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Coal and gas outburst seriously threatens the safety of underground coal mining. After the outburst, it will not only cause harm in the near-field outburst roadway but may also have a strong impact on the far-field ventilation network connected to the outburst roadway, expanding the impact of the disaster. In order to define the propagation law of shock wave and airflow induced by the outburst and its influence on the far-field ventilation network, the coal and gas outburst experimental system was used to carry out an experimental study under different air current and local resistance conditions in this paper. The results show that, under different air current states, the first overpressure peak increases with an increase of outburst pressure and decreases with an increase of propagation distance. Compared with the propagation characteristics in a windless roadway, the first overpressure peak and attenuation coefficient of shock wave propagating downwind are smaller, whereas opposite in upwind state. The local resistance enhances the impact and disturbance ahead of it and weakens that after it. When shock airflow propagates downwind, the increase of shock airflow velocity is approximately equal to the original airflow velocity in the roadway, whereas the airflow direction may reverse when the shock airflow propagates upwind. This paper provides some references to prevent the impact expansion of coal and gas outburst, which are of great significance for the optimization of ventilation network and emergency management.

Coal and gas outbursts are a violent release of energy in part driven by rapidly desorbing gas from the fragmenting coal. We present a coupled two-phase model of coal and gas outbursts to define the timing, rate and magnitude of gas desorption and its contribution to the resulting energetics. The model involves a fragmenting ejection of the outburst from an overpressurized coal that retreats omnidirectionally from a point and develops a deepening crater. This model is applied to represents both experiments and in situ observations. These results indicate that the outburst is initially driven by free gas before desorbing gas rate exceeds this free gas liberation rate early into the outburst (at ∼17 s in our model). The cumulative mass of desorbed gas only exceeds the free gas later into the event at approximately double this duration (at ∼29 s in our model). During the outburst, ∼55 % of the expansion energy is contributed by desorbing gas. Using the initial gas emission rates for both non-tectonic and tectonic coals defines a power-law relationship between the initial gas desorption rate and the desorption gas contribution (∼14 %–92 %), indicating that the desorbing gas plays a decisive role in outburst development. Furthermore, taking the gas emission model as a boundary conditions for numerical simulations, the gas pressure potential energy (GPPE) released in the first millisecond at the maximum gas emission rate is derived to characterize its effects on the dynamic characteristics of the outburst two-phase flow. The maximum energy release intensity considering gas desorption is ∼5 times that without gas desorption for non-tectonic coal. For tectonic (mylonitized) coals the energy release is a further ∼4 times greater than that of non-tectonic coals. This paper presents a novel quantitative study defining the role of gas desorption in outbursts and contributes to the understanding of causal mechanisms and precursory phenomena preceding catastrophic outbursts.

In order to prevent the accidents in underground coal mines, an index system for safety supervision ability evaluation is established in the present paper. The index system is composed of goal laye...

The dynamic effect of coal and gas outburst seriously threatens the safety of underground equipment and workers in mines. In this paper, the models for outbursts are established, and according to the energy transformation during gas expansion process, three parameters of the release of gas pressure potential energy are defined and the gas dynamic characteristics of two-phase flow in the initiation stage are quantitatively studied under the four factors: initial gas pressure, particle volume fraction, particle size and outburst hole size. The gas dynamic characteristics in numerical simulations are verified by experiments. The results show that for the influence of the factors on the gas dynamic characteristics of two-phase flow, initial gas pressure >outburst hole size >particle volume fraction ≈particle size. The solid particles block the pressure potential energy release from chamber, so does the caliber. However, the maximum of pressure drop occurs when the caliber is 80% of the chamber, which explains the outbursts in mines are so violent due to the caliber smaller than the internal space. This paper provides a novel quantitative research method of gas dynamic characteristics of coal and gas outburst, which is of guiding significance to the design of outburst prevention facilities and emergency rescue measure.

