Study On The Influence Law Of Coal (Rock) Surface Roughness On Ultra-Low Friction Effect

With the increase of mining depth,coal mine impact ground pressure presents new characteristics,the deep rock body tends to be more broken into block system rock body,high ground stress and dynamic disturbance conditions,coal and rock seam extrusion and friction with each other,so that the surface of coal rock produces obvious scratches,coal rock body is prone to ultra-low friction effect,and then induce impact ground pressure disaster.For the sliding friction characteristics of obvious scratches between the top and bottom plates and coal seams observed at the site of ultra-low friction type impact ground pressure,it is considered that the surface roughness of coal rock must have an important influence on the development process of ultra-low friction effect,so the surface roughness of coal rock is used as the research object,based on three working conditions such as fine sandstone as the top and bottom plates,fine sandstone as the top plate and coarse sandstone as the bottom plate,and coarse sandstone as the top and bottom plates,and the intermediate blocks are used with different surface roughness of the coal block,using acoustic emission to monitor the acoustic signal in the test of ultra-low friction effect,the use of self-developed test equipment to analyze the law of the influence of surface roughness of coal rock on the body ultra-low friction effect under external loads such as vertical disturbance,axial pressure and horizontal impact force,to establish the risk index of ultra-low friction effect,for the prevention and prediction of ultra-low friction type impact ground pressure,for deep coal rock surface roughness on the ultra-low friction effect provide scientific reference.The test results show that:(1)The horizontal displacement curves under static load,horizontal impact force,perturbation amplitude and perturbation frequency of the three working conditions all show the characteristics of consistent existence of three stages: breeding stage,excitation stage and stabilization stage;the smaller the roughness of coal surface,the larger the horizontal displacement value and the more intense the ultra-low friction effect;the ultra-low friction effect of coal rock body is most significant within the perturbation frequency of 2Hz-2.5Hz,which provides the basis for effective prevention of ultra-low friction effect of coal rock body.The larger the disturbance amplitude under the three working conditions,the larger the horizontal displacement and horizontal acceleration,the smaller the horizontal displacement abrupt change time,and the ultra-low friction effect is enhanced;the larger the horizontal impact force under the three working conditions,the larger the horizontal displacement and horizontal acceleration,the smaller the horizontal displacement abrupt change time,and the ultra-low friction effect is enhanced;as the surface roughness of the coal block increases,the horizontal displacement and horizontal acceleration show a first decreasing and then increasing With the increase of surface roughness of coal block,the horizontal displacement and horizontal acceleration show the change law of decreasing and then increasing,and there is an inflection point JRC3.76.(2)Condition 1 sandstone surface roughness is small,the horizontal acceleration is the largest,the easier the coal rock body destabilization damage,the most significant effect of ultra-low friction;the larger the surface roughness of coal and sandstone,the smaller the horizontal displacement abrupt change time,the easier the coal rock body destabilization occur ultra-low friction type impact ground pressure;disturbance frequency has an excitation effect on ultra-low friction,the actual mining should pay attention to the top and bottom slab rock type.(3)The smaller the surface roughness of sandstone,the greater the acoustic emission burst energy,the larger the horizontal displacement value,the most significant ultra-low friction effect,the larger the surface roughness of sandstone,the larger the fluctuation amplitude of acoustic emission energy in the whole ultra-low friction effect test,the more the coal body tends to be broken,which then leads to other serious dynamic disasters;in actual mining,the small surface roughness of sandstone,monitor the acoustic emission changes on the lower surface of the coal seam,and the large surface roughness of sandstone,monitor the acoustic signal changes on the upper surface of the coal block.(4)The hazard index relative roughness R is divided into Ⅰ,Ⅱ,Ⅲ and Ⅳ levels to represent the strength of ultra-low friction effect.The coal seam under level Ⅰ slips as a whole without broken coal blocks,while the coal seam under level Ⅳ slips and is accompanied by a large number of broken coal blocks,providing a basis for predicting ultra-low friction type impact ground pressure.There are 64 figures,11 tables,and 82 references in this paper.