Conventional borehole pressure relief can meet the requirements for preventing rock bursts, but it can also easily destroy the roadway, resulting in system support failure. Taking coal-like samples with boreholes as the research object, the pressure relief effects of the same-diameter boreholes and variable-diameter boreholes are compared and analyzed by a uniaxial compression test. The joint pressure relief mechanism of the variable-diameter drilling hole is discussed. The experimental results show that the stress–strain curve of variable-diameter drilling sample occurred the phenomenon of pre-peak stress drop and post-peak stress plateau, which indicates that the variable-diameter drilling hole can enhance the plastic characteristics of coal-like samples. The borehole size dramatically influences the variation of various pressure relief indexes. The evolution law of AE counting the pre-peak and post-peak of borehole samples verified the abovementioned law. Variable-diameter drilling can enhance the plasticity of samples, weaken the brittleness and reduce the impact tendency. Under the maximum size of the variable-diameter drilling hole and the same-diameter drilling hole is same, the pressure relief effect is more significant. The results obtained in this paper can provide a new theoretical basis and technical guidance for borehole pressure relief and roadway support.

1. Currently, as shallow Earth mineral resources are gradually depleting, resource development is shifting toward deeper regions, becoming the new norm. Deep mining operations face the challenges o...

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.

The catastrophic evolution of damage fractures and seepage in surrounding rocks under coupled actions significantly impacts the safety of rock mass engineering, such as mining and tunnel construction. To address this, we developed a test platform to observe the spatiotemporal evolution of water inrush from the floor of a mining coal seam. The platform comprises a test bench, servo loading system, water pressure control system, flexible loading system, and intelligent monitoring system. This setup enables flexible loading during overlying rock movement, conducts three-dimensional simulation tests on mining water inrush solid-flow coupling, simulates various crustal stresses, quantitatively monitors water inrush flow and pressure in specific floor areas in real time, and observes the entire process of water inrush crack formation. Using this system and nonhydrophilic similar simulation materials, we conducted experimental simulations on pressurized water inrush in the floor after coal seam mining. We analyzed the visual fracture development process of the floor, the distribution characteristics of water gushing flow in the floor area, and the sudden changes in instant water inrush and stress variation law of the water-resisting layer in the floor. The test results vividly illustrate the catastrophic process of water inrush in the coal seam floor. Our study reveals that, under the combined effects of water, rocks, and stresses, coal mine floor crack expansion exhibits periodic changes. The flow sensor demonstrates a noticeable upward trend during floor crack group expansion, allowing for early warning before water inrush disasters occur by leveraging changes in physical parameters such as flow rates and water pressures. This platform offers a novel and vital tool for addressing rock mechanics challenges in coal mining and for experimental research and testing of mine water inrush mechanisms, prevention, and control.