Roof stability evaluation of large section open-off cut in lower slice of slicing mining
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摘要: 为了研究分层开采下分层工作面大断面开切眼顶煤稳定性问题，以大柳塔煤矿活鸡兔井1−2煤层下分层203开切眼顶煤的14个钻孔为研究背景，采用理论分析、数值模拟和现场钻孔窥视分析了上分层开采与下分层开切眼掘进对开切眼顶煤塑性区的影响，并通过岩体完整性指数对顶板结构稳定性进行评价。从顶煤结构形态来看，由于上分层开采造成开切眼顶煤局部超挖或欠挖现象，开切眼的最大超挖量为1.2 m，最大欠挖量为0.8 m，顶煤不平整率为27.7%。理论分析结果表明：受上分层开切眼顶煤采动影响，底煤塑性区深度为2.02 m；受下分层开切眼掘进扰动影响，顶煤塑性区深度为1.50 m。钻孔窥视结果表明：将开切眼顶煤塑性区分别按理论计算和钻孔窥视划分为理论塑性区与实测塑性区，上分层采动影响造成的底板实测塑性区深度范围为1.06~2.04 m，下分层开切眼掘进扰动影响造成的顶煤实测塑性区深度范围为0.34~1.50 m，上分层采动影响造成的底板实测塑性区比理论塑性区平均小17.63%，下分层开切眼掘进扰动造成的顶煤实测塑性区比理论塑性区平均小25.82%。数值模拟分析结果表明：上分层采动影响造成的底煤塑性区深度范围为1~2 m，下分层开切眼掘进扰动影响造成的顶煤塑性区深度为1 m。上述3者所得结果一致性程度较高。开切眼顶煤稳定性评价结果表明：顶煤完整性指数范围为42.9%~87.9%，顶煤厚度与完整性指数呈正相关，与裂隙发育呈负相关，顶煤完整性评价为良好以上的占比超过1/2，说明顶煤整体结构基本完整。该研究结果可为分层开采下分层大断面开切眼同类工矿条件的顶煤厚度留设及支护方案设计提供参考。Abstract: In order to study the roof stability of large-section open-off cut in lower slice of slicing mining, the 14 boreholes in the top coal of the 203 open-off cut in the lower slice of 1−2 coal seam in Huojitu Mine of Daliuta Mine is taken as the research background. The influence of the upper slice mining and the lower slice open-off cut driving on the plastic zone of the top coal of the open-off cut is analyzed by theoretical analysis, numerical simulation and field borehole peep technology. And the stability of the roof structure is evaluated by the rock mass integrity index. From the perspective of the top coal structure form, the top coal of the open-off cut is partially over-excavated or under-excavated due to the upper slicing mining. The maximum over-excavation of the open-off cut is 1.2 m, the maximum under-excavation is 0.8 m, and top-coal uneven rate is 27.7%. The result of theoretical analysis show that due to the influence of upper slice mining of the top coal of the open-off cut, the depth of plastic zone in the floor is 2.02 m. Due to the disturbance of the lower slice mining of the open-off cut, the depth of the plastic zone in the top coal is 1.50 m. Borehole peep results show that the plastic zone of the open-off cut top coal is divided into the theoretical plastic zone and the measured plastic zone according to the theoretical calculation and borehole peep respectively. Due to the influence of upper slice mining, the depth of the measured plastic zone in the floor is 1.06-2.04 m. Due to the disturbance of the lower slice mining of the open-off cut, the depth of the measured plastic zone in the top coal is 0.34-1.50 m. The measured plastic zone caused by the influence of upper slice mining on floor is 17.63% smaller than the theoretical plastic zone. The measured plastic zone of the top coal caused by the disturbance of lower slice mining of the open-off cut is 25.82% smaller than the theoretical plastic zone. The result of numerical simulation analysis shows that due to the influence of upper slice mining, the depth of plastic zone in the floor is 1-2 m. Due to the disturbance of the lower slice mining of the open-off cut, the depth of plastic zone in the top coal is 1 m. The results obtained by the above three methods are highly consistent. The stability evaluation results of the top coal in the open-off cut show that the top coal integrity index ranges from 42.9% to 87.9%. The top coal thickness is positively correlated with the integrity index and negatively correlated with the fracture development. The proportion of top coal integrity evaluation as good or above is more than 1/2, indicating that the overall structure of top coal is basically complete. The research results can provide reference for the design of top coal thickness retention standard and support scheme of large section open-off cut in lower slice of slicing mining under similar mining conditions.
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图 6 顶煤钻孔窥视裂隙发育分布
Figure 6. Distribution of fracture development in top coal borehole peeping
图 7 全段钻孔裂隙数分布
Figure 7. Distribution of fracture number in whole section of borehole peeping
图 8 顶煤理论塑性区范围与实测塑性区范围划分
Figure 8. Division of theoretical plastic zone and mearsured plastic zone of top coal
图 10 顶煤两侧塑性区范围与弹性区划分
Figure 10. Division of plastic zone and elastic zone on both sides of top coal
图 12 开切眼掘进对顶煤塑性区影响
Figure 12. Influence of open-off cut driving tunneling on the plastic area of top coal
图 13 顶煤厚度与完整性指数关系
Figure 13. Relationship between top coal thickness and integrity index
表 1 岩石力学参数
Table 1. Rock mechanics parameter
地质参数 体积模
量/GPa剪切模
量/GPa内聚力/
MPa抗拉强
度/MPa摩擦角/（°） 容重/
（kN·m−3）中粒砂岩 1.1 0.83 2 0.6 37 25.8 粗粒砂岩 1.4 0.96 2.5 0.75 34 25.6 11煤层 0.43 0.34 0.6 0.3 28 14.3 12煤层 0.43 0.34 0.6 0.3 28 14.3 细粒砂岩 0.67 0.48 2.4 2.16 42 32.58 粉砂岩 1.43 1.12 2.75 1.84 38 24.6 
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表 2 开切眼顶煤与1−2煤层力学参数
Table 2. Mechanical parameters of top coal in the open-off cut and 1−2 coal seam
力学参数 弹性模量/GPa 抗压强度/MPa 抗拉强度/MPa 1−2煤层参考值 1.8~3.5 20~40 1.4~5 顶煤实验力学值 0.96~2.64 3.9~14.5 0.86~2.2
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表 3 不同结构类型所对应的
$ \alpha $ Table 3. The α coefficients corresponding to different structural types
结构类型 岩体块度尺寸/m $ \alpha $ 整体状 ＞1.0 1.0 块状 0.6~1.0 0.8 层状 0.3~0.6 0.5 碎裂状 0.1~0.3 0.2 散体状 ＜0.1 0.1
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