China’s total coal production in 2021 exceeded 4.13 billion tons, 52% of the world’s total. Coal gangue, a solid waste of coal mining accounts for 15–20% of coal production, when directly discharged on the ground surface as waste heaps, it occupies large areas of land and cause environmental pollution. This paper summarizes the existing gangue backfilling methods, their working principles, efficiency, and application status. The methods that are meeting Middle and Western China’s mining demands are discussed in detail. The state-of-the-art technologies that can realize high-efficiency, centralized, and large-scale underground backfilling of coal gangue are analyzed. This paper shows that the industrial implementation of these technologies can increase the current maximum disposal capacity of coal gangue by three times, reaching five million tons per year. The equipment innovation and automation are analyzed, and the environmental effect of coal gangue backfilling is discussed. This review offers inspirations and guidelines for coal gangue disposal and the environmental hazard reduction of coal mining.

Solid backfill coal mining technology has been widely applied in coal seams that are at risk of hard roof. Using actual measured strain–stress curves of the backfill body and the similarity theory, this study designed and employed four experimental models for physical simulation, corresponding to roof-controlled backfilling ratios of 0%, 40%, 82.5% and 97% using the geological conditions of Face No. 6304 in the Jining No. 3 coal mine—a solid backfill coal mining face under a hard roof. A non-contact strain measurement system and pressure sensors were used to monitor the deformation of the overlying strata and changes in abutment stress ahead of the face during mining of the models for varying roof-controlled backfilling ratios. The results indicated that the solid backfill body was able to support the roof. As the roof-controlled backfilling ratio was increased, the maximum subsidence of the roof and the maximum height of the cracks decreased. When the roof-controlled backfilling ratio was 82.5% or higher, the working face did not display any obvious initial fractures or periodic fractures, and both the value and the impact range of the abutment stress ahead of the face decreased.

A method of paste backfill recovery for residual room coal pillars is hereby proposed. The principles and processes of this method are systemically explained to address issues such as mining-induced earthquakes from spontaneous destabilization, surface subsidence, and low recovery rates. These are caused by the instability of residual coal pillars due to their spontaneous combustion in room-and-pillar mining in medium-to-small coalmines in the northern Shaanxi area. This method is based on the local abundance of surface aeolian sand and solid wastes to be used as paste-backfilling materials in coalmines in the northern Shaanxi area. Uniaxial compressive strength, bleeding rate, and slump tests were performed on paste-backfilled samples constituted at different ratios based on the types of materials involved in paste backfilling in the northern Shaanxi region, thereby helping to confirm the optimal ratios for paste-backfilling materials for the Ershike coal mine. A simulation was conducted to investigate the failure, goaf vertical stress distribution, and surface deformation properties of paste-backfilled pillars and coal pillars, where paste backfilling was used with paste-backfilling materials constituted at different compressive strengths. This was to verify the experimental results that would be obtained with paste-backfilling materials constituted at different ratios, and reveal the mechanism by which paste backfilling of residual room pillars can maintain the mine’s surrounding rock stability. These study results are of great instructive significance to the safe recovery of residual room pillars in China’s western mining areas.

There is a huge amount of solid waste generated in coal resource exploitation and utilization, leading to effects on the environment and hindering sustainable development. Aiming at the difficulty of disposal of coal-based solid waste from high-yield, high-efficiency mines, this research proposed a technique of gangue grouting filling in subsequent space (GGFSS) for coal mining and explored the movement of key strata backfilled using GGFSS technique and surface deformation characteristics using theoretical analysis and a field measurement method. The results indicate that the equivalent backfilled ratio (EBR) when using GGFSS is defined as the ratio of the grouting volume to available void volume, which is mainly affected by bed separation void volume, grouting volume, and the void volume of the caving zone. Using an EBR ground control mechanical model, the changes in the displacement and bending moment of key strata with the variation of the EBR were investigated. The critical EBR for the rupture of key strata was determined to be 74.44%. On this basis, the calculation methods of equivalent mining height (EMH) and the subsidence factor of GGFSS were proposed and then a surface deformation prediction model of GGFSS was established based on the principle of the probability integration method. The predictions implied that, at an EBR greater than 75%, the surface deformation could be significantly reduced. Engineering applications verified the effect of GGFSS on the control of ground movement. In-situ measurements of concentration, density, and particle size of the filling body were all close to the those designed values: the GGFSS technique shows longer grouting duration and a larger amount of grouting and its filling body can support impervious key strata above the working face in a mine, significantly decreasing surface subsidence.

In order to effectively recover the residual coal resources, such as coal pillars and irregular coal blocks induced by large-scale extensive mining, in this study, we proposed a shortwall block mining (SBM) technology and examined the development pattern of the water-flowing fissure zone (WFZ) in the overlying strata during the SBM process. By analyzing the overlying rocks’ movement rules in SBM, the main controlling factors affecting the development of the height of the water-flowing fissure zone (HWFZ) determined are as follows: mining height, block length, and the width of the protective coal pillar among the blocks. Moreover, based on the elastic foundation beam theory, the mechanical model for the calculation of HWFZ in SBM was established. Based on the first strength theory, the calculation formula of the development HWFZ was derived. Using this model, the calculated HWFZ after SBM was 50.3 m, whereas the measured heights of the leakage of drilling washing fluid were 47.98 and 50.06 m, respectively. The calculated values almost fit well with the field-measured data, verifying the reliability of the proposed mechanical model. The results of this study can provide a significant reference for enhancing the recovery ratio of coal resources and optimizing water protection mining theory.