In the process of coal-gas outburst, the gas-solid two-phase flow of pulverized coal and gas will induce large-scale damage to underground mining. In this work, in order to study the dynamic evolution law of gas-solid two-phase flow of coal-gas outburst, and clarify the short-time destructive effect of outburst dynamic phenomenon, an EDEM-FLUENT coupled model is constructed to realize the numerical simulation of coal-gas outburst two-phase flow. The simulation results show that the flow velocity of pulverized coal in a short time (tens of milliseconds) approaches to the maximum velocity rapidly, which can reach 60 m/s. The velocity of pulverized coal is inversely proportional to the particle size. The initial acceleration of particles is slow, and then the acceleration increases rapidly. The accumulation angle of pulverized coal in the outburst hole is about 21° and is far less than the natural accumulation angle of pulverized coal, which is consistent with the general phenomenon of coal-gas outbursts. The results also show that the shock wave overpressure of the coal-gas outburst of numerical simulation is similar to that of the physical simulation test, and the difference is less than 10%. And the pressure change in the roadway is completed in short time. In terms of spatial relationships, the pressure at the position closest to the outburst mouth is not the maximum, and the maximum pressure exists at a certain position away from the outburst mouth.

We explore the propagation modes of shock waves driven by coal and gas outbursts in both the near- and far-field. Near-field response is three-dimensional (3D) at the face, but the far-field is constrained to one-dimensional (1D) flow within the roadways. Fluent models are applied to simulate the 3D propagation of shock waves at the outburst source with 1D models utilizing Flowmaster being sufficient distal from the face. These models are linked via a Mesh-based parallel Code Coupling Interface (MPCCI) to define shock wave propagation at all scales – from mine face to distal roadways. The results demonstrate the suitability and fidelity of the Flowmaster 1D simulation in representing the time history of overpressure. The shock wave attenuation in each part of the MPCCI coupled model is consistent with experimental results. This work provides a logical, consistent and robust method to solve for the complex coupling at multiple length- and time-scales and its implementation as an “outburst” pipe network. Additionally, it has significant utility in designing for outburst mitigation, disaster ventilation and other safety measures.

The quality of borehole sealing has significant influence on the gas extraction. Inorganic sealing material has the advantages of low cost, multiple functions and high performance; therefore, it has been widely used in many fields. In the paper, the single factor experiment was conducted on the new inorganic sealing material, and the effect of the polymer and the expansive agent on the properties of the new inorganic seal material was studied, on the basis of which such three factors as polymer-to-cement weight ratio, dosage of dispersant, and dosage of the expansive were used as the research object of the orthogonal experiment; the flexural strength, compressive strength and expansion coefficient were used as the evaluation indicators to analyze the effect of such three factors on the properties of the inorganic material. The results of the research show that the final proportion of the new inorganic sealing material is: 1.2% dosage of dispersant, 6% polymer-to-cement weight ratio, and 0.1% dosage of expansion agent. The water cement ratio exerts great influence on the mechanical properties of the material; the higher the water cement ratio is, the lower the compressive strength and the flexural strength are. Furthermore, the water cement ratio also has significant influence on the fluidity of the slurry; the water cement ratio is determined to be 1.5:1. According to the aforesaid proportion, the sealing performance test was conducted on the new inorganic sealing material, and the comparison was made with the Portland cement material. The results of the test show that the time required for the air space to restore from the initial pressure value to the atmospheric pressure value is much greater than that needed for the cement material, so the sealing performance of the inorganic sealing material is much better than that of the Portland cement materials. It is of practical significance to develop the new inorganic seal material, which can improve the quality of sealing, increase the gas extraction rate and reduce the mine gas accidents.

