综放开采顶煤与覆岩力链结构及演化特征

综放开采顶煤及覆岩非连续结构体系中力链形成机制及其演化规律,是采场支架载荷计算、优化采放工艺和矿压控制的重要基础。借助颗粒体双轴加载双向流动光弹实验,拍摄到综放开采过程中顶煤与覆岩中的力链分布,并基于拓扑学理论对力链网络结构进行了研究。研究表明:初始状态下,顶煤与覆岩中力链分布均匀;开采后在放煤口附近形成拱形力链,并随着工作面的推进向工作面前方和上部延伸。顶煤与覆岩力链主要有3种构型,即链状,环状和链-环耦合,分别分布在工作面前方,未受扰动的覆岩区和受扰动的覆岩区,可用Betti数作为表征力链构型的参数。通过对综放采场力链分布特征分析,揭示了工作面前方支撑压力形成机理和工作面支架受载荷作用的力学本质。对力链强度、力链方位角和接触力频率的统计分析,发现上部覆岩中未受开采扰动区域的强力链分布均匀,而受扰动区域的强力链沿着拱迹线发育,工作面前方的强力链始终以竖直方向的链状力链为主。

Structures and evolution characteristics of force chains in top coal and overlying strata under fully mechanized caving mining

The mechanism of force chain formation and its evolution laws in the non-continuous structure system of top coal and overlying strata are the important foundation for the calculation of support loading,the optimization of coal mining technology and the control of mine pressure. By photoelastic experiment of particles under biaxially loading and bilaterally flowing conditions,the distribution of force chains in top coal and overlying strata of fully mechanized caving mining is captured and force chain network structure is studied by topology. The study shows that the distribution of force chain in overlying strata and top coal is uniform in the initial state. After mining,the arched chain is formed near the drawing opening,and extends towards the front and upper part of the working face as the working face advances. Three main configurations of force chains in overburden strata and top-coal are identified,namely,chain,loop and chain-loop coupling respectively,which are distributed in front of the working face,undisturbed overlying strata and mining disturbed overlying strata. Besides,these configurations can be described by Betti number. Through the analysis of the distribution characteristics of the force chains in mining field,the paper reveals the forming mechanism of the supporting pressure in front of the working face and the mechanical essence of the loading action of the working face. Based on the statistical analysis of force chain strength,force chain azimuth and contact force frequency,the force chains in top coal and overlying strata display statistical features as follows:strong chain distribution of undisturbed areas in the upper overburden is relatively uniform,whereas in the mining disturbed area strong force chains develop along the arch line;In front of the working face,the vertical force chain is the majority all the time.