Types,occurcenec mechanism and prevention of overall istability induced rockbursts in China coal mines

The overall instability induced rockburst is a new type of rockburst in the process of deep coal mining in China in recent years,and its released energy and destructiveness are far greater than the common local rock burst.By using the methods of field investigation,theoretical analysis and field monitoring,based on the analysis of the engineering characteristics and rockburst appearance features of three overall instability induced rockburst accidents in China’s coal mines,the overall instability induced rockburst in China is classified into three categories,namely the overall instability induced rockburst in island working face,the overall instability induced rockburst in main roadway and the overall instability induced rockburst in bottom coal.Regarding those three types,the mechanical mechanism models of three types of overall instability induced rockburst were established.Then,the rockburst risk assessment method and prevention countermeasures of three types of overall instability induced rockburst were proposed.Finally,the mechanism of the three types of overall instability induced rockburst was presented.The occurrence mechanism of the overall instability induced rockburst in the isolated working face is that when the total stress formed by the superposition of the self weight of the overlying strata and the transfer load on both sides of the goaf exceeds the overall bearing capacity of the isolated working face,the overall instability failure of the elastic core in the middle of the island working face induces the rock burst disaster.The occurrence mechanism of the overall sliding instability induced rockburst in bottom coal is that when the abutment pressure of the working face exceeds the critical stress of rockburst and slip of bottom coal,meanwhile incurring the rockburst and slip of bottom coal,forming the whole sliding unstable rockburst of bottom coal.The mechanism of overall instability induced rockburst of main roadway coal pillar is that the stress of main roadway coal pillar is highly concentrated under the superposition of self weight stress,structural stress,roadway excavation,and pressure relief transfer stress,etc.When the stress concentration exceeds the overall bearing capacity of coal pillar,the elastic core in the middle of the coal pillar will have an overall instability impact,leading to serious impact damage on both sides of the coal pillar.Due to the complex mining conditions in deep mines,a variety of concealed overall instability rockbursts can be found during the mining process.Therefore,to prevent rockbursts,it is necessary to strengthen the risk identification and prevention of such concealed overall instability rock bursts.The research results have certain reference significance for the safe mining of working face under similar conditions.