In view of problems with roadways with a compound roof, such as the occurrence of instability in the roof strata, ease of separation of the layer caving, difficulty of maintenance, and poor safety, we established a mechanical calculation model of a roadway with compound roof using the elastic mechanics theory, taking the stability control of a roadway with compound roof at a coal mine in Guizhou Province, China as the research background, and based on the actual characteristics of the coal seam and the roof and floor slate. Expressions of the separation layer and instability limit load of compound roof were derived, and the calculation and verification were carried out in combination with the actual conditions. By means of numerical simulation, the distribution and evolution laws of stress, displacement and plastic zone of roadways with a compound roof were studied, and the deformation characteristics and instability mechanism of roadways with a compound roof were revealed: (1) in early stage deformation of roadway, the amount is large, the speed is fast, and the scale is wide; (2) compound roofs are vulnerable to abscission and instability, the bearing capacity of the two sides is low due to softness and cracking, the shear failure of side angles and vertex angles weakens the strength of surrounding rock, and the self-bearing capacity of surrounding rock is low; (3) the bolt and anchor bear relatively large tensile force, and the support structure is easy to be broken up. On this basis, the stability control principle of a roadway with compound roof tunnel was put forward: fast and timely support; high-strength bolt strong support; improving the stability of the roof and the bearing capacity of the two sides; restraining the shear failure of the key bearing parts such as the side angles and the bottom angles, and targeted stability control technology for roadways with a compound roof was developed. The field industrial test showed that the deformation of this roadway with a compound roof was effectively controlled and the overall stability of the roadway was effectively improved. The results of this study could provide useful reference for a roadway with a compound roof under similar conditions.

In this paper, to investigate mixed-mode I-II fracture behaviors, three different asymmetric notched semi-circular bending specimens (ANSCB) were designed by adjusting the angle and the distance between supporting rollers to conduct asymmetric three-point bending tests. Several aid technologies, including acoustic emission (AE), digital image correlation (DIC), crack propagation gauge (CPG), and scanning electron microscopy (SEM), was utilized to monitor and assess the fracture characteristic. Meanwhile, the fractal dimension of the fracture surface was assessed based on the reconstructed digital fracture surface. The results show that mixed-mode I-II ANSCB three-point bending fracture is a brittle failure with the characteristics of the main crack being rapidly transfixed and the bearing capacity decreasing sharply. Based on the DIC method, the whole fracture process consists of a nonlinear elastic stage, fracture process zone, crack initiation stage and crack propagation stage. The crack initiation is mainly caused by the tension-shear strain concentration at the pre-existing crack tip. At the microscale, the crack propagation path is always along the grain boundary where the resultant stress is weakest. According to the monitoring of the AE, it can be found that micro-tensile cracks are mainly responsible for the asymmetric three-point bending fracture. The data obtained by CPG suggest that the subcritical crack growth rate is positively correlated to the ultimate load. In addition, asymmetric loading leads to a coarser fracture surface, and thus a higher fractal dimension of the fracture surface. The current study can provide a better understanding of the mixed-mode I-II fracture behaviors of rock.

Different from the traditional goaf-side entry in the mining face, a goaf-side entry driving heading mining face can greatly alleviate the problem of mining and excavation replacement tension under the high-intensity mining condition of a single-wing mine, withstanding the whole process of the fracture, rotation, and sinking of key blocks in the overlying rock layer, which is extremely difficult to maintain. Taking the roadway layout in a single-wing mining face of a coal mine in Neimenggu, China as the research background, first, the stress environment and structural stability characteristics of a goaf-side entry driving heading mining face is qualitatively analyzed with the theoretical analysis method according to five different stages. Secondly, the distribution and evolution law of stress and displacement with a goaf-side entry driving heading mining face are systematically studied during the whole process of advanced mining, excavation, and mining with the numerical simulation method, and the reasonable width of the section of the coal pillar is determined to be 6.0 m. Finally, the deformation laws of a goaf-side entry driving heading mining face are revealed with the field survey method: (1) the stage of advanced mining—the function relation between the distance of the excavation and mining face and roadway displacement is approximately the logistic function; (2) the stage of goaf-side entry driving—the function relation between roadway displacement and the driving distance basically forms the exponential function. Based on the above research, the dynamic segmentation control principle of “high-resistance support, dynamic monitoring, sectional control, consolidation coal sides, and stable roof control” and the dynamic segmentation control technology of “section combined strong support of anchor, net, cable, and beam, narrow coal pillar grouting and reinforcement in key periods, strengthening support of the roof with a single pillar π steel beam”, and industrial tests are carried out on site. The monitoring results of the underground pressure show that the deformation failure of the goaf-side entry driving heading mining face is effectively controlled with the control principle and technology, the difficult problem of mining and excavation replacement tension is alleviated with the single-wing mine, and the useful reference and reference for the engineering practice under similar conditions are provided.

In order to study the influence of the softening and swelling of weakly cemented soft rock on the stability of roadway surrounding rock, based on the background of the general return airway in the south wing of Yuwu coal mine, 4 different schemes are designed according to whether the softening or swelling effect of weak cemented soft rock is considered. Based on the numerical simulation program, FLAC^3D was used to analyze the distribution characteristics of the shear stress, displacement, and plastic zone of the surrounding rock of the roadway under these 4 designs. On this basis, in view of the geological conditions of the roadway, a new type of grouting+anchor cable mesh+bottom arch combined support plan is proposed. The research results show that, under the conventional anchor-net-cable-spraying support scheme, the surrounding rock of the roadway can remain stable without considering the softening and expansion of the weakly cemented soft rock in contact with water and its maximum displacement and plastic zone depth are only 66.9mm and 2.8m. When considering the softening and swelling of weakly cemented soft rock roadways, due to the synergistic effect of the two, the maximum displacement of the surrounding rock of the roadway and the depth of the plastic zone will reach 517.4mm and 6.7m, respectively, which will continue to increase with excavating along the roadway and lead to ultimately destabilization and destruction. After adopting the combined support of grouting+anchor cable mesh+bottom arch, the maximum displacement of the surrounding rock of the roadway and the depth of the plastic zone will be reduced by 77.192.0 and 18.772.4, respectively, and they will basically remain stable after excavation of 5 days.