厚煤层综放开采顶煤分区破坏特征研究

Study on zone failure characteristics of top-coal in fully-mechanized top-coal caving mining of thick coal seam

顶煤破坏机理是综放开采的一个基本理论问题,研究顶煤渐进破坏过程可为冒放性准确判别奠定基础。为提高顶煤冒放性预测精度,采用理论分析、数值计算和现场实测等手段对山西新柳煤矿顶煤分区破碎特征进行了研究。将液压支架简化为恒刚度弹簧建立顶煤力学模型,借助Ritz法和最小势能原理得到了工作面前方和控顶区上方顶煤位移场和应力场,分析了考虑初始地应力和开挖卸荷效应的采动应力分布特征;定义顶煤破坏危险性系数为应力圆半径同圆心至强度曲线垂直距离之差,实现顶煤破坏危险程度的定量表征;根据破坏面上正应力大小将剪切破坏划分为压剪和拉剪2种形式,推导出2种剪切破坏模式之间的过渡条件;以顶煤破坏危险性系数k=0等值线、水平应力σ_(h)=σ_(ts)等值线和控顶区上方抛物线形拉剪破坏边界线为界,将顶煤划分为弹性状态→压剪破坏→拉剪破坏→拉伸破坏4个阶段;对综放开采顶煤渐进破坏过程进行了模拟分析,借助FISH语言对顶煤破碎分区进行提取,模拟结果同理论结果较为吻合,但控顶区上方顶煤漏斗形拉剪破坏区同拉伸破坏区之间存在一条狭窄的剪切-拉伸混合破坏带;最后对顶煤裂隙发育特征进行了实测,煤壁前方为闭合型剪切裂隙,煤壁后方为张开型拉伸裂隙,与理论分析所得顶煤分区破碎特征吻合,验证了顶煤分区破坏模型的准确性。

Top-coal failure mechanism is a basic theoretical problem in fully-mechanized top-coal caving mining,and the study of the progressive failure process of top-coal can lay a foundation for the accurate identification of caving.In order to improve the prediction accuracy of top-coal caving,this paper studied the fragmentation characteristics of top-coal in Shanxi Xinliu Coal mine by means of theoretical analysis,numerical simulation and in situ measurement.The hydraulic support was simplified as a constant stiffness spring to establish a top-coal mechanical model.With the help of the Ritz method and the principle of minimum potential energy,the displacement field and stress field of the top-coal in front of the working face and above the top control area were obtained,and the initial in-situ stress and excavation unloading were considered.According to the mining stress distribution characteristics,the top-coal failure risk coefficient was defined as the difference between the radius of the stress circle and the vertical distance of the strength curve,so as to realize the quantitative characterization of the risk of top-coal failure;according to the size of the normal stress on the failure surface,the shear failure was divided into two forms:compression shear and tension shear,and the transition conditions between the two shear failure modes were derived;Taking the top-coal failure risk coefficient k=0 contour line,the horizontal stress σ_(h)=σ_(ts) contour line and the parabolic tensile shear failure boundary line above the top control area as the boundary,the top-coal was divided into four stages:elastic state→compression shear failure→tensile shear failure→tensile failure.The progressive failure process of the top-coal in fully-mechanized top-coal caving mining was simulated and analyzed,and the top-coal crushing zone was extracted with the help of FISH language.The numerical results were in good agreement with theoretical analysis except that a shear-tension mixed failure region appeared between extension shear and tension failure scopes.Finally,the development characteristics of top-coal cracks were measured.The front of the coal wall was a closed shear crack,and the back of the coal wall was a closed shear fracture.It was an open-type tensile fracture,which was consistent with the regional fracture characteristics of top-coal obtained by theoretical analysis,which verified the accuracy of the top-coal subregional failure model.