综放开采顶煤裂隙场扩展的应力驱动机制研究

为探究采动应力场作用下顶煤裂隙场发育特征，采用室内实验、数值模拟、理论分析和现场实测等方法对综放开采顶煤裂隙场扩展的应力驱动机制进行了分析。顶煤冒放性同采动裂隙发育程度呈正相关，推导出顶煤裂隙发生I,II和I-II型扩展的应力场条件和优势扩展裂隙角确定方法，顶煤裂隙扩展与否和扩展类型受到主应力大小和主方向的影响;煤层回采后，顶煤最大和最小主应力均存在超前峰值现象，最大主应力演化存在增大和减小2个阶段，最小主应力则经历增大、减小和反向增大3个过程;煤壁前方最大和最小主应力方向在平行于推进方向的垂直平面(α)内向采空区旋转，两者在平面α内的旋转角度一致，煤壁后方发生反向回旋，最大主应力偏离平面α，最终旋转至工作面倾斜方向;最小主应力在水平面内的旋转角度同推进方向与初始最小地应力方向之间的夹角相等，最大主应力在水平面内不旋转;由于主应力增大和主方向旋转，顶煤裂隙首先发生I型扩展，最大主应力峰值附近，顶煤裂隙在高围压作用下发生纯II型扩展，煤壁附近，顶煤裂隙在开挖卸荷作用下发生I-II混合型扩展，破碎顶煤最终于支架后方冒落;由于主应力方向的旋转效应，顶煤采动裂隙向采空区倾斜，根据顶煤裂隙扩展机理的不同，将顶煤划分为原岩应力区、微裂隙加密区、剪切破坏区、拉剪混合破坏区和散体冒落区。

Propagating mechanism of top coal fracture field in longwall top coal caving mining

In order to understand the fracturing mechanisms of top coal,lab testing,numerical modeling,theoretical analysis and field measurement are used to study the driving forces of top coal fractures.Top coal cavability is positively proportional to the development of mining induced fractures.Stress conditions for different propagation modes (I,II and I II) of top coal fractures are determined where dominant propagation angle is considered.Propagation and associated pattern are dependent on the magnitude and direction of principal stresses.There are peak points of major and minor principal stresses occurring ahead of the longwall face.The major principal stress remains in loading state while minor principal stress undergoes loading,unloading and reverse loading processes.Major and minor principal directions rotate to the gob in a vertical plane (α) parallel to the advancing direction in front of the longwall face.Rotation angle of two principal stresses keeps equal in plane α.Reverse rotation occurs subsequently at the rear of the longwall face.The major principal direction deviates from plane α and becomes parallel to dip direction.In horizontal plane,the rotation angle of minor principal stress is equal to the angle between advancing direction and initial minor principal axis and that of major principal stress is zero.Due to the increase of principal stress magnitude and rotation of principal direction,top coal fracture propagates in mode I first.Then,the mode turns into mode II because of high minor principal stress.In the proximity of longwall face,the fractures propagate in the mix mode I II.Because of principal stress rotation,mining induced fractures in top coal incline to the gob consistently.Based on the propagation modes,top coal is divided into five zones,including initial stress zone,microcrack increasing zone,shear failure zone,tensile shear failure zone and caving zone.