综放开采覆岩破断与顶煤力链结构演化特性分析

Analysis on evolution characteristics for overburden and chain of top-coal using fully mechanized top coal caving mining

力链结构体系在综放开采中承受荷载和传递荷载,是描述顶煤与覆岩由连续向非连续和散体转化的重要途径,以此为切入点,借助综放开采相似材料模拟实验和散体介质双轴加载双向流动光弹试验装置,对综放开采过程中覆岩破断演化特征和散体顶煤与非连续覆岩关键层中的力链结构演化特征进行了研究,并提取力链做为覆岩矿压的演变判据。实验结果表明:在相似材料综采过程中,覆岩破断演化经历了微裂、局部断裂、加速断裂、完全断裂和彻底垮落。在光弹采场中,力链承受竖向荷载,亚关键层中的力链由于黏结作用,产生水平力。随着煤岩颗粒的放出,亚关键层逐渐破坏,放煤口上方的力链消失,由于力链的前移,造成了工作面矿压的增大。随着煤岩颗粒的继续放出,放煤口上方出现较大的力链拱结构,拱结构屏蔽范围内,关键层中的强力链分布密度降低,煤体中的强力链竖向分布降低,水平分布显著。

The force chain structure system is subjected to bear and transfer load in the fully mechanized caving mining. It is an important way to describe the transformation of top coal and overlying rock from continuous to discontinuities. As a breakthrough point,with the simulation experiment in the fully mechanized caving mining and biaxial loading double flow photoelastic test device of granular media,the evolution characteristics of overlying rock fracture and the evolution characteristics of the force chain structure in the key strata in top coal and the discontinuous overlying strata during the fully mechanized caving mining process are studied. The force chain is used as the evolution criterion for the overburden rock pressure. The experimental results show that the overlying rock experiences crack of micro, local fracture, accelerated fracture, complete fracture and complete collapse. In the photoelastic stope, the force chain is subjected to the vertical load. The force chain in the subcritical layer produces the horizontal force due to the bonding effect. With releasing coal and rock particles, the sub critical layer is gradually destroyed and the force chain over the coal caving outlet is lost. Due to the forward movement of the force chain, an increase of mining pressure in the working face is caused. With the continuous release of coal and rock particles, a large force chain arch structure appeared over the coal caving outlet. The distribution density of the strong chain in the key layer decreases and the vertical distribution of the strong chain in the coal layer decreases and the horizontal distribution is significant.