In China, backfill mining has been selected as an effective approach to realize the green mining of underground coal resources, where backfill materials are the major factor in the development of backfill mining. In order to provide a better reference for further research and development of backfill mining, the experience and research achievements are reviewed in this paper. Firstly, the backfill materials that have been successfully applied in Chinese underground backfill coal mining are divided into two categories according to whether water is used during the backfill mining operation. Then, the primary considerations of each backfill material during its preparation, transportation and activation stages are discussed and evaluated. Finally, suggestions for backfill material exploration are proposed in terms of the future backfill mining of coal resources in Western China, where there is serious surface desertification.

Strip filling mining significantly improves coal recovery rates and fosters sustainable development in the coal industry. To investigate the overburden movement patterns of strip filling mining, a mine in Tuokexun was selected as the study site. The stability of the composite structure in upward mining faces, as well as the stress distribution and fracture characteristics of the overburden at different stages of strip filling mining, were analyzed using theoretical methods, numerical simulations, and similarity experiments. The results show that, under the synergistic effect of coal pillars and filling material, a stable support structure can be achieved with an isolation coal pillar width of 15 m and a filling body width of 150 m. During the filling mining stage, the overburden damage range exhibits an upward-sloping trapezoidal distribution, with the lower section experiencing greater damage than the upper section, though the overall integrity remains intact, significantly reducing the risk of impact hazards. During the caving mining stage, the initial breaking spans of the immediate roof and main roof are 40 m and 80 m, respectively, with periodic breaking spans of 20 m, compared to traditional horizontal mining, the insufficient collapse of the lower goaf side requires focused protection. As the mining face advances, overburden displacement stabilizes, and stress concentration remains low without any significant stress mutations, contributing to the stability and safety of underground operations.

Gravel layers are vital ecological barriers in Gobi Desert mining areas. However, open-pit activities increase wind and soil erosion. Thus, the effects of fly ash addition, water content, and compaction on the shear strength and wind erosion resistance of soil crusts were explored by compaction tests, direct shear tests, and wind tunnel experiments. (1) The results of the direct shear test and vane shear test show that the modified soil sample achieved the maximum shear strength under the conditions of 15% fly ash content, 13% water content, and 3 compaction cycles. (2) The results of the wind tunnel test indicate that the wind erosion resistance of the gravel layer soil crust was improved after fly ash treatment. Compared to the untreated soil crust, the wind erosion amount of the treated soil was reduced by 23%. (3) Microscopic analysis revealed that hydration products from fly ash filled the soil pores, enhancing particle bonding and soil structure, using a scanning electron microscope (SEM) and an X-ray fluorescence spectrometer (XRF). (4) Considering the water scarcity in the Eastern Junggar Coalfield of China, a revised rehabilitation scheme was selected, involving 11% water content and single compaction, offering a balance between performance and economic efficiency. This study provides a novel approach to gravel layer restoration in arid mining regions using fly ash as a soil stabilizer, offering a sustainable method to enhance wind erosion resistance and promote fly ash recycling.

Adsorption thermodynamic characteristics are an important part of the methane adsorption mechanism, and are useful for understanding the energy transmission mechanism of coalbed methane (CBM) migration in coal reservoirs. To study the effect of coal pore characteristics on methane adsorption heat, five different types of rank coals were used for low-pressure nitrogen, low-pressure carbon dioxide, and methane adsorption experiments. Pore structure and adsorption parameters, including maximum adsorption capacity and adsorption heat, were obtained for five coal samples, and their relationships were investigated. The results show that the low-pressure nitrogen adsorption method can measure pores within 1.7–300 nm, while the low-pressure carbon dioxide adsorption method can measure micropores within 0.38–1.14 nm. For the five coal samples, comprehensive pore structure parameters were obtained by combining the results of the low-pressure nitrogen and carbon dioxide adsorption experiments. The comprehensive results show that micropores contribute the most to the specific surface area of anthracite, lean coal, fat coal, and lignite, while mesopores contribute the most to the specific surface area of coking coal. Mesopores contribute the most to the pore volume of the five coal samples. The maximum adsorption capacity has a significant positive correlation with the specific surface area and pore volume of micropores less than 2 nm, indicating that methane is mainly adsorbed on the surface of micropores, and can also fill the micropores. The adsorption heat has a significant positive correlation with the specific surface area and pore volume of micropores within 0.38–0.76 nm, indicating that micropores in this range play a major role in determining the methane adsorption heat.

The efficient and safe extraction of ultra-thick coal seam in the Xinjiang East Junggar Basin has been a major focus in the future of mining in China. This paper systematically studied the overburden strata fracturing process and the structure evolution characteristics based on a typical ultra-thick coal seam condition in Xinjiang, using both physical and numerical modeling studies. The interactions between shields and the roof strata were also examined, from the perspective of ground support. The results indicated that roof structure was mainly in the form of voussoir beam at the early mining stage, where overburden stability was affected by the rock mass properties and mining parameters. The support load mainly included top coal and immediate roof gravity load and the load caused by main roof rotary consolidation. As a result of mining disturbance and strata movement, the overlying strata re-fractured in the later mining stage. The roof structure changed from beam to arch gradually and propagates upwards with the increase of multi-layer mining times. The support load was mainly the gravity load of the friable rock mass within compression arch. The results will provide a guideline for the improvement of roof stability under similar mining conditions in Xinjiang.

To identify mechanism of sand particle size effect on the mechanical properties of gypsum cement, 11 grades of sand particles with a size of 0.1–3 mm were used to produce 99 specimens for uniaxial compression and permeability coefficient testing. Based on this, the distribution characteristics of internal stress and horizontal displacement are discussed using the numerical analysis. The results obtained show that the sand particle size effect on the uniaxial compressive strength of similar materials is negatively correlated within the range from −16.51% to 49.79%. SEM observations imply that, in the case of small particle sizes, gypsum crystals develop into denser needle-like structures, while for larger particle sizes, they are mostly loose lamellar structures. Permeability tests indicated that the larger the sand particle size, the greater the permeability, indicating that the internal pore connectivity is better, and the crevices are easier to penetrate when the specimen is compressed. Numerical simulations indicated that the larger the particle size, the larger the extreme deformation value of the specimen in the horizontal direction, and the more uneven the deformation distribution. In addition, specimens with larger particle sizes had a larger total area, where the tensile stress exceeded the ultimate tensile strength, and were more prone to tensile failure.