Abstract: To investigate the relationship between ultra-low friction rock burst and water content characteristics of coal body during mining, a mine in Shenyang was selected as the research object. The water content and water immersion height of coal block and were used to simulate the overall and layered water content characteristics of deep coal body, respectively. The ultra-low friction effect test on deep water-bearing coal block was carried out. The results show that: (1) When the vertical disturbance frequency is 2.0–3.5 Hz, there is a significant influence area for coal blocks with different water contents and immersion heights. Currently, the strength and resistance of ultra-low friction effect change significantly. (2) Compared to dry coal block, when the moisture content of the coal block is 11.7% (natural moisture content), 13.12%, 14.54%, 15.67% and 16.12% (saturated moisture content), the average increasing or decreasing amplitude of the ultra-low friction effect strength is 76.64%, 2.74%, 25.09%, 36.90% and −17.49%, and the average coal-rock interface friction is 5.04, 4.96, 4.74, 4.64 kN and 4.65 kN, respectively. (3) Compared to non-soaking condition, when the coal block is immersed in water at a height of 25, 50 mm and 75 mm, the average increasing or decreasing amplitude of the ultra-low friction effect strength is −16.28%, 19.83% and 100.98%, and the average coal-rock interface friction is 7.30, 6.73 kN and 7.16 kN, respectively. (4) The ultra-low friction effect strength is the highest when the moisture content is 11.7% and the immersion height is 75 mm. It is the weakest when the moisture content is 16.12% and the immersion height is 25 mm. In the actual working conditions, it is necessary to reasonably control the moisture content of coal body and the immersion height to prevent the occurrence of ultra-low friction type rock burst disasters.

Key words: rock mechanics, ultra-low friction effect, coal rock block, water-bearing features, coal-rock interface