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Development and selection of fuzzy variable weight vector and its application on fuzzy comprehensive decision-making (FCDM) are studied in detail in this paper. Firstly, a parameter contained variable weight vector is developed based on the definition of variable weight vector, and then further extended to obtain the fuzzy variable weight vector. Its capability on weights changing can be adjusted by changing the parameter. In order to make the fuzzy variable weight vector for different changes of states to be selected and applied easily, the concept of fuzzy dispersion degree, which can be used to measure the balance of decision factors' states, is proposed; And then the concept of fuzzy average relative adjustment degree, which can be used to measure the capability of fuzzy variable weight vector on weight changing, is also proposed. Based on the concepts of fuzzy dispersion degree and fuzzy average relative adjustment degree, relationship between the weight changing capability of the developed fuzzy variable weight vector and the parameters it contains is analyzed. With consideration of keeping balance among states, steps on selecting fuzzy variable weight vector with its corresponding capability on weight changing are presented. Based on the fuzzy combined weighting method, a FCDM model with fuzzy variable weight is developed. The fuzzy structured element is used to express fuzzy numbers and fuzzy operations in the model. An analytical algorithm of the FCDM model based on the fuzzy structured element is presented. The developed model was then applied on evaluating and predicting for coal and gas outburst of coal mining panels. The research finding provides an alternative way for fuzzy operations and determination of weights in other fuzzy analysis models. [ABSTRACT FROM AUTHOR]

Protective layer mining (PLM) is one of the most effective regional measures against gas outburst, and the most preferred technique to prevent and control gas outburst. This paper attempts to disclose the effect of close-range PLM in Hezhuang Coal mine, Western Henan Coalfield. Firstly, coal seam I 7 was selected as the lower protective layer, and coal seam II 1 was taken as the overlying coal seam. Considering the situation of actual production, a simulation model for lower PLM was established on Fast Lagrangian Analysis of Continua in 3 Dimensions (FLAC3D). The established model was adopted to simulate the mining of the working face 11030# of the lower protective layer (I 7) at the mining depth of 50, 100, 200 and 250 m, respectively. Through the simulation, the authors summarized the laws of stress evolution and deformation of the working face 11030# of the overlying coal seam (II 1) in the upper part of the stope. The research results are as follows: After the lower PLM, the stress distribution of 11030# II 1 in the strike direction can be divided into three parts from the open-off cut to the stopping line: original stress zone, pressure relief zone and stress concentration zone; the stress distribution of 11030# II 1 in the dip direction can also be divided into the three parts from the top to the bottom. However, the stress distribution in the dip direction is less uniform than that in the strike direction. Meanwhile, the 11030# II 1 had an unobvious deformation in the original stress zone, compressive deformation in the stress concentration zone, and expansive deformation in the pressure relief zone; the maximum expansive deformation was observed in the middle of the pressure relief zone. The research results lay the theoretical basis for engineering application of lower PLM. [ABSTRACT FROM AUTHOR]

The low permeability of coal seams is the primary difficulty for gas production. Hydraulic cutting is one of the most effective technologies for increasing permeability and stimulating gas production. This paper investigates the hydraulic cutting styles in boreholes and the optimal equivalent borehole diameter after discharging the pulverized coal particles. This paper introduces the hydraulic cutting equipment and cutting styles and determines that the cutting cylinder is the most suitable style for a soft coal seam that is prone to gas outburst. The numerical simulation suggests that the radius of the stress-relaxed range increases quickly when the equivalent borehole radius is small, and the rate slows when the borehole radius becomes large. Then the result was verified by a field experiment in Pingmei coalfield. The gas drainage flowrate and stress-relaxed range greatly increased after initially outputting 2 tons of coal from the borehole, whereas the second outputting 2 tons of coal did not appreciably increase the stress-relaxed range and the flowrate. Too much or too little coal discharge is not optimal, and the borehole radius is recommend to be between 0.3 m and 0.4 m after the hydraulic cutting considering the pros and cons in Pingmei coalfield. The results are helpful for the engineering application of the hydraulic cutting technology, for increasing coal seam permeability, and for stimulating gas production. The method for finding the optimal coal discharge in this paper is also helpful for other coal mines. [ABSTRACT FROM AUTHOR]

Composite coal seam is a kind of special coal seam that is formed after complex geological structure action, including a tectonic coal sublayer. Gas can't be drained easily from this coal seam, which cause coal and gas outburst accidents (CGOA) occur frequently. A new hydraulic flushing technology was proposed in this paper to improve gas drainage. Accordingly, a new set of mechanical equipment, technology process, roadway layout system and gas extraction monitoring system are provided by drawing lessons from the Guhanshan coal mine. The stress variation and damage failure were investigated by numerical simulation on the basis of flushed-out coal and borehole geometry. The gas drainage effect, coal seam permeability and outburst risk-sensitive indexes of the special coal seam were obtained by field measurements. According to the results, hydraulic flushing can enlarge the stress unloading and plastic damaged zone around boreholes dramatically, and the coal seam permeability can be increased largely. • A new technology was proposed to enhance gas drainage in the special low-permeability composite coal seam with a tectonic coal sublayer. • The stress damage and permeability increase mechanism of hydraulic flushing were revealed by theoretical analysis and numerical modeling. • Abundant field experiments were carried to investigate and verify the gas drainage effect in the coal seam after hydraulic flushing. [ABSTRACT FROM AUTHOR]

