddle-shaped distribution with a pronounced concentration at the mid-rib, identifying this as the dominant zone for rib bulging failure. (3) In the post-mining entry-forming stage, the roof deviatoric stress field demonstrates marked asymmetric evolution, with the distortion energy on the solid-coal side substantially exceeding that on the gob side; moreover, the low-position roof strata exhibit high distortion and poor stability, rendering them prone to bending fractures. Grounded in these mechanisms, a full-cycle differentiated surrounding rock control technology is developed, integrating pre-mining directional roof pre-splitting, active tough support reinforcement, post-mining temporary roof control and pressure relief, and gangue retaining with rib collaborative protection. The key parameters include a roof cutting height of 7 m, a cutting angle of 15°, NPR constant-resistance anchor cables with W-steel belts, and temporary support extending 300 m behind the working face. Field monitoring reveals staged deformation evolution, with stabilization achieved 250 m behind the working face. Maximum roof subsidence, floor heave, and total roof-floor convergence were 180 mm, 329 mm, and 422 mm, respectively, below the 500 mm allowable threshold for ultra-deep retained entries.

Aiming at the “three‐low” challenges (low permeability, low gas saturation, and low critical desorption‐to‐storage ratio [CDSR]) of Chinese coalbed methane (CBM) reservoir materials, this study adopted chlorine dioxide (ClO ₂ ) chemical modification on long‐flame, coking, and anthracite coal materials. Integrated macroseepage experiments with microscale characterization were used to quantify the regulation of key CBM parameters. Results show that ClO ₂ simultaneously enhances permeability, gas saturation, and CDSR. Under optimal conditions, coking coal permeability rose from 0.62 to 4.85 mD (+682%); permeability of long‐flame coal and anthracite increased by 15.0% and 8.9%, respectively. Average gas saturation of the three ranks increased by 18.7%–25.3%, and critical desorption pressure dropped by 15.6%–22.3%. Microscopically, ClO ₂ oxidizes coal materials to generate –OH and –COOH groups (peak areas +38.5%–46.2%) and dissolves clay minerals (kaolinite content −10.8%–14.5%), thereby widening fractures and refining pores. Coal rank responses differ: Anthracite requires 3.0% ClO ₂ for 36 h, whereas long‐flame coal reaches optimum at 2.0% ClO ₂ for 24 h. The findings demonstrate that ClO ₂ can overcome the limitations of conventional stimulation techniques and provide a practical pathway for efficient development of “three‐low” CBM reservoirs in China.

To alleviate strong strata-pressure bursts during ultra-thick coal extraction, we selected the 26 m number five seam of the Chenjiagou Coal Mine as a full-scale prototype. Three objectives were pursued: (1) elucidate the initiation mechanism of high-energy roof failures under top-coal caving (TCC); (2) quantitatively link the failure sequence of key strata to burst intensity; and (3) deliver field-oriented prevention criteria. A 1:300 physical similarity model and UDEC plane-strain simulations were combined to monitor roof deformation, stress evolution and dynamic response during extraction. Results demonstrate that pressure bursts are driven by abrupt kinematics of the overburden, triggered by sequential breakage of key horizons: the secondary key stratum collapsed at 130 m face advance, followed by the main-key stratum at 360 m. Their combined rupture generated a violent energy release, with roof displacement accelerating markedly after the main horizon failed. We therefore propose two dimensionless indices—the dynamic load factor (DLF) and stress concentration factor (SCF)—to characterize burst severity; peak values reached 1.62 and 2.43, respectively, while pronounced stress accumulation was localized 6–15 m ahead of the face. These metrics furnish a theoretical basis for early warning systems and control strategies aimed at intense rock burst.

To reduce the cost of coal mine filling materials, a novel composite cementitious material was developed by utilizing coal-based solid waste materials, including fly ash, desulfurized gypsum, and carbide slag, along with cement and water as raw materials. Initially, a comprehensive analysis of the physical and chemical properties of each raw material was conducted. Subsequently, proportioning tests were systematically carried out using the single-variable method. During these tests, multiple crucial performance indicators were measured. Specifically, the fluidity and bleeding rate of the slurry were evaluated to assess its workability, while the compressive strength and chemically bound water content of the hardened sample were tested to determine its mechanical properties and hydration degree. Through in-depth analysis of the test results, the optimal formulation of the composite cementitious material was determined. In the basic group, the mass ratio of fly ash to desulfurized gypsum was set at 70:30. In the additional group, the carbide slag addition amount accounted for 20% of the total mass, the cement addition amount was 15%, and the water–cement ratio was fixed at 0.65. Under these optimal proportioning conditions, the composite cementitious material exhibited excellent performance: its fluidity ranged from 180 to 220 mm, the bleeding rate within 6 h was less than 5%, and the 28-day compressive strength reached 17.69 MPa. The newly developed composite cementitious material features good fluidity and high strength of the hardened sample, fully meeting the requirements for mine filling materials.

