Numerical simulation of fractured water-conducting zone by considering native fractures in overlying rocks
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摘要: 导水裂隙带高度的确定对松散承压含水层下煤矿安全开采和矿区生态环境保护具有重要意义。以往根据塑性区判断导水裂隙带范围的数值模拟方法不能完全反映覆岩的破断机制。为了更准确地预测导水裂隙带发育高度,应用断裂力学方法,将裂纹尖端K场区内的应力强度因子断裂判据与摩尔-库伦屈服准则结合,提出了原生裂隙存在时的岩石断裂准则。利用自仿射分形模型建立起原生裂隙场分布,并通过有限元分析软件COMSOL Multiphysics将原生裂隙场和岩石断裂准则应用到导水裂隙带发育的数值模拟中,对淮北煤田青东煤矿的839工作面开采进行了模拟计算。结果显示,考虑原生裂隙时,导水裂隙带在贯通后高度达到92.5 m。与传统数值模拟和经验公式法相比,考虑原生裂隙的模拟结果与现场测量结果更为接近。这说明,采用自仿射分形模型所生成的裂隙场可以较好地模拟岩体内复杂而无序的原生裂隙分布,且与传统数值模拟和经验公式法相比,考虑原生裂隙的模拟方法能够更好地反映导水裂隙带的发育规律。Abstract: The height of the fractured water-conducting zone(FWCZ) is vital to the mine safety and the ecological environment protection of the mining areas. Previous numerical simulation method which judge the range of the fractured water-conducting zone through plastic zone can not fully reflect the failure mechanism of overburden. In order to predict the height of FWCZ more accurately, the fracture criterion of rock in the presence of native fracture is proposed by combining the fracture criterion of stress intensity factor with the Mohr-Coulomb yielding criterion. Native fracture field was constructed with self-affine fractal model and the finite element analysis software COMSOL Multiphysics was utilized to apply the native fracture field and the rock fracture criterion to the numerical simulation of the FWCZ's development in Qingdong Coal Mine. The results show that the height of FWCZ reaches 92.5 m when considering the native fractures. In contrast with the traditional "plastic zone" method and empirical formula method, the ratio of the height of the FWCZ to the mining height in the proposed method is closer to the field measured value, indicating that the fracture field generated by the self-affine fractal model can appropriately simulate the complex and disordered distribution of native fractures in rock mass. Therefore, the proposed method could better reflect the development mechanism of fractured water-conducting zone.
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