During the “12th Five-Year Plan” period (2011–2015), the safety production situation of coal mines in Guizhou province was generally good. The main types of accidents are gas, flood and roof accide...

Characteristics and trends of coal mine safety development

Coal-gas compound dynamic disasters in China: A review

Experimental and numerical investigations on dynamic mechanical responses and failure process of gas-bearing coal under impact load

A new method for coal and gas outburst prediction and prevention based on the fragmentation of ejected coal

Large and super-large section chamber groups in coal mines are frequently affected by dynamic loads resulting from production activities such as roadway driving and blasting The stability of the surrounding rock is poor, and it is difficult to control In this paper, a similar simulation test was used to study the deformation and evolution laws of the surrounding rock of a triangle-shaped chamber group under different dynamic loads The results showed that under dynamic loading, the vertical stress of the surrounding rock of the chamber group increased in an oscillatory form The maximum stress concentration coefficient reached 409 The damage degree of the roof was greater than that of the two sides The deformation of the roof was approximately 12 times that of the two sides For the chamber closer to the power source, the stress oscillation amplitude of the surrounding rock was larger, and the failure was more serious The force of the anchorage structure showed a phased increasing characteristic; additionally, the force of the anchorage structure on the adjacent side of the chambers was greater than that on the other side This study reveals the deformation and failure evolution laws of the surrounding rock of large section chamber groups under dynamic loading

Similar simulation study on the deformation and failure of surrounding rock of a large section chamber group under dynamic loading

To explore the law of ground deformation from shallow-buried close-distance multi-seam mining, an observation station was built in the Bulianta Coal Mine to measure and record the periodic variation of related parameters about ground subsidence and surface cracks with the advancement of working face. From the data observed from the field, it can be found that, when lower seam mining, the ground subsidence above the previously mined area was deeper and steeper than that above the left pillar; besides, the influence scope of the former was larger than that of the latter. In terms of ground cracks, the ground cracks were formed ahead of the working face and developed rapidly during the period of the breakage of the immediate roof. Besides, the average interval of the ground cracks above the previous gob was 14.75 m, and still existed and hardly changed after the advancement of the working face; while that above the left pillar was 27.8 m and most of them were closed. In addition, when the advance rate of the working face was 12.8 m/day, the advance influence distance of the mining surface crack reached the minimum of 13.6 m. This finding is helpful for protecting the surficial environment in mining area during and after mining operations and is also of significance to conduct green mining in other mining areas.

Ground Subsidence and Surface Cracks Evolution from Shallow-Buried Close-Distance Multi-seam Mining: A Case Study in Bulianta Coal Mine

Experimental study of the impact of gas adsorption on coal and gas outburst dynamic effects

Environmentally friendly techniques for high gas content thick coal seam stimulation─multi-discharge CO2 fracturing system

With mining technology and mechanization degree being improving, fully mechanized caving mining technology (FCM) has become a main method for thick coal seam extraction in China. However, roof-coal caving characteristics in turn restrict its recovery efficiency, especially for the coal seam with complicated structure (CCS), that is, the coal seam comprises hard or soft coal and gangue. In order to explore the key factors influencing the roof-coal caving and recovery characteristics, related research work has been conducted as follows: firstly, a mechanical model of CCS has been established, which indicates the strength of the coal and gangue will directly affect the roof-coal recovery. Meanwhile, based on the geological settings of Qinyuan coal mine, numerical simulation on roof-coal caving law under different thicknesses of hard or soft coal and gangue has been performed using UDEC software. The results show that the maximum principal stress will increase with the increase of mining depth, making the roof-coal to break easily. Furthermore, the range of the plastic zone of the top coal and the damage degree of the top coal increase with the increase of mining depth. Physical modeling results show that when an extraction-caving ratio is 1, the number of times the coal arch forms is 0.43 at every caving, up to a maximum of 3; the number of times coal arch forms with an extraction-caving ratio of 2 is 4.65 times larger than that with an extraction-caving ratio of 1. The probability of coal arch formation with an extraction-caving ratio of 3 is minimal, about 0.4, which is due to that the arch span is large and the curvature is small, so it is difficult to form a stable arch structure. According to the mechanical characteristics of roof-coal in Qinyuan coal mine, deep-hole blasting technique has been used to reduce the fragments of roof-coal crushed. The results show that this technique can effectively improve the recovery of roof-coal.

/pdf/study-on-roof-coal-caving-characteristics-with-complicated-3uqk0sfue6.pdf

Study on Roof-Coal Caving Characteristics with Complicated Structure by Fully Mechanized Caving Mining

Since most coalfields in China are commonly characterized by high gas content and low permeability, there is an urgent need to improve coal seam permeability and further enhance coal bed methane (CBM) extraction efficiency. As an emerging fracturing technology, the CO2 gas fracturing (CGF) technology has been widely used because of its advantages of low cost, environmental protection and high fragmentation efficiency. In order to improve the fracturing ability of CGF technique and optimize the release orifices of discharge head, computational fluid dynamics model was used in this paper to simulate the flow fields of dynamic pressure of gas jet released from the orifices with different structures and other geometrical parameters. The results show that the orifice structure has a great influence on the flow field of gas jet, but little influence on the magnitude of the dynamic pressure. Besides, the maximum dynamic pressure of gas jet linearly decreases with the increase in the number of release orifices. Based on a series of simulation results, the discharge head which has single group of orifices with structure c, diameter of 24 mm can be identified as the best choice for fieldwork. Then, two field experiments were conducted in Pingdingshan and Changping coal mines to evaluate the enhanced CBM extraction efficiency by CGF. The results indicate that the CGF can effectively create a large number of cracks in a large range around the fracturing borehole in the coal seam and further significantly improve the permeability. And the CBM extraction efficiency can be improved to a higher level from a lower level and maintained for a long time. Besides, the effective influence radii caused by CGF in Pingdingshan and Changping coal mines are 15.19 m and 12.5 m, respectively. Compared with other fracturing techniques, the CGF technique has a promising application prospect.

Xuelin Yang

Papers

Ground Subsidence and Surface Cracks Evolution from Shallow-Buried Close-Distance Multi-seam Mining: A Case Study in Bulianta Coal Mine

Experimental study of the impact of gas adsorption on coal and gas outburst dynamic effects

Environmentally friendly techniques for high gas content thick coal seam stimulation─multi-discharge CO2 fracturing system

Study on Roof-Coal Caving Characteristics with Complicated Structure by Fully Mechanized Caving Mining

Optimization and Field Application of CO2 Gas Fracturing Technique for Enhancing CBM Extraction