In the mining process of the II1 coal seam at Zhaogu No. 2 coal mine, a method of stratified mining is employed, leaving relatively wide coal pillars in sections. To enhance the resource recovery rate, the mine carries out the cooperative mining of the sectional coal pillars and the lower layer coal seam. The 14,022 cooperative working face of fully-mechanized and fully-mechanized top-coal caving at Zhaogu No. 2 coal mine is taken as the research object. Through numerical simulation, theoretical calculations, and on-site industrial trials, a comprehensive analysis of the overburden structural characteristics and the support adaptability at the working face is conducted. It is clarified that a stress arch bearing structure can be formed above the sectional coal pillars during cooperative mining, and this structure is controlled by key strata. The formation of a stress arch bearing structure in the overburden above the sectional coal pillars provides protection for the underlying mining area. A formula for calculating the working resistance of hydraulic supports under the stress arch in sectional coal pillar is derived. Based on these results, the working resistance of hydraulic supports in the coal pillar area is calculated and selected. Field application shows that the working resistance of the support is 10,000 kN in the fully-mechanized top-coal caving working face, and is 9000 kN in fully-mechanized working face, meeting the support requirements and ensuring safe mining at the working face. This study provides a valuable engineering reference for achieving cooperative mining of abandoned sectional coal pillars and lower layer coal seam in stratified mining method.

In order to reveal the disastrous mechanism of seepage instability of karst collapse column considering variable mass effect, a variable mass fluid-solid coupling mechanical model of water inrush is established, by considering the random distribution characteristics of a collapse column. Taking Qianjin coal mine as the research background, based on the Weibull distribution theory, the heterogeneous distribution characteristics of rock mass is described, and COMSOL Multiphysics numerical simulation software is employed to simulate the seepage characteristics and inrush water changes in collapse columns under different conditions of homogeneity, water pressure, and initial porosity. The research results show that the greater the homogeneity is, the more water conduction channels are formed, and the porosity increases accordingly, when considering the influence of different homogeneity on the seepage characteristics of broken rock mass, which eventually leads to water inrush accidents and a sharp increase in water inflow. Besides, when studying the seepage evolution law of different water pressures on a broken rock mass, an elevation of water pressure dramatically increases the porosity and seepage rate of the water. Over time, the broken rock particles gradually migrate and the fine particles are transported and eroded by the water flow, resulting in changes in the seepage characteristics and the formation of potential water diversion channels. Finally, when taking into account the effect of different initial porosity on the fractured rock mass seepage characteristics, the greater the original porosity is, the higher the seepage velocity is, and the particle migration increases the permeability. This leads to a more pronounced conductive water passage formation, which reveals the disastrous mechanism of seepage instability of karst collapse column considering variable mass effect.

Deep faults significantly impact the structural stabilities and deformation behaviors of their overburden rocks, which are key factors in underground engineering and geological hazard research. Considering the problem of deep-fault-overburdened breaking during mining of super-thick coal seams and taking the Yaoqiao Coal Mine as the research object, the mining fracture evolution characteristics and overburden displacement law of the non-structured and fault-bearing overburden corresponding to fully mechanized caving mining are compared and analyzed using numerical simulations and physical similarity simulations. The results of this study show the following: 1) The fracture height of the overlying rock presents a specific change law with advancement of the working face; the initial rapid increase to a maximum height of 74 m is achieved when the working face advances to 90 m; with the development of the plastic zone indicating past yield, the fracture height decreases to 54 m and becomes stable, and the final caving angle of the fracture stabilizes at 70°. 2) In coal mining under normal fault conditions, when the working face advances from the upper to lower walls, the roof forms a masonry beam structure that slows down fault activation and crack development. When moving away from the fault, the overburden movements and water-conducting cracks are fewer, and the crack height is lower than that without faults. When approaching the fault, the influence of the faults in the fracture zone increases, and the height of fracture development reaches the maximum value after crossing the fault, highlighting the significant influence of the fault on fracture development. 3) Through a similarity simulation test, it is shown that the overburden caving zone is further compacted by the overburden rock and that the roof collapses in a large range, resulting in rapid upward development of the overburden rock cracks and separation of the central overburden rock cracks that are gradually compacted and closed. These findings are expected to have important theoretical and practical significance for deep underground engineering design, geological disaster prevention, and fault activity monitoring.

