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Protective layer mining, as a dominating method for preventing coal and gas outburst, is generally adopted in highly gassy coal mines. In the absence of a suitable thickness coal seam to serve as the protective layer, the rock-coal composite protective layer was proposed in this paper. We conducted a series of simulations and engineering measurements to investigate the protective effect under the mining of the rock-coal composite protective layer of the Zhongtai coal mine located in the Hebi area of Henan, China. The numerical simulation analysis showed that, after the completion of protective layer mining, the minimum vertical stress of the No. 2-1 coal seam had been reduced to 3.46 MPa. The maximum vertical displacement of the No. 2-1 coal seam is 455.01 mm. The maximum expansion deformation of the No. 2-1 coal seam is 9.77‰; the effective pressure relief range is as long as 160 m. The similarity simulation experiment revealed that, after the completion of protective layer mining, the minimum vertical stress of the No. 2-1 coal seam is 4.0 MPa. The maximum vertical displacement of the No. 2-1 coal seam is 640 mm. The maximum expansion deformation of the No. 2-1 coal seam is 26.37‰; the effective protection range reaches 130 m. The engineering measurements demonstrated that the variation law of gas drainage parameters in the protected layer corresponds to the protected layer's vertical stress distribution law in numerical simulation and similarity simulation. With the exploitation of the composite protective layer, the protective layer's pressure begins to release. The average gas drainage concentration is 2-3 times of that before the composite protective layer mining. [ABSTRACT FROM AUTHOR]

For the characteristics of high frequency and strong suddenness of dynamic disasters in deep coal mines, the traditional detection and evaluation techniques applied to shallow coal mine failed to accurately judge the risk degree of disasters. Therefore, it is of great significance to use advanced detection technologies and appropriate evaluation methods to improve the accuracy and efficiency of risk assessment in the process of coal mining. The present paper applies the rapid detection and multi-source dynamic detection technologies used in the field of mining with the purpose of improving the reliability of detection technologies for typical dynamic disaster. In this study, the data fusion technology was used to analyze data obtained from laboratory experiments, engineering survey, detection and historical data, so as to form the final dynamic and static indicators. Then, the new combined evaluation models with time series of coal and gas outburst as well as rock burst were established respectively to carry out the comprehensive risk evaluation using the least-squares method and the time-varying weight method. After the comprehensive analysis on the results of the above two evaluation models, the risk areas of the typical dynamic disasters were judged and classified. Finally, the evaluation models were coded to build an early-warning software platform that could achieve automatic evaluation and the actual 3D visualization of coal mining areas. The early-warning software platform was applied to risk assessment of dynamic disasters in Gengcun Coal Mine in Yima City, Henan Province, China. The results of the 6-month experiment showed that the risk assessment accuracy and reliability of the proposed evaluation models was 100% and 90% respectively, which indicates that the newly developed approach is reliable and can be recommended for applying in more coal mines to improve the process safety risk control. [ABSTRACT FROM AUTHOR]

Coal mine methane (CMM) drainage is an effective method to curb the occurrence of coal and gas outburst and gas explosion, to reduce the amount of greenhouse gas emission, and to make full use of the clean energy(methane). Sealing in-seam horizontal boreholes plays a vital role in CMM drainage. Reasonable sealing length is an important factor to achieve high extraction efficiency and reduce the cost of construction. To determine the minimum reasonable sealing length of drainage boreholes, the radius of the fracture zone was obtained based on the ideal elastoplastic model, and this radius was taken as the minimum sealing length. The influencing factors of the minimum sealing length were analyzed and engineering verification test was taken in Zhongmacun mine in Henan province, China. The research results show that the minimum reasonable sealing length should be longer for a larger radius of the coal roadway and the coal seam with a deeper buried depth, while the minimum reasonable sealing length can be shortened with the increase of uniaxial compressive strength and the supporting stress of the coal roadway. The 11.07 m of sealing length calculated by theories was basically consistent with the 12 m of sealing length verified by the method of drilling cuttings. The reasonableness of sealing length (12 m) was verified by the test results of methane concentration and flux within 40 days. All those outcomes can provide references for other mines to determine the minimum reasonable sealing length of in-seam boreholes for CMM drainage. [ABSTRACT FROM AUTHOR]

