综放开采顶煤与覆岩力链结构及演化光弹试验研究

综放开采过程中顶煤和覆岩由连续向非连续和散体介质状态转变,描述矿压在断裂覆岩和碎裂顶煤中的形成、传递方式和作用机理是综放开采矿压理论研究的难点.基于光弹试验原理,借助散体介质双轴加载双向流动光弹试验装置,对综放开采过程中散体顶煤与非连续覆岩关键层中力链网络结构及演化特征进行研究.研究发现:地层载荷在煤岩体中构成了错综复杂的弱-强力链网络.综放开采打破了初始力链网络结构的平衡,顶煤与覆岩中形成梁-拱复合力链拱结构,覆岩荷载以强力链形式传递到工作面前方煤体.随着工作面推进和顶煤放出,覆岩梁-拱力链网络不断扩展和演化,形成更大规模的力链拱结构.关键层弯曲、断裂和失稳运动,使工作面前方的强力链拱脚出现回缩现象,力链分布密度和强度增加,导致工作面来压现象.地层内水平力作用使顶煤与覆岩内的梁-拱力链结构效应较更加明显,整体拱结构形态愈加完整,强力链网络结构更加紧致,关键层断裂失稳时力链拱对工作面煤层的作用力更加显著.

Photoelastic experimental study on the force chain structure and evolution in top coal and overlaying strata under fully mechanized top coal caving mining

In top coal caving mining,the state of top coal and overburden strata changes from continuous media to discontinuous and loose aggregate media.It is difficult to theoretically describe the transition and action of mining induced pressure in discrete top coal and fractured overlaying strata.Based on the photoelastic experiment principle,the network structure and the evolution characteristics of force chains in discrete top coal and discontinuous overlaying key strata are investigated during fully mechanized top coal caving mining by employing photoelastic test equipment that allows biaxial loading and bilateral particle flowing.The study shows that overburden load in discontinuous strata displays a complicated network composed by weak and strong force chains.Top coal caving mining destroys the equilibrium of the initial force chain network structure,and a composed beam-arch force chain structure forms in top coal and overlaying strata,where the overburden load is transformed into the front coal seam in the form of strong force chains.With mining face advancing and top coal caving,the beam-arch force chain network in overlaying strata develops,and a larger force chain arch structure forms.Bending,breaking and instable movement of the key strata give rise to an inverse moving of the force chain arching foot and a compaction process of the strong force chain network.The distribution density and intensity of force chains evidently increase,resulting in strong pressure phenomena taking place in the mining face.Under the biaxial loading condition,the effect of the beam-arch force chain structure becomes much evident in the earth.The entire structure of the force chain arch displays perfectly,the structure of the strong force chain network becomes denser,and due to breaking and instability of the key stratum,the pressure phenomenon of the force chain arch in front of the mining face and coal seam manifests much pronounced.