Abstract
Earth dams play a vital role in water resource management, ensuring sustainable surface and groundwater supply. A key challenge in their design and operation is controlling seepage and understanding the hydraulic behavior of alluvial foundation layers, which directly impacts dam stability and safety. This study evaluates the effects of permeability and thickness of alluvial layers on seepage, hydraulic gradient, and uplift force, using data from an earth dam in East Azerbaijan. Numerical modeling was performed with GEOSTUDIO software and the Seep/W module. Three permeability levels (1×10⁻⁶, 1×10⁻⁷, and 1×10⁻⁸ m/s) and three thicknesses (10, 20, and 30 m) of the alluvial layer were analyzed. Results showed that increasing permeability from 1×10⁻⁷ to 1×10⁻⁶ m/s raised seepage by 745.92%, while increasing thickness from 20 to 30 m increased seepage by 16.85%. Reducing permeability from 1×10⁻⁶ to 1×10⁻⁷ m/s lowered the hydraulic gradient by 51.21%. Uplift force increased by 1.18% at 1×10⁻⁶ m/s permeability and by 1.06% at 30 m thickness. These findings highlight permeability’s greater influence over thickness on hydraulic behavior. The study underscores the importance of controlling permeability and optimizing geotechnical parameters to minimize seepage, manage hydraulic gradient, and enhance earth dam stability, offering practical solutions for improved design.
Keywords: Numerical Modeling, Permeability, Alluvial Layer, Hydraulic Gradient, Uplift Force


Introduction: Earth dams are essential for water resource management, facilitating flood control, water supply, and energy production. However, the hydraulic behavior of alluvial foundation layers poses significant challenges, influencing seepage, stability, and safety. Excessive seepage can lead to structural instability, as highlighted by recent studies (e.g., Johnson et al., 2023, reported a 50% seepage increase with high permeability layers). Despite advances in numerical modeling, the combined effects of permeability and thickness of alluvial layers remain underexplored, particularly for optimizing dam performance. This gap necessitates further research to ensure safer and more efficient dam designs. This study aims to investigate how variations in permeability (1×10⁻⁶, 1×10⁻⁷, 1×10⁻⁸ m/s) and thickness (10, 20, 30 m) of alluvial layers affect seepage rate, hydraulic gradient, and uplift force in earth dams. By employing numerical simulations, the research seeks to identify optimal design parameters, offering practical insights for enhancing dam stability and reducing seepage-related risks in similar structures.

Methodology: The study utilized GEOSTUDIO software with the SEEP/W module to perform numerical seepage analysis using the finite element method. The earth dam model was constructed based on real geotechnical and hydrogeological data, incorporating accurate dam geometry and boundary conditions (upstream and downstream water levels). Three permeability levels of the alluvial foundation layer (1×10⁻⁶, 1×10⁻⁷, and 1×10⁻⁸ m/s) and three thicknesses (10, 20, and 30 m) were tested to assess their impact on hydraulic behavior. Material properties, such as hydraulic conductivity and layer dimensions, were defined precisely, and boundary conditions were consistently applied across all scenarios. The model was validated by comparing simulated results with piezometer field data, ensuring reliability. Sensitivity analysis was conducted to evaluate the influence of each parameter on seepage, hydraulic gradient, and uplift force. Detailed outputs, including seepage rates and pressure distributions, are presented in the main text (e.g., Fig. 1 for seepage profiles, Table 1 for gradient values), providing a comprehensive basis for analysis.

Results and Discussion: the simulations demonstrated that permeability of alluvial layers has a far greater impact on hydraulic behavior than thickness. Increasing permeability from 1×10⁻⁷ to 1×10⁻⁶ m/s resulted in a 745.92% surge in seepage rate, while increasing thickness from 20 to 30 m only raised seepage by 16.85% (see Fig. 2 in the main text). Reducing permeability from 1×10⁻⁶ to 1×10⁻⁷ m/s decreased the hydraulic gradient by 51.21%, significantly improving seepage control (Table 2). Uplift force showed limited sensitivity, increasing by 1.18% at 1×10⁻⁶ m/s permeability and 1.06% at 30 m thickness, indicating its minor role in overall stability risks. Compared to prior studies, such as Johnson et al. (2023), which noted a 50% seepage increase with high permeability, our results align but provide a more detailed analysis of hydraulic gradient and uplift force dynamics. The innovation lies in quantifying the relative dominance of permeability over thickness—a 729.07% difference in seepage impact—offering a clearer design focus. While Johnson et al. emphasized seepage alone, this study highlights the combined effects on multiple hydraulic parameters, providing a more holistic understanding. The optimal configuration of 1×10⁻⁷ m/s permeability and 20–30 m thickness balances efficiency and cost, contributing actionable insights for dam design. These findings underscore the need for precise permeability control to enhance stability, offering a practical framework for engineers working on earth dams.

Conclusion: This study reveals that permeability of alluvial layers predominantly influences earth dam performance, with a 745.92% seepage increase when raised from 1×10⁻⁷ to 1×10⁻⁶ m/s, compared to a 16.85% rise with thickness increased from 20 to 30 m. Hydraulic gradient decreased by 51.21% with lower permeability, while uplift force showed minimal variation (1.18% increase at 1×10⁻⁶ m/s). The optimal design parameters permeability of 1×10⁻⁷ m/s and thickness of 20–30 m—effectively reduce seepage and enhance stability, offering a cost-efficient solution. These findings provide a scientific basis for improving earth dam design and ensuring long-term safety.