During the process of close-distance seam group mining, the coal pillar in the upper coal seam is a stress-concentrated area, which leads to a loss of stability of the roadway during mining of the lower coal seam. This lack of stability introduces great safety hazards to coal mines. To solve the problem of stress concentration of coal pillars, the method of gob-side entry retaining by roof cutting is proposed to remove the coal pillar. In this study, FLAC3D was used to analyze the depth and angle of pre-split blasting. LS-DYNA was used to analyze the spacing of the blasthole. Using the methods of theoretical analysis and numerical simulation, we determined that the optimal depth of the pre-split blasting was 6 m, the optimal angle for pre-split blasting was 15°, and the optimal spacing of the blasthole was 500 mm. A field test was carried out in the 1010201 ventilation roadway of the Yuwang Coal Mine, China. The on-site peeping results showed that when the spacing of the blasthole is 500 mm, connecting cracks can form under the action of blasting stress. After the working surface is mined, the roof strata could collapse and fill the gob over time when the depth and angle of the pre-split blasting are 6 m and 15°, respectively.

With the increase of mining depth, the gas management problem in coal and gas outburst mine is more prominent. At the same time, gas is used as a clean resource to mine together with coal which is to realize the simultaneous extraction of coal and gas more practical significance. The relation between coal mining and gas extraction is mutually reinforcing and restricting. It is of great theoretical significance and application value to study simultaneous extraction of coal and gas technique optimization. The Qidong Coal Mine of the Wanbei Coal and Electricity Group is a coal and gas outburst mine. The spacing of the coal seam is small, the occurrence conditions are complex, and the mining is difficult. This study used theoretical analysis, numerical simulation, and engineering analogy to investigate the coordinated mining technology of coal and gas in outburst coal seams.

In order to ensure the application of gob-side entry retaining by roof cutting for thick and hard sandstone roofs, the key technology of pre-split blasting was studied. The LS-DYNA was used to analyze the blasting effect of the energy-gathering pipe. Using the methods of theoretical analysis and numerical simulation, it was determined that the optimal cutting height was 16 m and the optimal cutting angle was 15°. The effect of pressure relief by roof cutting was verified by FLAC3D. It is proposed to use deep-hole loosening blasting to solve the problem of the sandstone with a thick hard roof being difficult to collapse. A group of loose blasting holes was designed to be arranged every 20 m in the gob-side roadway. The depth of the #1 blasthole was 47 m, and the angle to the horizontal direction was 20°; the depth of the #2 blasthole was 65 m, and the angle to the horizontal direction was 15°. A field test was carried out in the 7135 ventilation roadway of Qidong Coal Mine China. The on-site peeping results showed that the blasting with the energy-gathering pipe had a good effect of directional slitting. After deep-hole loosening blasting, the thick hard sandstone roof collapsed and filled the gob in time. The monitoring curves of the hydraulic support showed that the hydraulic support resistance of the working face in the side with roof cutting was much smaller than that of the side without roof cutting, and the effect of pressure relief by roof cutting was good.

Filling mining is a main technology of mining coal resources under buildings, and it has a good effect on preventing ground subsidence. Taking Wangtaipu coal mine of the Shanxi Jincheng Anthracite Coal Mining Group as the engineering background, in order to solve the problem of traditional closed brick wall at the end of working face, which consumes a lot of manpower and material resources, and low efficiency, a technology of rapid-molding in-closed retaining-wall was proposed. Through theoretical analysis and engineering analogy, the overall structure and size of the mold bag were designed. Through the experiment of high-water bleeding rate and slurry expansion, it was determined that the best water-cement ratio was 0.85:1, and the best additive content was 25kg/m³. Taking economic factors into consideration, it was determined that liquid sodium silicate was used as the admixture. The XV2308 working face was selected for on-site testing and the on-site monitoring of the roof pressure, the roadway deformation, and the stress of the coal body. The results showed that there was no large area roof pressure on the working face, the coal body was under stable force, the stress concentration coefficient was small, the coal pillar had no plastic failure, and the roadway deformation was small. Through on-site monitoring of ground subsidence, the results showed that the amount of ground movement and deformation were small. The maximum value of subsidence was 12mm, which could meet the requirements of safety production and had significant economic benefits.