MECHANISM STUDY OF OVERLYING STRATA MOVEMENT INDUCING ROCKRURST ON TOP-COAL CAVING FACE

Based on the voussoir beam theory,the bi-directional(up and down wards) movement model of top-coal caving face was promoted.Accordingly the energy and stress sources of rockburst were analyzed.By the seismic observation technology,the microseism(MS) effect of the overlying strata movement was observed and the achieved results are as follows:(1) the MS activity is periodic,before rockburst,the total energy continuously gets larger,and when rockburst happens,it gets up to the largest,and then it drops extraordinarily;(2) before rockburst happens,the events firstly get higher and then drop.The rockburst happens during the process of events reducing;(3) the average elevation can reflect the development state of the movement of overlying strata.Before rockburst happens,the average elevation gets higher,and when or pre of the rockburst,the elevation gets up to the largest value,while it drops abruptly after rockburst happening:(4) during the MS activity cycle,the spatial distribution of seismcities gets higher in elevation and vast in space before rockburst.When rockburst happens,it gets up to the peek values and the strata near the working face active strongly.As a result,the rockburst mainly happens during the overlying strata moving downwards,hence it?s possible to observe and prevent rockburst by monitoring the upward movement of the overlying strata.