A two-dimensional unsteady seepage model for coal using a finite element program is developed, and the temporal variations of key factors such as water pressure and hydraulic gradient are analyzed in this paper. Additionally, the triaxial rock mechanical experiment and utilized pneumatic fracturing equipment on raw coal samples to investigate both hydraulic and pneumatic fracturing processes are conducted. Through these experiments, the relationship between pressure and crack formation and expansion are examined. The analysis reveals that the pore pressure gradient at the coal inlet reaches its peak during rapid surges in water pressure but diminishes over time. Conversely, the pore pressure gradient at the outlet side exhibits a gradual increase. Hydraulic fracturing is most likely to occur at the water inlet during sudden increases in water pressure. Besides, as the permeability of coal decreases, the duration for seepage stabilization prolongs due to the intensified pore pressure gradient resulting from sudden increases in water pressure. Moreover, an extended period of high hydraulic gradient further increases the risk of hydraulic fracturing. The experimental findings indicate that coal samples initially experience tensile failure influenced by water and air pressure. Subsequently, mode I cracks form under pressure, propagating along the fracture surface and becoming visible. The main types of failure observed in hydraulic and pneumatic fracturing are diametrical tensile failure, and the development of fractures can be categorized into three distinct stages, which contains the initial stage characterized by slight volume changes while water pressure increases, the expansion stage when pressure reaches the failure strength, and the crack closure stage marked by little or even decreasing volume changes during pressure unloading. The acoustic emission signal accurately corresponds to these three stages.

To study the seepage law and sectional morphological characteristics in splitting sandstones of different grain sizes, three‐dimensional morphological scanning tests and seepage characteristics tests are conducted on the splitting rock samples of siltstone, fine‐, medium‐ and coarse‐grained sandstone, and the differences in morphological characteristics and seepage law in different grain size sandstones are compared and analyzed. The test results show that the sections of siltstone and fine‐grained sandstone have the overall morphological characteristics of “one high and one low” with large undulation, while the sections of medium‐ and coarse‐grained sandstone have a more uniform distribution and less undulation. In the relationship between pressure gradient and flow velocity, siltstone and fine‐grained sandstone are precisely characterized by the Forchheimer formula, and medium‐ and coarse‐grained sandstone are well characterized by the Izbash formula, and the fitting effect is good. The results of the study are of great reference significance for improving the cross‐sectional morphological characteristics and seepage law of the splitting rock samples.

With the deep extension of coal mining in China, fault water inrush has become one of the major disasters threatening the safety production of coal mine. Based on the control equations of steady state and non-Darcy seepage in fractured rock mass, the multi-parameter nonlinear dynamic seepage equations of fractured rock mass are established in this paper. Based on the nonlinear dynamics theory, the function of the state variable in the system is derived, and the influence of the gradual change of non-Darcy flow factors on the structural stability of seepage system is studied. The research achievements show that there are three branches in the equilibrium state of the seepage system. Specifically, the stability of the equilibrium state changes abruptly near the limit parameter. The seepage dynamic system of fractured rock mass has the delayed bifurcation, and the coal mine disaster such as fault water inrush occurs easily at the bifurcation point. The research results are of great significance to enrich the theory of fault water inrush in coal mine, and to reveal the disastrous mechanism of fault water inrush and guide its prevention and control technology in coal mine, which can provide the theoretical reference for predicting the water seepage stability in fractured rock mass.

To obtain the seepage evolution rule and water inrush mechanism of the collapse column, a multi-field coupled mechanical model for water inrush disasters caused by the collapse column is established in this paper, on the basis of the specific engineering conditions of the 1908 working face in the Qianjin coal mine. The mechanical model is composed of internal column elements within the collapse column and surrounding rock masses. The research focuses on the seepage evolution rule in the roof collapse column under different mining conditions and investigates the permeation instability mechanism of collapse column based on the transition of flow state. The research results indicate that the seepage pathway evolves continuously, ultimately forming a channel for water inrush, as the working face advances towards the collapse column. Besides, the water inflow increases rapidly when the working face advances 100 m, then gradually stabilizes, indicating that the seepage channel entry of the collapse column is in a stable stage. Meanwhile, mass loss in the collapse column gradually moves upward. the collapse column remains stable as a whole in the initial stage of water flow, with a small permeability, exhibiting linear flow. As time steps increases, particle loss in collapse column gradually extends to the upper part, forming a stable seepage channel. The flow velocity shows fluctuations with a slow declining trend over time.

