千米深井超长工作面采动应力旋转特征及应用

千米深井超长工作面采动应力环境更为复杂,围岩破坏程度和控制难度升高,威胁开采安全。为提高该类采场围岩控制效果,采用理论分析、数值模拟和现场实测等综合研究手段,从采动应力旋转角度分析该现象对围岩稳定性的影响及其应用原则。结果表明:千米深井超长工作面围岩裂隙发育程度升高,稳定性受到采动应力大小和方向的双重影响,含裂隙围岩存在优势裂隙扩展角,采动应力旋转造成围岩承载能力降低,采动应力旋转角度愈大,围岩稳定性愈差;采动后,121304工作面采动应力发生旋转,旋转轨迹与采动影响程度、工作面推进方向密切相关,距采空区边界愈近,采动应力旋转速度和旋转角度愈大;煤层和低位岩层最大主应力在平行和垂直于工作面推进方向的竖直平面内旋转,倾角减小,最小主应力则首先向平行和垂直于工作面推进方向的竖直平面内旋转,然后在上述平面内与最大主应力同步旋转,倾角增大;岩层位态升高,采动应力旋转角度先增大后减小,高位岩层采动应力旋转轨迹受121303工作面采空区影响,采动应力旋转轨迹向临近工作面采空区偏转;根据工作面推进方向与采动应力旋转轨迹的关系,提出围岩中存在一组、多组优势裂隙及裂隙随机分布条件下工作面推进方向确定原则,并分析了采动应力旋转现象对覆岩“砌体梁”结构稳定性的影响。

Mining-induced stress rotation and its application in longwall face with large length in kilometer deep coal mine

Due to the increase in bury depth and face length,the mining induced stress environment becomes increasingly complex.The damage degree and controlling difficulty of surrounding rock grow rapidly in longwall mining.Such changes drastically threaten the mine safety.In order to improve surrounding rock control in such longwall face,the mining induced stress rotation and its influence on surrounding rock stability is investigated with theoretical analysis,numerical simulation and field measurement.The results show that pre-existing fracture shows an increasing trend in rock masses surrounding longwall face with large face length in kilometer deep coal mine.Surrounding rock stability is thus influenced by both the magnitude and orientation of mining induced stress.The pre-existing fracture causes the appearance of optimal propagation angle of the failure fracture.Mining induced stress rotation leads to the decrease in the load-bearing capacity of surrounding rock,whose stability is negatively related to the rotation angle of mining induced stress.After mining the 121304 longwall face,stress rotation phenomenon occurs,and rotation trace is closely related to the influence intensity of the mining and face advance direction.With the decrease in the distance from the edge of gob,the rotation angle and rotation speed of mining induced stress increase quickly.The major principal stress of coal seam and lower overburden strata rotates toward horizontal direction in the vertical planes parallel with and perpendicular to the face advance direction.The minor principal stress first rotates into the referred vertical planes and then rotates consistently with the major principal stress in the vertical planes.At the same time,the minor principal stress rotates toward vertical direction gradually.Rotation angle experienced by mining induced stress increases with the growth in vertical distance from coal seam.In higher overburden strata,the rotation trace of mining induced stress is influenced by the gob remaining after the extraction of the 121303 longwall face,which deviates to the gob.According to the relation between face advance direction and the rotation trace of mining induced stress,the determination method of face advance direction is proposed for the surrounding rock with one set and many sets of fractures with stable orientation as well as that with random-distributed fractures.Besides,the influence of mining induced stress rotation on the voussoir beam structure of overburden strata is discussed.