The essence of both rockburst and coal and gas outburst lies in fast energy release. In order to explore the energy action mechanism of coal and gas outburst induced by rockburst in rockburst and coal and gas outburst combined mines, the split Hopkinson pressure bar (SHPB) experimental device was firstly used to conduct uniaxial impact failure test of coal specimens prone to outburst under different strain rates, and their energy dissipation laws under impact loading were obtained. Next, under the engineering background of coal and gas dynamic phenomena induced by rockburst with different intensities in Xinyi Coal Mine and Pingdingshan Coal Group No. 12 Colliery in Henan Province and Dingji Coal Mine of Huainan Mining Group in Anhui Province, experimental study results were combined with numerical simulation analysis to discuss the energy mechanism of coal and gas outburst induced by rockburst. The study results show that the outburst can be divided into two different processes—critical outburst and outburst—according to the evolution law of outburst energy, and the critical energy conditions for coal and gas outburst are proposed. The minimum destructive energy range for the critical outburst of coal mass is obtained as (5–10) × 104 J/m3. Under some low gas, high stress, or strong disturbance conditions, applied loads can become the main energy sources causing critical failure and even crushing and throwing of coal mass. The coal mass will present an interval splitting structure under dynamic loading, which is obviously different from the failure mode of coal mass under static actions. [ABSTRACT FROM AUTHOR]

In order to reveal the occurrence mechanism of coal and gas outburst and optimize the measures to prevent the disaster, a coal mine in Henan Province was undertaken as the research background. Based on the geological and mining conditions of the coal mine, the gas geological analysis method is applied to determine the outburst occurrence and to classify the risk levels. A multifactor pattern recognition method is used to determine the risk probability of the dynamic disasters such as coal and gas outburst. The relationship between geological structure, rock mass stress, and mine dynamic hazards is determined using geo-dynamic division method and FLAC3D numerical simulation. The occurrence and manifestation characteristics of the dynamic hazards are determined. COMSOL Multiphysics software is used to evaluate the original prevention measures and to optimize the measures. The research results determine the main influencing factors and regional distribution law of coal and gas outburst, which is of great significance to the risk prediction and prevention of dynamic disasters such as coal and gas outburst. [ABSTRACT FROM AUTHOR]

Coal and gas outburst disaster of the No. B-1 Coalbed, Henan, China, have lasted for nearly 60 years, and the threat will become more and more serious as mining depths continuously increase. However, coal and gas outburst characteristics and factors of the coalbed have not been studied in detail. To effectively prevent and control coal and gas outburst, we analyzed the type, intensity, location and precursors of coal and gas outburst occurring in the No. B-1 Coalbed. Moreover, the effects of geological conditions (burial depth, faults, folds, coalbed thickness and dip) and mining disturbances on coal and gas outburst were studied. The results showed that these outburst accidents were mostly typical, small-sized and medium-sized outburst, which mainly occurred at the coal roadway working faces. There were many precursors such as blasting sound, changes in coal structure, and abnormal gas emission prior to the accidents. Within a burial depth of 500 m, the average outburst intensity had a stronger correlation with the burial depth, which was more obvious at a burial depth of 301∼400 m, and less obvious at a burial depth of 401~500 m. However, the distribution of these outbursts barely changed within the burial depth. Up to 99.15% of coal and gas outburst occurred at faults, folds, and areas with changes in coalbed thickness and dip. Up to 68.25% were induced by blasting and 18.04% occurred during shelving, coal-shoveling and no operation. The No. B-1 Coalbed was characterized by delayed outbursts. Moreover, specific suggestions were recommended for the prevention and control of coal and gas outburst. The study is useful to government regulators and staffs engaged in the prevention and control of coal and gas outburst. [ABSTRACT FROM AUTHOR]