Abstract:Gob-side entry retaining mining is one of the important directions of sustainable development of coal in China.The evolution of pressure relief gas migration reservoir area in mining overburden is different from that of traditional mining methods.In order to further accurately identify the pressure-relieved gas migration reservoir area of overburden strata in gob-side entry retaining mining,the characteristics of fractures on the roof-cutting side and the non-roof-cutting side were studied by numerical and physical-similarity simulation.The dynamic development process and strain distribution law of mining-induced overburden fractures were analyzed.The method of identifying the location of pressure-relieved gas extraction target area in gob-side entry retaining min-ing was proposed,and the field implementation was carried out.The research shows that the low-position over-burden rock is affected by roof cutting and is prone to fracture and collapse,while the overburden rock cracks on the uncut side of the high-position overburden rock area are relatively developed,and the development height of the cracks on the cutting side and the non-cutting side is the same.The shape of mining-induced fractures and the strain shape of overburden rock are trapezoidal.With the periodic fracture of rock strata,the mining-induced frac-tures develop upward in a leap-forward trend.The angle of mining-induced bed separation fracture in different regions is concentrated at 0°-10°,and the angle of vertical fracture zone is mainly concentrated at 80°-120°.Based on the identification of key strata,the angle and number of mining-induced fractures,and the strain charac-teristics of overlying strata,combined with the ventilation mode,a method for determining the target area of pres-sure-relieved gas extraction in gob-side entry retaining mining is proposed.The extraction boreholes are arranged in the area of"acute angle development area of mining-induced fractures+high gas volume fraction".It is deter-mined that the extraction target area of the trial working face is 30-46 m from the vertical distance of the coal seam roof and 30-55 m from the horizontal distance of the auxiliary transportation roadway.The overall gas ex-traction effect during the mining period of the trial working face is good,indicating that the extraction borehole designed based on the determination method of the pressure-relieved gas extraction target area of the gob-side entry retaining mining is reasonable.The research results can provide some reference for the design of pressure-relieved gas extraction boreholes under the "Y" type ventilation mode of gob-side entry retaining mining.

Abstract:The large-scale and high-intensity mining of coal has led to increased mining-related damage,including surface subsidence,ecological degradation,and damage to buildings,railways,and high-voltage transmission lines.These issues have intensified the conflict between resource extraction and environmental protection,making low-loss coal mining an essential requirement for sustainable development.This paper provides a comprehensive analysis of coal mining subsidence control technologies in China,including backfill mining,coordinated mining,partial mining,and grouting bed separation.The implementation principles and application methods of these subsidence control technologies are discussed in detail,along with an analysis of their advantages and disadvantages,existing challenges,applicable conditions,and research advancements.Based on practical engineering applications,the paper examines the effectiveness of surface subsidence control using grouting bed separation,backfill mining,and coordinated mining technologies,highlighting their limitations and future development trends.The results show that grouting bed separation technology offers the advantages of minimal interference with underground mining operations,facilitates green mining practices,and supports the utilization of solid waste.Additionally,further research in China is needed in the following areas:the development of cost-effective,high-performance backfilling materials and process optimization;investigation of the surface deformation mechanisms during coal seam mining to improve subsidence prediction theories;development of efficient coal pillar recovery methods and enhancement of long-term pillar stability;and optimization of the grouting process for bed separation technology,while evaluating the impact of slurry on the groundwater environment.