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The action mechanism of blast shock wave and detonation gas in rock blasting remains unclear. This article attempts to reveal the action mechanism of blast shock wave and detonation gas through high-speed schlieren system, overpressure test system and AUTODYN numerical simulation analysis. 5 cartridges under different explosive types and charge structures were designed, and the dynamic action evolution of detonation products can be visualized from schlieren photos. The action change of blast shock wave and detonation gas in the flow field were compared under the said five conditions. The numerical simulation results were compared with the schlieren experiment results, and the detonation wave process in explosives was reversely deduced. The results showed: the blast shock wave initially expand along with the detonation gas, both propagate outwardly around the point of detonation in a spherical shape. During propagation, the blast shock wave is gradually separated from the detonation gas, and the blast shock wave propagates at a higher velocity compared with the detonation gas. In the scenarios of different charge structures, the features for which the blast shock wave is separated from the detonation gas are varied, the time of separation will shorten as the constraining effect of the cartridge shell intensifies. In the scenarios of different explosive types, the wave patterns of shock wave and detonation gas are essentially the same. However, the velocity and pressure change of shock wave and detonation wave may deviate in the course of propagation, due to different physical and mechanical parameters of explosive materials. In the presence of slot, shock wave and detonation gas will first propagate outwardly from the slot, then the flow is carried out in the other direction, and the pressure and speed in the incision direction will increase, the energy along the slot direction is concentrated and the tube wall is first damaged, resulting in the effect of directional damage. In the numerical simulation, the fluctuation pattern and schear experimental results of explosion shock wave and explosion gas are more consistent in morphology.

Coal is the main energy source in China, and the western region in China is the main coal production area. The protection and utilization of coal mine water is the major technical challenge in the coal mining. The coal green mining research team of China Energy Group has pioneered the technology of underground coal mine reservoirs, which has been widely implemented in the Shendong mining area in Western China, providing over 95% of water needed for mining and ensuring the sustainable development of the mining area. To further enrich and improve the theoretical and technical system of underground coal mine reservoirs, this technology has been promoted and applied under different geological and working conditions in the western coal mining areas to ensure national energy security and water resources protection. The research team has built the original technology experimental platform system for coal mine underground reservoirs, including the comprehensive intelligent experimental platform for underground water transport and protection, the physical modelling platform for coal mine underground reservoirs under multiple coal seams, the dam structure experimental platform for coal mine underground reservoirs, the simulation experimental platform for deep well construction in western areas, the water-rock coupling mechanism experimental platform for underground water reservoirs, the integrated water treatment process experimental platform, and the impact experimental platforms for coal mine underground reservoirs, etc. On these platforms, the researches can be carried out consisting of the transport law of underground water, the optimization of dam structure parameters, the safety and stability of reservoirs, water-rock coupling mechanism, the optimization of mine water treatment, and the impact of caving rock mass on the dam structure under different coal seam occurrence conditions in the western mining areas of China. These platform systems provide a theoretical support and technical verification for the construction, operation, and safety of coal mine underground reservoirs. By utilizing these experimental platforms, various experimental research studies have been conducted, including the stability and seepage of coal mine underground reservoirs under multiple coal seams, the structural safety of coal mine underground reservoirs dam, and the water-rock coupling mechanism of coal mine underground reservoirs. These research results have been applied in actual engineering practice to ensure the safe and stable operation of coal mine underground reservoirs.

