The pore structure in coal seams has a significant impact on the occurrence and migration characteristics of coalbed methane. The High Pressure Air Blasting (HPAB) is one of the main feasible technologies to improve the efficiency of unconventional gas extraction. Currently, there is little research on the visualization of the evolution of pore structure and seepage characteristics in coal under HPAB, resulting in unclear understanding of the formation of 3D pore network structure in coal under HPAB, the interconnection of pores and fissures, and the mechanism of gas seepage and diffusion under HPAB. Therefore, it is necessary to study the evolution characteristics of pore structure and seepage characteristics of coal under HPAB. The HPAB test was carried out based on a self-developed HPAB device. Statistical analysis of crack propagation law of coal under HPAB from a macroscopic perspective. During the experiment, a microscopic visualization model of coal before and after HPAB was established using CT scanning and Avizo software. The vessel axial skeleton algorithm in Avizo software was adopted to extract the connectivity channels between connected pores and fissures, which realizes the 3D visualization of coalbed methane seepage in the spatial topology structure at the microscopic scale. The seepage, migration, diffusion process and distribution law of coalbed methane in the micro-pore structure of coal have been studied. The mechanism of coalbed methane seepage and migration has been revealed from a microscopic perspective. The research results indicate that: (1) There are four main cracks on the coal surface that approximately run along the direction of principal stress under HPAB and confining pressure. The direction of crack development and propagation in coal under HPAB is influenced by natural defects such as joints and bedding. (2) Before HPAB, the representative elementary volume (REV) of coal has a high degree of curvature in the connectivity channel of pore and fissure. After HPAB, the degree of curvature in the REV is significantly reduced, with a decrease of up to 26.72%. (3) The original micro-pores and newly formed fractures developed and expanded outward under HPAB, forming a relatively developed 3D fracture network channel. Compared with before HPAB, the streamline distribution inside the REV is denser and more numerous. The maximum flow rate and maximum velocity of coalbed methane migration have increased by 112.90 times and 5.24 times, respectively. The research results provide experimental and theoretical basis for improving the efficient extraction of coalbed methane in low-permeability coal seams by HPAB.

High pressure air blasting (HPAB) is a new type of waterless physical expansion method for enhancing coalbed methane extraction from low-permeability coal reservoirs. In order to explore the influence of shocks by multiple HPAB on the cumulative damage evolution of coal, shocks by multiple HPAB experiments were conducted using simulated coal samples and a self-developed HPAB device. During the experimental testing process, The wave velocity of coal samples under shocks by multiple HPAB was tested using an ultrasonic tester, and the time-domain signal of the ultrasonic wave was converted into a frequency-domain signal using Fourier transform theory. the evolution of acoustic waves and damage morphological characteristics of coal with increasing HPAB times was analyzed. Additionally,The evolution process of the three-dimensional pore and fracture structure of coal samples under Shocks by multiple HPAB was studied from a microscopic perspective using CT scanning and 3D reconstruction technology. The experimental results indicate that (1) With increasing shock by HPAB times, the damage in the area near the blasthole increased linearly, while the damage in the middle and far zones exhibited a slow growth during the first first-third shock by HPAB and a rapid growth during the third-fifth shock by HPAB. The damage in the near blasthole decreased rapidly with increasing distance from the blasthole. Compared with the near blasthole, the cumulative degree of coal damage in the middle and far zones is relatively small. (2) With increasing shock by HPAB times, The time-domain signal of near-field ultrasound changes from a regular waveform to a disordered and distorted waveform, and the amplitude shows a gradually decreasing trend. The main frequency band shifts from high-frequency signals to mid low frequency signals, and the main frequency band signal decreases from 48.48 kHz before HPAB to 4.88 kHz after the fifth shock by HPAB. (3) Compared with before HPAB, After the fifth shock by HPAB, the number of pores increased by 29.27%, the maximum equivalent radius of pore increased by 16.27%, the number of throats increased by 25.28 times, the maximum equivalent radius of throats increased by 55.08%, and maximum channel length of throat increased by 25.44%. With increasing shock by HPAB times, the microcracks inside the coal evolve from closed and semiclosed pores to open pores, forming a well-developed three-dimensional pore fracture network channel. The research results aim to provide theoretical and experimental basis for the study of cumulative fatigue damage and mechanical performance degradation effects of coal under shocks by multiple HPAB.

Geological storage of CO₂ in coal seam is an effective way for carbon emission reduction. Evaluating the adsorption-induced swelling behavior of confined coal is essential for this carbon emission reduction strategy. Based on the thermodynamic theory and the Gibbs adsorption model, a thermodynamic method for evaluating the gas adsorption-induced swelling behavior of confined coal was established. The influences of factors such as stress, gas pressure, and the state of gas on the adsorption-induced swelling behavior of confined coal were discussed. The predicted swelling deformation from the thermodynamic method based on the ideal gas hypothesis was consistent with the experimental result only under the condition of low-pressure CO₂ (2 MPa). However, the method based on the real gas hypothesis always had better prediction results under both the low- and high-pressure CO₂ conditions. From the perspective of phase equilibrium and transfer, in the process of CO₂ adsorption by the confined coal, gas molecules transfer from the adsorption site of high chemical potential to the low chemical potential. Taking the real gas as ideal gas will result in the surface energy increase in the established model. Consequently, the prediction result will be larger. Therefore, for geological storage of CO₂ in coal seam, it is necessary to take the real gas state to predict the adsorption-induced swelling behavior of the coal. In the process of CO₂ adsorption by the confined coal, when its pressure is being closed to the critical pressure, capillary condensation phenomenon will occur on the pore surface of the confined coal. This can make an excessive adsorption of CO₂ by the coal. With the increase in the applied stress, the adsorption capacity and adsorption-induced swelling deformation of the confined coal decrease. Compared to N₂ with CO₂, the coal by CO₂ adsorption always shows swelling deformation under the simulated condition of ultra-high-pressure injection. However, the coal by N₂ adsorption will shows shrinking deformation due to the pore pressure effect after the equilibrium pressure. Taking the difference in the adsorption-induced swelling behavior and pore compression effect, N₂ can be mixed to improve the injectivity of CO₂. This suggests that CO₂ storage in the deep burial coal seam can be carried out by its intermittent injection under high-pressure condition along with mixed N₂.

The construction safety of underground structures, such as deep foundation pits, is seriously threatened under conditions of explosion vibration and underground water flow. The basalt fiber reinforced polymer (BFRP) anchor offers advantages such as light weight, high strength, strong corrosion resistance, good insulation, and cleanliness without pollution. It is widely used in mines, foundation pits, slopes, reservoir embankments, and other areas. To study the dynamic performance of BFRP anchors under impact loads, the LS-DYNA numerical simulation software was used to analyze the dynamic mechanical response of BFRP anchors under different impact loads and multiple impact load conditions. The research results indicate that: (1) The BFRP anchor can withstand energy impacts exceeding 2.5 kJ. At this level, the deformation of the BFRP anchor undergoes three stages: elastic deformation, plastic deformation, and elastic deformation rebound. (2) The stress and displacement of the BFRP anchor increase continuously with the rise in impact energy, with the highest stress and displacement values occurring at the joint. (3) The BFRP anchor can endure three impacts with an energy of 1.25 kJ. During the first and second impacts, the stress and strain initially increase and then decrease over time. However, during the third impact, the BFRP anchor fractures and fails, with stress and strain increasing continuously over time. The research results provide theoretical basis and reference for foundation pit support and slope anchoring y under dynamic load in special engineering geology.