Coal and gas outbursts are the most serious disaster in the underground mining. During an intense outburst, ejection of millions tons of coal and cubic meters of gas with high kinetic energy can cause death or injuries and even destroy underground facilities, the intensity of outburst shock waves and gas flows is highly related to the gas expansion energy, and the gas expansion energy requires the participation of a large amount of desorption gas. There is a significant difference in the gas desorption law between the pulverized coal and the unaffected coal. To investigate the effects of fast-desorbed gas on the propagation characteristics of outburst shock waves and gas flows, the particle size distribution characteristics of pulverized coal were obtained by site investigation. Then, gas desorption experiments were conducted for coal particles of various sizes at different gas pressures and temperatures. The results indicate that a segmentation function is reasonable for representing the gas desorption law during coal and gas outbursts. Based on the gas desorption law, numerical simulation for the propagation characteristics of outburst gas flows were conducted. The results show that fast-released gas compresses the air within the roadway, thereby generating outburst shock waves that propagate at high speed. The intensity of the outburst shock waves decrease with time. Simultaneously, the gas convective transport velocity is lower than that of the outburst shock waves, large areas of high-concentration gas in roadways are induced by the outburst gas flows.

In order to clarify the characteristics of gas-bearing coal adsorption-instantaneous pressure relief deformation, and reveal the mechanism of the effect of gas desorption on the outburst. Through the gas-bearing coal adsorption-instantaneous pressure relief test system, the adsorption-instantaneous pressure relief test using briquette/raw coal samples was used to conduct a comprehensive comparison and analysis of the deformation characteristics of the two coal samples. Studying the damage of coal with different adsorption characteristics gases under the condition of adsorption-instantaneous pressure relief, and use strain gauges to monitor the microscopic deformation of the coal, and analysis of the adsorption of briquette/raw coal at constant pressure-instantaneous similarities and differences of deformation characteristics during pressure relief. “The results showed that under the same test conditions of adsorption equilibrium pressure, the degree of crushing of coal samples after instantaneous pressure relief is CO2 > CH4 > N2. At the moment of instantaneous pressure relief, the strain of the raw coal/briquette suddenly decreases, characterized by swelling deformation. Under the same temperature and pressure conditions, the expansion energy of CO2 is the highest, followed by CH4 and N2. Due to the raw coal has not completely destroyed the joints, only elastic deformation occurs, and the strain rises rapidly within a short period of time, resulting in shrinkage deformation. However, during the instantaneous pressure relief of the briquette, swelling and deformation occurred, and the coal was destroyed. The research results have certain significance for the exploration of coal and gas outburst mechanism.

Coal is the most important primary energy in China. Although the proportion of coal in China's total energy consumption continues to decline it will still be the main energy in China for a long time in the future. As the largest contributor to China's greenhouse gas emissions, the energy conservation and emission reduction of coal industry will be the most critical step for China to cope with global climate change and solve environmental problems at present and in the future for a long time. The object of this study was coal mining in China. Life cycle assessment (LCA) was used to quantify carbon emissions in whole process of coal mining, including mining, ventilation, drainage, power consumption, transportation, and post-mining activities. The analysis result shows that the carbon emissions of producing tons of coal are 164.403 kg of carbon dioxide equivalent per ton. The analysis further emphasizes that the methane contributes the most, accounting for 62.21% of the total emissions, and plays an important role in the full life cycle of coal mining. Therefore, it presents a potential to mitigate the environmental impact of coal mining, and its main task is to recover and recycle methane. Based on the technical level, this study puts forward the low-carbon development countermeasures for coal enterprises. Then the technical system of methane emission control and utilization is constructed from three aspects: coal-bed methane development, gas extraction, and utilization and gas utilization. Finally, a trinity resource utilization system of coal mine gas is constructed. This study hopes to help practitioners to realize the importance of coal mine methane to the coal mining process. If the efficient resource utilization of methane be realized, it could not only save energy and reduce emissions in coal enterprises, but also promote the safety production of coal mines and improve the economic benefits of coal mines. It is also of great significance for optimizing China's energy structure, realizing low-carbon transformation, and safeguarding China's strategic energy security.

