In this study a comparison of Discrete Fracture Network (DFN) modeling and empirical relationships based on conventional engineering rock mass classifications is carried out in order to determine the elastic properties of fractured rock masses. Uncertainties are considered by a stochastic description of the fracture network geometry and a probabilistic approach, utilizing Monte Carlo simulation techniques, for the various other input parameters. The proposed workflow is applied to two sandstone outcrops. Geometric information on the fracture systems is obtained from terrestrial laser scanning providing the input parameters (orientation, size and intensity) for each fracture set including probability density functions required for DFN modeling. After adding the mechanical properties of intact rock and fractures obtained by laboratory tests, the DFN approach allows to calculate values for rock mass deformation modulus and Poisson's ratio assuming either isotropy or vertical-transverse isotropy. These estimates are compared to values derived from empirical relationships based on engineering rock mass classifications. The comparison of the two approaches and, in particular, of the different empirical relationships reveals a significant scatter in the estimated rock mass properties. Only those empirical equations which incorporate intact rock properties in addition to the classification score yield plausible results, i.e., a pronounced weakening due to the fractures, and are in agreement with the estimates of the DFN approach. The additional effort of generating a DFN model shows its benefits if an anisotropic rock mass and/or spatially varying properties have to be considered, thus, providing a comprehensive hydromechanical characterization of anisotropic fractured rock masses.

在这项研究中，基于常规工程岩体分类对离散断裂网络 (DFN) 建模和经验关系进行了比较，以确定断裂岩体的弹性特性。对于各种其他输入参数，通过裂缝网络几何形状的随机描述和概率方法（利用蒙特卡罗模拟技术）来考虑不确定性。建议的工作流程适用于两个砂岩露头。裂缝系统的几何信息从地面激光扫描中获得，为每个裂缝组提供输入参数（方向、大小和强度），包括 DFN 建模所需的概率密度函数。加上实验室试验得到的完整岩石和裂缝的力学特性后，DFN 方法允许在假设各向同性或垂直-横向各向同性的情况下计算岩体变形模量和泊松比的值。将这些估计值与基于工程岩体分类的经验关系得出的值进行比较。两种方法的比较，特别是不同经验关系的比较揭示了估计岩体特性的显着分散。只有那些除了分类得分还包含完整岩石特性的经验方程产生合理的结果，即由于裂缝导致的明显弱化，并且与 DFN 方法的估计一致。如果必须考虑各向异性岩体和/或空间变化特性，则生成 DFN 模型的额外工作显示了它的好处，因此，