Research On The Energy Evolution Laws Of Surrounding Rock Unloading And The Rockburst Mechanism In Solid Coal Roadway Excavation

In this paper,the rockburst mechanism in solid coal roadway excavation is taken as the main research content.From the perspective of unloading and energy evolution in the roadway surrounding rock,the statistical analysis,numerical simulation,laboratory experiments and theoretical analysis are used to research the distribution laws of surrounding rock stress and energy during a roadway excavation.From the energy point of view,the rockburst mechanism in solid coal roadway excavation is discussed,and the corresponding discriminating methods are proposed.The following results are achieved:(1)According to the literature statistics,the factors affecting rockburst in roadway excavation are coal seam thickness and its rockburst tendency,mining depth,geological structure,the thickness of remaining coal under the roadway floor,coal pillar stress concentration,excavation speed and the distance from excavation head-on,etc.Taking a mine in Xianyang mining area as an engineering background,the actions causing an rockburst of various factors and their influence degree are simulated and analyzed.It was found that the factors such as mining depth,lateral pressure coefficient,coal seam thickness,the ratio of width to height of a roadway and excavation speed increase the distribution concentration of stress and energy in roadway surrounding rock to varying degrees.(2)The mechanics model of stress distribution in the surrounding rock during roadway excavation is established.Based on the elastoplastic theory and the damage evolution laws of loaded coal,the distribution formulas of stress,energy density and regional energy in surrounding rock failure zone,plastic zone and elastic zone considering unloading expansion effect are derived.(3)According to the stress distribution and variation characteristics in the surrounding rock before and after roadway excavation,the experimental schemes of conventional triaxial loading,unloading confining pressure and loading axial pressure,unloading confining pressure and axial disturbance and constant confining pressure axial disturbance of coal are designed.It is concluded that under the action of static load,the coal is generally shear failure in the form of splitting,while under the action of source disturbance,it is tension failure in the form of cracking;The initial confining pressure and loading rate have positive correlation with the coal strengthening,and the coal strength changes obviously at low loading;On the contrary,the unloading rate exacerbates the deterioration of coal,and the influence of low unloading rate is more prominent;Whether the coal is failure under the action of shock source disturbance depends on the level of superimposed stress of the initial stress and the shock source amplitude,and the actual failure stress level is generally greater than the static load strength under the corresponding confining pressure;When the strain shows a significant nonlinear change,the coal is predicting impending failure.(4)The influence of different factors on energy evolution in coal was researched.It is found that the original rock energy storage increases exponentially with the initial confining pressure,and it is also believed that the initial confining pressure and the loading rate increase the energy storage capacity of the coal under static load conditions,that is,the energy required for the failure of the loaded coal increases with the initial confining pressure and the loading rate;While the unloading rate is opposite;When the coal is failure,the conversion rates of deformation energy and dissipated energy are not obviously affected by various factors,which are about 50%.Under the shock source disturbance,the energy in the coal changes periodically,and the conversion rate of deformation energy decreases,the conversion rate of dissipated energy increasing.Whether it can be destroyed depends on the interaction between the energy storage in the initial stress environment and the energy carried by the shock source.An index about the response ratio of energy and pressure drop is put forward,which can reflect the abnormal change of stress environment where the coal is located,and can be used as a precursor indicator of coal failure.(5)From the point of view of energy accumulation,dissipation and release,the rockburst mechanism in solid coal roadway excavation is explored,and at the moment of rockburst,the variation of the acceleration and velocity of the coal being washed,and the convergence of roadway section is discussed.It is considered that whether the rockburst can be induced under the action of shock source depends on the energy storage level in the surrounding rock after the initial stress field and the shock source field are superimposed;When the rockburst occurs,the volume of the coal being washed is rapidly expanded as the energy density decreases,resulting in a sharp contraction or even extrusion closure of the roadway section;Moreover,the shorter the experience time,the higher the projection velocity of the coal being washed;Combined with the velocity distribution function,an index about the critical rockburst velocity ratio is proposed,which indicates that the roadway rockburst is instantaneous,sudden and dramatic;.And a multi-factor comprehensive discriminant method for maximum energy density factor,average energy density factor,the response ratio of energy and pressure drop,and the critical rockburst velocity ratio is proposed,which can provide reference for the evaluation of roadway rockburst risk and the development of excavation roadway anti-rockburst measures.(6)The safety warning value of the average energy density factor in the surrounding rock is obtained through the case analysis on excavation rockburst of a coal roadway.According to the actual situation of the roadway,the anti-rockburst support parameters are designed and the corresponding suggestions for anti-rockburst and reducing rockburst are proposed.