Currently, resource integration in coal-burning facilities and clean energy reconstruction are being strongly pushed forward in China. As a clean fossil energy, unconventional natural gas, such as coalbed methane (CBM), exhibits promise as an energy development strategy. In China, there are abundant CBM resources in the considerable reserves of low-rank coal. Therefore, the study of low-rank coal is the key to realize the high-yield and high-efficiency development of CBM resources in China. In this paper, a new water injection device was designed to prepare coal samples with a variety of moisture contents, and a novel method to measure the gas desorption properties in coal containing water was introduced. On this basis, the gas desorption law in low-rank coal with different moisture contents was tested, and the effect of moisture on the gas diffusion properties in low-rank coal was analyzed. The results indicate that the initial gas desorption volume of low-rank coal is extremely large and that the gas desorption law in the moisture-containing low-rank coal can be described by Airey's empirical equation. It is also observed that the ultimate gas desorption volume, initial gas desorption rate and initial effective gas diffusion coefficient all shift toward the direction that is beneficial to CBM development. Therefore, reducing the moisture content in low-rank coals through certain techniques can dramatically enhance the gas migration behavior and achieve the purpose of high-yield CBM development.

Coal mine ventilation is an extremely complicated system that can be disturbed by several factors. This paper addresses the fact that the stabilization of airflow in the airways can be induced by methane buoyancy. The formation and characteristics of methane buoyancy are further elaborated and combined with the airflow stagnation accident that occurred in the Tangshan coal mine in China. Field tests and experimental studies were conducted to verify the role of methane buoyancy on the stability of airway airflow. The results indicate that methane buoyancy is generated in inclined airways with gas accumulation, which can be regarded as an increment of buoyancy. Methane buoyancy can induce airflow stagnation or airflow reversals, especially in airways with relatively low airflow velocity. To maintain the stability of the airflow, in those airways with gas emissions, a higher airflow rate and velocity should be ensured, and large airways inclination should be voided.

Relative permeability of gas gains great significance in exploring unconventional gas. This paper developed a universal relative permeability model of gas, which is applicable for unconventional gas reservoirs such as coal, tight sandstone and shale. The model consists of the absolute relative permeability of gas and the gas slippage permeability. In the proposed model, the effects of water saturation and mean pore pressure on gas slippage permeability are taken into account. Subsequently, the evaluation of the model with existing model is done and then the validation of the model is made with data of tight sandstones, coals and shales from published literatures. The modeling results illustrate that a strong power-law relationship between relative permeability of gas and water saturation and the contribution of gas slippage permeability to relative permeability is determined by water saturation and mean pore pressure simultaneously. Furthermore, a sensitivity analysis of the impact of the parameters in the model is conducted and their effects are discussed.

Coal mine ventilation is an extremely complicated system that can be affected by many factors. Gas ventilation pressure is one of important factors that can disturb the stabilization of airflow in airways. The formation and characteristics of gas ventilation pressure were further elaborated, and numerical simulations were conducted to verify the role of gas ventilation pressure in the stability of airway airflow. Then a case study of airflow stagnation accident that occurred in the Tangshan Coal Mine was performed. The results show that under the condition of upward ventilation, the direction of gas ventilation pressure in the branch is the same to that of the main fan, airflow of the branches beside the branch may be reversed. The greater the gas ventilation pressure is, the more obvious the reversion is. Moreover, reversion sequence of paralleled branches is related to the airflow velocity and length of the branch. Under the condition of downward ventilation, the airflow in the branch filled with gas may be reversed. Methane in downward ventilation is hard to discharge; therefore, accumulation in downward ventilation is more harmful than that in upward ventilation. Keywords: Gas accumulation, Gas ventilation pressure, Airflow stability, Underground ventilation

Coal mine ventilation is an extremely complicated system that can be disturbed by several factors. This report addresses the fact that the stabilization of airflow in the airways can be induced by gas ventilation pressure. The formation and characteristics of gas ventilation pressure are further elaborated and combined with the airflow stagnation accident that occurred in the Tangshan coal mine in China. Field tests, numerical simulations and experimental studies were conducted to verify the role of gas ventilation pressure on the stability of airway airflow. The results indicate that gas ventilation pressure is generated in inclined airways with gas accumulation, which can be regarded as an increment of natural ventilation pressure. Gas ventilation pressure can induce airflow stagnation or airflow reversals, especially in airways with relatively low airflow velocity. To maintain the stability of the airflow, mine ventilation structures must be strictly managed to ensure a higher airflow rate and velocity in those airways with gas emissions and avoid arranging airways with large dips.

