A DFN (Discrete Fracture Network) modelling approach is developed to couple stresses with fracture transmissivities and to evaluate large scale rock mass hydraulic conductivity. The transmissivity-stress coupling relies on a negative exponential correlation between normal stress acting on a fracture and fracture transmissivity, bounded by residual and maximal apertures. The remote stresses and the local stress fluctuations induced by the fractures themselves are combined in a semi-analytical approach to compute the normal stress acting on each fracture of a DFN. Directional equivalent hydraulic conductivities are numerically computed in all directions from a spherical permeameter setup. The resulting properties are first a cloud of points, where each point defines a direction and an equivalent hydraulic conductivity. The distribution of equivalent hydraulic conductivities is analyzed to define mean values, preferential directions and anisotropy ratio. The entire workflow is developed in the numerical platform DFN.lab. The capacity of the method to investigate the impact of the in-situ stresses on the rock mass hydraulic conductivity is illustrated for fracturing and in-situ stress conditions similar to the conditions at the Forsmark site in Sweden. We find that the stress fluctuations induced by the fractures have a significant impact on the resulting hydraulic conductivity field. They limit the anisotropy ratio to values close to a factor of 3 while the transmissivity distribution is correlated to orientations and spans several orders of magnitude. Sensitivity analyses, performed by changing the parameters of the transmissivity-stress law, show quantitatively how the directional hydraulic conductivities are rather controlled by the orientations of the in-situ stresses or by the underlying connectivity structure of the DFN.

中文翻译：

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耦合应力和导水率，用于定义裂隙岩石的等效定向水力传导率


开发了 DFN（离散裂隙网络）建模方法，用于将应力与裂隙透射率耦合，并评估大尺度岩体水力传导率。导水率-应力耦合依赖于作用在裂缝上的法向应力和裂缝导水率之间的负指数相关关系，以残余孔径和最大孔径为界。远程应力和裂缝本身引起的局部应力波动以半解析方法相结合，以计算作用在 DFN 每个裂缝上的法向应力。方向等效水力传导率是根据球面渗透仪设置在所有方向上进行数值计算的。生成的属性首先是一团点，其中每个点定义一个方向和等效的水力传导率。分析等效水力传导率的分布以定义平均值、优先方向和各向异性比。整个工作流程是在数值平台 DFN.lab 中开发的。该方法研究了地应力对岩体水力传导率影响的能力，该方法在压裂和地应力条件下进行了说明，类似于瑞典 Forsmark 现场的条件。我们发现，裂缝引起的应力波动对产生的水力传导率场有重大影响。它们将各向异性比限制为接近 3 倍的值，而导水率分布与方向相关，跨越几个数量级。 通过改变导水率-应力定律的参数进行敏感性分析，定量地显示了定向水力传导率如何受原位应力的方向或 DFN 的底层连接结构的控制。