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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]

Highlights • Counted and analyzed the information of 47 Kilometer-Deep Mines in China. • Analyzed the situation of typical dynamic disasters in kilometer-deep mines. • Discussed the problems in the prevention and control of typical dynamic disasters. • Give out the measures for prevention and control of typical dynamic disasters. Abstract To ensure the safety of kilometer-deep mining and prevent the occurrence of typical dynamic disasters (rock burst and coal and gas outburst), this paper counted and analyzed the status quo of mining and typical dynamic disasters currently for 47 deep mines in China. The results show that the 47 deep mines are mainly distributed in 8 provinces; the proportions of mines affected by rock burst and coal and gas outburst are 53.2% and 29.79%, which are 29.23 times and 2.66 times the national average. Typical dynamic disasters in deep are more serious than that in shallow, the number of mines affected by rock burst will increase greatly in particular. The proportion of kilometer-deep mines that threatened by both coal and gas outburst and rock burst is 12.77%. Existing techniques used for prevention and control of typical dynamic disasters in kilometer-deep mines all refer to shallow mining; however, the following problems occur in deep mining: the mechanism of typical dynamic disasters and mechanism of complex disasters are not clear; the typical disaster early warning system is imperfect, and it's difficult to do precision mining in deep. Focusing on these problems, this study presents forward countermeasures from following directions: research on mechanism of deep typical dynamic disasters and coupling mechanism of complex dynamic disasters, establishing deep mine multi-parameter dynamic disaster monitoring and warning mechanisms and related equipment research, establishing deep mine typical dynamic disasters prevention and control systems, and research on the basic theory and equipment for precision mining in deep. [ABSTRACT FROM AUTHOR]

• CH 4 drainage efficiency of LCO 2 -ECBM by in-situ experiment was elucidated. • In-situ experimental parameters and displacement radius were identified. • Mechanisms of LCO 2 -ECBM recovery were analysed. • Variation in microstructure of coals after liquid CO 2 saturation was revealed. • CO 2 –CH 4 displacement effect at different pressures and flows were obtained. More than 60% of China's coal seams have the feature of low permeability, which severely restricts the gas drainage efficiency when using traditional drilling method. The development of enhanced coalbed methane (ECBM) technologies is essential to prevent coal and gas outburst (CGO) disasters caused by high levels of coal bed methane (CBM). This paper proposes an ECBM technology by liquid carbon dioxide (LCO 2 -ECBM), based on permeability improvement by thermal damage and CO 2 -CH 4 displacement effect. In-situ experiment conducted in the No. 6 coal seam of Zhangji mine shows the effectiveness of LCO 2 -ECBM technology, which had drainage efficiency 1.9 times higher than that of the traditional drilling method. The mechanisms of LCO 2 -ECBM recovery were theoretically deduced and experimentally verified. The evolution of adsorbed pores (ADP) and seepage pores (SEP) in coal samples before and after LCO 2 saturation were revealed. The ADP specific area, SEP volume, and permeability in the saturated coal samples were both greater than those of the raw ones. Moreover, the periodic features of binary-gas competitive adsorption in ADP and SEP were revealed by the variation of the CH 4 concentration in the displacement test. The feasibility of LCO 2 -ECBM technology was proved by in-situ experiment and laboratory tests, and it provided a new means for preventing CGO hazards. [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]