Coal is a kind of natural pore-fracture dual medium, which determines the diffusion and seepage characteristics of gas inside under the stress conditions. In turn, the gas migration has an effect on the mechanical damage properties of coal and is closely related to the occurrence of coal-gas outburst. The occurrence of outburst is inevitably accompanied by the instantaneous displacement mutation of gas-bearing coal, which is difficult to explained by conventional plastic zone analysis. And the process from plastic failure to instability is still vague, which makes the instability critical of outburst difficult to determine. Therefore, aiming at the outburst in the working face, we put forward a progressive failure and outburst hypothesis model based on the limit analysis method of strength reduction theory. Then, the limit instability criterion of gas-bearing coal is modified, and the coal-gas outburst in the strength reduction process is simulated by using the cyclic calculation method of COMSOL software. It describes the characteristics of fluid–structure coupling and progressive failure instability of gas-bearing coal. Finally, we use the limit safety factor to describe the outburst criticality and the outburst risk. We find that the initial uncovering coal area, stress and gas pressure play an important role in controlling outburst, especially the coal stability is extremely sensitive to gas pressure changes under high stress. And based on these, the outburst prevention and control measures are put forward. The method has potential application value for the risk assessment and prevention of outburst on site.

To control the human factor risk for oil and gas drilling industry, the types of work activities involved in drilling were identified, the major accident risk types of human errors were selected, the probability and severity levels of the risks associated with each activity were quantified, and the human factor risk levels of major work activities involved in drilling processes were calculated. Quantitative results demonstrate that the highest risks during the drilling process include being struck by an object, injury by machine, and overexertion; conversely, the lowest risks include exposure to harmful substances or environments and fire and explosion. The highest risk activities are associated with, for instance, penetration drilling, the trip in and out, and the hoisting and lifting operations. Conversely, the relative lowest risk activities include auxiliary operations, well logging and mud logging, equipment inspection and maintenance. The total risk value of all main drilling activities is 11.3947 S/w-h. Twelve risk control measures were selected, and the Delphi method was taken to quantify the human factor risk mitigation capacity resulting from the selected risk control measures. The results demonstrate that the human risk control measures exist in three tiers of effectiveness, with each tier being separated by nearly an order of magnitude. The types of most risk mitigation are risk codes, such as injury by machine, fall from height, and contact with harmful material. The most minimal risk mitigation types include muscle strain and fire and explosion. Finally, these data will be valuable for drilling companies to strategically allocate limited resources to their safety management plan, and they can evaluate the expected effectiveness resulting from risk control measures.

A better understanding of gas-solid coupling laws for deep, gassy coal seams is vital for preventing the compound dynamic disasters such as rock burst and gas outburst. In this paper, a gas-solid coupling theoretical model under the influence of ground stress, gas pressure, and mining depth is established and simulated by using COMSOL Multiphysics software. Research results indicate that under the influence of factors such as high ground stress and gas pressure, the mutual coupling interaction between coal and gas is much more significant, which leads to the emergence of new characteristics of gas compound dynamic disasters. Reducing the ground stress concentration in front of the working face can not only minimize the possibility of rock burst accidents, which are mainly caused by ground stress, but also can weaken the role of ground stress as a barrier to gas, thereby decreasing the number of outburst accidents whose dominant factor is gas. The results have a great theoretical and practical significance in terms of accident prevention, enhanced mine safety, disaster prevention system design, and improved accident emergency plans. Keywords: Deep mining, Gassy coal seam, Gas-solid coupling, Dynamic disaster

