Scale Effect on the Apparent Anisotropic Hydraulic Conductivity of Geomaterials

Properties of geomaterials often exhibit stratification and anisotropy due to various influencing factors such as weathering and sedimentation. However, the measurement of anisotropy is a difficult task since anisotropy not only depends on the direction but also varies with scale. In the current study, hydraulic conductivity is considered a typical geomaterial property and simulated by random field theory. A novel method based on two-dimensional and three-dimensional analytical expressions is proposed to estimate the apparent hydraulic conductivity (k) in different directions and determine the corresponding anisotropic ratios. A series of simulation tests on specimens with various dimensions from one strong anisotropy site are also performed via the finite element method. The analytical solutions of the proposed method are verified by numerical results. Results indicate that the anisotropic ratio shows a substantial sensitivity to the sample scale. A decrease in sample scale can result in the reduction of the anisotropic ratio; as a result, k gradually approaches to a point level's value, and the effect of anisotropy decreases. This work not only sheds light on the gap between the laboratory results and the field's inherent properties but also provides guidelines on upscaling small-scale (e.g., laboratory scale) results to field-scale applications.