In the process of deep mining, the dynamic disasters of coal and rock occur frequently under the action of high stress and high seepage pressure, the essence of which is energy-driven coal rock failure. In order to explore the energy evolution law and damage mechanism of sandstone with intermittent cracks under the coupling effect of stress and seepage, in this paper, by comparing the differences in mechanical characteristics between fractured rock and intact rock, the energy evolution characteristics, crack propagation, and micro-damage mechanism of fractured rock under different confining pressures and seepage pressures are analyzed. The research shows that: (1) The local stress drop phenomenon occurs in the fractured rock during the loading process, and the stress–strain shape is ‘bimodal’. At the same time, there is stress concentration at both ends of the fracture. (2) The energy conversion of the fractured rock changes in stages during loading. As confining pressure rises, the energy storage limit and the maximum dissipation energy go up. The increase in seepage pressure reduces the energy storage limit, while the dissipation energy shows an upward trend. The energy consumption ratio curve shows ‘concave’ evolution during the loading process. (3) Based on the dissipation energy and residual stress, the damage state of the specimen is analyzed, and the proposed damage variable can reasonably explain the whole process of the damage evolution of intermittent fractured rock under stress and seepage. (4) The increase in confining pressure increases the friction between the particles inside the sample and promotes the transformation of the sample from tensile failure to shear failure. The seepage pressure reduces the friction between the particles in the sample through the air wedge effect to deepen the damage degree, thus promoting the tensile failure of the sample.

To explore the static pressure dynamic disaster mechanism of coal-and-gas outburst (CGO) fluid, the self-developed multi-field coupling large-scale physical simulation test system of coal mine dynamic disaster was used to carry out gas outburst and CGO physical simulation tests in straight, L-shaped and T-shaped roadways. The influence of roadway shape on the evolution of static pressure was explored, and the role of pulverized coal in the process of static pressure dynamic disaster was clarified. The results indicated that the static pressure showed a fluctuating downward trend during the outburst process. When gas outburst, the middle and front parts of the roadway in the straight section roadway were the most serious areas of static pressure disasters in the three shapes of roadways. The duration and range of high static pressure disaster in L-shaped roadway were larger than those in T-shaped and straight roadways in turn. When CGO, the most serious area of static pressure disaster in L-shaped and T-shaped roadways moved backward to the middle of the straight section roadway, and there was a rebound phenomenon in the process of static pressure fluctuation decline, which showed the pulse characteristics of CGO. During the outburst, the static pressure dynamic disaster hazard of L-shaped roadway was higher than that of T-shaped roadway, and the static pressure at the bifurcation structure decayed faster than that at the turning structure, which indicated that T-shaped roadway was more conducive to the release of static pressure in roadway, thus reduced the risk of static pressure disaster. When gas outburst, the static pressure attenuation of the fluid in the roadway before and after the turning and bifurcation structure was greater than that of CGO. The peak static pressure and impulse of the fluid during gas outburst were 2 times and 4–5 times that of CGO respectively. The presence of pulverized coal reduced the attenuation of static pressure and the hazard of dynamic disaster, prolonged the release time of energy, and led to the change of the maximum static pressure disaster area.

Coal and gas outburst disaster seriously restricts the safe development of deep coal resources. This study aimed to elucidate the evolution characteristics of dynamic behavior and two-phase flow migration mechanism throughout the various stages of outburst. The dynamic characteristics of fluids at different outburst stages were analyzed in terms of impact force and static pressure primarily based on physical simulation tests of outbursts. Based on gas dynamics, a complex wave system distribution model of the turning structure was constructed, and a numerical simulation revealed the migration mechanism of outburst fluids within the turning structure. The results show that the shock in the stage1 shows an evolutionary trend of multi-peak oscillations. Coal–gas two-phase flow in the stage2 mainly has strong disaster-causing characteristics at the front end and middle of the straight roadway, and the impact force has a sudden and intermittent steep increase-drop phenomenon. Impact force decline process has a recovery phenomenon, the larger the solid–gas ratio, the faster the impact force attenuation. Coal powder can promote the attenuation of static pressure, and the larger the solid–gas ratio, the greater the attenuation. The fluid in the high-velocity jet region is fast and unevenly distributed, and the static pressure is negatively distributed, with expansion-compression phenomenon. In the turning roadway, there is a steep increase in velocity, and the distribution is strong–weak, which is consistent with the phenomenon of steep increase in impact force in the test. The research results are of crucial guiding significance for accurately assessing the impact range of outburst accidents, optimizing the design of disaster prevention facilities, and formulating emergency rescue plans for accidents.

The blockage of a tunnel drainage system has a significant impact on the stability and operation safety of a tunnel lining structure. In this paper, changes in the pore water pressure, stress and displacement of a tunnel lining under different blocking conditions are studied by means of indoor test and numerical simulation. The results show that the calcium carbonate crystallization phenomenon in the tunnel’s initial support concrete gradually appears with the passage of time, which leads to a decline in concrete quality and has a negative impact on its compressive strength and elastic modulus. The pore water pressure, stress and displacement increase with the precipitation of calcium carbonate crystals and the intensification of drainage system blockage. However, the influence of calcium carbonate crystallization on pore water pressure, stress and displacement is relatively limited within 40 days. The study provides a reference for tunnel construction in complex geological environments.

Coal and gas outbursts are complex, dynamic phenomena in coal mining. Outburst two-phase flow (OTPF) poses a serious threat to the safety of underground equipment and operators during an outburst. In this study, by means of physical simulation test, the dynamic disaster characteristics of OTPF in roadway with and without branches were discussed. The experimental results showed that pulverized coal flow was initially shaped like an arc-shaped jet. The average migration velocity of OTPF under non-branched right-angle turning roadway (L-Rd) was larger than under branched right-angle turning roadway (F-Rd). In the straight section, the mass of pulverized coal under L-Rd was generally larger than under F-Rd, whereas in the turning section, the opposite was observed. The branch roadway enhanced the flow capacity of outburst pulverized coal in main roadway. An alternating pattern of strong and weak impact forces was observed. The impact dynamic disaster-causing intensity of F-Rd increased by 33.4% compared to L-Rd in the straight section and by 19.2% in the turning section. The impact force was generally higher under F-Rd relative to L-Rd, indicating that the branch roadway increased the disaster-causing risk of OTPF in main roadway. Moreover, the static pressure was generally lower under F-Rd relative to L-Rd, indicating that the branch roadway weakened the static pressure damage in the main roadway. The findings of this study hold significant value for the design of mine roadways and the establishment of emergency shelters.