Coal seam gas drainage is not only the effective measure for gas outbursts control, but also has the great significance for the use of gas energy and reduction of greenhouse-gas emissions. Coal permeability is the key parameter of gas drainage, and the permeability model of mining-damaged coal has the important theoretical guidance value for gas drainage in low permeability coal seams. In order to better understand the permeability model of damaged coal, the key points during the establishment of permeability model, which are the selection of coal structure, selection of boundary conditions and influencing factors, were first analyzed. Then, the expression and application of permeability models of mining-damaged coal in recent 20 years were reviewed. According to the contribution of new fractures, the permeability models of mining-damaged coal were divided into the empirical permeability models (EPM), volumetric strain permeability models (VSPM), plastic strain permeability models (PSPM) and damage variable permeability models (DVPM). After that, the quantitative characterization of key parameters, scientific issues of permeability models of mining-damaged coal were reviewed and discussed. Finally, the prioritization of 18 indexes affecting the permeability were determined, and the potential research directions of permeability models of mining-damaged coal were pointed out. The results of this paper can provide the theoretical guidance for the improvement of permeability model of mining-damage coal in the future. • The expression and application of permeability models of mining-damaged coal in recent 20 years were reviewed. • The quantitative characterization of key parameters, scientific issues of permeability models of mining-damaged coal were reviewed and discussed. • The prioritization of 18 indexes of factors affecting the permeability were determined. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

With the decrease of gas pressure in cleat, changes occur in the absolute permeability of coal-bed methane (CBM) reservoirs during primary depletion. To investigate this variation, based on the volumetric balance among the factors of bulk coal, solid grains and pores, how the MATCHSTICK strain changes with pore pressure is studied in this paper first. Furthermore, how permeability varies with the strain changes is researched and then the regularity of permeability changes is proposed. The rationality of applying MATCHSTICK strain changes to analyze permeability is proved by the curves of strain and permeability changes obtained from production field and laboratory. [ABSTRACT FROM AUTHOR]

Abstract: A new outburst prevention method based on injecting and freezing, considering of the important role of gas pressure and the mechanical characteristics of coal in the sprout and occurrence in the coal and gas outburst, was put forward in this paper. The curves of stress and strain with different freezing temperatures were drawn, and the effects of the water content, compaction force as well as freezing temperature on mechanical properties was discussed, through the experiment on the outburst-prone coal seam injected frozen water. It was found that the uniaxial compression strengths of coal obviously rise, its Young''s modulus show a rise tendency,, and the effective stresses of gas-filled coal obviously rise and its strengths is further improved after the gas pressure falls with the freezing temperature decreasing. [Copyright &y& Elsevier]

Abstract: In this paper, we describe the principle, technique, and steps of fast predicting the outburst risk before coal un-covering in shaft and cross-cut, including the selection of indexes for the prediction, fast test of gas pressure, coring technique for obtaining an whole coal core, and the determination of outburst parameters. Using this technique, we can finish testing the original gas pressure of coal within 20 h, making it possible to accurately predict the outburst risk before coal un-covering in shaft and cross-cut in 3~5 days. In addition, we can, according to the prediction result, give out the residual pressure and the smallest pre-drainage rate of gas. The comparison of prediction data among more than 10 shafts and cross-cuts shows that the index of initial gas relief expansion energy can more accurately reflect the outburst risk of coal seams. [Copyright &y& Elsevier]

Abstract: This paper, starting with the existence of general introduction of associated coal bed methane (CBM) with coal, expatiates in five parts on the transfer rules of CBM changing with time in three-dimensional rock space of the coal mine under the effect of mining activity and ventilation; On the basis above, the principle having been validated in practice is also pointed out for us to follow in methane extraction from coal mines. Finally, it draw conclusion that mining areas with high gas concentration(including coal and gas outburst), low permeability, and composite coal seams can realize the coal mine methane (CMM) extraction and ground development in a high efficient way as long as we follow the miming activities and the gas migration rules under the effect of negative pressure ventilation. [Copyright &y& Elsevier]

