Most coal mine field application processes are carried out using empirical formulas because of the insufficient understanding of the fracture development law of the static blasting technology. This lack of understanding results in poor coal seam gas extraction. In this study, a stress–damage coupling model was established to investigate the construction parameters of the static blasting technology using COMSOL simulation software. Then, a stress–damage–seepage coupling model was designed to study the evolution of the fracture field (seepage field) during the static blasting process using realistic failure process analysis simulation software. Finally, the influencing factors and fracturing effects were analyzed comprehensively. The research results show the following. (1) Comparing the simulation results with previous field tests reveals that the seepage law of the numerical simulation of the static blasting technology is consistent with the field test results, verifying the rationality of the stress–damage–seepage coupling model. (2) The development of coal seam fractures is affected by the expansion pressure, elastic modulus, and guide hole arrangement; the guide hole arrangement can play a role in guiding the development direction of fractures and enhancing the effect of fracturing. (3) The coal body mainly experienced the following five stages of fracturing: coal body compaction, microdamage formation, microfracture formation, large fracture formation, and fracture propagation. In addition, because of the rapid release of soundless cracking agents during the large fracture formation stage, the gas flow decreased in a short time. (4) The static blasting technology causes the coal seam permeability coefficient to increase. Compared with conventional extraction, the effective influence radius in the horizontal direction increases by 5.1 times, and the effective influence radius in the vertical direction increases by approximately 3 times. The static blasting technology can increase the number of coal seam fractures and significantly reduce the coal seam gas pressure, thereby enhancing coal seam permeability and realizing safe coal mining.

The objective of this work was to investigate the damage characteristics and failure modes of gypsum rock under dynamic impact loading. Split Hopkinson pressure bar (SHPB) tests were performed under different strain rates. The strain rate effects on the dynamic peak strength, dynamic elastic modulus, energy density, and crushing size of gypsum rock were analyzed. A numerical model of the SHPB was established using the finite element software, ANSYS 19.0, and its reliability was verified by comparing it to laboratory test results. The results showed that the dynamic peak strength and energy consumption density of gypsum rock increased exponentially with strain rate, and the crushing size decreased exponentially with the strain rate, both findings exhibited an obvious correlation. The dynamic elastic modulus was larger than the static elastic modulus, but did not show a significant correlation. Gypsum rock fracture can be divided into crack compaction, crack initiation, crack propagation, and breaking stages, and is dominated by splitting failure. With increasing strain rate, the interaction between cracks is noticeable, and the failure mode changes from splitting to crushing failure. These results provide theoretical support for improvements of the refinement process in gypsum mines.

Owing to differences in deformation characteristics of roadways with different section shapes and depths, it is difficult to determine the support form and grouting depth of a roadway, which can cause serious deformation to the roadway. To address the challenges in determining the shape and grouting depth of a roadway section when the mine depth is known, the loose zone range of the roadway was tested using the acoustic method, and the loose zone evolution law under different conditions was performed by numerical simulations. The research results revealed that when the ratio of the maximum principal stress to the minimum principal stress is eta > 3, the distribution of the rock loosening zone under different cross-sectional shapes was roughly "butterfly-shaped", and the "smoother" the cross section in the design of the roadway, the smaller the range of the rock loosening zone. With the increase of burial depth, the rock loosening zone and sealing depth also increase; the rock loosening zone and burial depth have a power function relationship the rock loosening zone range = a.burial depthb; the sealing depth and burial depth have a linear relationship R = aH + b.

