Search

Small fault area in coal mine has great risk of coal and gas outburst. However, the damage effect of small faults on coal pore structure still lacks systematic research. Taking a small reverse fault under Pingmei No. 2 mine as an example, this paper collects the hanging wall coal samples within 5 m from the fault plane and the coal samples 50 m from the fault plane, where there is no fault development. The pore structure characteristics of the two coal samples were analyzed and compared by means of a scanning electron microscope, mercury injection, liquid nitrogen adsorption, and Raman spectroscopy. The test results show that compared with the coal samples without faults, the coal samples at faults form micron-scale fracture zones with constant spacing, stable occurrence, and flat two walls. The pore volume and pore specific surface area of different pore sizes increase, the pore peak of mesopore (100~1000 nm) shifts from 1000 nm to 200~400 nm, and its connectivity is enhanced. The number of micropores (<10 nm) increased significantly, and the ink bottle type pores developed. Faulting also has a certain impact on the macromolecular structure of coal, which shows that the D peak area decreases and the area of G peak increases, indicating that the order degree of macromolecular structure of coal increases. [ABSTRACT FROM AUTHOR]

Coal mining has to develop to deeper strata with the increasing demand for coal, which leads to frequent coal and gas outburst disasters. Especially, when there is a deformed coal in the coal seam, the outburst disasters are easier and more intense. Coal and gas outburst disasters can be promoted by the fragmentation. In order to clearly explain the reasons for the impact of fragmentation on deformed coal and gas outburst, mercury intrusion porosimetry, low-temperature liquid N2 adsorption test, and scanning electron microscope were carried out in this paper. The differences in pore characteristics of intact coal and deformed coal under different particle size conditions were analyzed from pore shapes, pore size distributions, and fractal dimensions. The damage paths of fragmentation on various kinds of pores in intact coal are as follows: macropores, mesopores, minipores, and micropores, and those on various kinds of pores in deformed coal are as follows: macropores, micropores, mesopores, and minipores. According to the fractal dimension theory and experimental results, the calculative results of fractal dimensions show that the fragmentation and tectonism reduce the surface roughness and structural complexity of macropores and mesopores and increase those of minipores and micropores in deformed coal. Finally, combined with the coupling effect of fragmentation and tectonism on pores, the reason of deformed coal with high crushing degree in fields of outburst was explained. The research provides the basis for the prevention of coal and gas outburst. [ABSTRACT FROM AUTHOR]

Confining pressure is closely related to the deformation and failure characteristics of gas-containing coal and is one of the key factors for gas outburst-rockburst coupled dynamic disaster. Firstly, this paper briefly summarized the triaxial compression test results of gas-containing coal under different confining pressures, including deformation and stiffness and failure and strength. Then, based on the second developed MatDEM gas-solid coupling program, the macro- and microdeformation and failure process of coal samples under different confining pressures and constant gas pressure were simulated, and the distribution of particle stress, pore stress, and crack, as well as energy conversion characteristics, was obtained. Finally, the influence mechanism of confining pressure on deformation and failure of gas-containing coal was discussed, and the occurrence conditions of coal and gas outburst, rockburst, and their coupled dynamic disasters were distinguished. The results show that the peak strength and residual strength after failure of gas-containing coal both increase approximately linearly with the increase of confining pressure, while the elastic modulus does not change much or increases continuously, which is closely related to the number of microdefects in the coal sample. The strengthening effect of confining pressure on rock stiffness and strength mainly comes from external support and compaction. The total number of cracks decreases with the increase of confining pressure, while the number of shear cracks increases, and the inclination angle between the formed macroscopic main crack and the horizontal plane gradually decreases. The maximum cumulative elastic energy and residual elastic energy both increase with the increase of confining pressure, which leads to the increase of the impact tendency index of coal samples. [ABSTRACT FROM AUTHOR]

