In order to explore the mining pressure development rule of gob‐side entry retaining during deep thin coal seam mining, FLAC^3D numerical simulation is applied to analyze the stress distribution rule of gob‐side entry retaining, observing the left third working face of 49^# coal seam in No. 8 mining area of Xinxing Coal Mine as the research object. The results show that the working face stress field is asymmetrical which is caused by the reserved roadway and the over goaf. After roadway tunneling, features of obvious stress redistribution are formed. The vertical and horizontal stress in the coal seam develop a U‐shaped distribution. The vertical stress in the roadway is less than that in the lower roadway, and the horizontal stress is half that in the lower roadway. The phenomenon of high stress “nucleation” appears and becomes more obvious in the process of working face advancing, and the nuclear body disappears after working face advanced to the boundary line. With the working surface advancing, the trend of horizontal stress of gob‐side entry retaining decreases gradually and the vertical stress of gob‐side entry retaining is less than the original rock stress. The research findings provide a basis for the supporting design of gob‐side entry retaining in the deep thin coal seam and the stability control of surrounding rock.

After coal mining enters the deep, the mining environment changes dramatically, and engineering disasters become increasingly prominent, which are mostly related to rock instability and failure. As traditional support is difficult to meet production needs, it is necessary to improve the support system. Based on the engineering background of the Pinggang mining roadway, this work studies the migration law of overlying strata in deep goaf by theoretical analysis and numerical simulation. The results show that the vertical stress and plastic failure range of the surrounding rock in front of the working face increase with the advance distance and when the working face advances to the first square, reaching the maximum. A stope spatial model considering the influence of horizontal stress is established. Combined with the theory of key strata, the stress transfer characteristics of overlying strata are analyzed. It can be seen that 0~30 m in front of the coal wall of the working face is the influence range of advanced abutment pressure, and the dynamic mining pressure in this range has a great influence. The inclined direction of the working face, 0~20 m away from the coal wall of the roadway, is the influence range of the solid coal abutment pressure. On this basis, the “migration- transfer- control” technical system of surrounding rock in deep stope face is put forward, i.e., the stress transfer of surrounding rock is caused by overlying rock migration, and the large deformation of surrounding rock is controlled by supporting means. Based on the original support scheme of the roadway, three reinforcement schemes are designed for the roof, the sidewalls, and both the roof and sides. The deformation control effect of the reinforcement scheme is far greater than that of the single factor, and the field monitoring effect is good. The research results aim to provide theoretical and technical support for the deformation control of mining roadways in the deep mining process.

The deformation and failure of underground engineering are usually caused by unloading. In this work, triaxial unloading confining pressure tests are carried out to simulate the failure process of rock mass caused by unloading, analyze the crack-characteristic stress, and study the energy evolution of rock under unloading and the pre-peak and post-peak energy characteristics combined with the energy theory. The results show that, when the confining pressure increases from 5 MPa to 20 MPa, crack closure stress σ_cc, crack initiation stress σ_ci, dilatancy stress σ_cd, and peak stress σ_p are 6.34 times, 2.75 times, 1.93 times, and 1.66 times higher than the original, respectively. By comparing the increase in crack-characteristic stress, it can be found that the confining pressure has a large effect on the crack closure stress and crack initiation stress, while the dilatation stress and peak stress have relatively little influence. From the perspective of energy evolution, the pre-peak axial absorption energy U₁ increases exponentially, the elastic energy U^e is similar to U₁, and the circumferential consumption energy U₃ and dissipation energy U^d are small. After reaching the peak stress, the growth rate of U₁ decreases slightly, U^e decreases rapidly, and U₃ increases rapidly but only as a small fraction of the total energy, while U^d grows almost exponentially and rapidly becomes the main part of the energy. Under each crack-characteristic stress state, the energy characteristic parameters gradually increase with the increase in confining pressure, which is manifested by the increase in slope in the linear fitting formula of energy characteristic parameters. The release process of the releasable elastic energy after the peak stress can be divided into three stages of “slow–fast–slow”, and the energy release process shows an obvious confining pressure effect.

