Philip's two-term infiltration equation has been widely used to infer soil saturated hydraulic conductivity (Ks), the accuracy of which is usually influenced by the size of infiltration rings and soil conditions. Previous studies have primarily focused on exploring the ring-size dependence of Ks estimations under specific soil conditions (e.g., soil isotropy and/or uniform initial water content). This study aimed to provide a comprehensive analysis by systematically considering eight heterogeneous and anisotropic soils with nonuniform initial water contents. Specifically, we examined the validity of Philip's infiltration equation as well as the recently proposed two forms (i.e., infiltration and time forms) of Parlange's infiltration equation both theoretically and in practical applications of double-ring infiltration. Then the time form of Parlange's equation was applied to infer Ks using double-ring infiltrometer measurements with different combinations of six inner ring diameters (10, 20, 40, 80, 120, and 200 cm) and three buffer index (defined as the ratio of the difference between inner and outer ring diameters to the outer ring diameter) values (0.20, 0.33, and 0.50). For each infiltrometer set, 20 stochastic Ks fields were randomly generated by adopting five standard deviation values (0.1, 0.3, 0.5, 0.7, and 0.9). Furthermore, we investigated the effects of five horizontal correlation lengths (30, 60, 150, 300, and 600 cm) on Ks estimations. The results demonstrated that Parlange's equation, compared to Philip's equation, was more universal in describing the cumulative infiltration relationship for the test soils. The combination of inner ring diameter and buffer index of 40 cm and 0.2, respectively, which satisfied most of the practical requirements for determining Ks in the Soil Water Infiltration Global (SWIG) database was optimal. When the horizontal correlation length exceeded a threshold (i.e., 150 cm in our study), the inner ring diameter was required to increase to 80 cm. Our findings contribute to accurate Ks estimations of different soils using double-ring infiltrometers.

This study investigates the influence of micro -scale entities such as inherent and induced fabric anisotropy on the stress-strain behaviour of granular assemblies. In tandem with this exploration, our objective is to formulate a novel correlation that quantifies the evolution of fabric tensor across diverse loading paths. This correlation can be introduced to enhance the micro -mechanical insights in conventional constitutive models. Employing the Discrete Element Method (DEM), we simulate the drained and undrained responses of 680 transversely isotropic particulate assemblies with diverse initial fabrics and particle Aspect Ratio (AR) under true triaxial loading conditions. We consider a second -order fabric tensor based on inter -particle contact orientations to trace fabric evolution during loading. To account for fluid-solid interaction under undrained conditions, we adopted the DEM-Coupled Fluid Method (CFM). The simulation results highlight the significant influence of the Lode angle, particle shape and initial fabric on the stress-strain behaviour of granular materials, with fabric evolution primarily affected by the stress state, void ratio and particle AR. Lastly, we propose a new correlation for the quantification of the fabric tensor using a multi -layer feed -forward neural network. The satisfactory performance of the suggested correlation is demonstrated through a comparison between DEM data and predicted fabric tensor values.

The present study focuses on investigating the effects of soil rotated anisotropy and spatial variability on slope failure in seismic conditions. The random finite element method aided by subset simulation is implemented, which ensures an efficient quantification of both the probability of failure and its associated consequence of failure. Several slope angles of gentle and steep slopes and soil properties that lead to a low probability of failure were selected for parametric studies. The comprehensive parametric studies of seismic slope stability analysis consider various factors such as slope inclinations, seismic coefficients, scales of fluctuation, and orientations of the major principal scale of fluctuation (i.e., the rotation angle of random field). The results underscore the importance of considering the combined effects of soil anisotropy and the orientation of the major principal scale of fluctuation for designing both gentle and steep slopes under seismic conditions and emphasize that care must be given to ensure the worst-case scenario is considered. Visual observations of failure mechanisms of gentle and steep slopes under seismic conditions were also shown to be very helpful in interpreting the variation of probability of failure due to soil spatial variation.