Investigation of Combined Leakage Control Methods with Simultaneous Numerical Analysis of the Cutoff Wall and Clay Blanket in Earth-fill Dams

Earth dams, as critical hydraulic structures, are essential for water resource management, enabling irrigation, flood control, and hydropower generation, but their performance is often compromised by seepage through the dam body and foundation, which reduces storage capacity, increases pore water pressure, and risks structural instability, potentially leading to catastrophic failure. This study evaluates the performance of two widely used seepage control methods—cutoff walls and clay blankets—based on the specifications of an earthen dam in East Azerbaijan, employing numerical modeling with GeoStudio’s Seep/W module to analyze their effectiveness in reducing seepage and controlling pore water pressure. The research focuses on key design parameters, including the depth and thickness of the cutoff wall, the length and thickness of the clay blanket, and the permeability of the dam foundation, which significantly influence seepage behavior and structural stability. The numerical model was developed using detailed geotechnical data from the dam site, incorporating soil properties, hydraulic conductivity, and boundary conditions to simulate real-world seepage patterns under steady-state conditions. The cutoff wall, modeled with depths ranging from 10 to 20 meters and thicknesses from 1 to 3 meters, demonstrated superior performance, with a configuration of 15 meters depth and 2 meters thickness reducing seepage by 70–90%, as it effectively intercepts flow paths through the permeable foundation layers, significantly lowering the hydraulic gradient and mitigating pore water pressure buildup. In contrast, the clay blanket, tested with lengths of 50 to 100 meters and thicknesses of 0.5 to 2 meters, achieved a seepage reduction of 30–50% with a configuration of 93 meters length and 1.5 meters thickness, primarily by increasing the seepage path length across the upstream face, though its impact on pore water pressure was less pronounced due to its surface-level application, which does not penetrate deep foundation layers. The numerical simulations revealed that the cutoff wall’s effectiveness stems from its ability to create a low-permeability barrier deep within the foundation, reducing the risk of piping and internal erosion, while the clay blanket’s performance is limited by its dependence on the foundation’s inherent permeability and susceptibility to cracking under differential settlement. Economically, the cutoff wall accounted for 49.8% of the total project costs, driven by high material and excavation expenses, whereas the clay blanket constituted 50.2% of the budget, benefiting from simpler construction techniques and lower excavation requirements, making it a more viable option for shorter dams or sites with less permeable foundations. However, the cutoff wall’s superior seepage reduction per unit cost highlights its cost-effectiveness for large-scale projects where long-term stability is critical. A key innovation of this study is the proposal of a hybrid seepage control strategy combining a cutoff wall and a clay blanket to optimize both performance and cost. The combined model, integrating a cutoff wall with a reduced depth of 12 meters and a clay blanket with a thickness of 1 meter, achieved an 85% reduction in seepage, surpassing the clay blanket’s standalone performance and approaching the cutoff wall’s effectiveness, while reducing execution costs by 10% compared to implementing either method independently. This hybrid approach leverages the cutoff wall’s deep seepage barrier to control foundation flow and the clay blanket’s upstream coverage to extend the seepage path, creating a synergistic effect that enhances overall stability. Sensitivity analyses further confirmed that foundation permeability significantly influences both methods’ performance, with highly permeable foundations requiring deeper cutoff walls, while moderately permeable foundations benefit more from the hybrid configuration. The findings underscore the importance of site-specific geotechnical assessments in seepage control design, as variations in soil properties and hydraulic conditions can alter the optimal configuration. From a practical perspective, the proposed hybrid solution offers significant advantages for earthen dam projects, reducing construction costs and improving long-term performance, which is particularly valuable in regions with limited budgets or challenging geological conditions. The 85% seepage reduction achieved by the combined approach minimizes water loss, enhancing the dam’s storage efficiency and supporting sustainable water management, while the 10% cost savings can translate into substantial financial benefits for large-scale infrastructure projects. These results also have broader implications for civil engineering, as the hybrid strategy can be adapted to other hydraulic structures, such as levees or canal embankments, where seepage control is a concern. The study’s reliance on GeoStudio’s Seep/W module highlights the power of numerical modeling in optimizing hydraulic design, allowing engineers to simulate multiple scenarios and refine configurations without costly field trials. However, limitations such as the model’s assumption of steady-state conditions and homogeneous soil properties suggest the need for future research to incorporate transient seepage, layered soil profiles, and long-term material degradation effects, such as clay blanket cracking or cutoff wall deterioration. Field validation of the hybrid solution in operational dams would further confirm its practical efficacy, particularly under varying hydraulic loads and environmental conditions. Additionally, exploring alternative materials, such as geosynthetic clay liners or concrete diaphragms, could enhance the hybrid system’s performance and durability. This research provides a robust framework for designing seepage control measures in earthen dams, demonstrating that a combined cutoff wall and clay blanket approach can achieve high efficiency at reduced costs, offering a practical and innovative solution for improving the stability and sustainability of hydraulic infrastructure in large-scale civil engineering projects, with potential applications across diverse geological and hydrological contexts.