Maintaining surrounding rock mass stability of roadways is essential to the safety of deep coal mining. In this study, the No. 2‐2092 roadway of the No. 2‐209 mining face in Ganhe coal was taken as the target roadway for field analysis. The selected region can be considered a typical area with dominating geological tectonic stress, based on the geological survey and in situ stress results. A mechanical model of roadway overburdens was developed to analyse the large deformation and stress field distribution. It is found that the large deformation is caused by the combined superposed stress field including laterally transferred stress formed in structures at overlying strata, mining‐induced advanced abutment pressure, and the regional in situ stress. Thus, a Two‐Direction Hydrofracturing Technique (TDHT) was proposed to reduce the pressure of the No. 2‐2092 roadway by altering the roof structure in the influenced zones. Compared with the original roadway without fracturing, it is found that the roof to floor convergence has dropped by nearly 47% after fracturing; the displacement of sidewalls has reduced by almost 31%, demonstrating the effectiveness of the proposed method in pressure relief. Results from this study can provide guidance on controlling the large deformation of roadways in deep underground mines.

Rock and soil masses in geotechnical engineering projects, such as tunnels, mines and slopes, undergo relative motion, exhibiting mechanical characteristics of solid–fluid transition under critical conditions. This work analyzes the characteristics of the solid–fluid transition interface and the mode of load transfer through biaxial compression particle flow photoelastic experiments on granular materials. The study documents that this interface forms an arch shape, marked by a force chain arch. The granular material exhibits two distinct states depending on its position: below the arch, the granular material is in a solid–fluid transitional state, with bearing capacity reduced, while above the arch, it is in a stable solid state, capable of bearing the overlying rock layer’s load. The presence of the force chain arch alters the direction of the originally downward-transferring load, redirecting it along the trajectory of the arch. Analysis of the force and stability of the force chain arch revealed that the arch shape parameters and boundary loads control the instability of the arch. Changes in the overlying and lateral loads lead to different types of instability of the force chain arch. The findings of the study are crucial for underground engineering construction and for the prevention of geological disasters related to granular material.

Considering the large mined area, wide strata moving range, strong mine pressure occurrence, and difficult roof control for the fully mechanized top coal caving in 20 m ultra‐thick coal seams, this study analyzes the strata structure evolution and mine pressure occurrence behavior through field test, numerical simulation, and theoretical analysis. Based on the mine condition of the Tashan Coal Mine in the Datong mining area, mechanical models are established for the compound overlying structures. The following can be demonstrated from this study: (1) The hard strata can form three different compound spatial structures at different positions in the overlying rock strata, including the lower combined cantilever structure I, the middle combined cantilever structure II, and the upper hinged structure. (2) Failure of the higher structure can induce compression on the lower structure, which changed the break span of the lower structure. (3) “Simultaneous and nonsimultaneous structural failures” of the compound spatial structure were caused by the variation of the break span of the multilayered structure. (4) Based on the weighting characteristics, there were three stages during work face weighting, including a gradual pressure increase stage (Stage I), an accelerated pressure increase stage (Stage II), and a fast pressure increase stage (Stage III). (5) The mine pressure occurrence demonstrated a “small to medium and to large” feature. (6) Prefracturing techniques should be additionally incorporated to prevent simultaneous failure of the multilayered structure. Findings of the work can demonstrate the emergence of strong mine pressure in the Datong mining area and have theoretical significance and reference value for maintaining safe mining in similar conditions.

Artificial support system takes advantages of self-bearing capacity of surrounding rock mass in roadway support, which is one of the important supporting ideas in modern times. The implementation way of an artificial support system is worthy of deep investigation. In this study, an HLBR hypothesis was proposed with comprehensive consideration of mechanical properties of surrounding rock mass based on the reinforced arch theory and axial variation theory. A model of bearing structure in surrounding rock mass was constructed, and the stress state on the bearing structure was analyzed. It was believed that when the axial ratio (k) of this bearing structure is equal to the lateral stress factor (λ) (which is the optimal axial ratio), the tangential stress on the bearing boundary reaches the minimum and is in uniform distribution. At this moment, the roadway and the supporting structure can make good use of the self-carrying capacity of surrounding rock mass, which is conducive to lowering the stress distribution level of surrounding rock mass. According to prestress diffusion characteristics of bolt, some ways to achieve HLBR were proposed, which were the optimal axial ratio design, difference support and local grouting modification, and finally performance of the original support design in a belt roadway of the mining district IV of a mine in Shanxi Province. A new supporting scheme was provided according to the HLBR hypothesis. In addition, the FLAC3D strain-softening model was modified by C++, which was used to interpret the reasonability of the suggested supporting scheme. The proposed HLBR hypothesis discloses ways to use self-capacity of surrounding rock mass. This study provides a new idea for roadway sectional design and roadway support design, which are beneficial to maintaining the stability of surrounding rock mass in roadways.

Rock joints are widely present in engineering rock masses, and their peak shear strength directly governs the stability of jointed rock masses. To investigate the influence mechanism of joint surface morphology on the peak shear strength, this study fabricated 35 sets of joint specimens with five distinct morphological types using a combination of three-dimensional laser scanning and CNC engraving technologies. Based on the scanning results, an improved 3D apparent dip angle distribution function was proposed, which more accurately captures the spatial distribution characteristics of joint surface morphology. By integrating this function, a new 3D roughness index was developed. This index exhibits a clear linear relationship with the sampling interval and decreases as the interval increases. Subsequently, a series of constant-normal-load direct shear tests on rock joints was conducted. Test results revealed a strong linear correlation between this roughness index and the initial (zero-normal-stress) peak dilation angle. Moreover, the degradation trend of the peak dilation angle with increasing normal stress can be effectively described by an exponential function. On this basis, a peak dilation angle degradation model was defined, which enables accurate prediction of peak dilation angles under varying normal stress conditions. By incorporating this model into the Mohr-Coulomb criterion, a peak shear strength model was established. Comparative analysis with existing models, including validation against published data on granite joints, demonstrates that the proposed model offers the highest prediction accuracy (R² = 0.978; mean relative error = 4.25%), making it suitable for reliably estimating the peak shear strength of rock joints.