This research was conducted in order to study the relationship between gas geology (initial gas pressure, initial permeability, and buried depth) and effective extraction radius and to achieve precise borehole layouts. Based on the in-hexagon borehole layout mode, the influence of geological factors on borehole effective extraction radius is quantitatively analyzed. Combined with gas geology, the precise borehole layout mode of gas extraction is constructed. The results show that: Based on the two evaluation indexes of borehole number and area redundancy rate, the optimal implementation scheme of the in-hexagon is selected; that is, when the effective extraction radius is R, the borehole spacing along the coal seam strike is $\sqrt{3}R$, and along the dip is 1.5R. Based on the four evaluation indexes of effective extraction space volume, relative gas emission, cost rate, and gas isobaric surface shape, the relationship between effective extraction radius and initial gas pressure, permeability, and burial depth is matched quantitatively. The effective extraction radius decreases with the initial gas pressure and buried depth and increases with the initial permeability. The effective extraction radius and initial gas pressure have a linear relationship $R=aP+b$, the effective extraction radius and initial permeability have a power function relationship $R=a{k}^b$, and the effective extraction radius and burial depth have a negative exponential relationship $R =a{e}^{-\mathit{bH}}$. The response surface interaction model analysis shows that the buried depth has the strongest influence on the effective radius of gas extraction, followed by the initial gas pressure and the initial permeability. Based on the effective extraction radius as a function of gas geology, the precise borehole layout mode of gas extraction is constructed, which can provide a reference for the construction design of underground gas drilling in coal mines. This will provide a technical guarantee for the efficient mining of gas and promote the sustainable development of gas resources.

To improve the gas drainage effect of low-permeability coal seams, the influence of the hole arrangement on the static blasting effect was studied through single-hole, double-hole, and guiding-hole blasting tests. A stress-damage coupling model was established to reveal the evolution of the stress field and the distribution of the damage zone under different construction parameters, and the evolution law of the damage zone under a multi-hole arrangement was investigated. The following can be inferred from the research results. (1) The crack initiation of double holes depends on the stress superposition between blasting holes, whereas that of guiding holes depends on the free surface inside the coal body. The increase in borehole diameter and spacing reduction between boreholes could improve the static superposition breaking effect. (2) The relationship between the guiding hole, borehole diameter, and borehole spacing was revealed from the two aspects of the stress field and damage zone. The purpose is to strengthen the blasting effect. The drilling diameter and spacing are measured, and the guiding hole strengthens the blasting effect. At the measurement level, it should be analyzed from the two dimensions of time and stress. The time dimension accelerates the migration of the stress turning point, whereas the stress dimension realizes stress superposition and finally strengthens the static cracking effect. (3) The damage zone evolution of static blasting technology is influenced by expansion pressure, construction parameters, and elastic modulus. The increase in the expansion pressure caused the damage zone of the coal body and a decrease in the elastic modulus. Under the combined action of the expansion pressure and elastic modulus, the damage zone expanded and penetrated. The guiding borehole would not only have a guiding function but could also enhance the breaking effect. (4) In the simulation test scheme, the reasonable ratio of borehole spacing to borehole diameter is approximately 13 to 14, and the reasonable construction parameters are 113 mm of borehole diameter, 1.4 m of borehole spacing, and the layout of multi-hole-guiding hole. Static blasting technology can increase the distribution of the damaged areas of coal seams, realize pressure relief and permeability enhancement of coal seams, and improve the safe construction of coal mining.

In order to realize the comprehensive utilization of the underground space formed by gypsum mining, with the core goal of building an oil storage depot in the gypsum mine goaf, the designed rock infiltration loading device was used to prepare gypsum rock samples immersed in oil for 0, 15, and 30 days for rock mechanics experiments. The influence of oil immersion on the mechanical behavior of the gypsum ore rock mass was studied, and the damage evolution mechanism of gypsum ore rock was explored through statistical fitting and normalized quantitative evaluation. The results show that, with the increase in oil immersion time, the peak stress and elastic modulus of gypsum rock both tend to decrease, and the decrease degree of each parameter is smaller when the confining pressure is higher. The normalized expression of each parameter of gypsum ore and rock with the oil immersion time was established, the deterioration coefficient of each parameter was defined, and the influence law of the oil immersion time on each parameter was analyzed. With the increase in oil immersion time, the internal friction angle of gypsum ore rock exhibited an increasing trend, while the other parameters exhibited a decreasing trend. The oil immersion time had the greatest influence on the cohesion of gypsum ore rock, followed by peak stress, internal friction angle, and elastic modulus. Moreover, it was further demonstrated that high confining pressure conditions weaken the deterioration effect of oil immersion on gypsum rock, i.e., high confining pressure conditions are more conducive to crude oil storage. The research results herein provide theoretical support for the improvement of the theory of “treatment and utilization synergy” in gypsum mine goaf.