Hydraulic weakening technology for unsupported top coal at the end of fully mechanized caving face
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摘要:
针对综放工作面端头的悬空顶煤长度过大、难以及时垮落的问题，基于高压水射流破煤造穴方法，提出了一种大倾角厚煤层端头顶煤水力破煤弱化技术。以东峡煤矿31123−1大倾角综放工作面为工程背景，建立了端头悬空顶煤力学模型，基于线性叠加原理推导了弯矩与剪应力共同作用下的悬空顶煤挠度方程，发现悬空顶煤自由端挠度最大，固定端因弯矩峰值产生最大拉应力，确定固定端处为水力弱化优选区域；揭示了高压水射流通过冲击破煤造穴、诱导裂隙扩展，切断顶煤与煤柱力学联系的弱化机制，并提出了钻孔定位→高压射流破煤→旋转造穴的标准化工序。运用数值计算和现场应用结合的方法，分析了采用该技术前后端头顶煤区域应力分布演化规律、巷道围岩变形特征与端头悬空顶煤垮落效果。结果表明：水力破煤弱化后，工作面煤柱内垂直应力和工作面超前支承应力峰值分别降低了29.6%和17.4%，巷道顶底板和两帮最大移近量分别降低了35.8%和37.8%，悬空顶煤长度由10 m减小至1 m。
Abstract:To address the issue of excessive unsupported top coal length and delayed caving at the end of a fully mechanized caving face, a hydraulic weakening technology for face-end top coal in steeply inclined thick coal seams was proposed based on the coal-breaking and cavity creation method using high-pressure water jet. Taking the 31123-1 steeply inclined fully mechanized caving face of Dongxia Coal Mine as the engineering background, a mechanical model was established for the unsupported top coal condition at the end of a fully mechanized caving face. Based on the principle of linear superposition, the deflection equation under the combined action of bending moment and shear stress was derived. It was found that the deflection at the free end of the unsupported top coal was greatest, while the fixed end generated the maximum tensile stress due to the peak bending moment, identifying this area as the optimal zone for hydraulic weakening. This study revealed that high-pressure water jets weakened the mechanical connection between the top coal and coal pillar through impact-induced coal fracturing, cavity creation, and fracture propagation. A standardized procedure of "drilling positioning→high-pressure jet coal breaking→rotational cavity creation" was proposed. By combining numerical calculation and field application, this study analyzed the evolutionary patterns of stress distribution in the face-end top coal zone, deformation characteristics of surrounding rock of roadways, and collapse effects of unsupported face-end top coal before and after applying the new technology. The results demonstrated that after hydraulic weakening for coals, the peak values of vertical stress inside the coal pillar and advanced support stress of the working face decreased by 29.6% and 17.4%, respectively. The maximum convergence of the roof-to-floor and rib-to-rib in roadways reduced by 35.8% and 37.8%, respectively, and the unsupported top coal length decreased from the original 10 m to 1 m.
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图 1 工作面布置与端头悬空顶煤结构
Figure 1. Working surface layout and unsupported face-end top coal structure
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图 2 端头悬空顶煤水力破煤弱化控制思路
Figure 2. Conceptual approach for weakening of unsupported face-end top coal
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图 7 弱化前后端头顶煤垮落形态
Figure 7. Collapse patterns of face-end top coal before and after weakening
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图 8 弱化前后端头区域应力分布
Figure 8. Stress distribution of face-end area before and after weakening
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图 9 弱化前后煤柱内应力曲线
Figure 9. Internal stress curve of coal pillar before and after weakening
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图 10 水力破煤弱化方案设计参数
Figure 10. Design parameters of hydraulic coal breaking weakening scheme
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图 12 工作面超前钻孔应力变化曲线
Figure 12. Stress variation curves of advanced boreholes in working face
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图 13 回采巷道表面位移变化曲线
Figure 13. Variation curves of surface displacement in mining roadways
表 1 顶底板及煤层物理力学参数
Table 1 Physical and mechanical parameters of the roof, floor and coal seam
岩体 密度/（kg·m−3） 弹性模量/GPa 泊松比 上覆岩层 2 540 11 000 0.30 砂质泥岩 2 290 7 615 0.16 中粗砂岩 2 583 12 000 0.29 细砂岩 2 540 11 000 0.30 泥岩 1 750 3 950 0.20 6−1/6−2号煤层 1 750 3 950 0.20 中细砂岩 2 583 12 000 0.29 下伏岩层 2 540 11 000 0.30 
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表 2 各岩层块体接触面力学参数
Table 2 Mechanical parameters of the contact surfaces of each rock stratum block
岩体 切向刚度/
GPa法向刚度/
GPa黏聚力/
MPa内摩擦
角/（°）抗拉强度/
MPa上覆岩层 15.09 37.73 4.65 32.00 4.00 砂质泥岩 9.70 24.40 1.50 18.00 0.50 中粗砂岩 5.56 14.40 3.50 19.00 0.80 细砂岩 9.50 28.70 0 21.00 0 泥岩 9.70 24.40 1.30 18.00 0.40 6−1/6−2号煤层 4.60 11.50 0.80 14.00 0.32 中细砂岩 2 583.00 12 000.00 0.29 5.56 14.40 下伏岩层 0.30 15.09 37.73 4.65 32.00
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