基于逆Broyden秩1拟牛顿迭代法的岩体裂隙网络渗流特性研究

A study of hydraulic properties of rock fracture networks based on rank-one inverse Broyden quasi-Newton method

岩体裂隙粗糙度和流体惯性效应是影响岩体裂隙网络等效渗透性的重要因素。首先回顾了单裂隙中裂隙粗糙度和流体惯性效应对其过流能力的影响;然后基于逆Broyden秩1拟牛顿迭代法求解控制裂隙内流体流动的非线性方程组,研究岩体裂隙粗糙度和流体惯性效应对离散裂隙网络（DFN）等效渗透性的影响;最后,基于两种不同边界条件,对离散裂隙网络模型内流体的流动特性进行了探讨。结果表明,当水力梯度较小（〈0.5）时,裂隙粗糙度和流体惯性效应对离散裂隙网络渗透性的影响很小;当水力梯度较大（〉0.5）时,裂隙粗糙度和流体惯性效应对离散裂隙网络渗透性的影响随水力梯度的变化而显著变化;在两种边界条件下,当水力梯度在0.1～10.0之间时,裂隙粗糙度和流体惯性效应对离散裂隙网络过流能力的最大影响分别为18.1%和27.5%。所以,当水力梯度较大时,需要在离散裂隙网络模型的渗流计算中考虑裂隙粗糙度和流体惯性效应的影响。

Fracture surface roughness and inertial effect of fluid in fractured rock masses are important factors for characterizing the hydraulic behaviors of rock masses in many rock engineering projects. This study focuses on the influences of fracture surface roughness and inertial effect of fluid on the hydraulic behaviors of 2D discrete fracture networks（DFNs）, by solving a set of nonlinear fluid flow equations using the rank-one inverse Broyden quasi-Newton method. Two different boundary conditions are applied to the DFNs; and then the permeability coefficients of the models are calculated. The results show that when the hydraulic gradient J is small（〈0.5）, the influences of the fracture surface roughness and the inertial effect of fluid on the permeability of DFN are negligible. When the hydraulic gradient J is relatively large（〉0.5）, the influences of fracture surface roughness and the inertial effect of fluid on the permeability of DFN increase with the increment of the hydraulic gradient. Under two kinds of boundary conditions, the maximum influences of fracture surface roughness and the inertial effect of fluid on the permeability of DFN can be as high as 18.1% and 27.5%, respectively, corresponding to the hydraulic gradient in the range of 0.1-10. Therefore, the fracture surface roughness and the inertial effect of fluid need to be considered when calculating the hydraulic properties of fluid flow in 2D rock fracture networks, especially when the hydraulic gradient is large.