Mechanism of mining advance speed on energy release from hard roof movement

Elastic energy released from broken hard roof is one of the main energy sources of rock burst. In order to un- derstand the influence mechanism of mining advance speed on energy release from broken hard roof,for the roof canti- lever beam structure in the caving zone,a triangular increasing load model based on the assumption of elastic founda- tion is established by using theoretical analysis and field monitoring methods. The analytical solutions of the bending subsidence,moment and elastic energy density of roof beam under the control of mining advance speed are deduced. For the lower broken voussoir beam structure close to coal seam,the analytical formulas of breaking step distance and breaking energy releasing with rotation angle are obtained. The study demonstrates that accelerating mining advance speed makes the cantilever length and peak stress concentration factor of roof cantilever beam increasing,the position of peak distance from coal wall decreasing,all of which can increase the bending deformation energy and release elas- tic energy of roof,among the three factors,the effect of cantilever length and peak stress concentration factor is more obvious. High-speed mining results in a lower degree goaf filling,which increases the rotation angle of key block B,re- sulting in breaking step of key block A and energy release increasing. It even makes the masonry beam structure,which is originally a lower non-contact breaking structure,become a high-level cantilever beam structure,whose elasticity re- leasing is greater. Large-energy mine earthquake not only can induce dynamic and static overlapping coal impact under high abutment pressure,but also cause roof falling accidents due to the fatigue damage and support failure of the ad- vanced top coal. By distinguishing the key strata and surrounding rock structure,two kinds of breaking modes of hard roof are confirmed. Micro-seismic monitoring shows that there is a positive correlation between the breaking and relea- sing of large-energy mine shocks from the breaking of hard roof and the mining advance speed. It is concluded that the bounded mining speed is 4 m / d under a hard roof condition and large mining height,which guides the optimization of mining intensity in Hujiahe Mine scientifically.