Backfilling mining is thought to play a significant role in controlling the deformation of coal and rock strata and the distribution of underground pressure. This study presents a numerical investigation of the influence of the strength of backfilling materials (BMS) on the deformation of coal and rock strata consisting of multiple goaf during excavation using the backfill mining method. In this study, a numerical three-dimensional fast Lagrangian analysis of continua (FLAC 3D) model was constructed to explore the relationship among the BMS, the displacement of coal and rock strata, and the distribution of underground pressure based on the geological conditions of a mining panel of the Hengda coal mine in the City of Fuxin, China. The numerical results suggest that as the BMS increase, the supporting ability of backfilling materials in goaf becomes stronger. At the same time, when the displacement of coal and rock strata decrease, the pressure on the surrounding rocks decreases and the pressure on the overlying stratum increases. However, the effect of BMS on the coal and rock strata has a limit. When the BMS equals and/or exceeds that of coal, the influence is not obvious. In addition, the displacement and underground pressure in the surrounding goaf are also affected, but in a relatively gentle way. Moreover, during the process of mining, as the BMS increases, the scope and arch area of the underground pressure in front of working face decrease instead. The higher the BMS is, the more stable the main key stratum is. The ability to resist compressional deformation of backfilling materials plays an important role in controlling the displacement of roof and relieving the underground pressure on the overlying stratum. Thereby, the roof stability in front of the working face is helpful for safety in the production of coal mines.

Exploring the propagation of stress waves in rocks with preexisting discontinuities is of great importance to reveal rock and geological engineering problems, particularly dynamic disasters like earthquakes and rockbursts in underground coal mining. In this paper, six 3D models established with COMSOL Multiphysics are employed to explore the influence of two preexisting faults with different orientations on the propagation process of explosion‐induced stress waves and the reflection effect. Considering the propagation process of stress waves, the interactive effect between two different size faults is discussed. The results show that the dip angles of the preexisting fault and the differences of the elastic modulus, density, and Poisson’s ratio between faults and rocks have great influence on the distribution of stresses and strain‐energy density. Immediately after the stress wave induced by blasting arrived at preexisting fault A, a relatively high concentration of the strain‐energy density was observed at the last wave before passing through fault A. The presence of faults leads to the reflection of most of the blast energy. When the stress wave propagates across fault A, the strain energy stored in the stress wave becomes attenuated; thus, most strain energy was absorbed by the fault’s domain. Finally, the modeling results were implicated in Chaoyang Coal Mine to account for the distribution of the observed seismic events. This study has guiding significance for the attenuation law of stress waves passing through joint/fissure zones in geological engineering, earthquake engineering, and underground mining engineering.

As the coal mine gets deeper and the stopes’ structures become more complex, gas and coal spontaneously burned composite disaster seriously threatens the efficient operation of coal mines. To study the interaction process and disaster-causing mechanism of gas and coal spontaneous combustion (GCSC), this paper establishes a numerical model to study the influence of drilling location/pressure and N₂ injection on the evolution of gas and coal spontaneously burned composite disaster in the goaf. The simulation shows that in the central part of the goaf, a combined area of gas and coal combustion poses a possibility of spontaneous combustion calamity, and the length of the compound disaster area is about 20 m. The methane (CH₄) explosion zone and the dioxygen(O₂) temperature rise zone do not overlap in the air entrance roadway and return air roadway, indicating that there is no risk of compound disasters. The optimal nitrogen (N₂) injection rate for this working face is 2000 m³/h, and the N₂ port should be located 25 m profound into the goaf, which can effectively drive the diffusion of N₂ and narrow the O₂ zone’s breadth. The findings have considerable engineering applications for revealing the evolution process, risk assessment and control for GCSC compound disasters in coal mines.