To analyze the airflow stabilization induced by gas accumulations in a mine ventilation network, a transient model for airflow caused by gas accumulations is presented. The Runge Kutta method is selected to solve this model. To quantify the average gas density in the transient model, a solution to the gas diffusion equation in airways is interpreted. The Crank-Nicholson difference method is applied to calculate the gas diffusion equation, and the chase method is selected to calculate the gas concentration distribution in airways. Furthermore, a coupled solution between the transient model and the gas diffusion equation is proposed, and a transient airflow ventilation network program for this coupled solution is developed. According to the simulations conducted in this work, it is concluded that the results agree well with the field test. Finally, it was found that gas accumulation in inclined airways can generate gas ventilation pressure, which can lead to airflow disorder.

Inspired by previous resistance models for porous media, a resistance expression of gas migration within coal seams based on the ideal matchstick geometry, combined with the Darcy equation and the modified Poiseuille equation is proposed. The resistance to gas migration is generally dynamic because of the variations in adsorption swelling and matrix shrinkage. Due to the limitations of experimental conditions, only a theoretical expression of resistance to gas migration in coal is deduced, and the impacts of tortuosity, effective stress and pore pressure on the resistance are then considered. To validate the proposed expression, previous data from other researchers are adopted for the history matching exercise, and the agreement between the two is good. Keywords: Porous media, Gas, Resistance, Tortuosity, Effective stress, Pore pressure

With the popularization and application of chemical process safety management (PSM) systems in the chemical industry, the use of such systems in China has become the focus of a large volume of research. In this article, 12 elements included in the current Chinese PSM system are divided into four stages from a structural point of view. This division will be helpful in the follow-up analysis. After a careful analysis of the evaluation results for one PSM pilot study in Nanjing, some correlations have been found between the results of the elemental evaluation. Small- and medium-sized chemical plants make up a large proportion of Chinese chemical plants and many chemical accidents take place in these plants, so a simplified PSM system in practical operation need to be found. Based on a previous PSM structural analysis, the secondary elements of the PSM system can be removed. This allows researchers to avoid the traditional method of analyzing PSM elements individually. In the concrete analysis process, a theoretical analysis of the correlation degree between elements can be combined with the results of accident investigations. The simplified Chinese PSM system consists of four core elements: Process safety information, process hazard analysis, training, and emergency management. Based on the current applications of these four core elements in China, a consideration of correlations between these elements is used to make several suggestions for improving China's PSM systems. © 2017 American Institute of Chemical Engineers Process Saf Prog, 2017

The movement and distribution of methane in coalmine roadways are major issues relating to coalmine safety. Once high concentrations of methane accumulate in downward ventilated tilted roadways, the movement of methane can be very special. A 1/50 experimental model was constructed for the study on high concentrations of methane behavior in downward ventilated parallel roadways. This experiment measured gas concentrations in the upper and lower parts of the methane accumulating roadway and the wind speeds both in the methane accumulating roadway and in its parallel roadway The experimental results indicate that the methane draft pressure (the additional natural draft pressure due to the density difference of methane and air when high concentrations of methane accumulate in tilted roadways) could lead to airflow reversion in a downward ventilated roadway; methane may flow with the reversed airflow into the parallel roadway. The reversed methane that flows into the parallel roadway could generate a new methane draft pressure, which would oscillate airflow under certain conditions. According to the experimental results with parallel roadways of different windage, a larger windage of the parallel branch could ensure a relatively stable airflow, and a smooth methane discharge process. Through analysis by oscillation theory and the Archimedes number, it is concluded that the parallel roadway windage affects the methane draft pressure-caused airflow disorder by two aspects: (1) a larger windage deceases the amplitude of airflow oscillation and (2) a larger windage decreases the methane flown into the parallel branch, which, in turn, decreases the critical wind velocity for airflow reversion in the parallel roadway. The effect of windage is proved by a numerical simulation of Jiulishan Mine at the end of this paper.