We used the 11,303 return air roadway of the Hongqingliang coal mine as the engineering background for a study exploring the impact of the structural morphology of the roadway on the stress distribution characteristics and the stability of a weakly cemented soft-rock mine roadway. This work studies the evolution law of stress and deformation, and the plastic zone of weakly cemented soft-rock roadways with retaining the top or bottom coal seams. The results show that when retaining the top coal is replaced by the bottom coal, the high-stress zone of the vertical stress is reduced, the peak stress is decreased, and the stress concentration coefficient is slightly reduced from 1.67 to 1.64. The peak value of the vertical displacement of the roof of the shaft which was 78.4% of that of the top coal also decreases significantly, while the peak value of the vertical displacement of the floor, which was 1.37 times that of the top coal, increases. The equal area method was used to change the aspect ratio of the roadway. When the aspect ratio decreased from 1.38 to 0.88, the high-stress zone of the vertical stress was reduced, the stress peak decreased, and the stress concentration coefficient decreased from 1.8 to 1.75. The vertical displacement of the roof increased by 27.7% from 10.91 mm to 13.93 mm, and the vertical displacement of the floor increased by 15.2% from 6.60 mm to 7.60 mm. The plastic failure range was significantly reduced, particularly at the bottom corners. These findings show that structural morphology has a great influence on the floor heave of weakly cemented soft rock. Reasonable retention of the top or bottom coal and the aspect ratio of the roadway can prevent the deformation and failure of the roadway in weakly cemented soft rock.

In order to study the prevention of roadway roof bending, sinking, and breaking and the prevention of dynamic disasters such as the appearance of rock bursts, three-point bending experiments of sandstone under different spans were carried out. By using stress loading system and acoustic emission technology, the acoustic emission characteristic parameters of the sandstone fracture process were analyzed, the precursory information of rock bending fracture was explored, and the evolution law of sandstone damage based on acoustic emission characteristics was obtained. The results showed that according to the variation of acoustic emission ringing count, the load-time curve was divided into four typical stages: the first stage showed an overall increasing trend; the second stage showed an obvious increasing trend; the third stage showed obvious accelerated growth and the acoustic emission ringing count reached the maximum at the moment of rupture. In the fourth stage, the amplitude and frequency of the ringing count are large and high. With the increase in span, the cumulative ringing counts of AE decreased, and the rate of change gradually decreased. The fracture process of three-point bending sandstone can reflect the precursor information of rock fracture from time domain, frequency domain, and R value (ratio of cumulative acoustic emission ringing count to cumulative energy count). In time domain, the evolution characteristics of AE cumulative ringing count stage II can be used to predict the three-point bending fracture of sandstone. The peak frequency shows a linear increase after a spike and then an accelerated increase to a rupture, and the boundary point between the spike and the linear and nonlinear can be obtained. The decrease in R value can indicate that the main crack is growing in the specimen. According to the damage rate, the characteristics of the damage variables can be divided into five stages: stationary and low, gradually increasing, gradually decreasing, main crack coalescence, and complete fracture. With the increase in span, the fracture damage shows a decreasing trend. The residual damage fluctuates between 0.38 and 0.40 due to the difference in crack propagation trajectory. It has theoretical research value for revealing the internal mechanism of rock bending and fracture and has engineering guiding significance for mine pressure and rock strata control and dynamic disaster prevention.

The water inrush from the roof of the coal mine is closely related to the movement failure of overburdened rock and the height of the water-conducting fracture zone. In this work, based on the research background of water disaster prevention and control of the No. 2 coal seam roofs in Jinxinda Coal Mine, the stability characteristics of overlying rock in the working face are analyzed through combining theoretical analysis and numerical simulation. According to the theory of key strata, the fracture conditions of hard rock and soft rock are analyzed, and the maximum height of the water-conducting fracture zone in the 201 working face is calculated to be 35.72 m. The crack evolution law of composite roofs was simulated and analyzed using discrete element software. It was found that the basic roof (4.50 m thick) and the fine sandstone (7.64 m thick) are the two inferior key strata, and the maximum development height of the water-conducting crack is 36 m, which is basically consistent with the field measured results. Transient electromagnetic exploration technology was used to detect the working face, and nine abnormal areas were found. In order to prevent the influence of water disasters in abnormal areas during mining, drilling verification is carried out in abnormal areas. According to the analysis of drilling verification, there are no water disasters in the geophysical anomaly area, but the management of the roof after mining should be strengthened during mining. The expected research results not only enrich the rock formation control theory and roof water inrush mechanism; they also have important practical significance in guiding the safety production of a coal mine.