The strong disturbance of upward mining of the short-distance multiseam results in frequent fractures in the coal seam to be mined, jeopardizing the operation safety due to the instability of the surrounding rock of the overlying stope and risks of coal and gas outburst. A lucrative alternative is the downward mining of multiseam, which wide implementation is limited by the lack of reliable data on stress evolution characteristics. In this paper, the evolution, nonlinear interaction, and superposition characteristics of mining-induced stress after multiple pressure relief in the short-distance multi-seam were investigated by the numerical simulation and physical simulation, taking the endowment and mining technology characteristics of group B short-distance multiseam in Pan'er Coal Mine in Anhui Province of China as an example. The numerical and physical models of multiple (2—5 times) mining activities in pressure relief multiseam (with five main coal layers) under downward mining are constructed and implemented with the FLAC3D software and 1 : 100 scaling, respectively. The results showed that a pressure relief arch, which bears and transfers stresses, is formed on the coal seam's roof and floor. In downward mining, the local arch expands to the long arch, which bearing capacity within the influence range of multiple mining disturbances is weak, and the arch structure is prone to instability. If a coal pillar is left in the upper coal seam after its mining, the lower coal seam mining will switch from the large-scale low-stress area under the goaf to the small-scale high-stress area of nonlinear interaction of the multiple mining stresses with the stress under the coal pillar. [ABSTRACT FROM AUTHOR]

The thick and hard rock strata (THRS) exist widely in coal measure strata, which control the movements of overlying rock strata in stopes. When THRS break, great energy is released, which could aggravate the risks of coal and gas outburst, rock burst, and other dynamic disasters. Therefore, the foundation and key of preventing dynamic disasters are to distinguish the THRS that could induce coal-rock dynamic disasters and to analyze the laws of rock stratum breaking and energy releasing. The paper proposed the theoretical calculation methods of the energy accumulation and attenuation of rock breaking which is greatly affected by the hanging length of rock strata and the spreading distance. One or more roof strata that play a leading role in inducing dynamic disasters of the underlying coal mass are defined as the key disaster-inducing strata (KDIS). The disaster-inducing coefficient (DIC) is defined and used as the criterion of KDIS. The greater the source energy, the shorter the spreading distance, and the smaller the attenuation coefficient are, the easier the roof strata are to become KDIS. The disaster-inducing ability of the main THRS was analyzed, and the igneous sill was judged as KDIS, taking the Yangliu Coal Mine as project background. The breaking laws of the igneous sill were obtained by the methods of UDEC numerical simulation and microseismic monitoring, which verified the criterion of KDIS. [ABSTRACT FROM AUTHOR]

Coal and gas outburst is a serious disaster in the mining, and crosscut coal is the most prone to cause the coal and gas outburst. In order to study the mechanism of outburst, this paper studied the stress distribution characteristics in front of the working face in the process of rock roadway driving before implementing crosscut coal firstly. On this basis, the hypothesis of stress distribution on the "strong and soft face" of coal-rock mass was proposed. And by using the hypothesis, the mechanical equation for the parameter changes of the plastic zone in front of the working face in crosscut coal was established, and the width and morphological characteristics of the plastic zone in crosscut coal were analyzed. The results show that during the process, as the working face moves forward, the shape distribution of the plastic zone in front of the working face changes from the "semielliptical" to "semibutterfly," And based on the distribution characteristics of plastic zone in working face in crosscut coal, modification proposals for outburst-prevention measures were proposed and provided technical support for the outburst-prevention measures and key parameters setting to prevent the coal outburst in crosscut coal. [ABSTRACT FROM AUTHOR]

To analyze the effect of small faults in the working face on coal and gas outbursts, the coal and gas outburst accident in the 21431 working face was studied with the 3DEC numerical simulation method, and the main research contents were the change laws of both stresses at the small fault and the overburden strata movement rate in the small fault zone of which the drop height and the strike were designed into different groups. The results show that the risk of small fault slip increases with the advancing working face. In addition, there is a positive correlation between the risk and the small fault throw. The movement rate of overburden strata in the small fault zone increases along with the rising of the small fault throw, which increases the energy transferred to the coal seam from the surrounding rock under the effect of the small fault. Hence, the effect of small faults on the working face on coal and gas outbursts was positively correlated with the small fault throw. Under the influence of a small fault strike, the closer it is to the small fault along the dip distance at the same working face, the greater the risk will be of a coal and gas outburst. And the bigger the small fault strike is, the greater is the stress concentration degree in front of the working face and the more the elastic energy is stored and the greater is the possibility of an outburst. The paper analyzes the influence of small faults on coal and gas outbursts in the working face, which has reference significance for the prediction and prevention of coal and gas outburst disaster in the working face. [ABSTRACT FROM AUTHOR]

