Influence Mechanism of Spatial Variability of Permeability Coefficient on Seepage Characteristics of High Core Rockfill Dams: Insights from Numerical Simulations

The spatial variability of permeability coefficients in multi-component materials poses significant challenges for the seepage safety of high core rockfill dams. This study systematically investigates the influence mechanism of the spatial variability of permeability coefficients on seepage characteristics through a stochastic framework combining random field simulation, non-intrusive finite element analysis, and multi-scheme numerical experiments. Based on the measured data and statistical analysis, random fields of permeability coefficients are constructed, and eight computational schemes are designed to analyze the differential impacts of spatial variability in zones of the core wall, cut-off wall, rockfill, overburden, and curtain. The results show that the spatial variability of permeability coefficients in the rockfill, overburden, and curtain materials has a negligible effect on the seepage behavior, with the coefficient of variation of the hydraulic gradient at feature points remaining below 0.04. In contrast, the spatial variability of permeability in the core wall and cut-off walls significantly affects the seepage characteristics. Specifically, the hydraulic gradient in the core wall increases by an average of 4.8%, with a maximum increase of 34%, and the coefficient of variation of the hydraulic gradient at feature points ranges from 0.15 to 0.18. The maximum hydraulic gradient at the release point of the core wall rises from 1.67 to 1.75 when the spatial variability is considered. Additionally, the spatial variability of permeability in the core wall leads to greater discreteness in the hydraulic gradient of the cut-off walls, weakening the coordinated anti-seepage effect between the main and secondary cut-off walls. The statistical analysis reveals that the hydraulic gradient at feature points follows a normal distribution. Furthermore, when the coefficient of variation of the core wall permeability increases from 1.46 to 2.03, the maximum hydraulic gradient at key points rises from 2.0 to 2.3. These findings highlight the necessity for the strict quality control of permeability parameters in core wall and cut-off wall materials to ensure the long-term seepage safety of high core rockfill dams.