Coal mine underground reservoir is one of the key technologies to solve the protection and utilization of water resources in western mining areas. The basis for maintaining the safe operation of the reservoir is engineering safety, and the dam body is the core to ensure engineering safety. This paper studies the safety and stability of coal pillar dam of underground reservoir in coal mine. The stress variation (vertical stress and horizontal stress), fracture development and expansion, displacement variation and other multi-parameter variation laws during the failure of coal pillar dam are comprehensively analyzed based on mechanical model, similarity simulation and numerical calculation methods, from the angle of roof rock pressure (vertical stress) and water storage height (horizontal stress). This paper studies the variation characteristics of various parameters during the failure of coal pillar dam, and puts forward the key information of coal pillar dam failure precursors, which provides the basis for the safe operation monitoring and early warning of on-site coal mine underground reservoir. The results show that under the action of vertical stress, the location of coal pillar dam damage caused by overburden stress is the dam roof on the side of underground reservoir of coal mine. The smaller the size of coal pillar is, the easier it is to produce stress concentration. The greater the bearing stress is, the greater the possibility of damage is. Based on this, the failure critical point of coal pillar dam is obtained. Under the action of horizontal stress, the coal pillar dam body experiences three processes: elastic stage, initial failure stage and failure increase stage. The coal pillar dam body shows obvious displacement only after reaching the ultimate strength. At this time, the coal pillar dam body is damaged. After the horizontal stress decreases, the displacement has a rebound trend, but the overall stability of the coal pillar dam body is affected and it is not suitable to continue water storage. The analysis of the main factors causing the instability of the coal pillar dam shows that under the combined action of vertical stress and horizontal stress, the instability of the coal pillar dam is mainly at the top plate, bottom plate and middle position of the small-size dam near the reservoir. Taking Shangwan mine as an example, the maximum bearing head height of the coal pillar dam is 50m, but the coal pillar dam has been damaged at this time. Even if the water level is lowered, the overall stability of the coal pillar dam is irreparably damaged. Comprehensive study of the characteristics and laws of coal pillar dam instability in coal mine underground reservoirs, combined with displacement changes and the physical and mechanical properties of coal pillar dams, obtained the precursor information of coal pillar dam failure, that is, respond to the reservoir before reaching the ultimate strength under the action of external force. For safety measures, it is recommended to focus on monitoring the stress change information of the coal pillar roof with a smaller size on the reservoir side during on-site monitoring and early warning to ensure the safe operation of coal mine underground reservoirs. The research results provide a basis for monitoring and early warning methods for the safety and stability of coal pillar dams in coal mine underground reservoirs.

The seepage characteristics of groundwater in the overlying fissures are the key factors to be considered in the later maintenance of coal mining and goaf, especially in the underground reservoir construction area of coal mines. It is also an important part of coal mine underground reservoir. In shallow groundwater-rich areas or under extreme summer rainfall conditions, underground reservoirs form vertical recharge, and analyzing the seepage characteristics of groundwater in overlying fissures provides a scientific basis for the safe operation of coal mine underground reservoirs and the protection of groundwater resources. In this study, the solid-liquid coupling similarity model test was used to obtain the development and stability of the overlying fissures in the mining area and the characteristics of groundwater seepage after the aquifer was connected. The analysis showed that the large abscission fissures and micro-fissures that extend far and wide are mostly water storage. , the vertical fissures running through multiple rock layers have strong water conductivity, and the hydraulic connection between the separation layer fissures is mainly formed by the vertical fissures in the two sides. Under the condition of vertical recharge, groundwater first infiltrates along the vertical fissures in an unsaturated manner, and is gradually saturated regionally from the upper and lower overlying fissures, finally forming a stable saturated infiltration form. On this basis, a mathematical model of groundwater seepage in saturated seepage state is established, and the numerical method is used to solve it. It is verified with similar simulation experiments that vertical fractures are the main water conduction channels, and their water conduction can account for up to 97%. At the same time, the migration speed of groundwater in vertical fractures is also many orders of magnitude higher than that in abscission fractures. Finally, through the sensitivity analysis, it is concluded that the vertical fracture seepage is positively correlated with the fracture development degree and the total water inflow, and negatively correlated with the rock permeability. The migration time of groundwater in overlying fissures is negatively correlated with the degree of fissure development, rock permeability and total water inflow.