In order to realize dynamic, continuous, and real-time prediction of coal and gas outburst risk in real time in blasting driving face, an outburst risk prediction method based on the characteristics of gas emission after blasting is proposed. In this study, the causes of abnormal gas concentration in blasting driving face are analyzed, and the identification method of abnormal gas concentration based on weighted K-nearest neighbor (weighted KNN) is proposed. The correlation between gas emission characteristics after blasting and K1 value is analyzed, and the prediction model of outburst risk based on convolutional neural networks (CNN) is established and applied in Jinjia coal mine in China. The results show that the causes of abnormal gas concentration mainly include ventilation stop, blasting operation, sensor adjustment, and other abnormalities. The accuracy of the identification method is 86.1%. Especially, the identification accuracy of blasting operation is 92%. There are strong correlations between the growth rate, peak value, and decay rate of gas concentration after blasting and K1 value, and the maximum correlation coefficient is 0.92. Using the prediction model, 28 times of jet holes and 1 small outburst event are predicted successfully, and the efficiency of the prediction model is 76.39%. By this technology, the utilization rate of gas information is improved, and the relationship between the change characteristics of gas concentration after blasting and the risk of coal seam outburst is established, which is of significant for improving the prediction accuracy and risk management ability of coal and gas outburst. [ABSTRACT FROM AUTHOR]

To understand the stability of coal and rock in areas of normal faults disturbed by the dynamic loads of blasting, the damage characteristics of coal and rock within a normal fault are investigated using similarity simulation tests. The mechanism for coal and gas outbursts within a normal fault is analyzed theoretically, and the results indicate that the maximum tensile stress in the vertical direction of the blasting hole in the normal-fault model is 1.17 times that in the no-fault model. The propagation of cracks near the blasting hole produces crushing circles, and more cracks are produced in the normal-fault model, causing severe damage to the coal seam and floor rock adjacent to the upper wall of the normal fault. Meanwhile, coal on the surface of the coal seam falls off. The cracks extend to the roof rock through the footwall of the normal fault. Cracks in the adjacent strata and coal seam interpenetrate those around the blasting hole, which is a potentially dangerous area for coal and gas outbursts. The cumulative damage caused by blasting vibrations increases the extent and scope of the damage to coal and rock, and broken coal and rock provide weak surfaces and gas flow channels that can lead to dynamic gas disasters. The research results will provide a theoretical basis for gas dynamic disasters induced by blasting disturbance in normal fault structures. Based on cases of coal and gas outbursts in the Didaoshenghe Coal Mine in Heilongjiang Province, China, an important reason for such incidents is considered to be the blasting areas of normal faults being disturbed by air-powered coal drilling. [ABSTRACT FROM AUTHOR]

Accurate determination of coalbed methane (CBM) content is of great significance to coalmine methane prediction, methane extraction, and gas outburst prevention. The adsorption time affects the CBM content by affecting the Langmuir adsorption constants when using the indirect method to determine the CBM content. To determine the reasonable adsorption time, representative coal samples (anthracite, lean coal, and gas-fat coal) and different destruction types (soft coal and hard coal) were selected. The experimental methods used are mercury intrusion porosimetry test, N2 adsorption/desorption test, and methane isothermal adsorption test. The results show that the pore volume and the specific surface area obtained by the BJH method and BET model increase with increasing coal rank and destruction type. For anthracite soft and hard coal, lean soft coal, and gas-fat soft coal, the N2 adsorption/desorption hysteresis loop is not closed when the relative pressure is low, indicating the existence of ink-bottle pores in these coal samples. For all tested coal samples, the longer the adsorption time is, the larger of coal methane adsorption capacity, Langmuir constant a , and CBM content are. The Langmuir constant b decreased with increasing the adsorption time. Under the condition that the reliability of the measured value is 85%, the reasonable adsorption times of coal samples are 28 h for anthracite, 18 h for lean coal, and 9 h for gas-fat coal. This study has practical help to improve the determination of CBM content, the prediction of coal seam gas outburst, and the development of CBM. [ABSTRACT FROM AUTHOR]

