"Three-Field" Monitoring Principle And Application Of Rock Burst Caused By Hard Roof In Fold Area

Rock burst in coal mine is one of the dynamic disasters of coal and rock,which has become the key factor restricting coal mine safety production.There are special geological conditions such as "fold development and hard roof" in many areas of China,which lead to the severe situation of frequent impact.Therefore,the impact mechanism of fold roadway induced by hard roof is studied.It is of great theoretical significance and practical value to monitor and warn the stress field,energy field and seismic field in mining area by regionalization and online.By means of theoretical analysis,numerical simulation,similarity simulation,neural network and engineering practice,the principle and application of "three field" monitoring for burst caused by hard roof in fold area are studied.The coupling model of stress,energy and seismic was established,and the "three fields" monitoring principle of rock burst was put forward.The stress threshold,energy composition and dynamic failure characteristics of coal and rock caused by seismic disturbance were studied.The three physical quantities in the process of impact were analyzed to meet the conditions of transfinite,large scale and transient respectively.Based on the coupling model,the "three-field" monitoring and early warning technology is proposed,and the "three-field" monitoring and early warning index is determined.The static stress model of surrounding rock of anticline,syncline and wing in fold area and the fracture release ability of roof are established,and the stress distribution of surrounding rock and the expression of roof fracture release energy are deduced.Static load stress of surrounding rock in syncline,anticline axis and wing decreases successively,and the roof breaking energy of anticline axis reaches the maximum.The impact criterion of maximum and minimum principal stress difference is put forward to reveal the roof impact mechanism in fold area.The impact types of synclinal axis,anticlinal and wing roadway are "high static load,weak disturbance","low static load,strong disturbance" and "static and static balance" respectively.On this basis,the influence of roof thickness,roof hardness,fold curvature,lateral pressure coefficient and dynamic load propagation distance on the dynamic and static load stress of roadway surrounding rock is analyzed.The process of impact caused by dynamic and static combined loading and the evolution characteristics of local stress field seismic field in the folding roadway are studied.The dynamic load disturbance enhanced the dynamic response characteristics of the surrounding rock,such as acceleration and acoustic emission,and the critical acceleration conditions of the impact failure in different areas of the fold were obtained.The intensity of dynamic response of the tunnel at the synclinal axis was the most serious.Revealed the "three fields" evolution and impact inoculation law of coal and rock in fold area under the influence of hard roof in the process of working face mining.The distribution evolution characteristics of stress,energy,plastic zone and seismic events are analyzed when the working face is mining in different area in fold,and the influencing factors such as roof dynamic load disturbance,roof thickness,hardness and bend of fold are analyzed.The "three field" early warning indexes of the test and the field impact were analyzed,and the clear indicators of precursor information were obtained through screening.The early warning index for stress field are seismic tomography,the index for energy field are impact deformation energy,four indicators with good early warning effect,such as b value and MS activity,and four indicators with moderate early warning effect,such as total area of fault and concentration of seismic source,which are used for seismic field monitoring.The weight of each index in the seismic field was obtained based on the MATLAB neural network model,and the prediction accuracy of the model was 87%.Finally,the entropy weight method was used to calculate the comprehensive weight of each index in the field,and the comprehensive warning model and criteria of rock burst caused by hard roof in the fold area were established.This paper puts forward the idea of monitoring and prevention of induced impact of roadway hard roof in fold area,including comprehensive monitoring and early warning system for "three fields" and pressure relief measures to reduce the dynamic and static load strength of roadway and roof coal in fold area.The research results have been applied in the 401111 working face of Hujiahe Mine,and the impact reduction effect is remarkable,and good social and economic benefits have been obtained.This paper has 151 figures,16 tables and 184 references.