In order to achieve the purpose of long-term stable mining of roadway, the strength and stability of rock mass are improved by means of grouting of fractured rock mass. In this paper, orthogonal test and numerical simulation methods were used to study the plugging performance of large amount of fly ash grouting slurry. The fluidity, water separation rate, compressive strength, setting time, stone rate and viscosity of the slurry were analyzed, and the optimal slurry ratio scheme was obtained. Under the optimal ratio scheme, the slurry transport process of the fractured rock mass was simulated, and the dynamic evolution law of the permeability of the slurry in the fractured rock mass was obtained. The study shows that the proportions of fly ash, ordinary Portland cement, loess, accelerant, expansion agent, bentonite water reducer and solidifying agent were 52.65%, 27.70%, 13.85%, 3%, 0.7%, 0.8%, 0.6% and 0.7% in the slurry ratio scheme, respectively. The slurry migration in the fractured rock mass experienced three stages, namely the filling and diffusion stage, the percolation and deposition stage and the sealing stage. The initial permeability was 971.9 mD and decreased to 45.79 mD after 1800 s, with a decrease of 95.3%. The slurry sealing performance was significantly improved, which has certain guiding significance for the application of underground grouting reinforcement engineering.

A self-made triaxial testing machine with thermal–hydraulic–mechanical–chemical (THMC) coupling and a tubular heating furnace, combined with in situ (IS) micro-computed-tomography technology was utilized in this study. The evolution of pore-fissure (PF) structure parameters (porosity, PF scale distribution, effective PF volume ratio, and permeability) of bituminous coal under stress-free (SF) and IS conditions with temperature was investigated, and then the mechanism of experimental results was analyzed. Results showed that (1) under SF conditions, at 300–550 °C, the coal samples after pyrolysis are dominated by elongated large fissures, with PF structure parameters positively correlating with temperature. After 400 °C, the number of PFs increases, with most PFs having equivalent diameter (R) ≤ 100 μm. (2) Under IS conditions, coal sample fissures are dominated by elongated large fissures at 300–350 °C and by holes at 350–600 °C. (3) Under IS conditions at 300–600 °C, the PF structure parameters of coal samples initially decrease with temperature and subsequently increase. The number of PFs fluctuates within a certain range, and the PF scale distribution dynamically shifts with temperature. (4) After 300 °C, the PF structure parameters of bituminous coal under SF and IS conditions show a bipolar distribution with temperature. Therefore, the weakening effect of stress on the PF structure of coal samples should not be overlooked during IS pyrolysis mining of coal bodies.

AbstractThe study aimed to examine the problem of the abandoned mine water and harmful gas downflow from the overlying Jurassic of Tongxin coal mine in the Datong mine area, China. A theoretical analysis, physically similar simulation, and field measurement were used. A fracture aperture mechanical model based on key stratum fracture was used to analyze the main influencing factors of high key stratum fracture and rotation. We also compared the fracture characteristics, displacement changes, and fracture development of the high‐key stratum. The results showed that: (1) the main influencing factors affecting the fracture characteristics of high key stratum are the thickness of coal seam mining, the thickness of high key stratum, and the distance between high key stratum and 3–5# coal seam. (2) When both 8309 and 8207 working faces reached critical mining, the high key stratum was fractured and the mining‐induced fracture was developed to the 14# coal seam goaf, which coincided with the field tracer gas measurement results of the 8309 working face, indicating that when the distance between 3 and 5# coal seam and the overlying 14# coal seam goaf is less than 220.9 m, 8309 and 8207 working faces will form the channel for water and gas inrush. (3) The fracture length of the high key stratum above the working face of 8207 is smaller than that of 8309, and the pipeline of water and gas transport channel formed after the critical mining of its working face is larger and wider, which makes it more prone to the disaster of water and gas inrush. Before mining the extra‐thick coal seam, it is necessary to detect and pump the water and gas in the 14# coal seam goaf, so as to avoid the water and gas inrush hazard during the coal seam mining.

The surface roughness of grout in fractured rock masses has a significant impact on the diffusion characteristics of grout, especially in millimeter-scale fractures. In this study, a self-constructed experimental system for grouting in rough fractured rock masses was used to conduct grout diffusion tests with varying fracture roughness, fracture aperture, and grouting pressure. A theoretical model was developed to account for the combined effects of fracture roughness, aperture, and grouting pressure on grout diffusion, and its validity was verified. The results showed that the theoretical calculations and experimental results had an error rate of around 12%, indicating the high reliability of the theory. Fracture aperture, grouting pressure, and fracture roughness all exhibited nonlinear relationships with the grout pressure distribution. With increasing diffusion distance, the grout pressure decreased, and the rate of decrease gradually slowed down. Fracture roughness and aperture had a relatively small impact on grout pressure, while grouting pressure had a significant influence on grout pressure distribution. The difference in grout pressure between the initial and final stages of diffusion was small, whereas in the middle stage of diffusion, the difference was more pronounced. This research provides a valuable reference for the selection of grouting techniques in the roadway surrounding rock projects.

