Buchu Zhang

The instability of jointed rock masses has been a persistent concern in China’s underground geotechnical engineering, particularly regarding rock mass instability triggered by structural activation, such as faulting. This form of instability constitutes a significant type of dynamic geological hazard in the field of geotechnical engineering. Research on the mechanism of jointed rock mass instability typically concentrates on various characteristics associated with structural activation but frequently neglects the interplay between coalescence instability within the jointed zones and the intact zones, as well as the development and evolution of abrupt water channels. To delve into the coalescence instability characteristics between jointed and intact zones, this study conducted uniaxial compression tests on macro-scale pre-fabricated jointed sandstone. The research results show that the failure process of the specimen consists of a strong deviation linear stage, a sub-critical stage, and an unstable stage. The main failure process occurs during the sub-critical stage.

In the western mining region, weakly cemented rock layers above the coal seams often lead to frequent catastrophic accidents during mining due to their instability. To address this, this paper analyzes the movement characteristics of surrounding rock in the recovery roadway and the effectiveness of from nearby large coal pillar roadways. A mechanical model for the failure of weakly cemented roadways was established, and numerical simulations were used to verify the feasibility of leaving small coal pillars along soft, thick coal seams. Additionally, existing measurements were used to evaluate the impact of leaving small coal pillars on the deformation of the surrounding rock in the recovery roadway. The results show that after changing the coal pillar retention to 5 m in the 130,205 working face of the Yangchangwan mining area, the roadway is in a low-stress zone, with minimal surrounding rock deformation, meeting safety requirements for production.

With the increasing depth of coal resource extraction, the surrounding rock in deep engineering faces a geological-mechanical environment characterized by high in-situ stress and elevated water pressure. Investigating the damage evolution and crack propagation patterns in jointed rock masses under the coupled effects of water and stress is crucial for understanding the destabilization and failure mechanisms of deep rock masses. This study employs equipment such as the ROCK TEST SYSTEM 816.01 shear apparatus and a force-thermal-water coupled shear test system to conduct a comprehensive investigation into the damage characteristics and shear crack propagation patterns of granite with varying joint angles under hydraulic coupling conditions.The research findings indicate that the injection of water pressure can effectively reduce the peak shear strength of granite by lowering the effective normal stress. As the joint angle increases, the peak shear strength of the specimens exhibits an overall "n"-shaped trend, with shear displacement showing a reversed "s"-shaped pattern, initially increasing, then decreasing, and increasing again at the peak. Both joint angle and water pressure significantly influence the damage incurred during the granite fracture process. With an increasing joint angle, the damage in the specimens demonstrates an initial increase, followed by a decrease, and then another increase. However, under the influence of water pressure, the damage in the specimens is higher compared to those without water pressure. The damage growth rate under water pressure follows a trend of initially increasing and then decreasing, with the maximum damage growth rate occurring at a joint angle of 30°.Furthermore, numerical simulations using the FRACOD software are conducted to simulate shear fracturing for the Yangba well in Enhanced Geothermal Systems (EGS) geothermal engineering. The results of the simulation calculations hold significant guidance for selecting wellbore positions in the target area of hot dry rocks.

The evolution law of lateral abutment pressure under the condition of fully mechanized mining in shallow coal seam is studied using the change process of coal pillar stress in disturbed section as the research object. The results of physical simulation experiment show that, after coal mining, due to the collapse of coal seam roof, the overlying strata of key layer will disturb the section coal pillar to different degrees, and the sudden change of degrees of abutment pressure near the coal wall reaches the maximum. Affected by the energy released by the fracture of key stratum, the stress mutation area shifts to the coal wall at a deeper level and the range of plastic zone increases. From the perspective of the numerical simulation, according to the change characteristics of coal pillar abutment pressure in the mining process, the dynamic load process of complex roof strata is divided into three stages: the stage not affected by mining, the stage of dynamic load action, and the stage of static load. In the first stage, the lateral abutment pressure is only affected by the roadway mining, causing stress concentration in the coal body. The stress concentration coefficient is small, and the supporting stress is stable. In the second stage, with the advance of the working face, the coal seam load changes continuously owing to the movement of overlying rock in the goaf, and the lateral abutment pressure changes evidently under the influence of dynamic load. In the third stage, the overlying load forms stress concentration in the coal seam and continuously transfers to the coal wall at a deeper level, which increases the limit equilibrium area of coal body. During this period, the range of plastic zone still increases at a certain rate for a period of time and finally tends to be stable.