Experimental Study on the Influence of Coal Surface Roughness on the Ultra-Low Friction Effect of Coal Rock

The ultra-low friction rock burst is essentially a new type of coal mine dynamic disaster induced by the ultra-low friction effect at the coal-rock interface. Taking Shenyang Hongyang San Mine roof-coal seam-bottom slab as the research object, and a simulation test of ultra-low friction effect of sandstone-coal-sandstone superimposed block under the joint action of axial pressure, vertical disturbance and horizontal impact was carried out the self-developed test device. The effect of coal surface roughness on the horizontal displacement amplitude, horizontal displacement abrupt change time, horizontal acceleration amplitude and horizontal acceleration abrupt change time of the working block was analyzed, and was obtained the influence law of coal surface roughness on the ultra-low friction effect. The results show that: (1) When the sandstone surface roughness is constant, with the increase of the coal surface roughness, the horizontal displacement and horizontal acceleration time history curve of the working block has three-stage characteristics, namely the incubation stage, the excitation stage, and the stable stage; (2) The coal surface roughness has an inflection point of 3.98. When the coal surface roughness is less than the inflection point of 3.98, as the coal surface roughness increases, the horizontal displacement in the excitation stage is greater than the horizontal displacement in the stable stage, the displacement difference decreases linearly, and the ultra-low friction effect weakens; (3) When the coal surface roughness is greater than the inflection point of 3.98, with the increase of the coal surface roughness, the horizontal displacement in the excitation stage is smaller than the horizontal displacement in the stable stage, and the horizontal displacement of the working block increases again. As the absolute value of the displacement difference increases, the ultra-low friction effect is more significant; (4) The horizontal displacement amplitude and horizontal acceleration amplitude show a linear decreasing and then linear increasing law with the roughness of the coal surface; (5) The horizontal displacement abrupt change time and horizontal acceleration abrupt change time increase linearly with the roughness of coal surface, and then increase linearly.