Study Of The Initiation Mechanism Of Ultra-low Friction Effect Of Rock And Coal Structure Containing Weak Interlayer

After the coal mining enters the deep underground,affected by the complex geology,stress condition and mining disturbance,a series of new characteristic scientific phenomena have taken place in the deep rock coal engineering response.The mechanism of ultra-low friction effect of deep rock mass is one of the key scientific problems.Therefore,it is of great scientific significance to reveal the mechanism of such impact disasters in deep roadway or working face and put forward reasonable prediction and prevention methods.In this paper,discrete element numerical calculation program Universal Distinct Element Code was used to establish weak-layer rock-coal composite structure and reproduce the phenomenon of ultra-low friction of rock mass.The simulation and existing test results could verify the feasibility of using UDEC numerical calculation program.The measuring points are arranged to monitor the real-time changes of the horizontal displacement of the coal block,the normal stress of the structural plane of the weak rock layer and the normal displacement of the structural plane.Based on the impact disaster of Yima Qianqiu coal mine,the real size rock coal composite structure is established to simulate the disaster process caused by roof fracture disturbance and impact ground pressure.In addition,the causes of impact ground pressure are studied,the main conclusions are as follows:The plastic damage of weak-layer rock coal structure is mainly concentrated in the weak layer.The horizontal displacement of coal structure is much greater than that of weak-layer rock coal structure.Firstly,with the increase of the weak layer thickness,the horizontal displacement of the coal block increases accordingly.Secondly,the horizontal displacement of the coal block under the same load conditions is greater than the sliding structure surface.Thirdly,the stronger the strength of the weak layer,the less difficult it is to deform andthe rock and coal structure is relatively stable and the smaller the coal block horizontal displacement.The nature of the weak layer has an obvious impact on the horizontal displacement of the coal block.Generally,the existence of the weak layer can aggravate the ultra-low friction effect and reduce the load threshold of the ultra-low friction effect.Vertical load fluctuates the normal stress of the structural surface,causing the friction strength of the structural surface,which is the fundamental cause of ultra-low friction.Horizontal dynamic load cannot lead to large fluctuations of normal structural surface stress,but can provide horizontal kinetic energy for the coal block.When the horizontal joint force of the coal seam is greater than the shear strength of the structural surface,the coal seam will also undergo sliding mutation.When the vertical dynamic load and the horizontal dynamic load work together on the rock and coal structure,the vertical dynamic load applies before or after the horizontal dynamic load,and the coal block can undergo a slide change,and the shorter the delay time,the greater the coal block horizontal displacement.The degree of friction increases with the load amplitude and the load frequency.In coal mining and unloading,the local stress of the rock coal structure changes,and the stress redistribution of the coal structure is stable.At some point,the rock coal structure is disturbed by mining or the top plate,changing the compression of the weakly layered rock coal structure surface,and periodic oscillation of the relative normal displacement and normal stress within a certain time,resulting in change-layer friction or shear strength.When the shear force exceeds the shear strength of the structural surface,the coal seam produces irreversible sliding along the structural surface,and rockburst occurs.