Abstract: Based on the theoretical calculation of the ideal elastic-plastic mechanics, FLAC3D numerical simulation analysis and multiple mining engineering practice, it could be judged that the forty-meter width of the coal pillar is significantly larger in Ningdong test mining sublevel. The in-situ underground combined test is implemented to have a real-time monitor of sixteen hollow inclusions’ 3D strain, the dynamic change of stress and deformation of the surrounding rocks in test roadways with coal pillars of different width (ten meters and twenty meters) pre and post the mining-induced influence of the working face. Test results show that there exists obvious core zone with significantly lower memory elastic stress in the coal pillar of forty-meter width, which is a favorable location for the roadway layout; the ad- vanced influence radius of mining-induced pressure is about forty-five meters, with the advance of the work face, mining-induced stress peak is gradually passed to the depths of the coal pillar during which stress increment constantly attenuates. Affected by mining-induced function, the original equilibrium state of the coal pillar 3D principle stresses gradually deteriorates, and, the test roadway with coal pillar of 10-meter width suffers less deformation than that of 20-meter width. Based on the above theoretical calculations and underground test results a reasonable width scope of district sublevel coal pillar design can be found (8.9 m to 12.5 m) in the test mine under specific geological condition, which provides empirical guides for the width design of district sublevel coal-rock pillar under similar mining conditions.

Key words: fully-mechanized mining with large height, coal pillar setting, numerical modelling, hollow inclusion, test study