Most of coal fields in China have low permeability, which is a key parameter to reflect the possibility of gas migration in coal seams, coal and gas outburst. Permeability is also a important factor for expectation and mine of coal-bed methane. Low permeability coal seams have significant Klinkenberg effect, and that with decreasing permeability of coal the Klinkenberg effect increases. However, most of previous permeability models do not consider Klinkenberg effect. It is known that when mean free path of gas molecules is close to the pore size of porous materials Klinkenberg effect appears, which is the essence of Klinkenberg effect. In this study, we build relationships between mean free path of gas molecules and Klinkenberg factor b. By using the relationships and the formula of effective permeability and absolute permeability, we establish a gas permeability evolution model of coal containing gas with Klinkenberg effect. Then we make a compare between our permeability model and other permeability models, such as Levine model, P-M model, S-D model, and the results show that the model considering Klinkenberg effect best accords with the experimental data under condition of fixed confining stress. We think that model considering Klinkenberg effect has important significance for expectation and mine coal-bed methane when it comes to low permeability coal seams.

This paper addresses airflow stabilization in airways induced by outburst gas flows after the disappearance of the outburst shockwave. Based on fluid dynamics theory, a mathematical model of an unsteady airflow in an airway was established. The formation conditions of additional force and gas ventilation pressure with their dynamic influences on airflow in an airway were investigated. The results of this study indicate that an additional force is created by the variation of the airflow rate after outbursts, and this force hinders changes to the airflow and maintains the airflow in its original state of motion. The gas ventilation pressure can be observed as an increase in the potential energy after coal and gas outbursts. For upward ventilation, the direction of gas ventilation pressure is positive and assists the ventilation. However, for downward ventilation, the direction of gas ventilation pressure is negative and hinders the ventilation. This hindrance may lead to an airflow reversal in the main airway.

The densities of airflow will be changed by the influx of high-concentration gas, and methane draft pressure will be formed in roadways with height differences. The existence of methane draft pressure may also cause air volume reduction, airflow stagnation and even lead to airflow reversal in some roadways of ventilation networks, resulting in airflow disorder. In recent years, a number of achievements have been made in studies on airflow induced by methane draft pressure with different roadway conditions; however, currently available literature fails to provide a summary study on airflow catastrophes induced by methane draft pressure. Therefore, this paper introduces the definition of methane draft pressure, its influences on ventilation networks, experimental and simulation research, and influence factors and prevention measures of airflow disorder induced by methane draft pressure. It is concluded that methane draft pressure is an important area for future studies on airflow disorder in roadways to cover.

In order to analyze the propagation characteristics of shock wave and gas flow induced by outburst intensity, the governing equations of shock wave and gas flow propagation were put forward, and the numerical simulation boundary condition was obtained based on outburst characteristics. The propagation characteristics of shock wave and gas flow were simulated by Fluent software, and the simulation results were verified by experiments. The results show that air shock wave is formed due to air medium compressed by the transient high pressure gas which rapidly expands in the roadway; the shock wave and gas flow with high velocity are formed behind the shock wave front, which significantly decays due to limiting effect of the roadway wall. The attenuation degree is greater in the early stage than that in the late stage, and the velocity of gas convection transport is lower than the speed of the shock wave. The greater the outburst intensity is, the greater the pressure of the shock wave front is, and the higher the speed of the shock wave and gas flow is. Keywords: Coal and gas outburst, Outburst intensity, Shock wave and gas flow, Propagation characteristics

In deep coal mines, coal and gas outbursts are common disasters because of the high in situ stress and high gas pressure in coal seams. To eliminate the outburst risk, gob-side entry driving is proposed during the roadway excavation. To analyse the outburst risk of gob-side entry driving in a coal seam, this study employed an innovative model that incorporates a stress equilibrium equation and gas transport equation. On the basis of numerical simulations, the distribution law of displacement and stress and gas pressure in the solid coal on both sides of the gob were determined. Specifically, the gas content distribution in the solid coal along the gob, and gas emissions law during the excavation with gob-side entry driving technique were measured. Both the R index method and three-parameter index method were used for outburst risk predictions during roadway excavation with gob-side entry driving. Results showed that the surrounding rock stress, coal seam displacement, and gas pressure and gas content all were significantly reduced on both sides of the gob, and both the R index method and three-parameter index yielded values less than the outburst risk critical values. These findings verify that gob-side entry driving is an effective method for outburst-prone coal seam excavation in deep mines.