In view of the high gas pressure and low permeability of deep coal seam, it is difficult to control gas, which affects the safety production of coal mine. The technical scheme of hydraulic fracturing to improve the permeability of coal seam is put forward, and the gas drainage technology is used to control the gas emission of coal seam. The fracturing effect under different water pressure, different gradient fracturing times, and in situ stress is analyzed by using 3DEC (3-Dimensional Distinct Element Code) discrete element software. The simulation analysis and field verification results show that the coal seam gas pressure increases linearly with the buried depth. In situ stress characteristics and hydraulic strength are the key factors affecting the effect of hydraulic fracturing. The fracturing radius increases with the increase of flow. When the construction pressure of hydraulic fracturing test is 18 MPa, the distance between fracturing hole and drainage hole is 8.5 m. The actual measurement shows that after hydraulic fracturing and gas drainage, the maximum gas emission is reduced by 51%, and the average gas emission is reduced by 58%. [ABSTRACT FROM AUTHOR]

Hydraulic fracturing can increase the fracture of coal seams, improve the permeability in the coal seam, and reduce the risk of coal and gas outburst. Most of the existing experimental specimens are homogeneous, and the influence of the roof and floor on hydraulic fracture expansion is not considered. Therefore, the hydraulic fracturing test of the simulated combination of the coal seam and the roof and floor under different stress conditions was carried out using the self-developed true triaxial coal mine dynamic disaster large-scale simulation test rig. The results show that (1) under the condition of triaxial unequal pressure, the hydraulic fractures are vertical in the coal seam, and the extension direction of hydraulic fractures in the coal seam will be deflected, with the increase of the ratio of the horizontal maximum principal stress to the horizontal minimum principal stress. The angle between the extension direction of the hydraulic fracture and the horizontal maximum principal stress decreases. (2) Under the condition of triaxial equal confining pressure, the extension of hydraulic fractures in the coal seam are random, and the hydraulic fracture will expand along the dominant fracture surface and form a unilateral expansion fracture when a crack is formed. (3) When the pressure in one direction is unloaded under the condition of the triaxial unequal pressure, the hydraulic fractures in the coal seam will reorientate, and the cracks will expand in the direction of the decreased confining pressure, forming almost mutually perpendicular turning cracks. [ABSTRACT FROM AUTHOR]

In order to deeply explore the destructive effect of the impulsive airflow on the mine antioutburst door when coal and gas outbursts occur in underground coal mines, a large-scale coal and gas outburst dynamic effect simulation experiment device is used to carry out the coal and gas outburst disaster simulation experiment. The impact load and deformation characteristics of the antioutburst door under the impact airflow during coal and gas outburst are analyzed, and the experimental results are discussed in depth through numerical simulation analysis and field example analysis. Based on this, the internal and external causes of the damage of the antioutburst door on the coal mine site are analyzed, the key technologies that need to be solved in the design of the antioutburst door's disaster resistance are studied, and the overall design of the structure optimization design of the antioutburst door is proposed. The research results show that after coal and gas outburst, the pressure on the antioutburst door will rise and fall, and the fluctuation will be greater. Under the same installation position, the farther the antioutburst door is from the protruding point, the less pressure it bears. In the middle and late stages of the outburst, intermittent negative pressure of the gas at the antioutburst door appeared. The key technologies for the design of the antioutburst door and its disaster resistance mainly include that strengthen theoretical and experimental research on the formation mechanism of outburst shock waves in mines, the interaction mechanism between disaster shock loads and dampers, and the magnitude of disaster expected shock loads; optimize the structure of the antioutburst door size, the width of the contact surface between the air door and the door wall, the stress distribution of the air door under impact load, the design of the safety hole, and the locking device; and improve the disaster monitoring and alarm capabilities of the antioutburst door and collect changes in antioutburst door pressure in real time. The research results provide a theoretical basis and technical support for the optimization of the antishock performance of underground antioutburst doors in coal mines and have important practical significance for improving the disaster resistance of the ventilation system. [ABSTRACT FROM AUTHOR]

