长壁工作面采动覆岩层理开裂机理及侧向裂隙发育规律

Mechanism of bedding cracking and development laws of lateral fracture in overlying strata induced by longwall mining

  • 摘要: 长壁开采煤层覆岩下沉变形过程中,岩层内部形成弯曲应力,并可能沿抗拉和抗剪强度较小的层理开裂形成侧向导水通道。针对相邻采空区积水侧向渗漏引起的工作面突水问题,研究了长壁开采覆岩层理开裂机理,分析了侧向裂隙发育规律。首先基于Winkler弹性地基梁理论建立采动覆岩弯曲下沉挠度方程,考虑煤柱和采空区上覆岩层不同支承压力与破坏程度确定对应的上覆载荷和地基系数,给出各层位岩层的下沉、转角、弯矩和剪力曲线计算公式。在此基础上,将采动覆岩层理裂隙分为张拉离层裂隙和剪切错动裂隙,并根据岩层非同步弯曲下沉特征与组合梁理论计算岩层内部弯曲应力分布情况,提出了张拉离层裂隙和剪切错动裂隙发育判断依据,给出了覆岩任意层理面上侧向裂隙发育位置、长度和隙宽等参数的计算方法。最后以凌志达煤矿15102工作面工程地质条件为依据,计算了上覆各岩层的挠度曲线和弯曲应力分布,分析了采动覆岩层理裂隙发育规律。结果表明,15102工作面在区段煤柱上方发育有超过50 m的剪切错动裂隙,超过了15101和15102工作面之间区段煤柱最大宽度;采空区边界上覆岩层中剪切错动裂隙和张拉离层裂隙共同发育;采空区中部上覆岩层中主要为张拉离层裂隙。采用钻孔窥视法探测了15101工作面采动侧向裂隙发育情况,对比验证了理论计算结果。根据研究结果确定沿层理发育的侧向裂隙是15101采空区积水侧向渗漏的主要导水通道。据此针对15102回采巷道制定超前钻孔注浆和滞后钻孔注浆措施,以及15101采空区积水疏排措施,从而有效减少了15102工作面回采巷道顶板淋水量,保证了巷道正常掘进和工作面安全开采。

     

    Abstract: The subsidence and deformation of strata induced by longwall mining will bring the bending stress inside the strata, which may result in bedding cracking for its relatively low shear and tension strength and forming lateral water-courses. Water in goaf areas may inrush through these watercourses and become a safety risk to the normal operation of the nearby mining face, so the development laws of the lateral fractures induced by longwall mining are analysed. First, the deflection equation of mining overlying strata based on the Winkler elastic foundation beam theory is established. Then the corresponding overlying pressure and foundation coefficients of strata above the coal pillar and goaf are determined according to the different abutment and damage, and the calculation formulas of the subsidence, rotation, moment and shear of every stratum are provided. Based on this, the mining-induced bedding fractures are divided into two classes, i. e. tension separation fractures and shear dislocation fractures, and the failure criteria of the two different fractures are proposed, and the calculation methods of the fractures position, length and width are provided. Finally, taking No.15102 working face at the Lingzhida coal mine as the research background, the deflection curve and bending stress of the overlying strata induced by mining are calculated and the development laws of the lateral bedding fractures are investigated. The results show that there are only shear dislocation fractures developing with a length of more than 50 m above the pillar, which is longer than the width of the pillar between No.15102 and No.15101 working face. The fractures above the goaf boundary include tension separation fractures and shear dislocation fractures. The lateral bedding fractures above the center of the goaf are mainly the tension separation fractures. Drilling imaging method has been adopted to observe the lateral fractures induced by No. 15101 mining, which is used to verify the theoretical analysis. According to the research, the lateral fractures developing along the bedding are the main watercourses that may cause water inrush from No.15101 goaf. Therefore, boring and grouting in front of and behind the heading faces of No. 15102 mining roadways were operated as well as water draining in No. 15101 goaf to effectively reduce water sprinkling in the roofs of No.15102 mining roadways, which can ensure the normal excavation of the roadways and safety mining of No.15102 work face.

     

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