Klinkenberg effect is an important phenomenon for gas flow in low permeability reservoirs, and its influence increases with the reduction of gas pressure. Unlike conventional gas reservoirs, coal seam is unique with its high compressibility and sorption-induced-swelling features. During the coalbed methane (CBM) recovery process, coal cleat width varies due to the net effect of effective stress and coal matrix shrinkage, thus the Klinkenberg coefficient cannot be treated as a constant like rock reservoirs. A brief review of previous studies shows that the influence of coal seam characteristics on Klinkenberg effect was ignored by other researchers. By using the bundled matchstick conceptual model of coal, two improved models are proposed in this paper, one is under constant effective stress and the other is under reservoir condition. The former shows that the proportion of permeability change due to Klinkenberg effect is greater than the result from original model, and the Klinkenberg coefficient varies substantially albeit the influence of effective stress is eliminated. The latter links apparent permeability and coal porosity together, and the results show good agreement with field data, especially when the gas pressure is relative low. It can be concluded that apparent permeability model is crucial for explicit prediction of gas permeability changes during CBM recovery process, which may be underestimated without due consideration of Klinkenberg effect. The development of the improved apparent permeability models has significant value in the accurate prediction of CBM production as a result of permeability changes.

In order to study the propagation law of shock waves and gas flow during coal and gas outburst, we analyzed the formation process of outburst shock waves and gas flow and established the numerical simulation models of the roadways with 45° intersection and 135° intersection to simulate the propagation of outburst gas flow and the process of gas transport. Based on the analysis of the simulation results, we obtained the qualitative and quantitative conclusions on the characteristics and patterns of propagation and attenuation of outburst shock waves and gas flow. With the experimental models, we investigated the outburst shock waves and gas flow in the roadways with the similar structures to the simulated ones. According to the simulation results, when the angle between the driving roadway and the adjacent roadway increased, the sudden pressure variation range in adjacent roadway and the influencing scope of gas flow increased and the sudden pressure variation duration decreased. The intersection between the driving roadway and the adjacent roadway has no effect on airflow reversal induced by the shock waves and gas flow. Keywords: Coal and gas outburst, Shock waves and gas flow, Propagation law, Cross roadway

The coal-bearing strata consist of rock and coal strata with diverse thickness or mechanical strength, and thus they, especially the thick–hard rock strata, are distinguishing in movement and failure laws during coal mining. The failure of the thick–hard rock strata may affect the strata stability and cause serious coupled dynamic hazards and environmental problems. In the paper, the failure model of thick–hard rock strata was derived theoretically, which was applied to calculate the failure laws of the thick–hard igneous sill, and then, the model was verified by the methods of numerical simulations and surface subsidence measurements. The results indicate that: (1) the failure laws of the hard roof strata were analyzed based on the four-edge-clamped thin-plate assumption, and thus, the square-form structure failure of the hard roof stratum, which case is defined as the SSF model, occurs most possibly with the square gob for larger normal stress components; (2) the SSF model was applied to calculate the failure laws of the thick–hard igneous sill, and it would be broken with the approximate square-form gob of 310 m long and 350 m wide in Yangliu Coal Mine, Huaibei Coalfield, China; and (3) both the simulation results and the surface subsidence measurements indicate that the initial failure length of the thick–hard igneous sill was about 320 m with the square-form gob, verifying the correctness of the SSF model. The results could provide the theoretical guide for mining rock strata control and dynamic hazards prevention.