Aiming at the problem of coal and gas outburst prevention and control in serious outburst dangerous coal seam under complex geological conditions in Qidong Coal Mine, the water jet drilling and expanding integrated device was used to implement the measures that expand holes and increase permeability by high-pressure water at a 912 working face. The experimental results show that when the pump pressure is between 13 MPa and 15 MPa, the particle size of pulverized coal can be effectively reduced and the discharge of pulverized coal can be increased. The coal output of a single hole is 0.8~2.3 t/m, with an average of 1.1 m/t. The unreamed conventional borehole has a single-hole initial gas drainage rate of 50.74 m3/d and a single-hole cumulative gas drainage rate of 736.12 m3 within 30 days. The initial single-hole gas drainage volume of the reaming borehole is 178.74 m3/d, and the cumulative single-hole gas drainage volume in 30 days is 2227.57 m3. After reaming, the initial gas drainage scalar of a single hole increases 3.52 times of the original unreamed conventional drilling and the average cumulative gas drainage scalar of a single hole reaches 3.03 times of the original unreamed conventional drilling. This technology and equipment have a good promotion and application value in gas treatment of soft, low-permeable coal seams. [ABSTRACT FROM AUTHOR]

Gas outburst is an important issue in deep coal mining. At present, the gas-rock coupling change mechanism and intensity prediction of gas outburst are not clear. The research of gas outburst simulation experiment is particularly important. The State Key Laboratory of Gas Disaster Monitoring and Emergency Technology of China independently developed a large-scale coal and gas outburst physical simulation test system. However, the influence of the design parameters of the testing machine on the stability and accuracy of the simulation experiment is unclear. The article analyzes the energy conversion in the process of gas outburst through experimental simulation phenomena and results. The experimental simulation results show that the energy released by the CO2 gas in similar materials is the most important energy source. The cracks of similar materials increase the nominal volume of similar materials, and the deformation energy stored in similar materials slightly increases. The experimental simulation results are consistent with the actual situation on site. Combined with CAE simulation analysis, the displacement and pressure of the indenter of the experimental machine remained basically unchanged during the experiment, and the system did not produce resonance. Comprehensive analysis shows that the design of the test machine meets the simulation requirements. [ABSTRACT FROM AUTHOR]

When the mountain tunnel projects passing through the complex formation with coal, it happened along with disaster accidents such as gas outburst, gas combustion, and gas explosion. These disasters should seriously threaten the safety and life of the construction personnel and affect the normal operation of the tunnel construction. Ventilation is the most effective means to control gas, fire, dust, heat, and other disasters. To study the effects of different ventilation modes in highway gas tunnels, Fluent software was used to simulate forced ventilation, exhaust ventilation, and mixed ventilation in a high gas tunnel of a highway in Hunan. The distribution law of the airflow velocity and gas concentration of these three ventilation modes were obtained to determine the optimal ventilation system. It was shown that vortex zones of different ranges formed in the tunnel for all three ventilation modes, and the gas concentration was higher in the vortex zone than in other regions. Mixed ventilation of them is superior to the other two modes, showing the best ventilation effect with regard to airflow velocity and gas concentration. [ABSTRACT FROM AUTHOR]

Coal seam water injection is an important technical method to prevent and control coal and gas outburst and other disasters. Water can soften coal and change its mechanical properties. In order to study the mechanical properties of coal samples with different moisture content, briquette coal samples with five moistures content (4%, 6%, 8%, 10%, and 12%) were selected to carry out triaxial compression tests under different confining pressures (0.1, 0.2, 0.4, 0.8, and 1.2 MPa). Then, the mechanical response mechanism of the water-bearing briquette coal was analyzed. The results show that the slope of the linear elastic stage of the stress-strain curve gradually decreases with the increase of moisture content. Water-bearing coal exhibits strain strengthening characteristics under high confining pressure, which transforms the water-bearing coal from brittle to ductile state. The peak stress under different moisture content conditions shows a linear relationship with the confining pressure. The internal friction angle decreases linearly with the increase of moisture content. The cohesion varies parabolically with the increase of moisture content and reaches the maximum value when the moisture content is 8%. The coal body with moisture content between 7% and 9% has a high bonding force, which is beneficial to the consolidation of the coal body. Therefore, ensuring a reasonable moisture content of coal through coal seam injection can provide a basis for preventing coal and gas outburst. [ABSTRACT FROM AUTHOR]

