回采速度对坚硬顶板运动释放能量的影响机制

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

坚硬顶板破断释放的弹性能是冲击矿压的主要能量源之一,针对回采速度对坚硬顶板破断释放能量的影响机制,运用理论分析结合现场监测手段,对垮落带内的顶板悬臂梁结构,建立了基于弹性地基假设的三角增压载荷悬臂梁模型,推导得到回采速度控制下顶板梁的下沉量、弯矩及弯曲弹性能密度的解析解。对距煤层较近的低位未触矸破断式砌体梁结构,建立回采速度影响下的回转角与破断步距及破断释放能量的解析式,并进行讨论得到结论:加快回采速度使顶板悬臂梁的悬臂长度L和峰值应力集中系数a增加,使峰值距煤壁位置x0减小,3者均能造成顶板弯曲变形能增大,释放弹性能增加,且悬臂长度L和应力集中系数a影响效果更为明显;高速回采造成采空区充填程度低,促使关键块B的回转角增大,造成关键块A的破断步距增大,破断释放的能量也大幅增加,甚至促使原本为低位未触矸破断的砌体梁结构变为高位悬臂梁结构,其破断释放的弹性能更大,大能量矿震产生的动载易叠加高静载煤体诱发冲击,同时使超前段顶煤支护失效,造成冒顶事故;通过对关键层及围岩结构的判别,证实了两种坚硬顶板的破断模式,且微震监测表明坚硬顶板破断释放大能量矿震与回采速度有明显的正相关性,并得到坚硬顶板条件大采高工作面临界回采速度为4 m/d,科学指导了胡家河矿的开采强度优化。

Elastic energy released from broken hard roof is one of the main energy sources of rock burst.In order to understand the influence mechanism of mining advance speed on energy release from broken hard roof,for the roof cantilever beam structure in the caving zone,a triangular increasing load model based on the assumption of elastic foundation 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 elastic 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,resulting 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 releasing 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 advanced 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 releasing 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.