Acoustic emission (AE) and electromagnetic radiation (EMR) monitoring technology have been widely used in coal and rock dynamic disaster monitoring. However, the prediction of coal and gas outburst using original signal directly may cause the false and missing alarms due to the failure to identify valuable potential information, which may lead to the decrease of prediction accuracy. This paper presents a new method to identify the precursor features of coal and gas outburst using two-dimensional Convolutional Neural Network (CNN). Empirical mode decomposition (EMD) was performed for AE or EMR signals, and the Intrinsic Mode Functions (IMFs) with Variance Contribution Rate (VCR) greater than 90% were merged into modified signal. Since the frequency of AE or EMR signal can change with different coal and rock fracture stages, one-dimensional modified signal was transformed into a two-dimensional time-frequency graph using the short-time Fourier transform (STFT). The time-frequency graph was input into CNN that recognizes the time-frequency characteristics of AE or EMR using SoftMax regression at the end of the network. Compared with the original signal, the precursor characteristics of modified AE or EMR signals can be better learned by CNN. The proposed method was applied to the Jinjia Coal Mine database which was identified as having outburst risk, and it was found that the recognition accuracy was better than other approaches. The proposed method achieves maximum recognition accuracy of 98.00% (AE), and 97.20% (EMR) in Jinjia Coal Mine database, respectively. • A precursor recognition method using CNN for coal and gas outburst is proposed. • The modified signal and its time-frequency characteristics have been analyzed. • CNN is sensitive to the modified precursor features of coal and gas outburst. • The method has been verified in a coal mine with coal and gas outburst risk. • The method improved the precursor recognition accuracy of coal and gas outburst. [ABSTRACT FROM AUTHOR]

Tectonically deformed coals are critically important in coalfield geology structure, coalbed methane exploration and exploitation, and coal and gas outburst. The mechanical property of coal macerals plays a key role in the deformation characteristic of tectonically deformed coals. However, it has not been well investigated the differences of nanoscale mechanical properties among coal macerals. In this work, by employing the depth-sensing nanoindentation, and establishing theoretical analysis and experimental verification, the paper finds the following results: 1) both hardness and elastic modulus are in the order of exinite < vitrinite < inertinite, and the creep displacement follows the order of exinite > vitrinite > inertinite, which correlates closely with macerals' relevant origin. 2) recovery resistance, R s , is in the order of exinite < inertinite < vitrinite, which is inherently related to hardness and elastic modulus; according to the differentce of R s , it can be discovered that the exinite is more prone to produce ductile deformation under the same tectonic stress, while the vitrinite is more likely to develop brittle deformation. 3) based on the difference of energy dissipation ratio, vitrinite < exinite < inertinite, the vitrinite concentration area in coal seam shows higher stability than the other two maceral groups before failure. Therefore, it is necessary to accurately measure the mechanical property differences among coal maceral groups at the nanoscale to better understand the deformation characteristic of tectonically deformed coals. • Range, order, creep characteristic and influencing factors for various maceral groups are respectively investigated. • Definition, meaning, order and indicator of the recovery resistance R s for various maceral groups are severally stablished. • Order, indicator and meaning of the energy dissipation ratio for various maceral groups are respectively explicated. [ABSTRACT FROM AUTHOR]

Hydraulic fracturing can increase coal seam fractures and reduce gas outburst risks, but the main challenge of its implementation in coal mines is to achieve uniform fracturing and gas reduction. In this paper, we studied the mechanism of water-driven gas release through two aspects: the H 2 O molecule is more easily adsorbed by coal than CH 4 , and water can decrease the gas adsorption capacity of coal. Comparative experiments of conventional hydraulic fracturing and blasting-fracturing technologies were carried out in #8 coal mine in Pingdingshan, China. We found that fractures and water contents around the blasting-based fracturing hole were more uniform than the conventional fracturing hole. After hydraulic fracturing, low water content coal usually has high gas content, which confirmed that gas in wet areas was displaced by water and driven to dry areas. To improve the uniformity of hydraulic fracturing, we proposed the uniform fracturing technology by combining blasting-fracturing holes and control holes. Blasting before hydraulic fracturing will increase the uniformity of fracturing and water distribution, and the control holes are used to monitor and release gas driven by water injection. The effective wetting range of conventional hydraulic fracturing was from −6 to 6 m along the strike direction and from −3 to 9 m along the dip direction with 94.71 m3 water injected. While the effective wetting range using uniform fracturing was increased to from −21 to 18 m along the strike direction and from −12 to 18 m along the dip direction with78.13 m3 water injected. Furthermore, number of boreholes to be drilled was largely reduced from 1300 to 132 when using the uniform fracturing technology to replace the dense hole technology in a 300 m long roadway. This research has suggested that uniform fracturing can effectively reduce gas outburst risk in gassy mines in China. • Analyzed water-driven gas release mechanism for coal and gas outburst control. • Developed uniform hydraulic fracturing by blasting and water-driven gas release. • Demonstrated uniform fracturing in field trails with less borehole required and less outburst risk. [ABSTRACT FROM AUTHOR]