According to the new stress distribution pattern and the strong strata behaviors as the characteristics of the coal pillars in the close‐distance multiseam coal pillar mining, the common characteristics of different types of overlying coal pillars were summarized and analyzed. Moreover, a theoretical model for the mechanism of strong strata behaviors in the close‐distance multiseam coal pillar mining was established, which was validated by the monitoring data of seismic computed tomography CT, microseism, and electromagnetic radiation (EMR). Furthermore, the results of the study indicated that the main factors affecting the strong strata behaviors were the static stress concentration caused by the overlying coal pillars and the dynamic disturbance caused by the fracturing and slipping of the overlying coal pillars and roof under the influence of mining. In the case of Xinzhouyao coal mine, the transmitted stress and lateral support pressure of the overlying coal pillars accounted for 78.3% and 16% of the vertical concentrated stress, respectively, and the areas closer to the overlying coal pillars were more susceptible to dynamic load disturbances. The monitoring results of seismic computed tomography CT and EMR demonstrated the static load stress concentration area was distributed near the overlying coal pillar, and the stress concentration degree was greater in the area of superimposed lateral support pressure and advanced support pressure. Moreover, microseismic spatial positioning revealed that the high‐energy microseismic events were mainly concentrated near the overlying large coal pillars and roof. The on‐site multiparameter detection results were highly consistent with the characteristics of actual strata behaviors and the conclusions of the theoretical model. This method could provide a reference for the quantitative calculation of stress distribution under similar conditions and the identification of the danger zone of strata behaviors.

Roadway deformation and rock burst are the two key challenges faced by the safe operation of coal mines. Aiming at the issue of large deformation of the gob‐side roadway under coal pillars in multiseam mining, this study has considered the case of the 8308 panel of Xinzhouyao coal mine in China. Based upon a combination of theoretical analysis, numerical simulations, and engineering practices, the mechanical model of “stress and deformation quantitative calculation of gob‐side roadway under overlying coal pillars” was established in this study. The analytical solutions of the vertical stress distribution and the plastic zone of the gob‐side roadway under overlying coal pillars were obtained. Finally, the accuracy of the mechanical model was verified using numerical simulations. The results showed that the coal pillar, upright above the gob‐side roadway, and the cantilever roof around the gob‐side roadway were the main factors leading to stress concentration and deformation around the gob‐side roadway. For the particular cases considered in this study, the peak stress of the gob‐side roadway could reach 1.8 times of the self‐weight stress of overlying strata. The rates of the contribution of the gob‐side roadway’s overlying pillar and the cantilever roof around the gob‐side roadway to peak stress were 78.3% and 16%, respectively. The obtained results have an essential reference significance for stress calculations and rock burst prevention design of gob‐side roadway under overlying coal pillars in multiseam mining.

Joints are the weak plane structures in coal. The existence of joints leads to coal failure, with different fracture modes and energy evolution laws. In this paper, the energy evolution and bursting liability index of coal failure with different joint inclination angles (JIAs) are analyzed. The results show that with an increase in joint inclination angle (JIA), the total energy and elastic energy of coal first decrease and then increase and the dissipation energy decreases gradually. The existence of joints changes the bursting liability of coal. With an increase in the JIA, the uniaxial compressive strength (Rc) of coal first decreases and then increases, the dynamic failure time (DT) gradually decreases, and the impact energy velocity index (W_ST) and the impact energy index (K_E) gradually increase. With an increase in the JIA, coal went from tensile failure to shear failure and tension shear mixed failure. After coal failure, the fractal dimension was between 1.7 and 2.4, decreasing first and then increasing; the larger the JIA and the degree of fragmentation, the more energy consumed at the moment of failure and the stronger the bursting liability of coal. The results have a guiding significance for the monitoring and prevention of rock bursts in coal mines.

To solve the high slurry pressure and severe wear at some sections in backfilling pipelines, this study investigates the solution of using an auxiliary pipe to increase the resistance and reduce the pressure of the mine backfilling pipeline. Using computational fluid dynamics, three auxiliary pipe models, a Z-shaped pipe, a S-shaped pipe and a spiral pipe were constructed and the velocity and pressure distribution characteristics of the filling slurry in the auxiliary pipes were analyzed. The function of friction loss in spiral pipes with different pitches and spiral diameters was established, and the amendment equation for calculating the effective stowing gradient was studied when using spiral pipes to increase resistance and reduce pressure. The results show that, compared with the Z-shaped pipe and the S-shaped pipe, the velocity and pressure in the spiral pipe change continuously and steadily, and there is no obvious sudden change in the local velocity and pressure. Therefore, it is difficult to burst the pipe. When the velocity is 2.5 m/s and the vertical height of the pipe is 2.5 m, the friction loss of the filling slurry in the spiral pipe can reach 3.87~21.26 times that in the vertical pipe, indicating that the spiral pipe can effectively play the role of increasing resistance and reducing pressure. The relationship between the friction loss and spiral diameter is a linear function, and the relationship between the friction loss and pitch is a quadratic function. The three are binary quadratic function relationships. The equation for calculating the effective stowing gradient is obtained, which provides a convenient method for engineering applications and industrial design.

The mechanism of rock burst induced by the superposition of dynamic and static loads in multicoal seam mining is unique. To investigate the propagation attenuation law of large‐energy microseismic events and the induced mechanism of rock burst under this condition, this study employs FLAC3D's dynamic module to simulate and analyze the influence of propagation distance, overburden structure in multicoal seam mining, and interlayer plastic zone on vibration wave attenuation. Results indicate that when coal seams are mined at close distances, vibration waves experience significant attenuation while passing through the plastic zone between two layers of coal. At equal attenuation distances, multicoal seam mining structures exhibit greater effects on vibration wave attenuation. Considering differences between rock‐burst induction mechanisms in close‐distance coal seam group mining versus single coal seam mining, a discriminant criterion for rock bursts induced by superimposed dynamic and static loads in multicoal seam mining is established along with a monitoring and early warning method suitable for such conditions.