During the establishment of the coal mine goaf reservoir, the strength of the coal pillar dam was weakened by various water–rock interactions triggered by water movement. To explore the influence of the water-bearing state on the shear characteristics of coal pillar dams, the 2–2 coal seam of Shangwan Coal Mine in the Shendong Mining area was taken as the research object and was prepared to coal samples with different moisture contents and different drying-saturation cycles, and the variable angle shear test of coal samples was carried out. The law of water absorption of coal samples under natural and pressurized conditions is obtained. The research results show that the shear characteristics of coal samples change significantly under the action of water, with the increase of moisture content and drying-saturation cycles, the lower the shear strength of coal samples is, the larger the peak shear strain is, and the cohesion and internal friction angle of coal samples decrease linearly. According to the relationship between cohesion, internal friction angle, moisture content, and drying-saturation cycle times, the Mohr–Coulomb model of coal samples considering moisture content and immersion times is established, which contributes to the load-bearing capacity estimation of water-bearing coal mass. Additionally, scanning electron microscope analysis revealed significant changes in the microstructure of coal samples under different moisture states: as the moisture content and dry-saturation cycles increase, the microstructure of the coal samples gradually transforms from orderly and compact to disordered and murky, elucidating the mechanism by which moisture weakens the mechanical properties of the coal samples. The research results provide a useful reference for engineering problems related to the stability evaluation of coal bodies involving the repeated erosion effect of water.

The role of coal mine underground reservoirs (CMUR) in ‘guide storage and use’ greatly solves the problem of mine water waste. Replenishment and prediction of reservoir water sources provide an important support for the successful development of key technologies concerning CMUR. To study water replenishment for CMUR, the hydrogeological conditions of the Shendong mining area were investigated as an example. Based on the relationship between the development height of the ‘two belts’ of shallow coal seams and the relative occurrence of location of aquifers, the aquifers are generalized and classified according to occurrences location. Taking Bulianta coal mine as the research background, a discrete element fluid–solid coupling numerical simulation model is constructed to analyze the development characteristics of mining-induced fractures after coal seam mining, and the water replenishment channel of the CMUR is determined. On this basis, analysis is made on the change law of water pressure in the aquifer, aquifuge and coal seam roof under mining action. Taking hydraulic head pressure and water velocity as the judgment basis, prediction and evaluation are made on the water replenishment capacity of CMUR. The research results can provide references for coal mine safety production and mine water protection and utilization. HIGHLIGHTS Based on the water-conducting fractured zone, the occurrence type of ‘coal-water’ is generalized.; The change law of aquifer under different ‘coal-water’ conditions is revealed.; The source and amount of water supply for CMUR were obtained under different conditions.;

In the practical processes of coal mines and tunnel, rectangular roadways are widely used in the underground environment. However, the stress distribution law of the rock mass around the rectangular roadways is relatively complicated that is influenced by different parameters, such as the in situ stress, geological structure, and properties of the surrounding rock mass. It is extremely significant to conduct systematic and in-depth research regarding the stress distribution and deformation failure mechanism of the rock mass around the rectangular roadways. Based on theoretical analysis, the stress distribution law of the surrounding rock of rectangular roadway under different rock mass strength grades is studied directly through rectangular roadway in this paper. This further reveals the distribution law of secondary stress field after excavation of rectangular roadway. A coal mine intends to excavate a roadway in rock mass, and then, the rectangular roadway is simulated by FLAC3D software. Then, the strain distribution and failure types of roadway surrounding rock under different rock mass properties are obtained. The results show that the failure of rectangular roadway is mainly shear failure and tensile failure. The roof and floor of roadway are mainly tensile failure, and the side of roadway is mainly shear failure. Moreover, the stress shifting and distribution of the rock mass around rectangular roadways is a complicated dynamic variation process. The damage degree of the floor and roof of the rectangular roadway is greater than that of the two sides of the roadway. Its variation is mainly related to the strength of surrounding rock mass.

Water supply prediction and control is one of the key issues in exploitation of coal mine underground reservoirs (CMUR). In order to investigate the water supply for underground reservoirs in coal mines, the aquifers were classified into three types (types I, II, and III) according to the relative location of aquifers. The discrete element fluid structure coupling numerical simulation model is constructed according to the classification results. The numerical simulation parameters are inversed based on the surface subsidence data and the advance support pressure, and then, the disturbed characteristics and water pressure variation law of different types of aquifers are studied. The research results show that the maximum water inflow of type III, type II, and type I aquifers is 739 m3/h, 377 m3/h, and 279 m3/h, respectively. The dynamic calculation process of underground reservoir capacity under mining disturbance is refined, and the regulation and storage methods of underground reservoir are preliminarily put forward.

