Abstract
The protective layer mining method of the traditional deep coal seam in has been confronted with great challenges, and it is difficult for coal and gas to be extracted together. Taking the occurrence conditions of III1 mining area of Luling Coal Mine located at Huaibei, China, as engineering background, the influence law of the lithology on stress environment in front of the stope was analyzed by theoretical analysis and numerical simulations. The mining‐induced mechanical effect of coal‐rock mass was studied under different protective layer mining modes. The results showed that the peak value of the advanced abutment pressure decreased with the decrease of lithologic strength under the same mining conditions. For simulated geological conditions, the stress concentration coefficient of soft rock and coal seam protective layer mining modes was 1.9 and 1.7, respectively. Under the mining stress path of different protective layers, the ratio of axial stress increase and confining pressure unloading in secondary unloading phase were 2 : 1 and 1.5 : 1, respectively. The axial stress‐strain curves of different protective layer mining modes had similar trends, and they had a volume expansion at the end of unloading (failure stage). In addition, it revealed the pressure‐relief antireflection mechanism of the protective layer mining. Under the same confining pressure condition, the peak stress and peak strain increased with the increase of loading and unloading velocity ratio. The reduced value of the confining pressure increased, while the volume expansion decreased at failure. The results were applied to III1 mining area in soft rock protective layer mining, which created the mining way of traditional coal seam protective layer. Furthermore, the gas control technology of soft rock protective layer working face was put forward for deep coal seam with low permeability and high gas, enriching the pressure‐relief mining theory of protective layer.
Highlights
In China, the deep resource exploitation has been one of the development strategies [1]. e geological conditions of coal resources are complicated, and the ground stress increases after entering the deep mine
All the factors interact and influence each other, and the gas disaster becomes more and more serious [2,3,4]. e traditional protective layer mining method of the coal seam encounters great challenges. ere is no suitable technical condition for coal seam to be mined as the protective layer, which increases the difficulty of coal and gas mining
It seriously restricts the development of coal mines under the new situation in China. erefore, it is urgent to seek an innovative and safe mining method of the protective layer, to realize the disaster prevention of deep coal seams with low permeability and high gas
Summary
In China, the deep resource exploitation has been one of the development strategies [1]. e geological conditions of coal resources are complicated, and the ground stress increases after entering the deep mine. Because of the flexible layer selectivity, adjustable mining thickness, no gas in mining layer, small threat to mining safety, and so on, the soft rock protective layer mining is used to achieve efficient gas control It has Advances in Materials Science and Engineering a wide application prospect in the selection of the first mining pressure-relief layer for the gas coal seams with low permeability in deep. Zuo et al [11] studied the effect of stress path on mechanical behavior of the surrounding rock under different mining unloading conditions of the limestone in Licun Coal Mine. Due to different mining modes (or stratum lithology) of the protective layer, there is significantly different stress environment in front of stope It shows different distribution characteristics of abutment pressure, corresponding to different loading and unloading stress paths. Based on the above analysis, the pressure-relief and permeability enhancement of the protective layer mining was explored under the specific mining geological conditions. e influence of lithology on stress environment in front of stope was studied. e mining-induced mechanical effect was analyzed for different protective layer mining modes, and the soft rock protective layer mining was put forward for on-site engineering application, which provided an important theory support for coal and gas mining by different protective layer mining modes
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