为了规范和优化大同矿区巷道支护设计,以大同矿区典型生产矿井为研究对象,采集了80 个具有代表性的矿井地质钻孔参数,采用理论分析的方法对覆岩结构特征进行分类,基于大同矿区的覆岩结构特征,提出了以覆岩结构指数为主要指标的巷道顶板稳定性分类方法,并采用数值模拟方法对大同矿区地质条件下锚杆、锚索的联合支护特征进行研究.结果表明:在预应力一定的条件下,当锚杆和锚索长度超出其有效长度后其自由端和锚固端压应力区趋于分离;在锚杆、锚索拉应力允许范围内,提高预紧力有助于提升其锚固效果;锚杆、锚索的联合支护使巷道浅部和深部围岩形成连续的压应力区,有利于巷道稳定.基于巷道围岩稳定性分类和锚杆、锚索支护机理,对大同矿区回采巷道支护参数进行规范和优化,并在大同矿区塔山、同忻、燕子山等多座矿井推广应用,社会经济效益显著.

Roof water inrush at the mine face and shortages of water resources are both problems in the karst mining area in southwestern China. In this study, field measurements, similar simulations, and theoretical analysis were conducted, a physical model of upward and downward mining in a test mine was constructed, and the dynamic evolution of water inrush and the mechanism of water inrush in karst roofs under different mining sequences were analysed. As a result, the problem of water inrush at the mine face was solved, and a method to utilize the karst groundwater water resources was proposed. The research showed that after downward mining, the maximum development height of the water-conducting fracture in coal seam 4 was 43.1 m, and the fracture mining ratio was 14.4. A water-inrush pathway formed at the connection between the mining-induced fractures and the roof karst aquifers, and the safe mining of coal seams 4 and 9 were threatened by water inrush from the goaf. So, the feasibility of upward mining was determined by the ratio test and "three zones" discrimination methods, and the evolution of water-inrush pathways during upward and downward-inclined mining were compared. Upward-inclined mining was proposed to control roof water inrush. Moreover, the quality of the water flowing into the goaf was compared with the Chinese standards for water use, and the water in the goaf of the lower coal group was suitable for water resource utilization. This research provides a basis for preventing and controlling roof water inrush disasters and for appropriate utilization of water resources in these mining areas.

Water inrush in the working face caused by seepage instability of fault fracture zone is a major disaster which threatens the safety production in a coal mine. Based on the principle of fluid mechanics, a nonlinear mechanical model with three flow fields is established in this paper. Combining with the actual situation of a fault fracture zone in a coal mine, a multicoupled numerical model is built in COMSOL Multiphysics, in order to study the water pressure and flow velocity in the three flow fields and the flow state of fluids in the aquifer and fault under different ratios of fault permeability and aquifer permeability. The research results show that the permeability in the fault fracture zone is an essential factor affecting the danger of water inrush, and the pressure and flow velocity in the boundary zone of the adjacent flow field varies significantly. Besides, the water inrush in the fault fracture zone is a gradual dynamic process, and the fluid flow from the aquifer through the fault gradually changes from a linear flow state into a nonlinear flow state. Meanwhile, the non-Darcy effect increases and decreases with the growth and decrease of the permeability in the fault fracture zone.

为了解夹矸厚度对含矸煤层煤壁稳定性的影响,采用理论分析与数值模拟相结合的方法,推导出夹矸层剪切破坏力学模型,进而建立含矸煤层煤壁稳定性数值模型,分析不同夹矸厚度下的煤壁前方水平位移、垂直应力的空间分布特征.结果表明:煤壁前方产生失稳影响区主要位于夹矸层周围,形成以夹矸层为中心的凸出区域;夹矸厚度较小时,夹矸层呈现出多块体联合破坏形态,而夹矸厚度较大时,夹矸层出现单块体逐个破断现象;力学分析得知:夹矸层破坏面发生剪切破坏的危险系数随着夹矸厚度的增大而逐渐减小,数值模拟结果与理论分析一致.