The compound dynamic disaster of coal and gas outbursts and rockburst is a typical hazard jeopardizing the mining of the high gas content coal seam under a hard roof condition. In this study, the hard roof's mechanism inducing this hazard is analyzed. Physical analog modeling experiments and in situ monitoring of mining-induced stress were performed during coal seam mining under a hard roof condition. The pattern of hard roof breakage effect on the stress-fissure field evolution was revealed. The elastic energy was released and propagated on both sides immediately after the hard roof breaking, leading to energy accumulation. Meanwhile, expansive roof collapse resulted in the intense weighting of the working face and rockburst. Thus, the coal and gas outburst occurred under the joint action of the impact energy generated by breaking the hard roof and gas expansion energy. In other words, the compound dynamic disaster happened. Synergistic stereoextraction integrating cross-seam drilling and along-seam drilling was combined with deep hole advanced presplitting blasting technology to cope with the compound dynamic disaster in the high gas coal seam under a hard roof condition. [ABSTRACT FROM AUTHOR]

At the present time, it is of major significance to study the solid-liquid-gas three-phase coupling relationship of coal, water, and gas in deep-mining stopes in order to prevent and control coal and gas outbursts in high-gas mines. In this study, the influence rules of water on the mechanical characteristics of coal, as well as gas diffusion and migration processes, was examined by combining theoretical analysis and laboratory testing procedures. The results showed that with increases in water content, the mechanical characteristics of coal bodies presented change trends of first increasing and then decreasing. In this study, it was found that the water content levels which corresponded to the maximum shear strength of the coal in the No. 8 coal seam in the study area had ranged between 6.77% and 11.9%, and the water content level corresponding to the extreme point was 8.66%. It was observed that under different water content conditions, the gas desorption speeds of the coal bodies gradually decreased over time. The gas desorption speeds rapidly decreased during the initial desorption stage and then gradually decreased over time. Furthermore, under the different water content conditions, the amount of gas desorption in the coal bodies was observed to gradually increase over time, with the initial desorption amounts displaying rapid increases. Then, with the passage of time, the increase speeds of the gas desorption amount gradually decreased and finally tended to remain at a stable value. It was found that with the increases in water content, the desorption speeds, initial desorption speeds, and desorption amount of gas in the coal bodies continuously decreased. In other words, the water content levels in the coal bodies were negatively correlated with the gas desorption speeds and desorption amounts of the coal bodies. In addition, the gas desorption speeds, initial desorption speeds, and desorption amounts were observed to change more sharply with the increases in water content. The results of this research hold important guiding significance for the improvement of the understanding of the mechanical properties of high-gas coal seams and the implementation of effective gas control measures. [ABSTRACT FROM AUTHOR]

Geohazards associated to submarine hydrothermal systems still represent a tricky enigma to face and solve for the scientific community. The poor knowledge of a submarine environment, the rare and scarce monitoring activities, and the expensive and sometimes complicated logistics are the main problems to deal with. The submarine low-energy explosion, which occurred last November 3, 2002, off the volcanic island of Panarea, highlighted the absence of any hazard scenario to be used to manage the volcanic crisis. The "unrest" of the volcanic activity was triggered by a sudden input of deep magmatic fluids, which caused boiling water at the sea surface with a massive CO2 release besides changes in the fluids' geochemistry. That event dramatically pushed scientists to develop new methods to monitor the seafloor venting activity. Coupling the information from geochemical investigations and data collected during the unrest of volcanic activity, we were able to (a) develop theoretical models to gain a better insight on the submarine hydrothermal system and its relationships with the local volcanic and tectonic structures and (b) to develop a preliminary submarine volcanic hazard assessment connected to the Panarea system (Aeolian Islands). In order to mitigate the potential submarine volcanic hazard, three different scenarios are described here: (1) ordinary hydrothermal venting, (2) gas burst, and (3) volcanic eruption. The experience carried out at Panarea demonstrates that the best way to face any submarine volcanic-hydrothermal hazard is to improve the collection of data in near real-time mode by multidisciplinary seafloor observatories and to combine it with periodical sampling activity. [ABSTRACT FROM AUTHOR]