Long-term erosion and repeated scouring of water significantly affect the technical properties of coals, which are the essential elements that must be considered in evaluating an underground reservoir coal column dam’s standing sustainability. In the paper, the coal pillar dam body of the 22 layers of coal in the Shangwan Coal Mine is studied (22 represents No. 2 coal seam), and the water content of this coal pillar dam body is simplified into two types of different water content and dry–wet cycle. Through acoustic emission detection technology and energy dissipation analysis method, the internal failure mechanism of coal water action is analyzed. This study revealed three findings. (1) The crest pressure, strain, and resilient modulus in the coal sample were inversely related to the water content along with the dry–wet cycle number, while the drying–wetting cycle process had a certain time effect on the failure to the sample. (2) As the moisture content and the dry–wet cycle times incremented, three features were shown: first, the breakage pattern is the mainly stretching fracture for the coal specimen; second, the number and absolute value of acoustic emission count peaks decrease; third, the RA-AF probability density plot (RA is the ratio of AE Risetime and Amplitude, and AF is the ratio of AE Count and Duration) corresponds more closely to the large-scale destruction characteristics for the coal samples. (3) A higher quantity of wet and dry cycles results in a smoother energy dissipation curve in the compacted and flexible phases of the crack, indicating that this energy is released earlier. The research results can be applied to the long-term sustainability assessment of the dams of coal columns for underground reservoirs and can also serve as valuable content to the excogitation of water-bearing coal column dams under similar engineering conditions.

Coal-rock combination refers to the coal and rock as a whole, and the failure of the whole structure of the combination is the main cause for the instability of the deep underground engineering. In deep underground engineering, the coal-rock combination is usually under certain hydrogeological conditions, and it is prone to seepage and rheological failure instability accidents due to the long-term action of water and stress. In this study, the creep constitutive model of coal-rock combination considering the influence of moisture content was established based on the Burgers creep model. According to the experimental results of triaxial creep of rock, the relationship between the moisture content and the parameter of the Burgers creep model was derived, and the correctness of the constitutive model in this study was verified. Then, through the C++ language, the core equation of the model was modified, and the numerical calculation of the model was realized by introducing the coal-rock combination creep model considering the influence of moisture content into FLAC3D numerical simulation software. Finally, the model was used to simulate and study the creep characteristics of coal-rock combination with different moisture contents under triaxial loading. The results showed that the stress environment and moisture content have significant effects on the creep characteristics of the coal-rock combination. Under the same stress state, with the increased of moisture content, the strain rate of the coal-rock combination exhibited a non-linear rapid increase in the constant-velocity creep stage, the limit creep deformation and the instantaneous elastic deformation increased, and the viscosity coefficient was significantly decreased. For example, when the axial stress was 5 MPa and the moisture content increased from 0% to 1.5%, the strain rate increased by 44.06%, the limit creep deformation increased by 20%, the instantaneous elastic deformation increased 10.53%, and the viscosity coefficient decreased by about 50%. When the moisture content is 0%, the axial stress increased from 5 to 14 MPa, and the limit creep deformation increased nearly four times. With the increase of moisture content, this value will further expand. The research conclusions can provide a certain reference basis for the long-term stability control of surrounding rock in underground engineering affected by the water.

The mechanism of preventing rockburst through deep-hole precracking blasting was studied based on experimental test, numerical simulation, and field testing. The study results indicate that the deep-hole precracking could change the bursting proneness and stress state of coal-rock mass, thereby preventing the occurrence of rockburst. The bursting proneness of the whole composite structure could be weakened by the deep-hole precracking blasting. The change of stress state in the process of precracking blasting is achieved in two ways: (1) artificially break the roof apart, thus weakening the continuity of the roof strata, effectively inducing the roof caving while reducing its impact strength; and (2) the dynamic shattering and air pressure generated by the blasting can structurally change the properties of the coal-rock mass by mitigating the high stress generation and high elastic energy accumulation, thus breaking the conditions of energy transfer and rock burst occurrence.