With the development of coal mining in rocky desertification mining area in Southwest China, water burst is becoming an important disaster in coal mine. In order to grasp the evolution characteristics of water gushing channels in coal mining in rocky desertification mining area, the 1402 working face in Xintian Coal Mine is taken as the research object, and the occurrence of aquifers on the roof of the working face is analyzed, and the water filling path of the aquifers is explored. Besides, the evolution characteristics of water passage in coal seam mining are comprehensively analyzed, by the methods of physical similarity simulation, numerical simulation, and microseismic monitoring. The results show that the key water resource is the atmospheric precipitation, which enters the mine through the original karst fissure and mining-induced fissure. With the continuous advance of working face, the fracture height of overburden increases gradually. Specifically, when the advancement distance of working face exceeds 135 m, the water-conducting cracks in the overlying strata develop to the bottom boundary of the Yulongshan limestone aquifer, and then, the mining-induced fracture and aquifer are conducted; when the working face advances 190 m, the overall overburden mining fissure is divided into fissure opening zone and fissure closed zone. Meanwhile, most of the microseismic events occur in the middle part of the karst roof, and the maximum height of microseismic event is 40 m away from the bottom boundary of the Yulongshan limestone, during the advancing process of the working face. When the mining fissure is connected with the original karst fissure, atmospheric precipitation enters the aquifer through the original karst fissure and enters the gob of working face through the mining fissure. The research results provide the references for prediction and prevention for the water burst disaster in rocky desertification mining area in Southwest China.

There are a large number of karst caves in the limestone rock strata in the karst mining area, and the karst water in rock strata seriously restricts the safe and efficient recovery of coal resources. In order to reveal the influence law of karst caves of rock strata on the evolution of water-conducting fissures in coal seam mining, the numerical simulation method in UDEC software is employed to analyze the development characteristics of water-conducting fissures in coal seam mining under the conditions of karst caves of different sizes. By comparing and analyzing the development characteristics of overlying fissures in rock strata and the displacement fields in coal seam mining under the conditions of different karst caves, the evolution law of water-conducting fissures in coal seam mining is obtained. The research results show that the size of karst cave directly affects the maximum height of the water-conducting fissures in the overlying rock strata in coal seam mining; when the thickness of the coal seam is 3.0 m, the larger the radius of karst cave is, the higher the development height of water-conducting fissures in the overlying rock strata is, and the greater the overall sinking displacement in the Yulongshan limestone is. When the radius of karst cave is between 10 m and 15 m, a through-type water-conducting channel is formed between the working face and the karst cave after the coal seam is mined, and the numerical simulation results are consistent with the field monitoring results. The research results provide an important reference for the prevention and treatment for water inrush disaster in karst mining areas.

为解决矿井采煤工作面超前支护因采用超前液压支架支护而导致顶板锚杆(索)失效且在直接顶破碎时超前支护段巷道变形严重等问题,以红岭煤矿1505工作面为工程研究背景,通过对巷道围岩变形破坏因素、特征的分析,建立了梯形巷道顶板超前支护围岩控制力学模型,并基于锚索梁锚注协同控制技术机理,提出锚索梁锚注的补强支护替代超前液压支架支护方式,现场试验效果良好.1505工作面回风巷超前支护范围内巷道两帮移近量为385 mm,顶底板移近量为339 mm,其变形量均在安全合理范围内,实现了工作面回采巷道全周期一次性主动支护.

In view of the variation law of water level in water injection drill between dou?ble-system layers of hard rock strata in Datong mining zone, the failure process and mechanism of boreholes during propulsion are analyzed by the numerical sim?ulation and the test measurement in this paper. After the coal seam is fully mined, it can be divided into the advanced deformation zone, the bending deformation zone and the compaction stable zone. Borehole damage intensifies from top to bottom. The junction of siltstone and sandy mudstone is a high-risk position. The results are verified by the water level measurement and the borehole peeping.

During the full‐mechanized caving mining, the overburden strata in the double system and extrathick coal seam of the Datong mining area are largely damaged. Water and harmful gas in the old goaf may be discharged when overburden fractures evolve to the upper goaf, which poses a major threat to the normal production of the panel. To study the movement of overburden strata and the evolution of fracture field under the full‐mechanized caving mining of the double system and extrathick coal seam, panel 8309 of Tongxin mine was taken as the research object; the evolution rule of fracture field in the full‐mechanized caving mining of the double system and extrathick coal seam was obtained through field measurement and physical similar simulation. The results show the following: (1) the far‐field and near‐field key strata play a decisive role in controlling the fracture evolution of overburden strata. When the far‐field key strata break and the development height of fractures reaches 220.9 m, panel 8309 is connected with the overburden goaf. (2) Based on the “O‐shape circle” theory of mining fracture, with the continuous advance of the panel, the overburden breaks periodically, and a “fracture surface” with a certain angle of 61°–67° can be formed along with the advancing direction of the panel. (3) When the key strata are broken and the development height of fractures reaches the maximum, the fracture surface is formed as the “main fracture surface,” which is the only downward discharge pathway for goaf water and harmful gas. The overall shape fracture surface is “inverted trapezoid” in the upper part and “positive trapezoid” in the lower part. (4) Based on the field measurement of the water level of borehole and the observation of mine pressure, the correctness of the evolution law of the similar simulated fracture field is verified.