Different configurations for cutoff walls in the design of Qeysaraq earth-fill Dam: A finite element approach

Dams are critical infrastructures for water resource management, flood control, and the provision of agricultural and drinking water. Among dam types, earth-fill dams are widely used due to their relatively low construction costs, adaptability to diverse geological conditions, and practicality in resourcelimited  settings. A major challenge for earth-fill dams is controlling seepage and internal erosion, which threaten safety and durability. Cutoff walls can enhance hydraulic performance by reducing seepage flow and hydraulic gradients. This study examines the effects of cutoff-wall depth (9, 12, 15, 18, 20 m) and thickness (1, 1.5, 2, 2.2, 2.5 m) on seepage flow, hydraulic gradient, and uplift pressure, based on specifications of an earthfill dam in East Azerbaijan, Iran, using the finite element analysis. Numerical simulations quantify the influence of variations in depth and thickness on key hydraulic responses. The results indicate that increasing depth up to 15 m reduces seepage by 53.4%, while increasing thickness up to 2 m reduces seepage by 33.7%. Optimized cutoff wall dimensions (depth = 15 m, thickness = 2 m) achieve a 51.2% reduction in hydraulic gradient and a 22.3% reduction in uplift pressure. An economic analysis shows that optimization can reduce excavation costs by 53%. Additionally, raising the reservoir water height behind the dam from 24.5 m to 31 m increases seepage flow by up to 27%, highlighting the influence of head on seepage. The results demonstrate that selecting a cutoff-wall depth of 15 m and thickness of 2 m provides substantial seepage and hydraulic-performance benefits while offering significant cost savings.